Ben Bradley wrote:
On Sun, 08 May 2005 16:19:28 -0700, Bob Cain
wrote:



Kevin Aylward wrote:
Well, I have been pressed for a bit on mic amp design, so I have
knocked something up here.

http://www.anasoft.co.uk/EE/MicAmpDe...AmpDesign.html

Thanks, Kevin. I don't even play circuit designer on TV so
could I ask you if it is possible to run Full Monty off of
+/- 15V (or even +/- 9V) without compromising the specs
other than signal swing? If so could you please indicate
what resistor values need substituting to get those
operating points?

I'm obviously trying to allow for the most common (thus
least expensive) power supply and also see if it could be
operated on batteries.

For us circuit Dummies, it would be really helpful if you
filled in the components that would effect the current
sources in the circuit

Oh, gee, you've got to design your own current sources, or at least
google for them.

If I have the time, I will provide those details. A good curent source
is actually quite tricky.


Kevin Aylward

http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

"Kevin Aylward" wrote in message

In principle this possible, because non-linear capacitors can charge up
giving a different average dc voltage but does a decent design actually do
this to any significance? Or are thermal tails significant in a typical
amp?


Well *something* does. One theory is capacitors v. crapacitors.

geoff

Bob Cain wrote:
Ben Bradley wrote:

Oh, gee, you've got to design your own current sources, or at
least google for them. ISTR Bob Pease writing about them in his Pease
Porrige. You can probably google for What's All This Current Source
Stuff, Anyhow? and find it.

Er, I didn't _want_ something that I could (possibly) teach
myself in four easy Googles, I wanted to know what the
designer thinks is best in the context of _his_ circuit.

Ya know, I just don't get this new thing of telling people
who asks a question that they should have consulted Google
first to eliminate the need to ask it. Since when did it
become a requirement that people first search for printed
answers before asking people? That's nuts if you ask me and
it seems to have become the de rigor response to questions
just about everywhere in this medium. What's up with that?
In real life if you tell someone to "look it up" when they
ask you a question you're liable to get a boxing lesson.

But thanks for the useful information that followed the jab.
Really. :-)


I didn't suggest google, because its unlikely that you will find
anything other then run of the mill stuff. Most nitty gritty transistor
level design is done in ics, and people don't seem to write much about
that on the web. Its all board level, they write about.

Kevin Aylward

http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

Geoff Wood wrote:
"Kevin Aylward" wrote in message

In principle this possible, because non-linear capacitors can charge
up giving a different average dc voltage but does a decent design
actually do this to any significance? Or are thermal tails
significant in a typical amp?


Well *something* does.

What evidence to you have that there is significant distortion occurring
in transients that is not measured during steady state?

As I noted, one can certainly identify *potential* sources of such an
effect, but the numbers indicate that the effects are minimal. One would
have to have a condition where, on steady state the distortion was say,
0.01% and on transients it jumped to say, 0.1%.

One theory is capacitors v. crapacitors.


Its highly unlikely for capacitors in amps to be a significant issue in
this regard. Indeed, there is usually only a few. There is of course
capacitance at all transistor junctions, and these capacitances are
non-linear.

There a significant very non-linear capacitance in a bipolar power amp
due to the base emitter difusion capacitance of the output devices. This
is:

Cbe = 40.Ic/2.pi.ft.

It is directly proportional to I, and so I is very non-linear with
applied V. Its effect is mitigated by being shunted by the transister
dynamic resistance, re.

Kevin Aylward

http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

"Kevin Aylward" wrote in message
news
Geoff Wood wrote:
"Kevin Aylward" wrote in message

In principle this possible, because non-linear capacitors can charge
up giving a different average dc voltage but does a decent design
actually do this to any significance? Or are thermal tails
significant in a typical amp?


Well *something* does.

What evidence to you have that there is significant distortion occurring
in transients that is not measured during steady state?

None, but the steady state specs are identical. AGreed, some more
meaningful spec would maybe help. What is it ?

One theory is capacitors v. crapacitors.


Its highly unlikely for capacitors in amps to be a significant issue in
this regard. Indeed, there is usually only a few. There is of course
capacitance at all transistor junctions, and these capacitances are
non-linear.

