What level of impedance is tubed equipment like tuners, phono
preamps, tuned CD players, and such line outputs are expected to
have? Somewhere around 10K to 50K? I think that the voltage
level of the audio is around 1Vrms, yes?

Robert Casey wrote:

What level of impedance is tubed equipment like tuners, phono
preamps, tuned CD players, and such line outputs are expected to
have? Somewhere around 10K to 50K? I think that the voltage
level of the audio is around 1Vrms, yes?

I like to keep the output impedances of all the above items down
to that of a cathode follower, ot bootstrapped follower,
ie, about from 500 ohms to 2k max.

The input impedances all should be over 47k.

The use of Ro 2k means that cables and input C of up to 0.004 uF can
be
tolerated before causing a -3 dB pole at 20 kHz.

Patrick Turner.

Robert Casey wrote:
What level of impedance is tubed equipment like tuners, phono
preamps, tuned CD players, and such line outputs are expected to
have? Somewhere around 10K to 50K? I think that the voltage
level of the audio is around 1Vrms, yes?

This thread has prompted me to compose a rather lengthy reply on the
subject of impedances, since there seems to be some blatant
science-fiction on the subject (not by authors of any of the replies to
this thread, except for one screamingly incorrect post that I only saw
indirectly because it was indavertently quoted).

First off, some conventions and definitions, if you know this stuff just
skip past it to the double-dashed line.

DEFINITIONS AND CONVENTIONS

For the purposes of this article, we'll use the term "impedance" since
it seems to be the term of choice in audiophile circles, even though
more correctly we should be speaking of "resistance," i.e. the real
component of impedance. We will therefore only be speaking in terms of
the scalar quantity R, not the phasor quantity Z.

R1 + R2 + R3 -- Resistors in series, values are additive.

R1 | R2 -- Resistors in parallel.
For two resistors, Rt = (R1*R2)/(R1+R2)

For more than two resistors, it's easier to add conductances and take
the reciprocal:

R1 | R2 | R3 ... | Rn:
Rt = 1/(1/R1 + 1/R2 + 1/R3 ... + 1/Rn)

Corner frequency: For a single pole circuit (one equivalent resistor and
one equivalent capacitor, high-pass or low-pass) -

Fo = 0.16/(R*C)
Where Fo is in Hertz, R is in megohms, C is in microfarads

Fo is that frequency at which voltage response is down to 71%, IOW power
response is about -3 dB. Above that (high-pass) or below that (low-pass)
the response asymptotically approaches normal pass-band response. In the
other direction, response asymptotically approaches a line representing
-6 dB per octave.

Another way of writing the corner frequency relationship:
Fo = 160,000/(R*C)
Where Fo is again in Hertz, R is in megohms, and C is in picofarads.

================================================== ===========

First off, there is a lot of mythology about "impedance matching". The
Maximum Power Transfer Theorem (which states that maximum power transfer
occurs when the load impedance equals the source impedance) is often
hauled out as "proof" of the necessity of such "matching." In general,
however, the MPTT is only of interest to radio people and telephone
companies. There is some application of MPTT to output stages, but most
experienced tube/valve enthusiasts learn early on that best *overall*
performance rarely occurs at the MPTT impedance point.

More applicable to most situations involving voltage amplifiers is
*voltage transfer*. This occurs when source impedance (output impedance
of the preceding stage) is minimized, and load impedance (input
impedance of the following stage) is maximized.

For the usual common-cathode triode amplifiers with no local feedback,
the output impedance of a stage Ro will be approximately Rp | Rl (where
Rp is plate resistance, and Rl is plate load resistance). Putting some
typical numbers to this: for a 12AX7 with an operating point such that
Rp is 60k ohms, and a plate load resistance of 100k ohms, the Ro will be
on the order of 38k ohms. But lets say we go to 6SN7 instead, with an Rp
around 7000 ohms, and a load resistance of 22k, then our Ro drops
significantly to about 5.3k!

If we change to a common-anode topology (cathode follower) output
impedance drops phenomenally - and output impedances of under 1k are
easily attainable even with small tubes. Similarly, if local feedback is
involved (either current-feedback via a cathode resistor, or voltage
feedback via an anode-to-grid resistor) output impedance can be affected
materially. The relations get quite complex; see RDH if you want the
gory details.

