Reply
 
Thread Tools Display Modes
  #1   Report Post  
Posted to rec.audio.tubes
Iain Churches[_2_] Iain Churches[_2_] is offline
external usenet poster
 
Posts: 1,719
Default Ground Busses

Patrick posted some interesting facts about ground buss
connections, which I have extracted from another thread
and pasted here, because I think the subject is important
enough to warrant its own thread.

He wrote:

The 0V rail of the preamp should be a short buss wire about 100mm long
with ends connected to the RCA plug 0V bodies at inputs and outputs.
ALL parts with OV connections should be made to this buss,
and the CHASSIS or CASE connected via a 5 watt 27 ohm R, and the case
taken to the green/yellow wire to the wall socket so the case can't
become live to mains or the B+. There should be NO direct connection of
the OV buss to the case.

--


I ask:

In other words the mains supply case should be bonded to the case,
and the 0V (signal grounds) taken to the ground point via a 27 Ohm
5W resistor?

Why is this?

My experience with ground buss amps is limited. I have never been
able to make them quiet enough. I found that the exact position in
which a wire was placed on the buss was critical, and that a difference
was audible.It may be there is something lacking in my implementation
of the buss.

I prefer to use a star ground, as follows. Earth (ground) connection
from the supply - the only green yellow wire in the amplifier is taken
straight to the chassis bonding screw. The input and output RCA
signal connectors I used are the isolated type (Neutrik NF2D)

http://www.neutrik.com/uk/en/audio/2...-0_detail.aspx

I run a separate wire (black) from each of the RCA input and output
ground tags to the star ground. Signal wires on the input side have
their shields connected at the RCA socket end only.

On the psu, I run separate grounds (heavier wire) from each cap
separately to the star. They are not linked. The only exception to
this is the 1st (reservoir) electrolytic , which is connected directly
to the neg terminal of the FW bridge, and then to the star.

This is a topology I have seen used on amps that perform well,
and has been taught to me as a good solution.
It seems to work. My 50W power amp has only 80µV
of noise (-108dB) and no audible hum even with the ear
against the speaker (Tannoy Gold 15 inch)

Regards to all
Iain



  #2   Report Post  
Posted to rec.audio.tubes
Patrick Turner Patrick Turner is offline
external usenet poster
 
Posts: 3,964
Default Ground Busses



Iain Churches wrote:

Patrick posted some interesting facts about ground buss
connections, which I have extracted from another thread
and pasted here, because I think the subject is important
enough to warrant its own thread.

He wrote:

The 0V rail of the preamp should be a short buss wire about 100mm long
with ends connected to the RCA plug 0V bodies at inputs and outputs.
ALL parts with OV connections should be made to this buss,
and the CHASSIS or CASE connected via a 5 watt 27 ohm R, and the case
taken to the green/yellow wire to the wall socket so the case can't
become live to mains or the B+. There should be NO direct connection of
the OV buss to the case.

--

I ask:

In other words the mains supply case should be bonded to the case,
and the 0V (signal grounds) taken to the ground point via a 27 Ohm
5W resistor?

Why is this?


Because chassis can have magnetically induced voltages in them,
they should never be used for the 0V rail.

And where you have preamp and power amp each with chassis used as the
0V, then
you can all too easily have a horrid earth loop with noise injected to
the signal
path. The use of the 27 ohms is a much higher resistance than the shield
of a coax cable
which is at 0V, so there won't be a significant signal across this
shield wire
between to components if the chassis are not strapped to the 0V buss.


My experience with ground buss amps is limited. I have never been
able to make them quiet enough. I found that the exact position in
which a wire was placed on the buss was critical, and that a difference
was audible.It may be there is something lacking in my implementation
of the buss.


It does take some getting right.

Especially in MC amps for unbalanced MC cart inputs, but I manage it all
easily enough
to keep doing it.


I prefer to use a star ground, as follows. Earth (ground) connection
from the supply - the only green yellow wire in the amplifier is taken
straight to the chassis bonding screw. The input and output RCA
signal connectors I used are the isolated type (Neutrik NF2D)


Nothing wrong with star grounding, ie all bits with a 0V terminal
go to ONE point, but in fact you don't have to and a length of thick
wire
is fine.
This buss should never be directly connected to the chassis.

Thge chassis ALWAYS MUST be EARTHED via the green/yellow wire.

The 0V should be connected indirectly to the chassis but via a lowish
resistance which is
maybe 100 times the resistance of the coax wire shielding between
components.



http://www.neutrik.com/uk/en/audio/2...-0_detail.aspx

I run a separate wire (black) from each of the RCA input and output
ground tags to the star ground. Signal wires on the input side have
their shields connected at the RCA socket end only.

On the psu, I run separate grounds (heavier wire) from each cap
separately to the star. They are not linked. The only exception to
this is the 1st (reservoir) electrolytic , which is connected directly
to the neg terminal of the FW bridge, and then to the star.


After awhile, you realize what 0V wires you really need, and
which ones are a must and which are just not a must.

This is a topology I have seen used on amps that perform well,
and has been taught to me as a good solution.
It seems to work. My 50W power amp has only 80µV
of noise (-108dB) and no audible hum even with the ear
against the speaker (Tannoy Gold 15 inch)


If the gain of a power amp is say 20x, or +26dB,
then if the noise is determined by the input tube
and measured with its grid taken to 0V,
and if the input tube has equivalent input grid noise of
4 uV, somewhat noisy really when some good tubes measure 1uV
with dc heaters, then your noise will be 80uV at the output.

But you're lucky. A preamp may not be any better, and
produce 50uV, and this converts to 1,000 uV, or 1 mV.

Relative to an average signal level of 1 Vrms you'd have an SNR of only
60dB unweighted.
But that's good enough for most folks though; they simply cannot hear
that 1mV of noise, ie, hiss and PS hum.
Many SS amps fail to be as quiet as ppl think they mostly are.

But with better than 60dB unweighted, most tube amps are fine about
noise.

In fact the howl from the OPT caused by the magnetic currents at audio F
are in fact at a much higher sonic level than the noise buried within
the signal.
SE amps are the worser in this regard.

The best OPT have been potted to reduce their howl.

Try connection of a dummy R load and turning up the gain with a music
signal
and you'll see what I mean.

The noise of the OPT is as unwanted as are the vibrations from speaker
cabinets excited by sound waves inside the cabs.

Audio gear that isn't meant to have any sound during operation
needs careful design!

My latest 845 amp creations tested with less than 1mV of hum in the
signal
but I sure had to pot the OPT.
Then I found the PT was a bit hummy with so many rectifiers on it that
have had to place that on a separate chassis and pot it very well.
Mains is turned on by a relay in the PSU chassis so NO mains wires
go into the power amp chassis and no ac hums in rails either,
and no very subtle vibration from the mains tranny shaking the
845 cathodes or other tubes.
In such a set up in my 845s, or in my 300 watters as seen at
http://www.turneraudio.com.au/300monobloc.html
there cannot be star grounding, but noise figures are extremely low, and
good.




Patrick Turner.





Regards to all
Iain

  #3   Report Post  
Posted to rec.audio.tubes
Ian Iveson Ian Iveson is offline
external usenet poster
 
Posts: 960
Default Ground Busses

Iain Churches wrote:

My experience with ground buss amps is limited. I have
never been
able to make them quiet enough. I found that the exact
position in
which a wire was placed on the buss was critical, and that
a difference
was audible.It may be there is something lacking in my
implementation
of the buss.


I guess the order in which connections are made along a bus
is significant. If you think of the bus as a resistor, then
a high-current return placed furthest from the ground will
produce a voltage gradient along the bus. If the next
connection is, say, the signal ground from the first gain
stage, that voltage could be significant.

OTOH, if the connections to the bus are made in order of
highest current, the voltages they produce will be
minimised.

But perhaps there is countervailing argument? If a sensitive
connection is close to the ground, then a voltage produced
by a high-current connection further along will be
attenuated. So perhaps the order is important, but it
doesn't matter to which end of the bus the ground is
connected? What you don't want is a high-current connection
and a sensitive connection both distant from ground.

I find a genuine star earth is hard to implement if there
are many ground connections to make. Exactly how do you
fashion a star?

The signal ground must be safe to touch if it is brought out
to exposed external connectors. If a resistance is placed
between the 0V and chassis ground, then it should be a low
enough value and high enough power to ensure that the fuse,
and not the resistor, will blow quickly if the signal ground
becomes live due to some fault. Perhaps some statutory
regulations apply?

Not a "pro", or an "expert", as usual, thankfully.

Ian


  #4   Report Post  
Posted to rec.audio.tubes
Iain Churches[_2_] Iain Churches[_2_] is offline
external usenet poster
 
Posts: 1,719
Default Ground Busses



"Patrick Turner" wrote in message
...


Iain Churches wrote:

Patrick posted some interesting facts about ground buss
connections, which I have extracted from another thread
and pasted here, because I think the subject is important
enough to warrant its own thread.

He wrote:

The 0V rail of the preamp should be a short buss wire about 100mm long
with ends connected to the RCA plug 0V bodies at inputs and outputs.
ALL parts with OV connections should be made to this buss,
and the CHASSIS or CASE connected via a 5 watt 27 ohm R, and the case
taken to the green/yellow wire to the wall socket so the case can't
become live to mains or the B+. There should be NO direct connection of
the OV buss to the case.

--

I ask:

In other words the mains supply case should be bonded to the case,
and the 0V (signal grounds) taken to the ground point via a 27 Ohm
5W resistor?

Why is this?


Because chassis can have magnetically induced voltages in them,
they should never be used for the 0V rail.

And why 25W?

Iain


  #5   Report Post  
Posted to rec.audio.tubes
Iain Churches[_2_] Iain Churches[_2_] is offline
external usenet poster
 
Posts: 1,719
Default Ground Busses



"Ian Iveson" wrote in message
.uk...
Iain Churches wrote:

My experience with ground buss amps is limited. I have never been
able to make them quiet enough. I found that the exact position in
which a wire was placed on the buss was critical, and that a difference
was audible.It may be there is something lacking in my implementation
of the buss.


I guess the order in which connections are made along a bus is
significant. If you think of the bus as a resistor, then a high-current
return placed furthest from the ground will produce a voltage gradient
along the bus. If the next connection is, say, the signal ground from the
first gain stage, that voltage could be significant.

OTOH, if the connections to the bus are made in order of highest current,
the voltages they produce will be minimised.

But perhaps there is countervailing argument? If a sensitive connection is
close to the ground, then a voltage produced by a high-current connection
further along will be attenuated. So perhaps the order is important, but
it doesn't matter to which end of the bus the ground is connected? What
you don't want is a high-current connection and a sensitive connection
both distant from ground.