But somewhere in the signal chain there is bound to be a series C.
Somewhere from mic pre through to speaker x-over.

One potential place for a degradation due to inferior crapacitors (to a
degree inherent in their necessary value, electros) is coupling capacitors
at mic pre input.

That is unless you are clever enough to come up with a safe and bullet-proof
direct-coupled mic pre that does phantom.

geoff

Geoff Wood wrote:
"Kevin Aylward" wrote in message
news
Geoff Wood wrote:
"Kevin Aylward" wrote in message

In principle this possible, because non-linear capacitors can
charge up giving a different average dc voltage but does a decent
design actually do this to any significance? Or are thermal tails
significant in a typical amp?


Well *something* does.

What evidence to you have that there is significant distortion
occurring in transients that is not measured during steady state?

None, but the steady state specs are identical.

Very unlikely. Its essentially, impossible.

What you mean, is that there is some one off quote that matches up by a
number. One needs to see what the details of the distortion spectrum
actually is, at many signal levels, and frequencies.

AGreed, some more
meaningful spec would maybe help. What is it ?

Full graphs, as noted above.


One theory is capacitors v. crapacitors.


Its highly unlikely for capacitors in amps to be a significant issue
in this regard. Indeed, there is usually only a few. There is of
course capacitance at all transistor junctions, and these
capacitances are non-linear.

But somewhere in the signal chain there is bound to be a series C.
Somewhere from mic pre through to speaker x-over.

But most can't effect an ab test between two amps, because they are
isolated from the amps. You are claiming that two amps, with the same
sound steady state spec, sound different on transients.



Kevin Aylward

http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

"Bob Cain" wrote ...
Er, I didn't _want_ something that I could (possibly) teach
myself in four easy Googles, I wanted to know what the
designer thinks is best in the context of _his_ circuit.

Ya know, I just don't get this new thing of telling people
who asks a question that they should have consulted Google
first to eliminate the need to ask it. Since when did it
become a requirement that people first search for printed
answers before asking people?

Since it became easier, quicker and reasonably comprehensive
by way of the WWW, HTTP, billions of web pages, and Google,
et.al.

That's nuts if you ask me and it seems to have become the
de rigor response to questions just about everywhere in this
medium.

Do you have the same strong objection to things like FAQ
lists?

What's up with that? In real life if you tell someone to "look
it up" when they ask you a question you're liable to get a
boxing lesson.

You must live in a different world. In MY "real life" I
*always* tell people how to do something for themselves
wherever possible rather than doing it for them. It is a
valuable learning for them to be self-reliant and it saves
me time to deal with things that actually require individual
attention.

"Things should be described as simply as possible, but no
simpler."

"Give a man a fish and you feed him for a day. Teach him to
fish and you have fed him for a lifetime."

Ben Bradley wrote:

Offhand cheap, if not yet completely obsolete, is the old LM/CA3046
NPN array, originally in a 14-DIP. I'm sure there is or was a cheap
PNP array as well.
I bet the LM394 would work nicely, but at $5 per matched pair,
you'd want to pick the best place(s) for it. The data sheet has some
interesting schematics, specifically the "high performance
instrumentation amplifier" which uses three of the darn things (could
they have designed it to use more?). Use a few in your next
high-volume design, maybe with good volume the price will go down.
There are also high-quality (i. e. expensive) matched transistor pairs
from THAT, and (also ISTR quads) from Analog Devices. I haven't
actually used any of these, though I have a couple of LM394's.

I have used the THAT arrays and they are really, really nice. Lower
noise than the LM394, and I think they are harder to destroy although
I have managed to destroy a few. The matching is excellent, the dielectric
isolation between devices is very good, and the only problem is that you
can't get them in onesie-twosies.

A cheap (moneywise, not timewise) way of generating lots of
'matched pairs' is get a bunch (100 or more, the more you get the
closer the matching, you'll use a lot anyway) of cheap transistors of
sufficient Vbe and other specs (probably min beta of 50), and sort
them by beta.

A cheap DVM with a transistor test function is usually sufficient for
this.