The impedance of the following stage will usually be just the value of
the grid resistor. The voltage transfer between stages will be:

Vo/Vi=Rg/(Ro+Rg)

Where Vo/Vi represents the ratio of loaded to unloaded voltage at the
output of the stage, and Rg represents the input resistance of the
following stage. (Note that if any pull-down resistors are included to
insure approximately zero DC offset at the output of a standalone
device, this resistor would simply be paralleled in with Rg).

Again, some numbers. With the 12AX7 stage above feeding a 6V6 stage with
a 220k grid resistor - Vo/Vi=220k/(38k+220k) or about 85%. Not a bad
voltage transfer ratio. Note that as source impedance decreases, or load
impedance increases, the voltage transfer ratio improves. With the 6SN7
as a driver instead, and the same load (grid) resistor, Vo/Vi jumps up
to almost 98%.

But voltage transfer ratio is not usually the most important criterion.
It's something you have to take into account when designing, but then
you forget about it. Much more salient is the effect that the system
impedances (resistances) have on the corner frequencies.

The first is the high-pass corner frequency, or bass rolloff. This is
given by the RC combination of the coupling capacitor (Cc) and the
series combination of Ro+Rg.

Fo=.16/(Cc*(Ro+Rg))

Note that if Ro Rg, then Ro essentially drops out of the equation,
and we can simply use the grid resistor Rg for our calculation. (The
same would be true if Rg were than Ro, but we rarely see this
condition in audio-frequency vacuum-state circuitry.)

Again, some numbers. For the 12AX7 driver, and a 0.05 uF coupling
capacitor, the bass rolloff frequency would be

Fl=0.16/(.05*(.220+.038)M) = 12.4 Hz.

For the 6SN7 driver, same coupling capacitor:

Flo=0.16/(.05*(.220+.0053)M) = 14.2 Hz.

Note that this isn't a huge shift. This is because, in both cases, the
load impedance is significantly greater than the source impedance.
Another way of looking at this: the lower you make the source impedance,
the less the circuit's frequency response will depend on the load impedance.

The other corner that has to be looked at is the low-pass
(high-frequency roll-off) corner. This pole exists because of
distributed capacitances in cabling, grid-to-cathode capacitance, and
Miller capacitance (an apparent amplification of anode-to-grid
capacitance). All these effects together can add up to tens or hundreds
of picofarads, and need to be taken into account. This corner occurs at

Fhi=160,000/(Cp*(Ro | Rg)) where Cp is total parallel capacitance in pF

How about some numbers? Let's say that the total load capacitance due to
circuit capacitances, tube capacitances, and cabling adds up to 220 pF.
For the 12AX7 driver,

Fhi=160,000/(220*.0324M)=22.4 kHz.

This doesn't give much leeway for high frequency response. How about the
6SN7 driver?

Fhi=160,000/(220*.0052M)=139 kHz.

Lots of treble headroom! Notice how the low source impedance effectively
swamps the effect of the parallel capacitance?

So here's the scoop:

1) Make your source impedance as low as practical.
2) Make your load impedance as high as practical (staying within the
recommended grid resistor maximum value!)
3) Run the calculations.
4) Redo if you aren't happy with the results.

Cheers,
Fred
--
+--------------------------------------------+
| Music: http://www3.telus.net/dogstarmusic/ |
| Projects: http://dogstar.dantimax.dk |
+--------------------------------------------+

In article nBodc.6175$2H4.3363@clgrps12, Fred Nachbaur
wrote:

First off, there is a lot of mythology about "impedance matching". The
Maximum Power Transfer Theorem (which states that maximum power transfer
occurs when the load impedance equals the source impedance) is often
hauled out as "proof" of the necessity of such "matching." In general,
however, the MPTT is only of interest to radio people and telephone
companies. There is some application of MPTT to output stages, but most
experienced tube/valve enthusiasts learn early on that best *overall*
performance rarely occurs at the MPTT impedance point.

Even the above statement on the "MPTT" is very misleading and is itself
essentially mythical.