Very interesting. Thanks.
Next time I build a prototype, I will try this out.

I find a genuine star earth is hard to implement if there are many ground
connections to make. Exactly how do you fashion a star?


My stars are not symnmetrical with the ground point in the
middle if that what you mean. On a power amp I put the
chassis bonding terminal close to the AC socket, and on
a preamp close to input 1.

I usually make up the star on the bench, as a cableform,
and then fit, trim the loose ends and solder.

The signal ground must be safe to touch if it is brought out to exposed
external connectors. If a resistance is placed between the 0V and chassis
ground, then it should be a low enough value and high enough power to
ensure that the fuse, and not the resistor, will blow quickly if the
signal ground becomes live due to some fault. Perhaps some statutory
regulations apply?

Not a "pro", or an "expert", as usual, thankfully.

Ditto. But thanks for your thoughts, Ian. This is an
interesting business.

Regards
Iain




  #6   Report Post  
Posted to rec.audio.tubes
Andre Jute Andre Jute is offline
external usenet poster
 
Posts: 1,661
Default Ground Busses

A star ground is just a circular bus or a very short bus. Grounding is
is tricky and tiresome in inverse proportion to the amount of thought
you give it, so I do something between what Iain does and what Patrick
does, and I call it a "star-point". Here you can see my star point
http://members.lycos.co.uk/fiultra/K...0T68MZ417A.jpg
on my T68bis "Minus Zero" amp. It is the short piece of stiff wire
sticking up at the right hand side of the aluminium cased resistor
behind the battery boxes in the centre of the top right hand
photograph. It's the bleeder resistor to the power supply and the star
point is at its 0V end. Notice how the convenitonally drawn schematic
http://members.lycos.co.uk/fiultra/t...17acircuit.jpg
tells you nothing of this, leaving you to work it out for yourself.
All the 0V wires are dropped over this stiff wire and soldered on.
Even on such a short bus I take care of the order of the wires as I
put them on. From this point a wire is taken to main's earth. The case
is connected to mains earth by a wire from very sturdy bolt held in
with serrated washers and nuts, which is placed as near as possible to
the mains socket; unfortunately it is not too clear in the photograph,
but it is just below the switch, near the top right hand corner of the
righthand output transformer in the picture.

Most schematics don't tell you enough about earthing. Here, for
instance:
http://members.lycos.co.uk/fiultra/Jute-EL34-SEntry.jpg
I've shown the star earth being implemented but have not said anything
about connecting the case to earth. Mind you, on some of the Lundahl
Modular Series 300B schemos I showed all the 0V connections in order,
with a note saying "mind the order of the grounding connections", and
two people wrote me letters saying that DIYers are not idiots who need
their hands held. (I was, when I started, and I'm very grateful to
people who made 90 mile round trips to come check over my
constructions before I fired them up.)

Andre Jute
Visit Jute on Amps at http://members.lycos.co.uk/fiultra/
"wonderfully well written and reasoned information
for the tube audio constructor"
John Broskie TubeCAD & GlassWare
"an unbelievably comprehensive web site
containing vital gems of wisdom"
Stuart Perry Hi-Fi News & Record Review

On Mar 2, 12:39*pm, "Iain Churches" wrote:
Patrick posted some interesting facts about ground buss
connections, which I have extracted from another thread
and pasted here, because I think the subject is important
enough to warrant *its own thread.

He wrote:
The 0V rail of the preamp should be a short buss wire about 100mm long
with ends connected to the RCA plug 0V bodies at inputs and outputs.
ALL parts with OV connections should be made to this buss,
and the CHASSIS or CASE connected via a 5 watt 27 ohm R, and the case
taken to the *green/yellow wire to the wall socket so the case can't
become live to mains or the B+. There should be NO direct connection of
the OV buss to the case.


--

I ask:

In other words the mains supply case should be bonded to the case,
and the 0V (signal grounds) taken to the ground point via a 27 Ohm
5W resistor?

Why is this?

My experience with ground buss amps is limited. I have never been
able to make them quiet enough. I found that the exact position in
which a wire was placed on the buss was critical, and that a difference
was audible.It may be there is something lacking in my implementation
of the buss.

I prefer to use a star ground, as follows. *Earth (ground) connection
from the supply - the only green yellow wire in the amplifier is taken
straight to the chassis bonding screw. *The input and output RCA
signal connectors I used are the isolated type (Neutrik NF2D)

http://www.neutrik.com/uk/en/audio/2...-0_detail.aspx

I run a separate wire (black) from each of the RCA input and output
ground tags to the star ground. Signal wires on the input side have
their shields connected at the RCA socket end only.

On the psu, I run separate grounds (heavier wire) from each cap
separately to the star. They are not linked. *The only exception to
this is the 1st (reservoir) electrolytic , which is connected directly
to the neg terminal of the FW bridge, and then to the star.

This is a topology I have seen used on amps that perform well,
and has been taught to me as a good solution.
It seems to work. My 50W power amp has only 80µV
of noise (-108dB) and no audible hum even with the ear
against the speaker (Tannoy Gold 15 inch)

Regards to all
Iain


  #7   Report Post  
Posted to rec.audio.tubes
Henry Pasternack[_2_] Henry Pasternack[_2_] is offline
external usenet poster
 
Posts: 70
Default Ground Busses

This is something I found on the Web. It was apparently posted on the
usenet, perhaps to this group or maybe rec.audio.tech, many years ago,
althought I'm unable to find any evidence of the article in the Google
archives.

I offer the article without comment, and don't make any claims as to
its accuracy. Perhaps there is some value to what is written, as quite
a few people have linked to or reposted copies on their websites. The
author has left his phone number and email address in the signature. If
you have any issues, you may wish to contact him there. I would, in fact,
be very interested in hearing if anyone manages to contact him that way.

-Henry

--- BEGIN REPOSTED ARTICLE ---

Someone suggested I write an article on power and grounding techniques
for equipment construction. This is a topic I can't really do justice to;
whole books have been written on the subject. In the spirit of reckless
misinformation, I'll try to summarize a few hints. Consider this an
introduction for advanced beginners, but bear in mind there is room for
expanding and improving the information contained below.

-Henry

* * * * * * *

If circuits worked exactly as they are drawn on schematics, there'd
be no need to worry about power and ground topologies or wire routing.
Instead, we could just wire up all the components willy-nilly making
sure only that all the specified connections were complete. In the
real world of electromagnetics, things aren't quite so convenient:

1) Ground isn't really ground. Ideally, ground is a zero-voltage
reference that never varies. In fact, every ground bus that
carries current has small voltage variations across its length
due to small but significant resistance.

2) Stray capacitance. Two parallel conductors form a capacitor
across which unexpected AC currents can flow.

3) Electromagnetic induction. By definition, every circuit forms
a loop. When a changing magnetic flux (due, perhaps, to the
strong field from a transformer or choke) exists in the loop,
a current will be induced.

Now I'll talk briefly about the consequences of these real-world effects.

Ground Loops.

A ground loop occurs when a ground circuit encloses a loop and a
source of energy causes current to flow through the loop. If the flow
of current causes a voltage drop in a sensitive gain stage, the
voltage can be amplified and appear as noise. A typical ground loop
occurs in the amplifiers I just built. Because I use grounded power
cords, the chassis of my monoblocks are joined electrically at the
power outlet. The signal grounds are connected (via the input jacks
and interconnect cable shields) at the preamp output terminals. The
signal grounds are also connected to chassis ground internally in each
amplifier. The result is a loop that picks up inductive noise or
leakage currents and couples them into the amplifier gain circuitry,
causing an audible hum in the speakers. The quick solution is to
break the loop by using a three-to-two wire converter on one power
cord. A better fix is to "lift" the internal connection between
signal and chassis ground in one or both amplifiers and install a 10
Ohm resistor. The resistor is a significant obstacle to the flow of
current compared to the stout power cords and effectively breaks the
loop.

Another sort of ground loop occurs internal to equipment, but for
a different reason. In any circuit, one can trace the flow of power
from the supply, out to various circuits, and back to ground. Each
power supply typically provides current to more than one circuit
branches. Topologically speaking, the branches form intermeshing loops
that originate and terminate at the power supply. In the regions
where the loops overlap (share common conductors), voltage drops in
one loop can impose unwanted signals in another.

When a circuit loop overlaps on the supply side of a power source,
the designer will use parallel capacitors and/or series resistors or
inductors to block or shunt away signal currents on the supply rails.
The series components keep unwanted signals from leaving their circuit
branches, and the parallel caps redirect those that escape to ground.
Purifying the supply rails in this manner is called "decoupling".
Decoupling also helps to rid the rails of noise that creeps in due
to magnetic or electrostatic fields (more on theis later).

On the ground side, it's very important to keep the return currents
separate from one another as they work their way back to the common
power supply terminal. Practically speaking, we want to minimize
overlapping loops in the ground circuit. This is done by using a
short, thick ground bus of very low resistance and connecting all
ground wires to it. The most effective solution is to provide
separate conductors for each ground current source and return them all
to a single point; this is known as "star" grounding and is standard
practice in audio design. In tube gear wired point-to-point, it may
be sufficient to route a heavy ground wire around the edge of the
circuit and make all connections directly to it at the closest
convenient point.

Inductive and Capacitive Coupling.

Every conductor carrying a signal current generates an electromag-
netic field that can couple to other circuit elements. In addition,
the environment in which equipment is used is loaded with power line
and radio frequency fields that can get into sensitive circuits and
cause noise and distortion. I'll give some very quick information on
minimizing these problems.

Electrostatic fields and capacitive coupling can be reduced by
distance and shielding. A grounded metal shield stops a static field
in its tracks by imposing an equipotential barrier. To keep the field
from sneaking past the shield, the sensitive circuit must be
completely enclosed. Capacitance decreases as the reciprocal of the
distance between conductors, so separating sensitive wires as much as
possible is the other solution to stray electrostatic coupling.
Keeping circuit impedances low will help a great deal by raising the
frequency at which the coupling becomes a problem (hopefully beyond
the bandwidth of the circuit or offending signal source).

Shielding with non-ferrous metals is useless against magnetic
induction. The answer to induced hum of magnetic origin is to keep
circuit loop area to a minimum. The smaller the loop, the smaller the
volume of magnetic flux enclosed and the lower the induced current.
For this reason, power and signal wires should be twisted tightly with
their ground conductors whenever possible. This increases capacitance
between the conductors, so watch out in high-impedance signal
circuits. Plan the layout of hum-sensitive circuits so that the
enclosed area is kept to a minimum. Place transformers, chokes, and
high-current conductors as far as possible from these circuits. Iron
or mu-metal shields may be of some help, but I wouldn't count on them.
It may be better to put the power supply in a separate box for
sensitive preamps.

