Bob Cordell's Power amplifier book

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#9,483
Mark Johnson said:
Methinks "settling time" may refer to the entire control loop, which comprises the audio power amplifier's forward path, the first stage of the DC servo (inverting integrator), and the proposed second stage (inverting N-th order lowpass active filter with alignment X).

Apply a unit impulse and watch it settle (or watch it oscillate)
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I sim it. An integrator followed by 2n butterworth low pass filter around 3Hz. An impluse of power supply, the output was settle after few hundred mili second. A sine and pulse input was good, no oscillation. Frequency response is not peaking.
 
#9,487
Bob Cordell said:
Making that inverter-LPF in the second op amp into a 2nd order filter at little expense is a neat idea. My only question is how much difference does it make in the real world after having already put in the first order of extra filtering.
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Bob, I am imagining that it might interact with this passage from your 2nd edition:
It is possible for the servo op amp to create distortion that will make its way onto the output of the amplifier. ... The very best way to reduce injected servo noise and distortion is to use high-quality parts and audio design practices in the servo
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Perhaps turning the second opamp into an Nth order lowpass filter, has the beneficial side effect of filtering out and discarding any audible distortion introduced by the first opamp (?). Which might mean that you can improve distortion performance; OR, that you can use much cheaper opamps and get the same distortion performance.

766645d1562373917-bob-cordells-power-amplifier-book-new_lpf_added-png
 
#9,488
Mark Johnson said:
Bob, I am imagining that it might interact with this passage from your 2nd edition:

Perhaps turning the second opamp into an Nth order lowpass filter, has the beneficial side effect of filtering out and discarding any audible distortion introduced by the first opamp (?). Which might mean that you can improve distortion performance; OR, that you can use much cheaper opamps and get the same distortion performance.

766645d1562373917-bob-cordells-power-amplifier-book-new_lpf_added-png
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These are good points. I usually use an OPA2134 for the DC servo and a polypropylene integrator capacitor.

Cheers,
Bob
 
#9,489
Another small ambiguity. On page 432 reference is made to RE1 in Figure 18.11 but there is no RE1 in Figure 18.11 - only R1 to R3. This could be confusing for a beginner using the book as a learning aid - refer to the resistor in question as R1 explicitly?
 
#9,490
chalky said:
Another small ambiguity. On page 432 reference is made to RE1 in Figure 18.11 but there is no RE1 in Figure 18.11 - only R1 to R3. This could be confusing for a beginner using the book as a learning aid - refer to the resistor in question as R1 explicitly?
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Thanks! Pointing out errors or ambiguities that you find is very helpful. I hope to put an errata page up on my website for the benefit of all readers. If there is a second printing (usually years down the road after a few thousand copies are sold), I'll have an opportunity to make those corrections.

Cheers,
Bob
 
#9,495
jackinnj said:
I enjoyed the commentary on passive components, good advice on NP electrolytics.

But what I enjoyed even more was the discussion of using SMPTE methodology for thermal "memory distortion" (do I have that correct?), and the Chapter 17 discussion of ThermalTrak.
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Thanks, Jack. Yes, you are correct about the methodology for exploring thermal memory distortion.

Cheers,
Bob
 
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