Can Feedback Servo Harm Your Amp? - diyAudio
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Old 8th June 2010, 07:15 PM   #1
Jay is offline Jay  Indonesia
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Default Can Feedback Servo Harm Your Amp?

Okay, so I am looking at a voltage feedback opamp connecting the output with the input of an amplifier (inverting configuration).

Why such servo is not too common? If the answer is price-to-performance ratio, well, I have too many opamps lying around. It couldn't be the reason.

Now that I'm re-thinking to build Mooly's amplifier, it came to me to use a servo to "any" amplifier I'm going to build. Why not? It can not hurt, yes?

Okay, you may think of another way to null the output, i.e. proper matching. So now do I have to think of the minimum output voltage where the servo is advisable? Actually I just want to use the servo regardless of the measured output Vdc (Eliminating the feedback capacitor is not a priority to me).

What kind of sound degradation you can expect from such servo? What kind of amplifier topology you cannot implement the servo in?

Thanks.
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Old 12th June 2010, 03:36 AM   #2
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DC servos are not too hard to implement, but care must be used with the frequency response. Make sure the time-constant is very long - like from 1Hz or even 0.1Hz to prevent oscillation. When designed well, they will not degrade the amp's sound at all.

DC servos are not too common because they can be eliminated by the proper use of caps for blocking DC and reducing gain at low frequencies. DC coupling is basically audiophile hype, IMHO, because as 99.99% of the audio industry, including recording studio equipment, know that caps when properly used are inaudible.
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Old 12th June 2010, 01:30 PM   #3
Jay is offline Jay  Indonesia
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Quote:
Originally Posted by DCPreamp View Post
DC servos are not too hard to implement, but care must be used with the frequency response. Make sure the time-constant is very long - like from 1Hz or even 0.1Hz to prevent oscillation. When designed well, they will not degrade the amp's sound at all.

DC servos are not too common because they can be eliminated by the proper use of caps for blocking DC and reducing gain at low frequencies. DC coupling is basically audiophile hype, IMHO, because as 99.99% of the audio industry, including recording studio equipment, know that caps when properly used are inaudible.
Hi, thanks. Yes I think their effect to the sound cannot be worse than the effect of the feedback cap. In an A/B test I believe I will not be able to detect any improvement with the DC servo, but I know very very well that in audio a critical change doesn't have to be able to be detected in an A/B test.

In this case I have an intuition that the servo has superior effect for the enjoyment of the sound.
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