In most cases it is good advice to keep wire runs short, to twist
conductors carrying opposite currents together (signal and ground,
power supply lines, filament wires, etc), to route wires near the
chassis, and to physically separate high-gain stages from components
and wires that carry high currents.

Practical Advice.

When laying out your circuit, look at the schematic and identify
all of the separate current loops from supply to circuit to ground.
Then come up with a scheme to keep these loops as separate as possible
on the ground side. The biggest source of ground current in most
amplifiers is the power supply ripple in the main filter capacitor.
This current, which contains noisy, high-current rectifier current
spikes, usually flows back to the power transformer through the
secondary center tap. A good strategy is to connect this lead
directly to the filter capacitor common terminal. Then run a short
stub (could be a half inch) to a second point that will serve as a
star ground for the signal circuitry. Another source of high current
ground flow in a power amplifier is the common lead from the speaker
terminals. You'll want to make sure the low-level signal star ground
does not have output ground currents flowing through it or you'll
increase the possibility of instability. What I'm describing here
is really a "star of stars" grounding scheme. If you view every
conductor as a resistor and try to keep associated voltage drops
from crossing loops, you'll end up with the best ground scheme.

Here's the grounding topology in my tube power amps:

The main electrolytic filter caps and driver decoupling caps are
all mounted on one circuit board. The three decoupling caps share
a common, wide circuit board ground trace. The ground for the main
filter cap, for the transformer center tap, and for the decoupling
caps all come together in one small area of the circuit board. The
driver stage ground points are located close together near the central
ground, but "out of the way" of the rectifier current flow. I slotted
the copper strategically to "steer" the charging current current away
from the driver-stage grounds (defining the stub conductor described
above).

The following wires attach to the driver-stage ground area on
the filter cap board:

1) A single ground wire from a local "star ground" on the driver
board that connects the input jack shield, global feedback
cable shield, and the input stage bias resistors grounds.

2) A single ground wire carrying the return current from the
B- supply. This supply is floating and connected to the
driver board by a tightly twisted pair. B- is bypassed
locally by electrolytic and film capacitors. A second
"star ground" on the driver board connects all the bypass
caps. The rationale is that low frequency hum currents
are handled by the electrolytics and don't make it off
the filter circuit board. Local bypass caps keep RF
signals on the supply lines from getting onto the driver
board. The current-sourced differential design greatly
reduces the coupling of the input and driver signal currents,
in the ground leads, justifying the use of a single B- supply
and ground wire. I agonized over this layout for a while,
but it seems to work quite well.

3) A ground wire from the negative bias board. The bias supply
is also floating and connected to the bias board (which also
holds the output coupling capacitors) via a twisted pair.
There is a 0.47uF film capacitor bypass on the bias board.

The common lead from the output tube cathodes connects to a
ground point that runs directly to the main star ground without
passing through the driver ground node. The power transformer
center tap comes in on its own stub directly to the main capacitor
common terminal.

The two B+ wires to the driver stage are very short and connect
directly to the driver board. The output stage B+ is supplied to
the output transformer primary center tap from a circuit area close
to the main filter cap positive terminal. The power cord ground
wire is connected to the chassis at a convenient lug near the back
panel AC socket. The filter cap board has a ground wire to a lug
on the chassis as well (and perhaps this is why I have a ground loop;
I need to experiment with the location of my connection from signal
ground to chassis ground).

A note on solid-state Class AB amplifiers and power rail routing.

The current drawn by the two halves of a Class AB output stage
is rectified and has heavy harmonic components. Because solid-state
amps draw a lot of current from the rails, there is a good chance of
inducing signal-related noise in low-level circuitry unless careful
layout is used. A good technique is to twist the positive and
negative rail leads together and route them directly to the output
devices, keeping them away from low-level conductors. The rails are
usually bypassed on the circuit board by electrolytic capacitors
which should have a dedicated ground wire for their common terminals.
This wire should be kept apart from the small signal ground lead.
Care should be taken to keep the negative feedback connection, which
typically connects to a node near the output output transistors, from
coupling to the power leads. A sophisticated design will use multiple
electrolytic capacitors mounted right at the output devices and
clever circuit board layout. I believe the famous Analog Devices
application note on a wideband current feedback amplifier has some
useful notes on this problem (does anyone have a reference?).

--

Henry A. Pasternack
Member Scientific Staff (514) 761-8734 (phone)
Bell Northern Research, Montreal (514) 761-8509 (fax)

  #8   Report Post  
Posted to rec.audio.tubes
Henry Pasternack[_2_] Henry Pasternack[_2_] is offline
external usenet poster
 
Posts: 70
Default Ground Busses

Andre Jute wrote:

A star ground is just a circular bus or a very short bus.


Not really, ANDRE. A star ground is the abstract notion of a purely
equipotential (equal voltage) single point connection that eliminates
ground loops by reducing the resistance of the common ground bus to
zero. It's impossible to achieve in practice, though, and trying to
take the approach too literally is likely to cause more harm than
good.

Grounding is is tricky and tiresome in inverse proportion to the
amount of thought you give it.


I would say the opposite is true. The less you think about grounding,
the less tricky it seems. With no thought at all, it becomes as simple
as pie. Or fruit tart, for that matter. Just connect all the ground
connections together any way you like, and don't worry. It's only
when you start to think about it that it truly becomes tricky.

Here you can see my star point [URL deleted].


You may be able to see it, but to my eyes the picture is impossibly
tiny to reveal any useful details. But, you know I have this problem
with photographs.

Most schematics don't tell you enough about earthing. Here, for
instance: [URL deleted]. I've shown the star earth being implemented
but have not said anything about connecting the case to earth.


Attempting to connect all the grounds together like that, willy-nilly,
is not the right approach. That's because in practice it's nearly
impossible to achieve a true equipotential connection for all those
wires. Also, there are other performance issues having to do with
all those long ground connections running about the amplifier.

... I showed all the 0V connections in order, with a note saying
"mind the order of the grounding connections", and two people wrote
me letters saying that DIYers are not idiots who need their hands
held.


Then the DIYers were idiots, because the subject is quite worthy of
elaboration. The problem I see with everything you say here is that
you fail to address the most important meat of the problem, which is
precisely how to determine the "order of the grounding connections"
and how this translates into a practical wiring and ground layout.

My opinion on this subject is there are many ways to wire an amplifier
to minimize hum and noise. Star grounding (and its variants) and
bus wiring are two common solutions. Rather than posting fuzzy
pictures and vague generalities, if you would like to help your
readers, you should teach them the principles involved (you do
know them, right?) so they can work out the optimum grounding
scheme for each project by themselves.

Of course, being a lying psychopath pornographic scumbag, I may
not really know what I'm talking about! Feel free to ignore
everything I say. In fact, I strongly urge you to do so! :-)

-Henry
  #9   Report Post  
Posted to rec.audio.tubes
West West is offline
external usenet poster
 
Posts: 98
Default Ground Busses


"Andre Jute" wrote in message
...
A star ground is just a circular bus or a very short bus. Grounding is
is tricky and tiresome in inverse proportion to the amount of thought
you give it, so I do something between what Iain does and what Patrick
does, and I call it a "star-point". Here you can see my star point
http://members.lycos.co.uk/fiultra/K...0T68MZ417A.jpg
on my T68bis "Minus Zero" amp. It is the short piece of stiff wire
sticking up at the right hand side of the aluminium cased resistor
behind the battery boxes in the centre of the top right hand
photograph. It's the bleeder resistor to the power supply and the star
point is at its 0V end. Notice how the convenitonally drawn schematic
http://members.lycos.co.uk/fiultra/t...17acircuit.jpg
tells you nothing of this, leaving you to work it out for yourself.
All the 0V wires are dropped over this stiff wire and soldered on.
Even on such a short bus I take care of the order of the wires as I
put them on. From this point a wire is taken to main's earth. The case
is connected to mains earth by a wire from very sturdy bolt held in
with serrated washers and nuts, which is placed as near as possible to
the mains socket; unfortunately it is not too clear in the photograph,
but it is just below the switch, near the top right hand corner of the
righthand output transformer in the picture.

Most schematics don't tell you enough about earthing. Here, for
instance:
http://members.lycos.co.uk/fiultra/Jute-EL34-SEntry.jpg
I've shown the star earth being implemented but have not said anything
about connecting the case to earth. Mind you, on some of the Lundahl
Modular Series 300B schemos I showed all the 0V connections in order,
with a note saying "mind the order of the grounding connections", and
two people wrote me letters saying that DIYers are not idiots who need
their hands held. (I was, when I started, and I'm very grateful to
people who made 90 mile round trips to come check over my
constructions before I fired them up.)

Andre Jute
Visit Jute on Amps at http://members.lycos.co.uk/fiultra/
"wonderfully well written and reasoned information
for the tube audio constructor"
John Broskie TubeCAD & GlassWare
"an unbelievably comprehensive web site
containing vital gems of wisdom"
Stuart Perry Hi-Fi News & Record Review

Great illustration. Did you have those schematics/illustrations
professionally made or is there a particular program you used? Thanks.

west


  #10   Report Post  
Posted to rec.audio.tubes
John Byrns John Byrns is offline
external usenet poster
 
Posts: 1,441
Default Ground Busses

I remember the guy that originally posted that article, he used to post
on the usenet newsgroup "rec.audio.high-end", it seems unlikely you
would have found it on the web.


Regards,

John Byrns


In article ,
Henry Pasternack wrote:

This is something I found on the Web. It was apparently posted on the
usenet, perhaps to this group or maybe rec.audio.tech, many years ago,
althought I'm unable to find any evidence of the article in the Google
archives.

I offer the article without comment, and don't make any claims as to
its accuracy. Perhaps there is some value to what is written, as quite
a few people have linked to or reposted copies on their websites. The
author has left his phone number and email address in the signature. If
you have any issues, you may wish to contact him there. I would, in fact,
be very interested in hearing if anyone manages to contact him that way.

-Henry

--- BEGIN REPOSTED ARTICLE ---

Someone suggested I write an article on power and grounding techniques
for equipment construction. This is a topic I can't really do justice to;
whole books have been written on the subject. In the spirit of reckless
misinformation, I'll try to summarize a few hints. Consider this an
introduction for advanced beginners, but bear in mind there is room for
expanding and improving the information contained below.

-Henry

* * * * * * *

If circuits worked exactly as they are drawn on schematics, there'd
be no need to worry about power and ground topologies or wire routing.
Instead, we could just wire up all the components willy-nilly making
sure only that all the specified connections were complete. In the
real world of electromagnetics, things aren't quite so convenient:

1) Ground isn't really ground. Ideally, ground is a zero-voltage
reference that never varies. In fact, every ground bus that
carries current has small voltage variations across its length
due to small but significant resistance.