I recall an Audio Amateur cover with an array of transistors laid
out on a sheet of paper, and a number (surely beta) written by each
one. Back then they had to sort the gain values manually, or even
worse, use a BASIC program to sort them.

I get a bin with a lot of trays, and I read the beta and drop the
transistor into the right tray for that beta or beta range. It is
always very interesting to watch the distribution of parts in the
different trays. Sometimes you get a bell curve, sometimes a bimodal
distribution where it's clear they have selected out a range to sell
elsewhere.
--scott


--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Kevin Aylward wrote:

As someone having the grandiose title of analogue ic design team leader
at Texas Instruments for 3 1/2 years, I never saw an analogue breadboard
once. People used to use kit parts, like 20 years ago, but not now. An
i.c. company has rows of engineers all sitting at desks simulating. When
the dies come back they are checked out in the lab. If there are issues,
that were not seen in simulation, new simulations are done to try and
identify the problem. Doing a change is a bit of work. Usually extra
transistors are placed on the die for prototypes so that they can be
fibed (electron beam wired up). Lasers are also use to cut metal routes.

Oh, so it is that why TI had to buy out Burr-Brown in order to get decent
quality linear parts?

(Sorry, I couldn't help the dig, but a good friend of mine is a B-B guy
who is constantly pulling his hair out over trying to get the TI guys
to understand process quality. My personal experience with the Excalibur
op-amps sort of bears him out, which is a shame since the selection of
BiFET op-amps has been decreased considerably since Motorola dropped their
MC34081 series and the Excaliburs are about the only things left.)
--scott


--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Kevin Aylward wrote:

In principle this possible, because non-linear capacitors can charge up
giving a different average dc voltage but does a decent design actually
do this to any significance? Or are thermal tails significant in a
typical amp?

For the servo amplifier guys, thermal tails are increasingly a problem
for power devices as the older high-mass packages like the TO-3 are
replaced with packages that have poorer heat storage and therefore
rely on better heat transfer. I can't imagine this being too big a
deal in an audio application because the time constants are so low, but
it might be a fun thing to try and measure. For shaker table applications
it can be a big deal.
--scott


--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Chris Hornbeck wrote:

"Kevin Aylward" wrote:

FWIW, this is not a "design"; it's a back of an envelope
sketch.

I never do paper designs, my sketches are always virtual.

And I'm just the opposite. Maybe that explains a lot of our
differing perceptions.

He means that if you take away his SPICE he can't cook.

Overall, several magnitudes away from anything interesting.

Oh? Show me a mic amp that has a basic cmrr on a par?

First you show me a mic amp.

Kaching!

--
ha

"Kevin Aylward" wrote in message
k...

As someone having the grandiose title of analogue ic design team leader
at Texas Instruments for 3 1/2 years,

Were you involved with TI's version of the NE5534?

Peace,
Paul

"Richard Crowley" wrote in message
...

"Give a man a fish and you feed him for a day. Teach him to
fish and you have fed him for a lifetime."

I'm afraid you've got that quote wrong. It should be:

"Give a man a fish and you feed him for a day. Teach him to fish and he'll
sit around in a boat all day and drink himself stupid."
- Les Barker, "Detritus"

Peace,
Paul

Hello Kevin,

Hi Joerg. Haven't noticed you here before yet.

Well, I didn't know that this fine NG existed until recently when I was
looking for advice on wireless mikes.

Yes. At the moment, the raw response goes way out to 10Mhz!!!

Wow! Just imagine what all those 13.56MHz ISM power generators would do
to it...

from the outset, this is supposed to be more of design tutorial in the
sense of identifying configurations, and there issues etc.

Just thought I'd mention it before something heads off to production.
But for a tutorial it shoudn't matter, as long as people don't blindly
copy it to make a real-world audio amp.

Regards, Joerg

http://www.analogconsultants.com

Kevin Aylward wrote:

Well, I have been pressed for a bit on mic amp design, so I have knocked
something up here.

http://www.anasoft.co.uk/EE/MicAmpDe...AmpDesign.html

A bit basic as it stands.

You *do* realise that your CMMR figures depend on having *absolute* resistor
( that's spelt with an 'o' btw ) values don't you ?

