The diyAudio Firstwatt F6

You are welcome to put more current through them, but any noise is not going to make it
through the 10K + 1,000 uF RC filter, and if it did it would be taken down another 20 dB
or so by feedback.

:cool:

Yes, I was mostly concerned about the soft voltage regulation with such low current. The gate bias voltage would drift around somewhat with power supply variations. Maybe 3 series red LEDs could be used in place of the zeners?
 
Moving Q1 and R12.
 

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PKI

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I would move the trace for the Q2 gate resistor (R12) to the top of the board, so you don't need to bite a piece of the source trace. You can easily do it in the center of the board, nothing on the bottom layer there.

Ok, I see the difficulties, but give it a though! :)
1) Move Gate traces on the top?
2) Make a turn around 7 and 8 pin of the input transformer to put that gate trace above. Does it make any sense? (Still at work... brain is melting) :)))
 
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...and after playing with P3 on the F5T and BA-3, I can say that personally, tuning for minimum THD does not sound the best to me.

Just curious. Did it sound best (to you) when you adjusted P3 to emphasize the second over the 3rd harmonic? Did you find any advantage of adjusting P3 over initial settings, with equal resistance on each side as best you could measure?

Steve
 

6L6

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Just curious. Did it sound best (to you) when you adjusted P3 to emphasize the second over the 3rd harmonic? Did you find any advantage of adjusting P3 over initial settings, with equal resistance on each side as best you could measure?

Best sounding to me was actually quite close to even resistance... Which was a dominant 2nd harmonic at the 1w level.

If you have the ability to look at the distortion residual waveform, such as with a distortion analyzer, adjust P3 for the ultimately smoothest wave.

In my experience adjusting for absolute minimum THD makes for a very fast, detailed, intricate, and precise sound. It also has no soul... These amps can be adjusted to be very pretty at no significant penalty in resolution. Make the 2nd dominant at 1w and it should all fall into
place .
 
I would move the trace for the Q2 gate resistor (R12) to the top of the board, so you don't need to bite a piece of the source trace. You can easily do it in the center of the board, nothing on the bottom layer there.

Ok, I see the difficulties, but give it a though! :)
1) Move Gate traces on the top?
2) Make a turn around 7 and 8 pin of the input transformer to put that gate trace above. Does it make any sense? (Still at work... brain is melting) :)))

Did i got it right ?
 

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Change to use both transformer styles?

The PCB will be designed to only mount the specified Jensen transformer, but I'll look into the possibility of a second set of pads, if possible, to mount a Lundhal or something... No promises.

Would it possible to set the board up so it could use either the leaded or the pcb transformer versions similar to what was done by Permaneder on the VFET amp board?

http://www.diyaudio.com/forums/grou...ass-csx1-sony-vfet-amplifier.html#post3904854

This way those of us who participated it in the recent group buy of the leaded units don't have to re-buy or modify to make them work.

Nice job so far!

Steve
 
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