Regards,

John Byrns


Surf my web pages at, http://users.rcn.com/jbyrns/

John Byrns wrote:
In article nBodc.6175$2H4.3363@clgrps12, Fred Nachbaur
wrote:


First off, there is a lot of mythology about "impedance matching". The
Maximum Power Transfer Theorem (which states that maximum power transfer
occurs when the load impedance equals the source impedance) is often
hauled out as "proof" of the necessity of such "matching." In general,
however, the MPTT is only of interest to radio people and telephone
companies. There is some application of MPTT to output stages, but most
experienced tube/valve enthusiasts learn early on that best *overall*
performance rarely occurs at the MPTT impedance point.


Even the above statement on the "MPTT" is very misleading and is itself
essentially mythical.

You quoted not one, but four discrete statements, not counting clauses.
Which one is "very misleading and itself essentially mythical", and why?

Cheers,
Fred
--
+--------------------------------------------+
| Music: http://www3.telus.net/dogstarmusic/ |
| Projects: http://dogstar.dantimax.dk |
+--------------------------------------------+

like always -ZM is here to amuse ya
energy preservation is always of first importance to me;
that's why I abandoned wimpy stages some time ago.......
and ,yes,MPT is sheeeeeettttttty aproach,at least for our gadgets
--
--
--
.................................................. ........................
Choky
Prodanovic Aleksandar
YU

"don't use force, "don't use force,
use a larger hammer" use a larger tube
- Choky and IST"
- ZM
.................................................. ...........................
"Fred Nachbaur" wrote in message
newsNtdc.25628$Sh4.16585@edtnps84...


John Byrns wrote:
In article nBodc.6175$2H4.3363@clgrps12, Fred Nachbaur
wrote:


First off, there is a lot of mythology about "impedance matching". The
Maximum Power Transfer Theorem (which states that maximum power transfer
occurs when the load impedance equals the source impedance) is often
hauled out as "proof" of the necessity of such "matching." In general,
however, the MPTT is only of interest to radio people and telephone
companies. There is some application of MPTT to output stages, but most
experienced tube/valve enthusiasts learn early on that best *overall*
performance rarely occurs at the MPTT impedance point.


Even the above statement on the "MPTT" is very misleading and is itself
essentially mythical.

You quoted not one, but four discrete statements, not counting clauses.
Which one is "very misleading and itself essentially mythical", and why?

Cheers,
Fred
--
+--------------------------------------------+
| Music: http://www3.telus.net/dogstarmusic/ |
| Projects: http://dogstar.dantimax.dk |
+--------------------------------------------+

Choky wrote:

like always -ZM is here to amuse ya
energy preservation is always of first importance to me;

My God, ZM, if you like energy preservation, what in the world are you
doing with tubes? :-p

Brings up an interesting side note: The Maximum Power Transfer point is
not the point of maximum efficiency. Maximum efficiency occurs when
source impedance is minimized compared to load impedance.

that's why I abandoned wimpy stages some time ago.......
and ,yes,MPT is sheeeeeettttttty aproach,at least for our gadgets

That's how I see it.

Still wondering which of the four statements John quoted got his
knickers all in a twist...

Cheers,
Fred
--
+--------------------------------------------+
| Music: http://www3.telus.net/dogstarmusic/ |
| Projects: http://dogstar.dantimax.dk |
+--------------------------------------------+

My God, ZM, if you like energy preservation, what in the world are you
doing with tubes? :-p


Well, at least in radio reception, you want to preserve as much energy
in that weak radio
signal you wish to copy. And you're willing to pay the electric bill to
make it happen.



Brings up an interesting side note: The Maximum Power Transfer point
is not the point of maximum efficiency. Maximum efficiency occurs when
source impedance is minimized compared to load impedance.

Your local friendly electric company doesn't go on MPT. They want all
the power to be
dissapated on the load side of the customers kilowatthour meters. They
want Max efficiency.
This can be confusing to a sophomore double E student when the prof is
talking about the
MPT idea. A good way to avoid this confusion would be to say "I have a
battery with
a Theveon(sp) equivalent resistance of 10 ohms. I want to size my load
resistance so it can
get as hot as possible, ie, to extract as much power as I can out of the
battery. Right now I
don't care about power wasted inside the battery. So what size
reisistor do I need?"
Then: "Okay, now I do care about the amount of power wasted in the
battery. I can
accept 1% wasted power. Now what size resistor should I use?"