Getting all fancy over common mode rejection is rather pointless if real
world components mess it up !

Graham

Kevin Aylward wrote:

Ben Bradley wrote:

Oh, gee, you've got to design your own current sources, or at least
google for them.

If I have the time, I will provide those details. A good curent source
is actually quite tricky.

Which is why a nice quiet voltage source and a resistor are often preferred
in practice in real designs.

Graham

On Tue, 10 May 2005 05:32:34 -0700, "Richard Crowley"
wrote:

You must live in a different world. In MY "real life" I
*always* tell people how to do something for themselves
wherever possible rather than doing it for them.

Build the mic pre yourself, then...

Kevin Aylward wrote:

Well, I have been pressed for a bit on mic amp design, so I have knocked
something up here.

http://www.anasoft.co.uk/EE/MicAmpDe...AmpDesign.html

A bit basic as it stands.

You *do* realise that your CMMR figures depend on having *absolute* resistor

( that's spelt with an 'o' btw ) values don't you ?

Getting all fancy over common mode rejection is rather pointless if real
world components mess it up !

Graham

Kevin Aylward wrote:

Ben Bradley wrote:

Oh, gee, you've got to design your own current sources, or at least
google for them.

If I have the time, I will provide those details. A good curent source
is actually quite tricky.

Which is why a nice quiet voltage source and a resistor are often preferred

in practice in real designs.

Graham

On Tue, 10 May 2005 08:12:19 GMT, "Kevin Aylward"
wrote:

Real-world CMRR is degraded by the real-world upstream
bandlimiting necessary in the real world. It's trivially
easy to *buy* an AD797 with 130dB CMRR. But a real amp
using it won't acheive that, or anything close (without
a transformer, or multi-staging instrumentation design, etc.)


I did note in another post, that a mere 1pf on the emitter to ground
reduces the single ended cmrr from the ideal 145db to 100db at 20khz.
One can take the output differentially, and it should be infinite,
ideally:-)

These big numbers are totally, completely, entirely bull****
in the context of a complete mic amp. CMRR will be limited
by the residual imbalances in input bandwith limiting, and
the yet to be explored feedback network. Remember, this has
to operate over a gain range of 60dB, or ideally more.

Without feedback to the input stage, you can't achieve needed
signal level acceptance. And, you need to be thinking about
how that is going to effect the teensytiny DC levels at your
feedback input "pins", the emitters. And how big a pop you're
going to make when you change gain.

Just a few thoughts, good fortune,

Chris Hornbeck

"playon" wrote ...
Build the mic pre yourself, then...

I actually intend to. I make a lot of my own equipment.
Thank you for your support.

As soon as I find the Jensen 990 schematic.
Used to be available online, but seems to have disappeared.

That wasn't directed at you, my comment was for god's gift to the
planet, Kevin A.

Sorry about any confusion.

Al

On Tue, 10 May 2005 17:10:45 -0700, "Richard Crowley"
wrote:

"playon" wrote ...
Build the mic pre yourself, then...

I actually intend to. I make a lot of my own equipment.
Thank you for your support.

As soon as I find the Jensen 990 schematic.
Used to be available online, but seems to have disappeared.

On Tue, 10 May 2005 17:10:45 -0700, Richard Crowley wrote:

"playon" wrote ...
Build the mic pre yourself, then...

I actually intend to. I make a lot of my own equipment. Thank you for your
support.

As soon as I find the Jensen 990 schematic. Used to be available online,
but seems to have disappeared.

You could just buy the 990 from John Hardy. Then you could use either
John's or Jensen's schematic to build your amp.

That would be the easy way.

But it wouldn't be the cowboy way.

On Tue, 10 May 2005 17:10:45 -0700, Richard Crowley wrote:


"playon" wrote ...

Build the mic pre yourself, then...


I actually intend to. I make a lot of my own equipment. Thank you for your
support.

As soon as I find the Jensen 990 schematic. Used to be available online,
but seems to have disappeared.


You could just buy the 990 from John Hardy. Then you could use either
John's or Jensen's schematic to build your amp.

That would be the easy way.