2) Stray capacitance. Two parallel conductors form a capacitor
across which unexpected AC currents can flow.

3) Electromagnetic induction. By definition, every circuit forms
a loop. When a changing magnetic flux (due, perhaps, to the
strong field from a transformer or choke) exists in the loop,
a current will be induced.

Now I'll talk briefly about the consequences of these real-world effects.

Ground Loops.

A ground loop occurs when a ground circuit encloses a loop and a
source of energy causes current to flow through the loop. If the flow
of current causes a voltage drop in a sensitive gain stage, the
voltage can be amplified and appear as noise. A typical ground loop
occurs in the amplifiers I just built. Because I use grounded power
cords, the chassis of my monoblocks are joined electrically at the
power outlet. The signal grounds are connected (via the input jacks
and interconnect cable shields) at the preamp output terminals. The
signal grounds are also connected to chassis ground internally in each
amplifier. The result is a loop that picks up inductive noise or
leakage currents and couples them into the amplifier gain circuitry,
causing an audible hum in the speakers. The quick solution is to
break the loop by using a three-to-two wire converter on one power
cord. A better fix is to "lift" the internal connection between
signal and chassis ground in one or both amplifiers and install a 10
Ohm resistor. The resistor is a significant obstacle to the flow of
current compared to the stout power cords and effectively breaks the
loop.

Another sort of ground loop occurs internal to equipment, but for
a different reason. In any circuit, one can trace the flow of power
from the supply, out to various circuits, and back to ground. Each
power supply typically provides current to more than one circuit
branches. Topologically speaking, the branches form intermeshing loops
that originate and terminate at the power supply. In the regions
where the loops overlap (share common conductors), voltage drops in
one loop can impose unwanted signals in another.

When a circuit loop overlaps on the supply side of a power source,
the designer will use parallel capacitors and/or series resistors or
inductors to block or shunt away signal currents on the supply rails.
The series components keep unwanted signals from leaving their circuit
branches, and the parallel caps redirect those that escape to ground.
Purifying the supply rails in this manner is called "decoupling".
Decoupling also helps to rid the rails of noise that creeps in due
to magnetic or electrostatic fields (more on theis later).

On the ground side, it's very important to keep the return currents
separate from one another as they work their way back to the common
power supply terminal. Practically speaking, we want to minimize
overlapping loops in the ground circuit. This is done by using a
short, thick ground bus of very low resistance and connecting all
ground wires to it. The most effective solution is to provide
separate conductors for each ground current source and return them all
to a single point; this is known as "star" grounding and is standard
practice in audio design. In tube gear wired point-to-point, it may
be sufficient to route a heavy ground wire around the edge of the
circuit and make all connections directly to it at the closest
convenient point.

Inductive and Capacitive Coupling.

Every conductor carrying a signal current generates an electromag-
netic field that can couple to other circuit elements. In addition,
the environment in which equipment is used is loaded with power line
and radio frequency fields that can get into sensitive circuits and
cause noise and distortion. I'll give some very quick information on
minimizing these problems.

Electrostatic fields and capacitive coupling can be reduced by
distance and shielding. A grounded metal shield stops a static field
in its tracks by imposing an equipotential barrier. To keep the field
from sneaking past the shield, the sensitive circuit must be
completely enclosed. Capacitance decreases as the reciprocal of the
distance between conductors, so separating sensitive wires as much as
possible is the other solution to stray electrostatic coupling.
Keeping circuit impedances low will help a great deal by raising the
frequency at which the coupling becomes a problem (hopefully beyond
the bandwidth of the circuit or offending signal source).

Shielding with non-ferrous metals is useless against magnetic
induction. The answer to induced hum of magnetic origin is to keep
circuit loop area to a minimum. The smaller the loop, the smaller the
volume of magnetic flux enclosed and the lower the induced current.
For this reason, power and signal wires should be twisted tightly with
their ground conductors whenever possible. This increases capacitance
between the conductors, so watch out in high-impedance signal
circuits. Plan the layout of hum-sensitive circuits so that the
enclosed area is kept to a minimum. Place transformers, chokes, and
high-current conductors as far as possible from these circuits. Iron
or mu-metal shields may be of some help, but I wouldn't count on them.
It may be better to put the power supply in a separate box for
sensitive preamps.

In most cases it is good advice to keep wire runs short, to twist
conductors carrying opposite currents together (signal and ground,
power supply lines, filament wires, etc), to route wires near the
chassis, and to physically separate high-gain stages from components
and wires that carry high currents.

Practical Advice.

When laying out your circuit, look at the schematic and identify
all of the separate current loops from supply to circuit to ground.
Then come up with a scheme to keep these loops as separate as possible
on the ground side. The biggest source of ground current in most
amplifiers is the power supply ripple in the main filter capacitor.
This current, which contains noisy, high-current rectifier current
spikes, usually flows back to the power transformer through the
secondary center tap. A good strategy is to connect this lead
directly to the filter capacitor common terminal. Then run a short
stub (could be a half inch) to a second point that will serve as a
star ground for the signal circuitry. Another source of high current
ground flow in a power amplifier is the common lead from the speaker
terminals. You'll want to make sure the low-level signal star ground
does not have output ground currents flowing through it or you'll
increase the possibility of instability. What I'm describing here
is really a "star of stars" grounding scheme. If you view every
conductor as a resistor and try to keep associated voltage drops
from crossing loops, you'll end up with the best ground scheme.

Here's the grounding topology in my tube power amps:

The main electrolytic filter caps and driver decoupling caps are
all mounted on one circuit board. The three decoupling caps share
a common, wide circuit board ground trace. The ground for the main
filter cap, for the transformer center tap, and for the decoupling
caps all come together in one small area of the circuit board. The
driver stage ground points are located close together near the central
ground, but "out of the way" of the rectifier current flow. I slotted
the copper strategically to "steer" the charging current current away
from the driver-stage grounds (defining the stub conductor described
above).

The following wires attach to the driver-stage ground area on
the filter cap board:

1) A single ground wire from a local "star ground" on the driver
board that connects the input jack shield, global feedback
cable shield, and the input stage bias resistors grounds.

2) A single ground wire carrying the return current from the
B- supply. This supply is floating and connected to the
driver board by a tightly twisted pair. B- is bypassed
locally by electrolytic and film capacitors. A second
"star ground" on the driver board connects all the bypass
caps. The rationale is that low frequency hum currents
are handled by the electrolytics and don't make it off
the filter circuit board. Local bypass caps keep RF
signals on the supply lines from getting onto the driver
board. The current-sourced differential design greatly
reduces the coupling of the input and driver signal currents,
in the ground leads, justifying the use of a single B- supply
and ground wire. I agonized over this layout for a while,
but it seems to work quite well.

3) A ground wire from the negative bias board. The bias supply
is also floating and connected to the bias board (which also
holds the output coupling capacitors) via a twisted pair.
There is a 0.47uF film capacitor bypass on the bias board.

The common lead from the output tube cathodes connects to a
ground point that runs directly to the main star ground without
passing through the driver ground node. The power transformer
center tap comes in on its own stub directly to the main capacitor
common terminal.

The two B+ wires to the driver stage are very short and connect
directly to the driver board. The output stage B+ is supplied to
the output transformer primary center tap from a circuit area close
to the main filter cap positive terminal. The power cord ground
wire is connected to the chassis at a convenient lug near the back
panel AC socket. The filter cap board has a ground wire to a lug
on the chassis as well (and perhaps this is why I have a ground loop;
I need to experiment with the location of my connection from signal
ground to chassis ground).

A note on solid-state Class AB amplifiers and power rail routing.

The current drawn by the two halves of a Class AB output stage
is rectified and has heavy harmonic components. Because solid-state
amps draw a lot of current from the rails, there is a good chance of
inducing signal-related noise in low-level circuitry unless careful
layout is used. A good technique is to twist the positive and
negative rail leads together and route them directly to the output
devices, keeping them away from low-level conductors. The rails are
usually bypassed on the circuit board by electrolytic capacitors
which should have a dedicated ground wire for their common terminals.
This wire should be kept apart from the small signal ground lead.
Care should be taken to keep the negative feedback connection, which
typically connects to a node near the output output transistors, from
coupling to the power leads. A sophisticated design will use multiple
electrolytic capacitors mounted right at the output devices and
clever circuit board layout. I believe the famous Analog Devices
application note on a wideband current feedback amplifier has some
useful notes on this problem (does anyone have a reference?).

--

Henry A. Pasternack
Member Scientific Staff (514) 761-8734 (phone)
Bell Northern Research, Montreal (514) 761-8509 (fax)


--
Surf my web pages at,
http://fmamradios.com/


  #11   Report Post  
Posted to rec.audio.tubes
Peter Wieck Peter Wieck is offline
external usenet poster
 
Posts: 2,418
Default Ground Busses

On Mar 2, 8:33*am, Patrick Turner wrote:

Good Stuff.


Patrick, reducing your and Iain's post to a very few salient points,
am I correct in deriving "best practice" as follows:

a) The chassis must be grounded to the mains ground
b) The circuit ground should be separate and isolated from the chassis/
case, connected via the 27ohm@5W resistor.
c) The circuit ground should be as short as possible and loops (such
as connecting signal-shields at both ends) are to be avoided.

I see safety addresssed by grounding the chassis directly to the mains
ground. I see any excess potentials within the circuit bleeding to the
case. I also see isolating the circuit from the case helping when
other components are connected (and grounded).

It seems that this solution is the one that was actually put into
place on the humming pre-amp...

Thanks in advance.

Peter Wieck
Wyncote, PA

  #12   Report Post  
Posted to rec.audio.tubes
Henry Pasternack[_2_] Henry Pasternack[_2_] is offline
external usenet poster
 
Posts: 70
Default Ground Busses

"John Byrns" wrote in message
...
I remember the guy that originally posted that article, he used to post
on the usenet newsgroup "rec.audio.high-end", it seems unlikely you
would have found it on the web.


http://ai.kaist.ac.kr/~suh/DIY/ground


  #13   Report Post  
Posted to rec.audio.tubes
Ian Thompson-Bell Ian Thompson-Bell is offline
external usenet poster
 
Posts: 493
Default Ground Busses

Henry Pasternack wrote:
Andre Jute wrote:

A star ground is just a circular bus or a very short bus.


Not really, ANDRE. A star ground is the abstract notion of a purely
equipotential (equal voltage) single point connection that eliminates
ground loops by reducing the resistance of the common ground bus to
zero. It's impossible to achieve in practice, though, and trying to
take the approach too literally is likely to cause more harm than
good.