Robert Casey wrote:




My God, ZM, if you like energy preservation, what in the world are you
doing with tubes? :-p



Well, at least in radio reception, you want to preserve as much energy
in that weak radio
signal you wish to copy. And you're willing to pay the electric bill to
make it happen.

That's an interesting viewpoint. Hadn't looked at it that way.

Brings up an interesting side note: The Maximum Power Transfer point
is not the point of maximum efficiency. Maximum efficiency occurs when
source impedance is minimized compared to load impedance.


Your local friendly electric company doesn't go on MPT. They want all
the power to be
dissapated on the load side of the customers kilowatthour meters. They
want Max efficiency.

Indeed. They even go to considerable trouble to cancel out the reactive
portion of the customers' loads (specifically positive reactance, i.e.
inductive, due to motors, transformers, etc.) with judiciously placed
capacitors along the grid (they usually just call 'em "reactors"). This
greatly reduces reactive currents, hence I^2*R losses in the lines.

This can be confusing to a sophomore double E student when the prof is
talking about the
MPT idea. A good way to avoid this confusion would be to say "I have a
battery with
a Theveon(sp)

Thevenin

equivalent resistance of 10 ohms. I want to size my load
resistance so it can
get as hot as possible, ie, to extract as much power as I can out of the
battery. Right now I
don't care about power wasted inside the battery. So what size
reisistor do I need?"

10 ohms. MPTT.

Then: "Okay, now I do care about the amount of power wasted in the
battery. I can
accept 1% wasted power. Now what size resistor should I use?"

990 ohms. Thanks for an *Excellent* illustration.

Cheers,
Fred
--
+--------------------------------------------+
| Music: http://www3.telus.net/dogstarmusic/ |
| Projects: http://dogstar.dantimax.dk |
+--------------------------------------------+

In article sFCdc.26008$J56.4483@edtnps89, Fred Nachbaur
wrote:

Indeed. They even go to considerable trouble to cancel out the reactive
portion of the customers' loads (specifically positive reactance, i.e.
inductive, due to motors, transformers, etc.) with judiciously placed
capacitors along the grid (they usually just call 'em "reactors"). This
greatly reduces reactive currents, hence I^2*R losses in the lines.

Are you sure about this, when I have heard power guys talking about
"reactors" they always seemed to be talking about inductors? I guess I
wouldn't put it past them to also call capacitors "reactors". I have
heard inductors and capacitors called "positive VARs", and "negative VARs"
respectively.


Regards,

John Byrns


Surf my web pages at, http://users.rcn.com/jbyrns/

John Byrns wrote:
In article sFCdc.26008$J56.4483@edtnps89, Fred Nachbaur
wrote:


Indeed. They even go to considerable trouble to cancel out the reactive
portion of the customers' loads (specifically positive reactance, i.e.
inductive, due to motors, transformers, etc.) with judiciously placed
capacitors along the grid (they usually just call 'em "reactors"). This
greatly reduces reactive currents, hence I^2*R losses in the lines.


Are you sure about this,

Yes. One of the lead engineers for BC Hydro, a fellow named Wilf Rigter,
took me through a tour of a large BC Hydro facility in Vancouver some
years ago, and explained it to me. He pointed out the huge "reactors"
and - with a wink - said "Those are simply 'capacitors' to people like
you or me."

when I have heard power guys talking about
"reactors" they always seemed to be talking about inductors? I guess I
wouldn't put it past them to also call capacitors "reactors". I have
heard inductors and capacitors called "positive VARs", and "negative VARs"
respectively.

There could certainly be regional differences also. Strictly speaking,
both inductors and capacitors are of course reactors, inductors
exhibiting a positive reactance (phasor pointing upward from the real
axis), whereas capacitors exhibit a negative reactance (pointing
downward from the real axis).

Cheers,
Fred
--
+--------------------------------------------+
| Music: http://www3.telus.net/dogstarmusic/ |
| Projects: http://dogstar.dantimax.dk |
+--------------------------------------------+

Argh, it should have been obvious that neither of us knows a thing about
"reactors". I went to Google hoping to find the definition of "reactor"
in this context, and found that a "reactor" is some kind of "Nuclear"
gadget, not a capacitor or inductor.