But it wouldn't be the cowboy way.


The schematic of the original 990 is available on my site in my 990 data
package:

http://www.johnhardyco.com/pdf/990.pdf

Some day I will update the schematic to include the "990A" and "990C"
variations. Thanks.

John Hardy
The John Hardy Co.
www.johnhardyco.com

"Kevin Aylward" wrote in message
meaningful spec would maybe help. What is it ?

Full graphs, as noted above.

Really needs to be waterfaall spectrum plots for dynamic interacting signal.




But most can't effect an ab test between two amps, because they are
isolated from the amps. You are claiming that two amps, with the same
sound steady state spec, sound different on transients.


Have you never noticed ?

geoff

Pooh Bear wrote:
Kevin Aylward wrote:

Well, I have been pressed for a bit on mic amp design, so I have
knocked something up here.

http://www.anasoft.co.uk/EE/MicAmpDe...AmpDesign.html

A bit basic as it stands.

Its a topology. I am working on some of the details, as I get time.


You *do* realise that your CMMR figures depend on having *absolute*
resistor ( that's spelt with an 'o' btw ) values don't you ?

No I don't, because they don't. Its specifically why I chose this
configuration.

CMRR is determined by the impedance seen on the emitter tails. Ideally,
infinite.

The basic CMRR of a simple stage is Va/4Vt, Va is the early voltage, Vt
the thermal voltage. (one 1/hoe of each transistor, 1/2hoe for the tail
current).. or is it twice that....

I hope you are not making the error that a differential output is
required to get CMR on a diff pair. All spice data is given with
reference to the output from one collector only. Taking both collectors
will give infinite rejection, weeeeell 213db in spice. If, the outputs
are differenced amplified with only 1% matching, it will still improve
all the figures I have given by 40db.

I'll see if I have the time to produce a paper on the analysis of this
circuit for CMRR. The bootstrap is quite easy to analyse.

Some words of advice Graham:-)

Never post technical claims to public NGs on circuits that can be
*first* verified in Spice. I would say, in probably 10,000 posts to the
electronics NGs, I have never made a claim that was in error regarding
such circuits. I am simply not that daft:-)

"An expert is someone who knows what someone else will say on the
matter". In this case, Spice.

Second, I may not be an expert in sound, but I am in analogue design,
don't confuse the two:-)


Getting all fancy over common mode rejection is rather pointless if
real world components mess it up !


Yes. That's why I didn't consider the opamp-transistor in the loop
configuration. CMRR depends on resister matching.

Ultimately, achieving 80db at 20khz, is down to things like cable
matching and all the over well known, but rather mundane issues. It may
not be posible, but this is a design tutorial after all. I am just
looking at a few simple configurations and their inherent limits.

Last bit of advice. Use Spice.

In my view, even for board level design, something like 99% of all
analogue design should be done in spice. There is so much that can be
verified and checked. The fact that it doesn't do *everything* is simply
irrelevant.

Kevin Aylward

http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

Pooh Bear wrote:
Kevin Aylward wrote:

Ben Bradley wrote:

Oh, gee, you've got to design your own current sources, or at
least google for them.

If I have the time, I will provide those details. A good curent
source is actually quite tricky.

Which is why a nice quiet voltage source and a resistor are often
preferred in practice in real designs.

I meant a *good* current source. A simple current source will outperform
a simple resister source, and is a complete no-brainer to "design".

The reasons that I wouldn't use a simple current source in a typical mic
amp is to save board space and cost, and the obvious prior noted reality
that other external factors end up limiting the CMRR anyway.

Kevin Aylward

http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

Chris Hornbeck wrote:
On Tue, 10 May 2005 08:12:19 GMT, "Kevin Aylward"
wrote:

Real-world CMRR is degraded by the real-world upstream
bandlimiting necessary in the real world. It's trivially
easy to *buy* an AD797 with 130dB CMRR. But a real amp
using it won't acheive that, or anything close (without
a transformer, or multi-staging instrumentation design, etc.)


I did note in another post, that a mere 1pf on the emitter to ground
reduces the single ended cmrr from the ideal 145db to 100db at 20khz.
One can take the output differentially, and it should be infinite,
ideally:-)

These big numbers are totally, completely, entirely bull****
in the context of a complete mic amp.

