M2(x) uses the voltage over the degeneration resistors as input for the autobias circuit based on the 4n35. Without degen resistors in the OPS, you would not have M2.
Yes, I can see that.......on schematic.....so we need a way to control bias without "degeneration".....
Then there should also be a good "sonic" reason to avoid degeneration.....like lower distortion, lower output impedance....larger class A envelope.....etc....
this should be high output f5m version😁😁😁Hold on to your hat... I think the circuit configuration is different than what we previously thought....
As you just said, there are no de-generative feedback resistors.
With this information at hand, I think the circuit is something like this:
View attachment 616955
After reading some of the threads on First Watt and Pass Labs designs, as well as the square law paper, this is my guess of the XA-25 front end, maybe it could be close… ? I have no clued how could be the output stage, optocoupler biased with runaway control, and DC coupled!
I'm gradually coming back to audio electronics, which I haven't worked on it for maybe 10 years, Since the Blowtorch threads and Charles Hansen designs. I lost a lot of electronics knowledge in the meantime, knowing that my job was more artistic as a sound engineer. When I retired I rather did amateur music as bass player with friends.
What are your thoughts, let’s go ;-)
I'm gradually coming back to audio electronics, which I haven't worked on it for maybe 10 years, Since the Blowtorch threads and Charles Hansen designs. I lost a lot of electronics knowledge in the meantime, knowing that my job was more artistic as a sound engineer. When I retired I rather did amateur music as bass player with friends.
What are your thoughts, let’s go ;-)
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