The key phrase here is 'reducing the resistance of the common ground bus
to zero'. it is all very well connecting all grounded leads to a single
point but if you then connect that by a single wire to the zero volts
point of the power supply you have immediately introduced a long no zero
common ground bus. So a star ground really only works if the star point
IS the 0V point of the PSU i.e the ground of the input filter cap.#

In power amps this is relatively easy to achieve and running a thick bus
from the PSU 0V past the power section to the preamp section should work
just a s well since the power currents will not flow through any of the
preamp sections of the bus.

In separate pre-amps or mic pre-amps or tube mixers where the supply is
remote from the pre-amp this is clearly not possible and there is the
added problem of separating power currents from input/output signal
currents (unless floating transformer inputs and outputs are used). One
solution I have seen is to have a local pre-amp power supply - indeed
this was very common practice in many tube based recording mixers of the
50s and 60s. Each pre-amp would have its own mains transformer and PSU
along with balanced floating inputs and outputs. All earth loop problems
were therefore local to the pre-amp and you could connect them together
however you liked to build a mixer without ever having to worry about
ground loops. An expensive option to be sure, but one that worked very well.

Cheers

ian
  #14   Report Post  
Posted to rec.audio.tubes
Eeyore Eeyore is offline
external usenet poster
 
Posts: 8,474
Default Ground Busses



Ian Thompson-Bell wrote:

Henry Pasternack wrote:
Andre Jute wrote:

A star ground is just a circular bus or a very short bus.


Not really, ANDRE. A star ground is the abstract notion of a purely
equipotential (equal voltage) single point connection that eliminates
ground loops by reducing the resistance of the common ground bus to
zero. It's impossible to achieve in practice, though, and trying to
take the approach too literally is likely to cause more harm than
good.



The key phrase here is 'reducing the resistance of the common ground bus
to zero'. it is all very well connecting all grounded leads to a single
point but if you then connect that by a single wire to the zero volts
point of the power supply you have immediately introduced a long no zero
common ground bus. So a star ground really only works if the star point
IS the 0V point of the PSU i.e the ground of the input filter cap.#

In power amps this is relatively easy to achieve and running a thick bus
from the PSU 0V past the power section to the preamp section should work
just a s well since the power currents will not flow through any of the
preamp sections of the bus.


But still a compromise.


In separate pre-amps or mic pre-amps or tube mixers where the supply is
remote from the pre-amp this is clearly not possible and there is the
added problem of separating power currents from input/output signal
currents (unless floating transformer inputs and outputs are used). One
solution I have seen is to have a local pre-amp power supply - indeed
this was very common practice in many tube based recording mixers of the
50s and 60s. Each pre-amp would have its own mains transformer and PSU
along with balanced floating inputs and outputs. All earth loop problems
were therefore local to the pre-amp and you could connect them together
however you liked to build a mixer without ever having to worry about
ground loops. An expensive option to be sure, but one that worked very well.


Far simpler is to have 2 (or more) stars and use these to direct current flow.
In particular, the PSU should have its own star and this is where ALL ripple
currents must flow. This can now be tied to the input 'star' with a
*non-current-carrying conductor* (or at least carrying only the B- smoothed DC).

It is *essential* to keep power and signal paths separate for hum free
operation.

Graham

  #15   Report Post  
Posted to rec.audio.tubes
Henry Pasternack[_2_] Henry Pasternack[_2_] is offline
external usenet poster
 
Posts: 70
Default Ground Busses

"Ian Thompson-Bell" wrote in message
...
The key phrase here is 'reducing the resistance of the common ground bus
to zero'. it is all very well connecting all grounded leads to a single
point but if you then connect that by a single wire to the zero volts
point of the power supply you have immediately introduced a long no zero
common ground bus. So a star ground really only works if the star point IS
the 0V point of the PSU i.e the ground of the input filter cap.#


True. But a better practical arrangement is to create a "star of stars".
The real key, IMHO, is to start with the schematic and draw out all
of the current loops in the circuit, from power supply out to the signal
circuitry and back, and also the input and output currents. Then you
find places where separate current loops share common paths, and
then separate out these loops so they meet at (to the greatest extent
possible) single points.

The connection to the chassis is done for electrostatic shielding. It's
done at a single point on the circuit's ground net. Where that point
should be is a subject for debate. To understand the implications, you
have to visualize the effects of currents flowing though and in the
chassis walls due to external potentials and electrostatic/electromagnetic
fields. Not easy if you really want to take it to the "next level". And
that's why that fellow in the article reposted said whole books can be
written on the subject.

If you try to follow a single technique from rote and vague instructions,
your results may be hit-and-miss. Always better, I say, to understand
the problem from first principles.

-Henry




  #16   Report Post  
Posted to rec.audio.tubes
Eeyore Eeyore is offline
external usenet poster
 
Posts: 8,474
Default Ground Busses



Henry Pasternack wrote:

"Ian Thompson-Bell" wrote

The key phrase here is 'reducing the resistance of the common ground bus
to zero'. it is all very well connecting all grounded leads to a single
point but if you then connect that by a single wire to the zero volts
point of the power supply you have immediately introduced a long no zero
common ground bus. So a star ground really only works if the star point IS
the 0V point of the PSU i.e the ground of the input filter cap.#


True. But a better practical arrangement is to create a "star of stars".
The real key, IMHO, is to start with the schematic and draw out all
of the current loops in the circuit, from power supply out to the signal
circuitry and back, and also the input and output currents. Then you
find places where separate current loops share common paths, and
then separate out these loops so they meet at (to the greatest extent
possible) single points.


100% correct.


If you try to follow a single technique from rote and vague instructions,
your results may be hit-and-miss. Always better, I say, to understand
the problem from first principles.


I couldn't agree more. With grounding it's almost all about directing current
flow in an appropriate way.

Graham

  #17   Report Post  
Posted to rec.audio.tubes
John Byrns John Byrns is offline
external usenet poster
 
Posts: 1,441
Default Ground Busses

In article ,
"Henry Pasternack" wrote:

"John Byrns" wrote in message
...
I remember the guy that originally posted that article, he used to post
on the usenet newsgroup "rec.audio.high-end", it seems unlikely you
would have found it on the web.


http://ai.kaist.ac.kr/~suh/DIY/ground


I meant originally, I assume this is one of the many copies on the web
that you said existed?


Regards,

John Byrns

--
Surf my web pages at, http://fmamradios.com/
  #18   Report Post  
Posted to rec.audio.tubes
Nick Gorham Nick Gorham is offline
external usenet poster
 
Posts: 134
Default Ground Busses

Andre Jute wrote:
A star ground is just a circular bus or a very short bus. Grounding is
is tricky and tiresome in inverse proportion to the amount of thought
you give it, so I do something between what Iain does and what Patrick
does, and I call it a "star-point". Here you can see my star point
http://members.lycos.co.uk/fiultra/K...0T68MZ417A.jpg
on my T68bis "Minus Zero" amp. It is the short piece of stiff wire
sticking up at the right hand side of the aluminium cased resistor
behind the battery boxes in the centre of the top right hand
photograph. It's the bleeder resistor to the power supply and the star
point is at its 0V end. Notice how the convenitonally drawn schematic
http://members.lycos.co.uk/fiultra/t...17acircuit.jpg


Given the topic of the thread, shouldn't the ground commection under the
rectifier be after the choke, not before?

--
Nick
  #19   Report Post  
Posted to rec.audio.tubes
Henry Pasternack[_2_] Henry Pasternack[_2_] is offline
external usenet poster
 
Posts: 70
Default Ground Busses

"Eeyore" wrote in message
...
Henry Pasternack wrote:
True. But a better practical arrangement is to create a "star of stars".
The real key, IMHO, is to start with the schematic and draw out all
of the current loops in the circuit, from power supply out to the signal
circuitry and back, and also the input and output currents. Then you
find places where separate current loops share common paths, and
then separate out these loops so they meet at (to the greatest extent
possible) single points.


100% correct.


Your posting that said essentially the same thing arrived on my server
slightly after I wrote the above, although the date shows you posted
it earlier... Apologies for making the same point twice.

I couldn't agree more. With grounding it's almost all about directing
current flow in an appropriate way.


And bearing in mind that current always finds its way to ground, and
learning to think about all the sneaky ways it does so, and the voltage
drops it creates along the way...

-Henry


  #20   Report Post  
Posted to rec.audio.tubes
Henry Pasternack[_2_] Henry Pasternack[_2_] is offline
external usenet poster
 
Posts: 70
Default Ground Busses

"John Byrns" wrote in message
...
I meant originally, I assume this is one of the many copies on the web
that you said existed?


I found the posting today on the Web.

-Henry




  #21   Report Post  
Posted to rec.audio.tubes
John Byrns John Byrns is offline
external usenet poster
 
Posts: 1,441
Default Ground Busses

In article ,
Ian Thompson-Bell wrote:

Henry Pasternack wrote:
Andre Jute wrote:

A star ground is just a circular bus or a very short bus.


Not really, ANDRE. A star ground is the abstract notion of a purely
equipotential (equal voltage) single point connection that eliminates
ground loops by reducing the resistance of the common ground bus to
zero. It's impossible to achieve in practice, though, and trying to
take the approach too literally is likely to cause more harm than
good.


The key phrase here is 'reducing the resistance of the common ground bus
to zero'. it is all very well connecting all grounded leads to a single
point but if you then connect that by a single wire to the zero volts
point of the power supply you have immediately introduced a long no zero
common ground bus. So a star ground really only works if the star point
IS the 0V point of the PSU i.e the ground of the input filter cap.#


In my experience it is not the input filter cap that is important here,
but rather that it is the final filter cap in the main PSU filter that
must be connected to the "star point" or its equivalent.

In power amps this is relatively easy to achieve and running a thick bus
from the PSU 0V past the power section to the preamp section should work
just a s well since the power currents will not flow through any of the
preamp sections of the bus.

In separate pre-amps or mic pre-amps or tube mixers where the supply is
remote from the pre-amp this is clearly not possible and there is the
added problem of separating power currents from input/output signal
currents (unless floating transformer inputs and outputs are used). One
solution I have seen is to have a local pre-amp power supply - indeed
this was very common practice in many tube based recording mixers of the
50s and 60s. Each pre-amp would have its own mains transformer and PSU
along with balanced floating inputs and outputs. All earth loop problems
were therefore local to the pre-amp and you could connect them together
however you liked to build a mixer without ever having to worry about
ground loops. An expensive option to be sure, but one that worked very well.


