Bob Cordell's Power amplifier book

I frequently recommend this book, maybe I am repetitious but it's hard to overstate how fundamental it is.
I have read that the later copies have some addenda and I would love to check this.
What year or edition/print run is your copy?

Best wishes
David

It's the tenth printing, dated January 1955.

There are no addenda at the back. It ends with the final Chapter XIX "Illustrative Designs for Single Loop Feedback Amplifiers"

Very sorry I can't help you, Dave.
 
Probably because you never tried (or never succeeded to implement) a double pole and a zero close to the ULGF (like you did in the simulation of your CFA). That is a pretty trivial exercise, however it would be as much dangerous as in yours, from a stability perspective.

Double poles have high sensitivity (that is, the ULGF will move significantly with component tolerances, bias conditions, signal level, etc...). I have never seen double poles in anything but simple filters (like the Sallen-Key topology) and switching mode power supplies.

It would be interesting to simulate the same amp when the output approaches the rails, something you always avoided to show, by keeping a comfortable margin of 10-15V-20V. That's when the beast shows it's ugly head. It would also be interesting to see the clipping behaviour (when the loop gain collapses without much control, and the conditional stability may hit you).

I know you proudly built this amplifier and are trying to promote it by all means. Even if you hit the jackpot once, this doesn't mean this amp will survive the abuse that an audio amplifier should be prepared to face in day to day operation. I can show you a 100W mosfet power amplifier with an ULGF of 40MHz, that appears to be very stable in simulation. Which doesn't mean I am ever going to even try building it, not to mention trusting it enough to feed a pair of (borrowed, since I don't have any) expensive speakers.

I don't promote anything here as this is just my hobby, but I want to learn more and I don't have good explanation about this difference between CFA and VFA Bode plots. I think what I did with TMC in my VFA is quite close to the maximum and that one was built and working for years. The ULGF of my CFA is not 40 MHz but 4.5 MHz only.
I hope Richard Marsh will give more information, he is testing and measuring this amp.
 
Once and forever, since this is coming again, and again, and then again... Given a phase margin, an ULGF, and a compensation method order, a CFA circuit topology does NOT provide more loop gain than what you could get with a standard VFA. To understand this, before going to the Lurie stability or the Bode integrals, there is an almost trivial justification: whatever Mr. Zan is going to mumble and moan, audio circuit topologies are still of the minimum phase breed. As such the gain and phase are NOT independent, therefore pushing up the loop gain, pushes down the phase margin, no exceptions (or free lunch, if you prefer). Changing the compensation order is the only way to break this rule, by adding N poles and N-1 zeroes in the unity circle (N=1 Miller compensation, N=2 TPC or TMC, N=3 Cherry NDFL compensation). I've heard of amplifiers (both linear and class D) compensated up to the 5th order, but I have never seen a schematic. The CFA circuit topology has other interesting properties, none of which really matters for audio.

Your example with 80dB loop gain @ 20KHz is either a typo, or you are talking a different and strange Bode language. Even if a two pole type compensation is involved, such an amplifier would have a ULGF higher (I would estimate some 8-10 MHz) that what could be of any practical importance for a power amplifiers (with the power stage limiting the bandwidth).

Hear, hear.

Enough of the CFA, already.
 
You are a very lucky man.
Apparently not, if I get comments like that.

If you are under the impression that all those amplifiers worked and keep working because of luck, I think you misunderstand the process of engineering for quantity manufacture. Come on. let's not be rude to each other.

You miss the point: going to 0.1 ohms is simply not worth it in an EF output stage.

Cheers,
Bob

I thought it was established beyond any doubt that 0R1 gives lower crossover distortion than higher values. It also reduces losses in the output stage, especially for sub-8R loads. What's not to like?
 
Phasemargin does not look to healthy, less than 10 degrees at 200 Khz.

heres my VFA. bit more heathy and still ppm distortion at 20 Khz 26V-pp

"Total Harmonic Distortion: 0.002709%"

This is LG of my 200W CFA mosfet and it is nothing like VFA. I never succeeded to have more than 60, 65 dB of the loop gain at 20 kHz with the VFA.

