Sean, Was that Marsh preamp the Tube version? :-)
Douglas Self on Negative feedback and distortion
I've been reading Douglas Self book on amplifier design and something he said that really makes me think twice.
As you have seen most amplifier makers claim that their amps either does not use global NFB at all or very little of it to improve dynamic (or transient response).
According to Self, the only parameter that matters is distortion and nothing else. I supposed he measures the extra harmonics that the amp produces given a sinusoidal input. In other words, distortion is measured in the frequency domain.
If I remember correctly in my Control Theory course way back in my college days, the frequency domain reponse cannot tell how the amp will response for a given step input. And the STEP RESPONSE is what can tell a lot about the behavior of an amp dynamic and transient response.
In his book, he is very adamant about his position that the only thing that matters is the amp frequency response.
I don't thing frequency response contains information about how any amp would respond to a step input but I could be wrong. Frequency response is only a steady state behavior of the amp. It cannot tell how much the amp would over-shoot, under-shoot, tendency to ringing, and so and so, given a step response. I don't think you can look at the frequency response and make any conclusion about the amp tendency to overshoot, undershoot, ringing and so on...
What do you think?
By the way, I think his book is excellent read into the theory an amplifier design if you can ignore some of his more dogmatic position.
As you have seen most amplifier makers claim that their amps either does not use global NFB at all or very little of it to improve dynamic (or transient response).
According to Self, the only parameter that matters is distortion and nothing else. I supposed he measures the extra harmonics that the amp produces given a sinusoidal input. In other words, distortion is measured in the frequency domain.
If I remember correctly in my Control Theory course way back in my college days, the frequency domain reponse cannot tell how the amp will response for a given step input. And the STEP RESPONSE is what can tell a lot about the behavior of an amp dynamic and transient response.
In his book, he is very adamant about his position that the only thing that matters is the amp frequency response.
I don't thing frequency response contains information about how any amp would respond to a step input but I could be wrong. Frequency response is only a steady state behavior of the amp. It cannot tell how much the amp would over-shoot, under-shoot, tendency to ringing, and so and so, given a step response. I don't think you can look at the frequency response and make any conclusion about the amp tendency to overshoot, undershoot, ringing and so on...
What do you think?
By the way, I think his book is excellent read into the theory an amplifier design if you can ignore some of his more dogmatic position.
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- 33 posts total
- 33 posts total