And in other 50s and 60s systems a whole rack full of microphone preamps
were powered from a common power supply without problems because only
power currents flowed through the wires from the power supply, the
signal input and output currents were isolated from the common power
wires by input and output transformers.

Oops on proof reading, I see that you already mentioned this in
parenthesis, oh well.


Regards,

John Byrns

--
Surf my web pages at, http://fmamradios.com/
  #22   Report Post  
Posted to rec.audio.tubes
John Byrns John Byrns is offline
external usenet poster
 
Posts: 1,441
Default Ground Busses

In article ,
"Henry Pasternack" wrote:

"John Byrns" wrote in message
...
I meant originally, I assume this is one of the many copies on the web
that you said existed?


I found the posting today on the Web.


Are you saying it wasn't originally posted on usenet?


Regards,

John Byrns

--
Surf my web pages at, http://fmamradios.com/
  #23   Report Post  
Posted to rec.audio.tubes
Peter Wieck Peter Wieck is offline
external usenet poster
 
Posts: 2,418
Default Ground Busses

On Mar 2, 2:13*pm, "West" wrote:
"Andre Jute" wrote in message

...
A star ground is just a circular bus or a very short bus. Grounding is
is tricky and tiresome in inverse proportion to the amount of thought
you give it, so I do something between what Iain does and what Patrick
does, and I call it a "star-point". Here you can see my star pointhttp://members.lycos.co.uk/fiultra/KISS%20192%20T68MZ417A.jpg
on my T68bis "Minus Zero" amp. It is the short piece of stiff wire
sticking up at the right hand side of the aluminium cased resistor
behind the battery boxes in the centre of the top right hand
photograph. It's the bleeder resistor to the power supply and the star
point is at its 0V end. Notice how the convenitonally drawn schematichttp://members.lycos.co.uk/fiultra/t68mzwe417acircuit.jpg
tells you nothing of this, leaving you to work it out for yourself.
All the 0V wires are dropped over this stiff wire and soldered on.
Even on such a short bus I take care of the order of the wires as I
put them on. From this point a wire is taken to main's earth. The case
is connected to mains earth by a wire from very sturdy bolt held in
with serrated washers and nuts, which is placed as near as possible to
the mains socket; unfortunately it is not too clear in the photograph,
but it is just below the switch, near the top right hand corner of the
righthand output transformer in the picture.

Most schematics don't tell you enough about earthing. Here, for
instance:http://members.lycos.co.uk/fiultra/Jute-EL34-SEntry.jpg
I've shown the star earth being implemented but have not said anything
about connecting the case to earth. Mind you, on some of the Lundahl
Modular Series 300B schemos I showed all the 0V connections in order,
with a note saying "mind the order of the grounding connections", and
two people wrote me letters saying that DIYers are not idiots who need
their hands held. (I was, when I started, and I'm very grateful to
people who made 90 mile round trips to come check over my
constructions before I fired them up.)

Andre Jute
Visit Jute on Amps athttp://members.lycos.co.uk/fiultra/
"wonderfully well written and reasoned information
for the tube audio constructor"
John Broskie TubeCAD & GlassWare
"an unbelievably comprehensive web site
containing vital gems of wisdom"
Stuart Perry Hi-Fi News & Record Review

Great illustration. Did you have those schematics/illustrations
professionally made or is there a particular program you used? Thanks.

west


Pillock:

You can do all of that using "Word" and the extra symbols chart. Most
word-processing programs are capable of all of that and more. On a
Mac, it is that much easier. So, you could finally furnish that long-
promised schematic on your "Slow B+" as the wherewithall is likely
already resident on your computer.

Peter Wieck
Wyncote, PA
  #24   Report Post  
Posted to rec.audio.tubes
Ian Thompson-Bell Ian Thompson-Bell is offline
external usenet poster
 
Posts: 493
Default Ground Busses

Eeyore wrote:

Ian Thompson-Bell wrote:

Henry Pasternack wrote:
Andre Jute wrote:

A star ground is just a circular bus or a very short bus.
Not really, ANDRE. A star ground is the abstract notion of a purely
equipotential (equal voltage) single point connection that eliminates
ground loops by reducing the resistance of the common ground bus to
zero. It's impossible to achieve in practice, though, and trying to
take the approach too literally is likely to cause more harm than
good.


The key phrase here is 'reducing the resistance of the common ground bus
to zero'. it is all very well connecting all grounded leads to a single
point but if you then connect that by a single wire to the zero volts
point of the power supply you have immediately introduced a long no zero
common ground bus. So a star ground really only works if the star point
IS the 0V point of the PSU i.e the ground of the input filter cap.#

In power amps this is relatively easy to achieve and running a thick bus
from the PSU 0V past the power section to the preamp section should work
just a s well since the power currents will not flow through any of the
preamp sections of the bus.


But still a compromise.


In separate pre-amps or mic pre-amps or tube mixers where the supply is
remote from the pre-amp this is clearly not possible and there is the
added problem of separating power currents from input/output signal
currents (unless floating transformer inputs and outputs are used). One
solution I have seen is to have a local pre-amp power supply - indeed
this was very common practice in many tube based recording mixers of the
50s and 60s. Each pre-amp would have its own mains transformer and PSU
along with balanced floating inputs and outputs. All earth loop problems
were therefore local to the pre-amp and you could connect them together
however you liked to build a mixer without ever having to worry about
ground loops. An expensive option to be sure, but one that worked very well.


Far simpler is to have 2 (or more) stars and use these to direct current flow.
In particular, the PSU should have its own star and this is where ALL ripple
currents must flow. This can now be tied to the input 'star' with a
*non-current-carrying conductor* (or at least carrying only the B- smoothed DC).


Presumably you mean no *signal* current carrying conductor.

This still leaves a common mode conductor carrying output signal current
which is of course supplied by the power supply. I am not clear how
multiple local stars solve the problem.

It is *essential* to keep power and signal paths separate for hum free
operation.


Which can only be achieved with transformers?

Cheers

Ian
  #25   Report Post  
Posted to rec.audio.tubes
Eeyore Eeyore is offline
external usenet poster
 
Posts: 8,474
Default Ground Busses



Ian Thompson-Bell wrote:

Eeyore wrote:
Ian Thompson-Bell wrote:
Henry Pasternack wrote:
Andre Jute wrote:

A star ground is just a circular bus or a very short bus.
Not really, ANDRE. A star ground is the abstract notion of a purely
equipotential (equal voltage) single point connection that eliminates
ground loops by reducing the resistance of the common ground bus to
zero. It's impossible to achieve in practice, though, and trying to
take the approach too literally is likely to cause more harm than
good.

The key phrase here is 'reducing the resistance of the common ground bus
to zero'. it is all very well connecting all grounded leads to a single
point but if you then connect that by a single wire to the zero volts
point of the power supply you have immediately introduced a long no zero
common ground bus. So a star ground really only works if the star point
IS the 0V point of the PSU i.e the ground of the input filter cap.#

In power amps this is relatively easy to achieve and running a thick bus
from the PSU 0V past the power section to the preamp section should work
just a s well since the power currents will not flow through any of the
preamp sections of the bus.


But still a compromise.


In separate pre-amps or mic pre-amps or tube mixers where the supply is
remote from the pre-amp this is clearly not possible and there is the
added problem of separating power currents from input/output signal
currents (unless floating transformer inputs and outputs are used). One
solution I have seen is to have a local pre-amp power supply - indeed
this was very common practice in many tube based recording mixers of the
50s and 60s. Each pre-amp would have its own mains transformer and PSU
along with balanced floating inputs and outputs. All earth loop problems
were therefore local to the pre-amp and you could connect them together
however you liked to build a mixer without ever having to worry about
ground loops. An expensive option to be sure, but one that worked very well.


Far simpler is to have 2 (or more) stars and use these to direct current flow.
In particular, the PSU should have its own star and this is where ALL ripple
currents must flow. This can now be tied to the input 'star' with a
*non-current-carrying conductor* (or at least carrying only the B- smoothed DC).


Presumably you mean no *signal* current carrying conductor.


Well ... if there's no current, then there'll be no signal too for sure. What I meant
basically was a link to simply ensure that the 2 stars are at the same potential.


This still leaves a common mode conductor carrying output signal current
which is of course supplied by the power supply. I am not clear how
multiple local stars solve the problem.

It is *essential* to keep power and signal paths separate for hum free
operation.


Which can only be achieved with transformers?


Not necessary. Transfomers introduce their own problems.

Graham



  #26   Report Post  
Posted to rec.audio.tubes
Ian Thompson-Bell Ian Thompson-Bell is offline
external usenet poster
 
Posts: 493
Default Ground Busses

Henry Pasternack wrote:
"Ian Thompson-Bell" wrote in message
...
The key phrase here is 'reducing the resistance of the common ground bus
to zero'. it is all very well connecting all grounded leads to a single
point but if you then connect that by a single wire to the zero volts
point of the power supply you have immediately introduced a long no zero
common ground bus. So a star ground really only works if the star point IS
the 0V point of the PSU i.e the ground of the input filter cap.#


True. But a better practical arrangement is to create a "star of stars".
The real key, IMHO, is to start with the schematic and draw out all
of the current loops in the circuit, from power supply out to the signal
circuitry and back, and also the input and output currents. Then you
find places where separate current loops share common paths, and
then separate out these loops so they meet at (to the greatest extent
possible) single points.


The problem I see with that is that all output currents must flow from
the power supply, through the load and back to the PSU 0V but they share
a common ground with the inputs. How do you separate these?

The connection to the chassis is done for electrostatic shielding. It's
done at a single point on the circuit's ground net. Where that point
should be is a subject for debate. To understand the implications, you
have to visualize the effects of currents flowing though and in the
chassis walls due to external potentials and electrostatic/electromagnetic
fields. Not easy if you really want to take it to the "next level". And
that's why that fellow in the article reposted said whole books can be
written on the subject.

If you try to follow a single technique from rote and vague instructions,
your results may be hit-and-miss. Always better, I say, to understand
the problem from first principles.

No argument about that!

Cheers

Ian
  #27   Report Post  
Posted to rec.audio.tubes
Ian Thompson-Bell Ian Thompson-Bell is offline
external usenet poster
 
Posts: 493
Default Ground Busses

John Byrns wrote:
In article ,
Ian Thompson-Bell wrote:

Henry Pasternack wrote:
Andre Jute wrote:

A star ground is just a circular bus or a very short bus.
Not really, ANDRE. A star ground is the abstract notion of a purely
equipotential (equal voltage) single point connection that eliminates
ground loops by reducing the resistance of the common ground bus to
zero. It's impossible to achieve in practice, though, and trying to
take the approach too literally is likely to cause more harm than
good.

