John Curl's Blowtorch preamplifier

[Netlist]

Gentleman, in my younger days, my mother ones told me that ego boosting was not productive.
I refrained from it ever since.

/Hugo

[Edmond Stuart]

Originally posted by scott wurcer
I like the artistic license in the drawings. Where does the distortion from the displacement current in the comp caps go (I'm assuming the two 22pF caps are the compensation)? Maybe this is whats left?

Hi Scott,

The distortion I was talking about doesn't stem from the 22pF caps, neither from C124 and R125 (another compensating thingy). The point is that the amp (as published in that patent) is highly unstable. To overcome this serious shortcoming, some kind of additional Miller compensation is definitely needed. Regrettably, such kind of compensation makes the EC mechanism completely ineffective.
For more info, you might start here: http://www.diyaudio.com/forums/showt...61#post1518061

Cheers,
Edmond.

[scott wurcer]

In that light, the usefulness of that patent escapes me.

[Edmond Stuart]

Originally posted by scott wurcer
In that light, the usefulness of that patent escapes me.

Me too, as well as the usefulness of a rocket launcher powered by animal farts (mentioned elsewhere on this forum).

[Bob Cordell]

Originally posted by john curl
Since I 'NAIL' you (and Scott) on just about everything, you should not 'guess' as to what I read or understand. Barrie Gilbert is no friend of mine, but he makes a strong mathematical point and prediction that PMA is finding in his simulations.
What do you mean that SPICE models are not virtually perfect? That is what you told me, in the past.
Bob Cordell, please remember our 16 page REBUTTAL to you and your modification of technical reality to suit your needs and ego, back in 1980. We did not invest the time and effort in TIM for 10 years to have some upstart tell us where the bear sits, when he did not know, himself. And you still have far to go, in my opinion.
We have not formally rebutted you yet in regards to PIM, but it will come, I am fairly sure.
Now, why don't you leave us alone to research PIM in our own way? Why bother PMA, me, or anyone else interested in it? This is the 'Blowtorch' thread, not one of your numerous other theads here, why do you come here to insult us? Are we getting close to something important?

John,

You don't "NAIL" anyone with your bluster and mostly unsupported assertions. Nor does your "rebuttal" on the TIM thing. That is obvious to anyone who read that and my response when they were made available for anyone to see.

There is nothing wrong with PMA doing what he is trying to do. As I said, I do not claim that PIM does not exist; just that the generalization that feedback and/or low open loop bandwidth makes it worse.

Indeed, I believe that if I was to measure a very low distortion high-feedback amplifier, your JC-1, and a no-feedback amplifier together with my PIM analyzer, I would find that the PIM was lowest in the high-feedback, low-distortion amplifier and highest in the no-feedback amplifier. I would expect that the JC-1 would lie in the middle. Obviously, that is just a guess on my part.

As good as SPICE is, I agree that it may be difficult to find PIM with confidence in SPICE transient simulations. However, it may be possible to infer PIM from phase shift changes in an AC simulation where the DC operating point is moved around on a DC-coupled amplifier.

Bob

[gerhard]

Originally posted by john curl
Since I 'NAIL' you (and Scott) on just about everything, you should not 'guess' as to what I read or understand. Barrie Gilbert is no friend of mine, but he makes a strong mathematical point and prediction that PMA is finding in his simulations.

This thread has turned boring, so I read it only if I have excess time,
but I would surely have noticed if you had nailed anybody.
(And I don't mean the connotation this had if you translated it word by word into German).
The habitual name dropping may impress hobbyists (maybe that's your target audience)
but nobody who's in the electronics industry for > 25 years and able to develop ideas of his own.

Originally posted by john curl
SBarrie Gilbert is no friend of mine, but he makes a strong mathematical point and prediction that PMA is finding in his simulations.
What do you mean that SPICE models are not virtually perfect? That is what you told me, in the past.

Spice models are not perfect, neither virtually or practically.
They are as good as the effort behind them. When I designed
some analog functions on AEG B1000 arrays in 5um bipolar back when
a VAX was a nice computer, we had _excellent_ Spice models
and excellent parasitics extraction that we could rely upon.
This cannot be said about most models you can download
from the web. Funny, how all transistor models generated by
the PSPICE model extractor share the same 5? Ohms base
spreading resistance!
Douglas Self wrote that the Signetics 5532/4 contained 3 nested
feedback loops that were required for its performance. Can you
see anything about this in the simplistic model published here?
For bipolars, Spice may be OK, but for LDMOS it's hopeless.
That's why there is a market for Agilent ADS , Genesys or
Microwave Office. OK, they have other merits, too.

Originally posted by john curl

Bob Cordell, please remember our 16 page REBUTTAL to you and your modification of technical reality to suit your needs and ego, back in 1980. We did not invest the time and effort in TIM for 10 years to have some upstart tell us where the bear sits, when he did not know, himself. And you still have far to go, in my opinion.
We have not formally rebutted you yet in regards to PIM, but it will come, I am fairly sure.

While I was was away, has this terminal rebuttal surfaced for anybody to read?
I have asked for it repeatedly to no avail.

Originally posted by john curl

Now, why don't you leave us alone to research PIM in our own way? Why bother PMA, me, or anyone else interested in it? This is the 'Blowtorch' thread, not one of your numerous other theads here, why do you come here to insult us? Are we getting close to something important?

I think you suppose that this is the Blowtorch Shrine. After ~20 years,
given your excellence, you should be so far away in the future that it should pose
no problem to publish some _hard_ facts about it. Seldom has such a
vapor theme produced such a large thread.

Regards, Gerhard

[syn08]

Originally posted by chascode


I think the TDS series Tek scopes only have 11-bit ADCs. That might be a limitiation. I never did care for the spectrum presentation provided by their FFT modules.

Best, Chuck Hansen

AFAIK it's 12bit but I don't think it really matters. The TDS3052 does 5 samples/nS which allows to estimate (after averaging) +/-100pS delays. If there is any measurable PIM effect, it's obviously well below that.

I don't care about the Tek FFT module myself, it's very primitive.

[macka]

I am I said

[KSTR]

Originally posted by gerhard
While I was was away, has this terminal rebuttal surfaced for anybody to read?
I have asked for it repeatedly to no avail.

Yes, there was a link posted on this thread a while ago. SY provided server space, IIRC.

- Klaus

[KSTR]

Originally posted by Bob Cordell
As good as SPICE is, I agree that it may be difficult to find PIM with confidence in SPICE transient simulations. However, it may be possible to infer PIM from phase shift changes in an AC simulation where the DC operating point is moved around on a DC-coupled amplifier.

Exactly. See attached plots of closed-loop gain vs DC bias at input (0V, +-1V, +-2V, and +-3V -- 3.2V is the clipping limit) of a simple amp with moderate "semi-global" feedback and common source MOSFET outputs. The increasing output capacitance with lower Vds is most probably the root cause here. Differences from bias polarity, emphasizing P-ch vs N-ch differences can be seen, too.

- Klaus