Regards,

John Byrns


In article XSFdc.7722$mn3.2609@clgrps13, Fred Nachbaur
wrote:

John Byrns wrote:
In article sFCdc.26008$J56.4483@edtnps89, Fred Nachbaur
wrote:


Indeed. They even go to considerable trouble to cancel out the reactive
portion of the customers' loads (specifically positive reactance, i.e.
inductive, due to motors, transformers, etc.) with judiciously placed
capacitors along the grid (they usually just call 'em "reactors"). This
greatly reduces reactive currents, hence I^2*R losses in the lines.


Are you sure about this,

Yes. One of the lead engineers for BC Hydro, a fellow named Wilf Rigter,
took me through a tour of a large BC Hydro facility in Vancouver some
years ago, and explained it to me. He pointed out the huge "reactors"
and - with a wink - said "Those are simply 'capacitors' to people like
you or me."

when I have heard power guys talking about
"reactors" they always seemed to be talking about inductors? I guess I
wouldn't put it past them to also call capacitors "reactors". I have
heard inductors and capacitors called "positive VARs", and "negative VARs"
respectively.

There could certainly be regional differences also. Strictly speaking,
both inductors and capacitors are of course reactors, inductors
exhibiting a positive reactance (phasor pointing upward from the real
axis), whereas capacitors exhibit a negative reactance (pointing
downward from the real axis).

Cheers,
Fred
--
+--------------------------------------------+
| Music: http://www3.telus.net/dogstarmusic/ |
| Projects: http://dogstar.dantimax.dk |
+--------------------------------------------+


Surf my web pages at, http://users.rcn.com/jbyrns/

John Byrns wrote:

Argh, it should have been obvious that neither of us knows a thing about
"reactors". I went to Google hoping to find the definition of "reactor"
in this context, and found that a "reactor" is some kind of "Nuclear"
gadget, not a capacitor or inductor.




Watch out when the "no nukes" kooks find out that there are "reactors"
in everyones'
houses! ;-)

John Byrns wrote:
Argh, it should have been obvious that neither of us knows a thing about
"reactors". I went to Google hoping to find the definition of "reactor"
in this context, and found that a "reactor" is some kind of "Nuclear"
gadget, not a capacitor or inductor.


Regards,

John Byrns

http://www.hammondmfg.com/5cchk.htm
Certainly you've been here before.

http://www.lub.lu.se/cgi-bin/show_diss.pl/tec_273.html
Interestingly the title uses the term "Reactor", and it's used in one
other place in the paper, but mostly he refers to them as "reactances".

http://www.capacitor.com.tw/series1.htm
A company in Taiwan

http://www.hilltech.com/trnsduct.html
Refers to inductors only as reactors

http://www.eagleware.com/pdf/apps/2024_Transforms.pdf
Probably the best reference: Quoting, "One of the most useful transforms
for filter design is the Norton. The series form is depicted in Table 1
(see Appendix). It replaces a series reactor, which may be an inductor,
capacitor or L-C resonator, with three reactors and a transformer. One
of the shunt reactors will always be negative. Initially it would seem
this transform is not useful but by applying it to this example, we will
see it is a powerful tool.

One just has to know how to search.

Cheers,
Fred
--
+--------------------------------------------+
| Music: http://www3.telus.net/dogstarmusic/ |
| Projects: http://dogstar.dantimax.dk |
+--------------------------------------------+

John Byrns wrote:

Argh, it should have been obvious that neither of us knows a thing about
"reactors". I went to Google hoping to find the definition of "reactor"
in this context, and found that a "reactor" is some kind of "Nuclear"
gadget, not a capacitor or inductor.

Here's one more for you. All you never wanted to know about power-factor
correction, and then some. Interestingly, sometimes he refers to
inductors as reactors, in other places either capacitors *or* inductors
qualify.

http://www.ipst.org/TechPapers/2003/IPST03Paper4a-4.pdf

Cheers,
Fred
--
+--------------------------------------------+
| Music: http://www3.telus.net/dogstarmusic/ |
| Projects: http://dogstar.dantimax.dk |
+--------------------------------------------+

Fred Nachbaur wrote in message news:XSFdc.7722$mn3.2609@clgrps13...
John Byrns wrote:
In article sFCdc.26008$J56.4483@edtnps89, Fred Nachbaur
wrote:


Indeed. They even go to considerable trouble to cancel out the reactive
portion of the customers' loads (specifically positive reactance, i.e.
inductive, due to motors, transformers, etc.) with judiciously placed
capacitors along the grid (they usually just call 'em "reactors"). This
greatly reduces reactive currents, hence I^2*R losses in the lines.