The key phrase here is 'reducing the resistance of the common ground bus
to zero'. it is all very well connecting all grounded leads to a single
point but if you then connect that by a single wire to the zero volts
point of the power supply you have immediately introduced a long no zero
common ground bus. So a star ground really only works if the star point
IS the 0V point of the PSU i.e the ground of the input filter cap.#


In my experience it is not the input filter cap that is important here,
but rather that it is the final filter cap in the main PSU filter that
must be connected to the "star point" or its equivalent.

In power amps this is relatively easy to achieve and running a thick bus
from the PSU 0V past the power section to the preamp section should work
just a s well since the power currents will not flow through any of the
preamp sections of the bus.

In separate pre-amps or mic pre-amps or tube mixers where the supply is
remote from the pre-amp this is clearly not possible and there is the
added problem of separating power currents from input/output signal
currents (unless floating transformer inputs and outputs are used). One
solution I have seen is to have a local pre-amp power supply - indeed
this was very common practice in many tube based recording mixers of the
50s and 60s. Each pre-amp would have its own mains transformer and PSU
along with balanced floating inputs and outputs. All earth loop problems
were therefore local to the pre-amp and you could connect them together
however you liked to build a mixer without ever having to worry about
ground loops. An expensive option to be sure, but one that worked very well.


And in other 50s and 60s systems a whole rack full of microphone preamps
were powered from a common power supply without problems because only
power currents flowed through the wires from the power supply, the
signal input and output currents were isolated from the common power
wires by input and output transformers.


I am not clear about that. The output signal currents (internal to the
transformer isolated circuit) flow from the psu through the output stage
and transformer primary and thence to the PSU 0V, so presumably each
needs a separate connection to/from the PSU?

Oops on proof reading, I see that you already mentioned this in
parenthesis, oh well.


Sort of, except I was assuming separate PSUs rather than one feeding a
rack of mic preamps.

Cheers

Ian

Regards,

John Byrns

  #28   Report Post  
Posted to rec.audio.tubes
Eeyore Eeyore is offline
external usenet poster
 
Posts: 8,474
Default Ground Busses



Ian Thompson-Bell wrote:

The problem I see with that is that all output currents must flow from
the power supply, through the load and back to the PSU 0V but they share
a common ground with the inputs. How do you separate these?


Clever local decoupling can achieve this for all but very low frequencies. A
technique used at Neve in fact.

Graham

  #29   Report Post  
Posted to rec.audio.tubes
Ian Thompson-Bell Ian Thompson-Bell is offline
external usenet poster
 
Posts: 493
Default Ground Busses

Eeyore wrote:

Ian Thompson-Bell wrote:

Eeyore wrote:
Ian Thompson-Bell wrote:
Henry Pasternack wrote:
Andre Jute wrote:

A star ground is just a circular bus or a very short bus.
Not really, ANDRE. A star ground is the abstract notion of a purely
equipotential (equal voltage) single point connection that eliminates
ground loops by reducing the resistance of the common ground bus to
zero. It's impossible to achieve in practice, though, and trying to
take the approach too literally is likely to cause more harm than
good.
The key phrase here is 'reducing the resistance of the common ground bus
to zero'. it is all very well connecting all grounded leads to a single
point but if you then connect that by a single wire to the zero volts
point of the power supply you have immediately introduced a long no zero
common ground bus. So a star ground really only works if the star point
IS the 0V point of the PSU i.e the ground of the input filter cap.#

In power amps this is relatively easy to achieve and running a thick bus
from the PSU 0V past the power section to the preamp section should work
just a s well since the power currents will not flow through any of the
preamp sections of the bus.
But still a compromise.


In separate pre-amps or mic pre-amps or tube mixers where the supply is
remote from the pre-amp this is clearly not possible and there is the
added problem of separating power currents from input/output signal
currents (unless floating transformer inputs and outputs are used). One
solution I have seen is to have a local pre-amp power supply - indeed
this was very common practice in many tube based recording mixers of the
50s and 60s. Each pre-amp would have its own mains transformer and PSU
along with balanced floating inputs and outputs. All earth loop problems
were therefore local to the pre-amp and you could connect them together
however you liked to build a mixer without ever having to worry about
ground loops. An expensive option to be sure, but one that worked very well.
Far simpler is to have 2 (or more) stars and use these to direct current flow.
In particular, the PSU should have its own star and this is where ALL ripple
currents must flow. This can now be tied to the input 'star' with a
*non-current-carrying conductor* (or at least carrying only the B- smoothed DC).

Presumably you mean no *signal* current carrying conductor.


Well ... if there's no current, then there'll be no signal too for sure. What I meant
basically was a link to simply ensure that the 2 stars are at the same potential.


But that link carries common mode current from one star to the PSU 0V so
how does that solve the problem?


This still leaves a common mode conductor carrying output signal current
which is of course supplied by the power supply. I am not clear how
multiple local stars solve the problem.

It is *essential* to keep power and signal paths separate for hum free
operation.

Which can only be achieved with transformers?


Not necessary. Transfomers introduce their own problems.

Graham


So how do you isolate signal currents from power supply ones? given that
output currents flow from the PSU through the load and back to the PSU
0V with or without transformers?

Cheers

Ian
  #30   Report Post  
Posted to rec.audio.tubes
Ian Thompson-Bell Ian Thompson-Bell is offline
external usenet poster
 
Posts: 493
Default Ground Busses

Eeyore wrote:

Ian Thompson-Bell wrote:

The problem I see with that is that all output currents must flow from
the power supply, through the load and back to the PSU 0V but they share
a common ground with the inputs. How do you separate these?


Clever local decoupling can achieve this for all but very low frequencies. A
technique used at Neve in fact.

Graham


Please elaborate. I can see local B+ decoupling is practical not to say
fairly common, but how do you locally decouple grounds?

Cheers

Ian


  #31   Report Post  
Posted to rec.audio.tubes
Henry Pasternack[_2_] Henry Pasternack[_2_] is offline
external usenet poster
 
Posts: 70
Default Ground Busses

"Eeyore" wrote in message
...
Ian Thompson-Bell wrote:
The problem I see with that is that all output currents must flow from
the power supply, through the load and back to the PSU 0V but they share
a common ground with the inputs. How do you separate these?


Clever local decoupling can achieve this for all but very low frequencies.
A
technique used at Neve in fact.


Once again, agreed. The way I do it is as follows:

The main capacitor board has a short ground bus running through it. The
power transformer center tap connects at one end of this bus. All the
charging currents associated with the rectifier are contained at this end.
The other end of the ground bus faces the signal circuitry.

The B+ lead to the output transformer comes off the first filter cap.
Current
flows to the transformer, through the output tube(s), plate to cathode, and
back to the filter cap ground bus. The wires in this circuit are routed
close
together (or twisted) to minimize loop area.

The second filter cap (or set of filter caps, or whatever) sits on an
extension
of the ground bus/ No output stage current flows in this extension. The
far
end of the extension is the input/driver circuit ground reference. On the
B+
side, RC or preferably LC decoupling is used to isolate the two loops at
signal frequencies.

The input jacks are electrically isolated from the chassis and connected to
the input circuit using a twisted pair. A separate ground bus runs the
length
of the input/driver stage. The input twisted pair ground is connected to
this
bus at the input tube end, and a wire connects the driver stage end (or the
signal circuit bus itself is extended) to the cap board signal ground.

There is a solid connection from the rectifier side of the power supply
ground
bus to the chassis. Then, the input jack grounds are optionally connected
to
the chassis by small (0.01uF) capacitors with short leads. These (in
principle)
bypass RF currents on the input cable shields to the chassis.

This is a pretty good approach that has worked well for me. A major source
of hum is unbalanced capacitance between the power transformer windings
and ground. With this arrangement, these currents flow through the chassis
and back into the supply through the rectifier side of the power supply
ground
bus, avoiding the signal circuitry.

Sometimes, though, in spite of careful design, the damned thing still hums.
In
that case, you have to experiment until you find the cause of the problem.

-Henry


  #32   Report Post  
Posted to rec.audio.tubes
Eeyore Eeyore is offline
external usenet poster
 
Posts: 8,474
Default Ground Busses



Ian Thompson-Bell wrote:

Eeyore wrote:
Ian Thompson-Bell wrote:

The problem I see with that is that all output currents must flow from
the power supply, through the load and back to the PSU 0V but they share
a common ground with the inputs. How do you separate these?


Clever local decoupling can achieve this for all but very low frequencies. A
technique used at Neve in fact.



Please elaborate. I can see local B+ decoupling is practical not to say
fairly common, but how do you locally decouple grounds?


It helps somewhat when using twin supply op-amp circuitry. You place a resistor
(say 100 ohms) in both supply rails and a cap (say 100 uF) from each pin of the
op-amp to local ground. The local ground is returned to the central 'star point'
or earth bus via the non-curent-carrying' conductor. This local decoupling results
in output currents (these are really the only ones of concern) circulating locally
to the op-amp, at least at all but low frequencies.

I suppose something similar can be achieved with single supply working too.
Imagine the series R being a very high value and you'll see that it approximates
to an individual local supply for each such decoupled stage.

Graham

  #33   Report Post  
Posted to rec.audio.tubes
Andre Jute Andre Jute is offline
external usenet poster
 
Posts: 1,661
Default Ground Busses



Porno Pas wrote:

This is something I found on the Web.


SNIP some soppy crap

The
author has left his phone number and email address in the signature. If
you have any issues, you may wish to contact him there. I would, in fact,
be very interested in hearing if anyone manages to contact him that way.

-Henry

--- BEGIN REPOSTED ARTICLE ---

Someone suggested I write an article on power and grounding techniques
for equipment construction.


SNIP some stuff probably more at home on rec.audio.opinion.

--

Henry A. Pasternack
Member Scientific Staff (514) 761-8734 (phone)
Bell Northern Research, Montreal (514) 761-8509 (fax)


Isn't he the fellow who was fired by Bell not too long after that? I
wonder why. Considering the article posted, it is not difficult to
guess.

Andre Jute
Visit Jute on Amps at
http://members.lycos.co.uk/fiultra/
"wonderfully well written and reasoned information
for the tube audio constructor"
John Broskie TubeCAD & GlassWare
"an unbelievably comprehensive web site
containing vital gems of wisdom"
Stuart Perry Hi-Fi News & Record Review
  #34   Report Post  
Posted to rec.audio.tubes
Eeyore Eeyore is offline
external usenet poster
 
Posts: 8,474
Default Ground Busses



Ian Thompson-Bell wrote:

So how do you isolate signal currents from power supply ones? given that
output currents flow from the PSU through the load and back to the PSU
0V with or without transformers?


Explained in my other reply.