Are you are suggesting that I am unaware of this? Sure, getting 140db
aint gonna happen.

What I have shown is the intrinsic ability of a few different
topologies. This is standard practise in any design. The object is to
determine what is achievable in the ideal case. This is to avoid the
case where much effort is expended on matters such as board layout,
trying to obtain a performance that is not achievable in principle from
the design. A basic design can easily be limited by the design itself,
not the external factors. We need know what designs do that.

CMRR will be limited
by the residual imbalances in input bandwith limiting,

Possibly. Depends on how good I design the current sources, they might
be worse. I would say cable mismatch to ground will cause a few issues.

?and
the yet to be explored feedback network.

What feedback network?

I believe that you haven't yet understood the design topology.

Remember, this has
to operate over a gain range of 60dB, or ideally more.

This is done by changing the resister RE from say 50 ohms, to 5k.


Without feedback to the input stage, you can't achieve needed
signal level acceptance.

Feedback and signal handling are completely unrelated. I have no idea as
to what feedback you are referring. This topology doesn't use global
feedback, only local feedback.

The signal acceptance i.e. signal handling range can be as large as
required, say by RE being 5K. At 2ma bias this is 10V. The distortion at
such a large value, is negligible.

I have omitted another standard topology description that does enclose
the input transistors within a global feedback loop, as this topology
relies on resister matching to obtain a good CMRR.

And, you need to be thinking about
how that is going to effect the teensytiny DC levels at your
feedback input "pins", the emitters. And how big a pop you're
going to make when you change gain.

Usually the resister is a variable resister in series with a capacitor,
so it don't pop or generate DC crackles, or effect DC levels. Do you
understand what a topological design means?

I think that you need to do a bit more work on understanding the
topology. Your statements, by and large, don't really make much sense to
me.

Kevin Aylward

http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

Geoff Wood wrote:
"Kevin Aylward" wrote in message
meaningful spec would maybe help. What is it ?

Full graphs, as noted above.

Really needs to be waterfaall spectrum plots for dynamic interacting
signal.



But most can't effect an ab test between two amps, because they are
isolated from the amps. You are claiming that two amps, with the same
sound steady state spec, sound different on transients.


Have you never noticed ?

No I havnt noticed. I don't do AB tests on amps. What I have done is
used lots of diferent power amps over 30 years, and never felt the need
to say, hey, this one seems a bit meaty then that last one I tried.
According to my memory of each amp, there all sound the same. For mixers
this is different, but this is always, in my experience, down to
turnover frequencies of the tone controls. When set flat, they all sound
the same, according to memory. Reverb/Echo units are another story. Some
just cant be set to sound good at all. The algorithms are often pretty
bad.

The onus is on the person claiming similar amps sound different, to
prove it.

Kevin Aylward

http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

Paul Stamler wrote:
"Kevin Aylward" wrote in message
k...

As someone having the grandiose title of analogue ic design team
leader at Texas Instruments for 3 1/2 years,

Were you involved with TI's version of the NE5534?

Way, way before my time.

Do you know how big TI is, and how many products they make?

This is a bit like all those daft yanks going, hey, your from London
right, do you know Keith Bookman, he's a mate I know from London?

Kevin Aylward

http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

John Hardy wrote:

Well, hello John.

On Tue, 10 May 2005 17:10:45 -0700, Richard Crowley wrote:


"playon" wrote ...

Build the mic pre yourself, then...


I actually intend to. I make a lot of my own equipment. Thank you
for your support.

As soon as I find the Jensen 990 schematic. Used to be available
online, but seems to have disappeared.


You could just buy the 990 from John Hardy. Then you could use
either John's or Jensen's schematic to build your amp.

That would be the easy way.

But it wouldn't be the cowboy way.


The schematic of the original 990 is available on my site in my 990
data package:

http://www.johnhardyco.com/pdf/990.pdf

Well, its nice for you to provide the circuit. For such a simple
amplifier design, the specs are quite good indeed.

The "finest op amp is a bit grandiose" though. Maybe in 1979 it was bit
more of an accurate claim.


