I just did a couple of tests with tube front end. I'm using a PCC88 tube with a CCS loading the plate, operating at 85V and 8mA in anode follower configuration. Found out that I need a low impedance, low distorsion FE to drive the output stage, otherwise I'm getting HF attenuation.
I need to add a cathode follower.
I need to add a cathode follower.
I need to add a cathode follower.
For me sound-wise that would be the last resort option. Rather use a lower Rp valve or an srpp.
Did some listening tests and I find out that I need to carefully choose the GNF resistor, with 4.7K resistor the sound in bass and low midrange was shy, with 10K the sound in lower region had more weight. Did anyone else who built a version of the beast noticed that?
So are you saying that you increased the gain of the amp and by virtue reduced the negative feedback by that amount?
I run 4.7K to the 330 for the feedback. If i changed that to 10K i would have a gain of 29dB and reduce the loop feedback by 6dB. This would definitely reduce the damping factor and increase the base sound but would also increase the DC output drift.
My two cents.
I had the same impression some time ago.
Changing the bias also influences the sound quality, stps of 0.1A are to be heard.
I remember you mentioned before that you have J2 at home, what is listening impression comparing with the beast?
On my amp I perceive a very "clean" and dynamic sound but not harsh, comparing with other amps I have.
So are you saying that you increased the gain of the amp and by virtue reduced the negative feedback by that amount?
I run 4.7K to the 330 for the feedback. If i changed that to 10K i would have a gain of 29dB and reduce the loop feedback by 6dB. This would definitely reduce the damping factor and increase the base sound but would also increase the DC output drift.
My two cents.
I see, what you DC output with 4.7K? Mine is around 80mV with any value of feedback resistor. The FE is capacitor coupled with OS.
Is it posible to do it if the front end is AC coupled?.... Offset can be handled by negate DC feedback.
How much of DC offset is "acceptable"?
Thanks.
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