That is very true.
I'm using zero degeneration, local cascode feedback at the front end, and around 15dB of Global feedback.
I have not tried the more conventional local feedback loop.
Are you concerned about the gain and phase margins of the global feedback loop, shown in post #467? http://www.diyaudio.com/forums/pass-labs/300233-f4-beast-builders-47.html#post4956892
http://www.diyaudio.com/forums/pass-labs/299383-pass-xa25-4.html#post4891599 "Mostly you are wrong. The Villars photo showed a mock up of the circuit I used as an illustration of cascoded performance that I showed at BAF, and is not related to the XA25."
Have the three witches of this thread ever thought of using lateral fets that are in production for the second stage - i'dunno, maybe parts from semelab or exicon - instead of the nearly extinct toshis?
---(am i making myself a fool, again????)----
anyway, this is the most thrilling thread I've read here in the last years.
cheers & bravo!
A.
---(am i making myself a fool, again????)----
anyway, this is the most thrilling thread I've read here in the last years.
cheers & bravo!
A.
Yes, this has been already thought of numerous times.
Certainly worth trying if you already have those parts laying around.
Hi Attila,
we are all fools living in a yellow submarine......
I tried meanwhile the circuit without degeneration in the second stage. The gain augmented in my build around 4dB, so I had to readjust the feedback or the OLG.
And I tell you.... I can not really decide if it sounds much better.... I would need a second system of high and proofed quality to make real statements.
At the moment I have the feeling degeneration in the second stage or not...is secondary,
more important seems to me the right choice of the gain resistor, the load resistor and the feedback resistor.
Here I hear the dramatic changes of sound, dark, bright, involving, dull......
trip continues, hope my two fellows start hearing their builds soon!
we are all fools living in a yellow submarine......
I tried meanwhile the circuit without degeneration in the second stage. The gain augmented in my build around 4dB, so I had to readjust the feedback or the OLG.
And I tell you.... I can not really decide if it sounds much better.... I would need a second system of high and proofed quality to make real statements.
At the moment I have the feeling degeneration in the second stage or not...is secondary,
more important seems to me the right choice of the gain resistor, the load resistor and the feedback resistor.
Here I hear the dramatic changes of sound, dark, bright, involving, dull......
trip continues, hope my two fellows start hearing their builds soon!
1) A little more open loop gain
2) Improved linearity
3) Reduced thermal distortion ie reduced to virtually zero
4) No thermal drift
I have mine around 120mA at the moment with the intent to experiment at higher bias levels.
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By raising the bias to .4 amps and lowering the output in simulation it did squeeze out a little lower distortion. THD is down to 0.00089 at 1 watt. I wish the transistor spice models that I found were better matched. But maybe that doesn't matter I was mainly looking for a trend here. I see Juma uses the toshiba's in an amplifier biased higher than .4 amps.