Some day I will update the schematic to include the "990A" and "990C"
variations. Thanks.

Comments:

Wow...some size of cap that 150pf stabilising one.

In general its desirable to put protection diodes across the base
emitters directly. A large negative common mode voltage could still, in
principle, breakdown the junctions, impairing the noise and hfe.
Fortunatly, in your final circuits there is a transformer, but it does
mean that one has to pay more attention to power supply sequencing on
power up.

I don't see any s/c protection. What happens into a short? Looks like
fries with that.

The statement about eliminating series caps and using a servo as a means
to avoid a postulated capacitor distortion mechanism is misleading. The
transfer function doesn't care whether the caps are physically in series
or not. The advantage is that it is easier to have very lower cut-off
frequencies, such that the voltage across capacitors at normal
frequencies are very low. This would avoid any postulated distortion, of
which is highly dubious to say the least, in any case.

Quible on your specs.

You have "phase margin" specified at two different frequencies. This
doesn't really mean anything. Phase margin is independent of frequency
in the usual sense. "Phase margin" is a stability term and is the
difference in phase from the 180 deg single frequency point at unity
loop gain. Sure, the phase margin will change at different gains, and
have a corresponding different frequency as to where the phase margin is
measured at, but this besides the point of what a phase margin spec is.

Maybe I should produce an op-amp verion of my driver for
http://www.anasoft.co.uk/EE/circuits...ortionAmp1.jpg

This does 0.001% 20Khz, at around 1Mhz full power BW, at +/-100V,
and claim "the finest op amp in the known 3 universes":-)

Kevin Aylward

http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

Kevin Aylward wrote:


I don't see any s/c protection. What happens into a short? Looks like
fries with that.


Might want to evaluate the circuit with a competent Spice program, Kev.

I prefer MicroCap myself.

Check the function of CR11 and CR12.

"Kevin Aylward" wrote in message
k...
Paul Stamler wrote:
"Kevin Aylward" wrote in message
k...

As someone having the grandiose title of analogue ic design team
leader at Texas Instruments for 3 1/2 years,

Were you involved with TI's version of the NE5534?

Way, way before my time.

Do you know how big TI is, and how many products they make?

Yes. But back when, their analog division was a small corner of a
mostly-digital company, and since you never got around to telling us *when*
you were at TI, I thought it was possible you were involved in that project.
It was one of their more subtle cock-ups.

Peace,
Paul

Dan Kennedy wrote:
Kevin Aylward wrote:


I don't see any s/c protection. What happens into a short? Looks like
fries with that.


Might want to evaluate the circuit with a competent Spice program,
Kev.
I prefer MicroCap myself.

Oh dear...like, wiring up with wires and osciloscopees...yeah great way
to probe currents, rather then then clicking on wires pins.

You know the Mackie thing verses, well...just about anything really?
Well, if you check the electronics NGs, you'll find that EWB is the
Mackie. Best of luck with your "Mackie".


Check the function of CR11 and CR12.

Oh....they're zeners are they? Limiting the output to (Vz-Vbe)/Re.

They should have little slants and/or names on them, otherwise their
1N41418s, which don't break down till 75V.

I do admit that the circuit of mine I referenced don't use the correct
zener diode symbol either, but this isn't a formal schematic. Just
didn't get around to changing them.

Kevin Aylward

http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

You still don't understand the circuit, do you?

When the base to output node voltage attempts to exceed the diode drop
of the 1N4148 it clamps at a point within the dissipation ratings of the
output devices and drivers.

Simple and clever.

But it doesn't surprise me that you are ignorant of one of the finer
audio circuits out there.

When are your handlers gonna get you back in the cage?

Dan






Kevin Aylward wrote:
Dan Kennedy wrote:

Kevin Aylward wrote:


I don't see any s/c protection. What happens into a short? Looks like
fries with that.


Might want to evaluate the circuit with a competent Spice program,
Kev.
I prefer MicroCap myself.


Oh dear...like, wiring up with wires and osciloscopees...yeah great way
to probe currents, rather then then clicking on wires pins.

