+/-1V around 3.6V TP1 to TP2. If your Q1,Q2 heat up wilder than that then raise your R2, R3 by 1 Ohm value. Ambient temperature equilibrium in a boxed build helps a lot if you will reset for when warmed up. The 369s are prone to draw more IDSS as their temperature rises. That gets under more control as the sensitivity versions get lower so the Rs R2,R3 go higher. In LMC we make economy in value to save on additional Johnson noise contributed by R2//R3. Just Blow over Q1,Q2 and you will see how sensitive in temp they are in LMC. Use the mini sinks. Its a matter of centering the voltage bias, THD does not change.
I would avoid parasitic inductance and capacitance there, especially across TP1-TP2. Very sensitive signal node.
You always compensate when setting for warm up time and environmental temp for it to hover close to 3.6V TP1-TP2 in the end. Takes ~10 minutes to settle from power on. If it tends to travel more than +/-1V until warm you probably got wilder IDSS and you try raise your R2, R3 by 1 Ohm first.
*As I have wrote one time before I avoid to actively CCS Q1, Q2 for LMC mode bcs that would inject its current noise directly in the 369s. Better compensate carefully for an acceptable settling and keep it natural there. High transconductance JFETs are positive Tempco strongly, I don't want to force them.
I only got 3 Ohm Rs//Rs (R2,R3) in my proto bcs those I had in hand in better quality at time of build vs proper 3.9 for my 11mA JFETs and has more cold to warm travel than most builds. After I boxed it and set it up for warm box ambient I did not revisit it. Never sounded like changing drastically even when I power it on and I start spinning records from cold. After half an hour it sounds generally bit better as most audio electronics do, that's all I have seen. Most of it getting better I suspect its the class A power amp I use though.
I use 5R6 R2/R3 for my 12.4mA JFETs - are these good or should I replace them with 5R1?
Regards
These are good. Better balance between degeneration and IDSS than in mine for instance. See your drifts after you got a box, now its rather useless to bother much. Do you use the minisinks? Those help.
You could use 100uF/63V instead of 0.1uF C3x for simplicity. Listen before and after. Maybe under the board to keep leads short. Or on top just leaning over R6x.
Yes I use the minisinks. Yepp, it's seemingly a moving target unboxed.
I'll wait. Thanks.
Regards
Needless to say, I received no call on the weekend. Finally got the caps tonight. If anyone is wondering about the physical difference between Nichicon FG "Fine Gold" and KZ "Muse", here they are:
They are both 470uF/50V.
With those in place I have finally finished the main circuit boards:
I feel like now I can focus on the PSU.