Quote:
Originally Posted by Robert Gribnau
Quote:
Originally Posted by etherman
As for negative feedback, I could not detect any audible effect in the produced audio. Or is it mainly to guarantee stability?
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I don't think it's mainly there for stability reasons but I could be out of my depth on this one.
You could temporarily try it out with a lower value for R11, at least to see if the phasing of the feedback is in order. With good phasing you should hear some drop in volume, with wrong phasing the feedback will be positive, which increases the volume and, if the feedback is strong enough, the amplifier starts to oscillate (howling-like sounds).
Just to be sure: Is one tap of the secondary connected to ground (and the other one to R11) like in the schematic? Without the connection to ground, the feedback from the secondary will not work. |
The secondary has one terminal connected to ground and the other to the negative feedback loop. The phase of the output signal is inverted relative to input (not sure about that). Attenuated output signal is fed back to the input sort of subtracting part of the input signal and reduces gain and therefore reduces distortion: this is how I understand it. Also, if negative feedback is properly executed it should contribute to stability. However in certain situations it may lead to oscillation. The frequency at which negative feedback has a significant effect is determined by the time constant of the RC combination in the loop.
I will try changing values. Right now I have 10k and 100 pF.
When I reach a reasonable result, I will post a schematic.
What would be the maximum B+ you suggest for a PCL82 pp amp like the Dansette Mk I?