You know the Mackie thing verses, well...just about anything really?
Well, if you check the electronics NGs, you'll find that EWB is the
Mackie. Best of luck with your "Mackie".


Check the function of CR11 and CR12.


Oh....they're zeners are they? Limiting the output to (Vz-Vbe)/Re.

They should have little slants and/or names on them, otherwise their
1N41418s, which don't break down till 75V.

I do admit that the circuit of mine I referenced don't use the correct
zener diode symbol either, but this isn't a formal schematic. Just
didn't get around to changing them.

Kevin Aylward

http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

Dan Kennedy wrote:



Check the function of CR11 and CR12.


Oh....they're zeners are they? Limiting the output to (Vz-Vbe)/Re.

They should have little slants and/or names on them, otherwise their
1N41418s, which don't break down till 75V.

I do admit that the circuit of mine I referenced don't use the
correct zener diode symbol either, but this isn't a formal
schematic. Just didn't get around to changing them.


You still don't understand the circuit, do you?

Oh, I do my son, I do. Trust me on this.


When the base to output node voltage attempts to exceed the diode drop
of the 1N4148 it clamps at a point within the dissipation ratings of
the output devices and drivers.

Impossible dude. CR11 and CR12 are the wrong way round. The only way
they can clamp is to exceed their reverse voltage breakdown, which is
75V. This would give 19A as a s/c current. At 15V that's 285W. Yeah,
safe as skiing backwards through revolving doors, blindfolded.

If you turn them round, then the circuit won't even work. The output
current would be limited to delta_vbe of the output devices and the
diodes / Re.


Simple and clever.

And wrong.


But it doesn't surprise me that you are ignorant of one of the finer
audio circuits out there.

Dan. You can't win. I've been at this way to long. What part of "I am an
expert" are you stll having trouble with?


When are your handlers gonna get you back in the cage?

See above mate.

Oh dear, this all so amusing. If you would get off your high horse, you
might actually gain some benefit from all of this.

Kevin Aylward

http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

Dan Kennedy wrote:
You still don't understand the circuit, do you?

When the base to output node voltage attempts to exceed the diode
drop
of the 1N4148 it clamps at a point within the dissipation ratings of
the
output devices and drivers.

Simple and clever.



Actually CR11 and CR12 work in conjunction with CR9 and CR10 and limit
the base drive voltages to 3 diode drops away from the output node
voltage.

In other words CR9 CR10 and CR12 protect Q8 and CR9 CR10 and CR11
protect Q9.

It is simple and clever.

Mark

"Kevin Aylward" wrote:

The onus is on the person claiming similar amps sound different, to
prove it.



That's ridiculous. How can I "prove" what I hear and you can't (or
won't)? It's like me telling a blind person that the top traffic light
is a different colour than the bottom one. How can I "prove" it?

I already told you that three similar power amps all sounded different
in exactly the same setting, but you refuse to believe it, instead
arguing some red-herring about insufficiently controlled scientific
testing methods. What's left?

I am absolutely NOT one of those audiophile types who makes ridiculous
claims about cables and standing my CD player on spiky feet, but some
things are just plain audible, even to me, and I ain't blessed with
golden ears.

--
"It CAN'T be too loud... some of the red lights aren't even on yet!"
- Lorin David Schultz
in the control room
making even bad news sound good

(Remove spamblock to reply)

"Kevin Aylward" ...

You can't win. I've been at this way to long. What part of "I am an
expert" are you stll having trouble with?


The fact that you've said this faaar too many times for it to be factual,
and the fact that you feel you must say it at all, makes it highly unlikely.

Sorry mate... humility takes precedence.

--
David Morgan (MAMS)
http://www.m-a-m-s DOT com
Morgan Audio Media Service
Dallas, Texas (214) 662-9901
_______________________________________
http://www.artisan-recordingstudio.com

Your not supposed to have to explain it to him...

Mark wrote:

Actually CR11 and CR12 work in conjunction with CR9 and CR10 and limit
the base drive voltages to 3 diode drops away from the output node
voltage.

In other words CR9 CR10 and CR12 protect Q8 and CR9 CR10 and CR11
protect Q9.

It is simple and clever.

Mark