Graham

  #35   Report Post  
Posted to rec.audio.tubes
Andre Jute Andre Jute is offline
external usenet poster
 
Posts: 1,661
Default Ground Busses

Here we go with the old Magnequest Scum methods again. What happens is
that Porno Pas, unable technically to fault what I write, rephrases
what I say in a slightly different manner and then pretends that what
I say is wrong. It's bull****. And the rest is just Porno Pas claiming
that whatever I say is white is really black. It is beneath contempt,
not worth answering. That's quite aside from the fact that I don't
hold cosy chats with child molesers. -- Andre Jute

Henry "Porno" Pasternack wrote:
Andre Jute wrote:
A star ground is just a circular bus or a very short bus.


Not really, ANDRE. *A star ground is the abstract notion of a purely
equipotential (equal voltage) single point connection that eliminates
ground loops by reducing the resistance of the common ground bus to
zero. *It's impossible to achieve in practice, though, and trying to
take the approach too literally is likely to cause more harm than
good.

Grounding is is tricky and tiresome in inverse proportion to the
amount of thought you give it.


I would say the opposite is true. *The less you think about grounding,
the less tricky it seems. *With no thought at all, it becomes as simple
as pie. *Or fruit tart, for that matter. *Just connect all the ground
connections together any way you like, and don't worry. *It's only
when you start to think about it that it truly becomes tricky.

Here you can see my star point [URL deleted].


You may be able to see it, but to my eyes the picture is impossibly
tiny to reveal any useful details. *But, you know I have this problem
with photographs.

Most schematics don't tell you enough about earthing. Here, for
instance: [URL deleted]. *I've shown the star earth being implemented
but have not said anything about connecting the case to earth.


Attempting to connect all the grounds together like that, willy-nilly,
is not the right approach. *That's because in practice it's nearly
impossible to achieve a true equipotential connection for all those
wires. *Also, there are other performance issues having to do with
all those long ground connections running about the amplifier.

... I showed all the 0V connections in order, with a note saying
"mind the order of the grounding connections", and *two people wrote
me letters saying that DIYers are not idiots who need their hands
held.


Then the DIYers were idiots, because the subject is quite worthy of
elaboration. *The problem I see with everything you say here is that
you fail to address the most important meat of the problem, which is
precisely how to determine the "order of the grounding connections"
and how this translates into a practical wiring and ground layout.

My opinion on this subject is there are many ways to wire an amplifier
to minimize hum and noise. *Star grounding (and its variants) and
bus wiring are two common solutions. *Rather than posting fuzzy
pictures and vague generalities, if you would like to help your
readers, you should teach them the principles involved (you do
know them, right?) so they can work out the optimum grounding
scheme for each project by themselves.

Of course, being a lying psychopath pornographic scumbag, I may
not really know what I'm talking about! *Feel free to ignore
everything I say. *In fact, I strongly urge you to do so! *:-)

-Henry




  #36   Report Post  
Posted to rec.audio.tubes
Eeyore Eeyore is offline
external usenet poster
 
Posts: 8,474
Default Ground Busses



Andre Jute wrote:

Here we go with the old Magnequest Scum methods again. What happens is
that Porno Pas, unable technically to fault what I write, rephrases
what I say in a slightly different manner and then pretends that what
I say is wrong.


It's nothing like what you wrote you bloody idiot.

Henry actually understands the fine detail of what he's talking about instead
of posting 'design by rote' guides.

Graham

  #37   Report Post  
Posted to rec.audio.tubes
Andre Jute Andre Jute is offline
external usenet poster
 
Posts: 1,661
Default Ground Busses

On Mar 2, 7:13*pm, "West" wrote:
"Andre Jute" wrote in message

...
A star ground is just a circular bus or a very short bus. Grounding is
is tricky and tiresome in inverse proportion to the amount of thought
you give it, so I do something between what Iain does and what Patrick
does, and I call it a "star-point". Here you can see my star pointhttp://members.lycos.co.uk/fiultra/KISS%20192%20T68MZ417A.jpg
on my T68bis "Minus Zero" amp. It is the short piece of stiff wire
sticking up at the right hand side of the aluminium cased resistor
behind the battery boxes in the centre of the top right hand
photograph. It's the bleeder resistor to the power supply and the star
point is at its 0V end. Notice how the convenitonally drawn schematichttp://members.lycos.co.uk/fiultra/t68mzwe417acircuit.jpg
tells you nothing of this, leaving you to work it out for yourself.
All the 0V wires are dropped over this stiff wire and soldered on.
Even on such a short bus I take care of the order of the wires as I
put them on. From this point a wire is taken to main's earth. The case
is connected to mains earth by a wire from very sturdy bolt held in
with serrated washers and nuts, which is placed as near as possible to
the mains socket; unfortunately it is not too clear in the photograph,
but it is just below the switch, near the top right hand corner of the
righthand output transformer in the picture.

Most schematics don't tell you enough about earthing. Here, for
instance:http://members.lycos.co.uk/fiultra/Jute-EL34-SEntry.jpg
I've shown the star earth being implemented but have not said anything
about connecting the case to earth. Mind you, on some of the Lundahl
Modular Series 300B schemos I showed all the 0V connections in order,
with a note saying "mind the order of the grounding connections", and
two people wrote me letters saying that DIYers are not idiots who need
their hands held. (I was, when I started, and I'm very grateful to
people who made 90 mile round trips to come check over my
constructions before I fired them up.)

Andre Jute
Visit Jute on Amps athttp://members.lycos.co.uk/fiultra/
"wonderfully well written and reasoned information
for the tube audio constructor"
John Broskie TubeCAD & GlassWare
"an unbelievably comprehensive web site
containing vital gems of wisdom"
Stuart Perry Hi-Fi News & Record Review

Great illustration. Did you have those schematics/illustrations
professionally made or is there a particular program you used? Thanks.

west


Good golly, no, I don't send out for simple art. Graphic arts is one
of my professions, though at the higher levels we called typopgraphers
or reprographers because it as much about technicalities as about art.
Here are some introductory books in a series of which I am general
editor:
http://members.lycos.co.uk/fiultra/T...%20GDitCA.html
and see also my key text for advanced designers "Grids" (Rotovision,
Switzerland, 1996) he
http://members.lycos.co.uk/fiultra/T...re%20Jute.html

The programme I use for schematics is QuarkXPress, a professional page
makeup programme; I just drew the symbols in it and duplicate them on
the "pasteboard". It really isn't worth buying QXP--- it is a fair
chunk over a thousand dollars in price --- or investing the
substantial time necessary to master the programme, just to draw
schematics. Try Microsoft Word's drawing module.

Andre Jute
"I was at a board meeting for the LA Chapter of the Audio Engineering
Society last night on XM Satellite radio audio and data transmission.
Sadly, we missed you there, and at the SMPTE and Acoustical Society
recent meetings as well. Everyone was asking, 'Where is that wonderful
Andre Jute? The world just doesn't rotate without him...'" -- John
Mayberry, Emmaco
  #38   Report Post  
Posted to rec.audio.tubes
Ian Iveson Ian Iveson is offline
external usenet poster
 
Posts: 960
Default Ground Busses

John Byrns wrote:

I meant originally, I assume this is one of the many
copies on the web
that you said existed?


I found the posting today on the Web.


Are you saying it wasn't originally posted on usenet?


Guys, please, this is the most futile, petty and puerile
bout of bickering I've ever seen. Truly. I even feel stupid
for reading it.

You're undermining the quality of rat squabbling. People
expect better than flyweight finger-poking.

Ian


  #39   Report Post  
Posted to rec.audio.tubes
Andre Jute Andre Jute is offline
external usenet poster
 
Posts: 1,661
Default Ground Busses

On Mar 2, 9:39*pm, Nick Gorham wrote:
Andre Jute wrote:
A star ground is just a circular bus or a very short bus. Grounding is
is tricky and tiresome in inverse proportion to the amount of thought
you give it, so I do something between what Iain does and what Patrick
does, and I call it a "star-point". Here you can see my star point
http://members.lycos.co.uk/fiultra/K...0T68MZ417A.jpg
on my T68bis "Minus Zero" amp. It is the short piece of stiff wire
sticking up at the right hand side of the aluminium cased resistor
behind the battery boxes in the centre of the top right hand
photograph. It's the bleeder resistor to the power supply and the star
point is at its 0V end. Notice how the convenitonally drawn schematic
http://members.lycos.co.uk/fiultra/t...17acircuit.jpg


Given the topic of the thread, shouldn't the ground commection under the
rectifier be after the choke, not before?

--
Nick


I published a wiring diagram as well. If you wire as instructed for
this little amp, all 0V ends are led directly to a single point. In
that case it doesn't matter where the earth is shown on the circuit
diagram (on which there isn't space to show the star point) because
there is a wiring schemo as well.

HTH.

Andre Jute
Visit Jute on Amps at http://members.lycos.co.uk/fiultra/
"wonderfully well written and reasoned information
for the tube audio constructor"
John Broskie TubeCAD & GlassWare
"an unbelievably comprehensive web site
containing vital gems of wisdom"
Stuart Perry Hi-Fi News & Record Review
  #40   Report Post  
Posted to rec.audio.tubes
Andre Jute Andre Jute is offline
external usenet poster
 
Posts: 1,661
Default Ground Busses

On Mar 2, 9:53*pm, John Byrns wrote:
In article ,
*"Henry Pasternack" wrote:

"John Byrns" wrote in message
...
I meant originally, I assume this is one of the many copies on the web
that you said existed?


I found the posting today on the Web.


Are you saying it wasn't originally posted on usenet?


It might not be Google at fault when the original of the article in
question cannot be found. The author might have withdrawn it from the
net when Bell Canada fired him because of it.

Regards,

John Byrns

--
Surf my web pages at, *http://fmamradios.com/


HTH.

Andre Jute
Thumbs well clear of the bricks
Reply
Thread Tools
Display Modes

Posting Rules

Smilies are On
[IMG] code is On
HTML code is Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Busses in Adobe Audition 1.5 Rivergoat Pro Audio 5 July 14th 06 04:01 AM
Audio Ground 10 ohms above powersupply ground?? Vacuum Tubes 1 December 12th 05 10:03 PM
Floating ground to common ground question. Lee Wasson Car Audio 0 June 7th 04 05:36 PM
VCAs vs. subs vs. busses vs. groups Luther Bell Pro Audio 16 May 17th 04 07:08 AM
why rca ground isolators just sound better than cleaning ground points Spockie Car Audio 21 May 13th 04 01:56 AM


All times are GMT +1. The time now is 09:29 AM.

Powered by: vBulletin
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Copyright ©2004-2024 AudioBanter.com.
The comments are property of their posters.
 

About Us

"It's about Audio and hi-fi"