Are you sure about this,

Yes. One of the lead engineers for BC Hydro, a fellow named Wilf Rigter,
took me through a tour of a large BC Hydro facility in Vancouver some
years ago, and explained it to me. He pointed out the huge "reactors"
and - with a wink - said "Those are simply 'capacitors' to people like
you or me."

when I have heard power guys talking about
"reactors" they always seemed to be talking about inductors? I guess I
wouldn't put it past them to also call capacitors "reactors". I have
heard inductors and capacitors called "positive VARs", and "negative VARs"
respectively.

There could certainly be regional differences also. Strictly speaking,
both inductors and capacitors are of course reactors, inductors
exhibiting a positive reactance (phasor pointing upward from the real
axis), whereas capacitors exhibit a negative reactance (pointing
downward from the real axis).

Cheers,
Fred



Theres even an "urban myth" that says plugging capacitors into your
wall outlet will make your power meter stop (or atleast slow down) due
to the caps correcting for the inductive loads around the house.
Around here,all of the "reactors" I've seen on the poles are big
square cans..probably huge oil-filled jobbers..most of them also have
only 1 wire going into the top,meaning the can must the gnd.
connection. (but I have seen a couple with 2 wires on top,possibly
multisection caps?)

"Fred Nachbaur" wrote in message
news:NSAdc.25695$J56.9635@edtnps89...


Choky wrote:

like always -ZM is here to amuse ya
energy preservation is always of first importance to me;

My God, ZM, if you like energy preservation, what in the world are you
doing with tubes? :-p

Brings up an interesting side note: The Maximum Power Transfer point is
not the point of maximum efficiency. Maximum efficiency occurs when
source impedance is minimized compared to load impedance.

that's why I abandoned wimpy stages some time ago.......
and ,yes,MPT is sheeeeeettttttty aproach,at least for our gadgets

That's how I see it.

Still wondering which of the four statements John quoted got his
knickers all in a twist...

Cheers,
Fred
--
+--------------------------------------------+
| Music: http://www3.telus.net/dogstarmusic/ |
| Projects: http://dogstar.dantimax.dk |
+--------------------------------------------+

I use xformer where I can-instead of RC connected stage;
that's what I call energy transfer.

cheers from NEITMTM Choky

(not exactly in too much talkin' mood )

In article DNtdc.25628$Sh4.16585@edtnps84, Fred Nachbaur
wrote:

First off, there is a lot of mythology about "impedance matching". The
Maximum Power Transfer Theorem (which states that maximum power transfer
occurs when the load impedance equals the source impedance) is often
hauled out as "proof" of the necessity of such "matching."

Quite true!

In general,
however, the MPTT is only of interest to radio people and telephone
companies.

It is of interest to radio people only in limited situations, and never
when there is any significant amount of power involved. Telephone
companies only give it lip service, succumbing to practical considerations
in most situations.

There is some application of MPTT to output stages, but most
experienced tube/valve enthusiasts learn early on that best *overall*
performance rarely occurs at the MPTT impedance point.

"Some"/"Rarely"?! No/Never would be closer to the truth, even power
output capability is not maximized by this approach.


Regards,

John Byrns


Surf my web pages at, http://users.rcn.com/jbyrns/

Nothing40 wrote:






There's even an "urban myth" that says plugging capacitors into your
wall outlet will make your power meter stop (or atleast slow down) due
to the caps correcting for the inductive loads around the house.


Only if you are a larger industrial customer with a meter that looks for
power factor.
Residential service rarely has such.

Speaking as an electrician of 28 years, unless the power factor is really
off (the electric company rarely lets this happen), a capacitor bank will
not lower your bill.

- Dyslexics of America Untie! keithw...


"Robert Casey" wrote in message
...
Nothing40 wrote:

There's even an "urban myth" that says plugging capacitors into your
wall outlet will make your power meter stop (or atleast slow down) due
to the caps correcting for the inductive loads around the house.


Only if you are a larger industrial customer with a meter that looks for
power factor. Residential service rarely has such.