What Limits Freqency response in a simple tube amp like the zen? - diyAudio
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Old 28th May 2004, 11:06 PM   #1
ark is offline ark  United States
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Default What Limits Freqency response in a simple tube amp like the zen?


What exactly determines the frequency response in a simple tube amp like the deceware se84cs amps. The output transformer alone?

Its rated at approx 20 Hz ~ 20 kHz
If say, I wanted to extend the top end get pretty evenly into the 50 khz plus range, what changes would I make?

Please, no "why would you want to do that replys" : )

I'm just trying to learn how this stuff works.

mr. kobayashi has got this nifty 300pp amp going into the 150khz range and I'd like to the same with my humble pocketbook and upgrade my zen clone if possible.

Thanks in advance,
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Old 28th May 2004, 11:40 PM   #2
SY is offline SY  United States
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Why would you want to do that? Oh... Humboldt. Never mind.

Anyway, I don't know that specific circuit, but in general, the limitations tend to be output transformer, grid capacitance of the output tubes, and Miller capacitance of driver stages. Of course, in a feedback amp, the limitation will usually be the compensation network which sets the dominant pole. And in a sense, that gets back to the output xfrmr, since the dominant pole has to be set low enough to take into account the transfomer's rolloffs.
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Old 28th May 2004, 11:41 PM   #3
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1/ First of the OPT has to able to pass such bandwidth.

2/ Given 1/ is O.K. then it's a matter of circuit topology, IOW design the amp from scratch with this bandwidth goal in mind.

3/ In order to do so, Miller and other stray capacitances has to be driven in such a way that it doesn't constitute a bandpass filter.

4/ Local and global feedback may help as may frequency and phase correction networks around the circuit and the OPT.

5/ Probably some more trickery depending on the design chosen.

6/ None of the above guarantee a good sounding amp but it's a good place to start provided it can be kept stable.


EDIT: SY just took pole position...
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