If you look at Dadod's graph and draw a line at about 26dB gain and look at the loop gain at 20KHz, the loop gain is over 50dB. If you look at MiiB's VFA plot at 26dB you have less than 30dB. There goes to show CFA has much higher loop gain at 20KHz than VFA even though MiiB's VFA has higher loop gain at lower frequency.

It is the -3dB of the open loop gain that matters. dadod's CFA has -3dB slightly above 20KHz, but MiiB's VFA has -3dB below 50Hz. All the high open loop gain means nothing if the open loop gain start rolling off too early.

If you compare loop gain at 1KHz, CFA here still beat the VFA by about 20dB.
 
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If you look at Dadod's graph and draw a line at about 26dB gain and look at the loop gain at 20KHz, the loop gain is over 50dB. If you look at MiiB's VFA plot at 26dB you have less than 30dB. There goes to show CFA has much higher loop gain at 20KHz than VFA even though MiiB's VFA has higher loop gain at lower frequency.

It is the -3dB of the open loop gain that matters. dadod's CFA has -3dB slightly above 20KHz, but MiiB's VFA has -3dB below 50Hz. All the high open loop gain means nothing if the open loop gain start rolling off too early.

If you compare loop gain at 1KHz, CFA here still beat the VFA by about 20dB.

Those graphs are loop gain not open loop gain, you don't need to subtract anything.
 
Apparently not, if I get comments like that.

If you are under the impression that all those amplifiers worked and keep working because of luck, I think you misunderstand the process of engineering for quantity manufacture. Come on. let's not be rude to each other.



I thought it was established beyond any doubt that 0R1 gives lower crossover distortion than higher values. It also reduces losses in the output stage, especially for sub-8R loads. What's not to like?

You never explain why 0.1ohm works reliably. I love to hear it. Did you just do it and it works OR do you have a theoretical explanation? Reputation is not a proof of your assertion, you are going to need more to explain this.

No offense, I can't really read your book and take it too seriously. You gave a lot of assertions, but you don't explain why. This is science, not magic, you make big assertion like this, you are going to have to do better than just say "I design for this and that companies and it works".

So far, your so called Class B is pretty much Class AB with Oliver's condition that you don't give credit to. From your Table 10.2, you pretty much followed Oliver's condition. You have about 30mV across Re IF everything is matched and perfect. If you have an offset of 5 to 10mV if you don't match hfe and/or Vbe, you will have 10 to 20% difference in current and the one that has 20% more current will heat up more and get hotter, in turn reducing the Vbe and further increase the current and go into current hogging.

That's the reason I am matching hfe and Vbe before I attempt to lower to 0.12ohm EVEN you claim that it is safe to use 0.1ohm. I am going to start out with 0.22ohm, measure the voltage across all the Re. If I see over 3mV difference, I won't even attempt lowering to 0.12ohm.

So please explain your assertion if you have one.

Sorry
 
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If you look at Dadod's graph and draw a line at about 26dB gain and look at the loop gain at 20KHz, the loop gain is over 50dB. If you look at MiiB's VFA plot at 26dB you have less than 30dB. There goes to show CFA has much higher loop gain at 20KHz than VFA even though MiiB's VFA has higher loop gain at lower frequency.

It is the -3dB of the open loop gain that matters. dadod's CFA has -3dB slightly above 20KHz, but MiiB's VFA has -3dB below 50Hz. All the high open loop gain means nothing if the open loop gain start rolling off too early.

If you compare loop gain at 1KHz, CFA here still beat the VFA by about 20dB.

A remarkable synthesis of almost all the of common errors, confusions and misunderstandings regarding the amplifier's loop gain. Please do your homework by reading the fundamentals, to many to quote on your Google friend.
 
Here are some more VFA plots...
 

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Apparently not, if I get comments like that.

If you are under the impression that all those amplifiers worked and keep working because of luck, I think you misunderstand the process of engineering for quantity manufacture. Come on. let's not be rude to each other.



I thought it was established beyond any doubt that 0R1 gives lower crossover distortion than higher values. It also reduces losses in the output stage, especially for sub-8R loads. What's not to like?

If I'm not wrong you are using 1 pair of BJT OPS transistors in your designs, not 2, 3 or 4 pairs. In such a case 0R1 will give lower THD than 0R3. If you are using 2, 3 or 4 pairs you should increase RE.

S