Sunn Model T preamp+33v charge pump bias question

[traktop]

I´ve built a 33v charge pump inside my model t build and included a 9/33v switch so I can make a side by side comparison.
I had fets drains biased to read about 3/4v from a 8.98v power source.
The most noticeable difference when powering the fx with 33v, (actually it was 35ish volts),  is a substantial increase in output volume level.
Regarding to sound differences, it felt drier, and less gainy compared to 9v sound. Maybe the sound was a little "fuller" with more body, (it could be the increase in volume and less gain cheating me through the 1w fender amp I´m using for testing...)  
Anyway, I  measured fets drains powered with 35v and got about  28v, (24v cranking the 50k trimmers).
My question is:
Should I have to rebias fets so I get about 17.5v, (will have to increase the trimmers to at least 100k), in order to get it "right"?
Cheers, Gilberto.

[rocket88]

I put in the notes that q1&q2 should be at 6.5v (~75% voltage) and q3 should be 5v(~55% voltage). I could be wrong but since you have the voltages lower it may be the reason for the less gaininess of the pedal. Try rebiasing q1&q2 to 25.3v and q3 to 19.4v.

I'm sure that having more voltage will increase the output and should add more oomph and body, just like any of the other amp in a box pedals, so that doesn't surprise me. By increasing headroom you may see slight less distortion too as a result. Sit haven't had time to build mine. I'm hoping next weekend I'll have less school work and can get to it. I did finally finalize my enclosure design and super stoked.

[traktop]

Thanks for the answer zach.
I first tried the suggested values when I built the pedal, but couldn´t get much gain, (my axe is a stratocaster), so I tried maximizing gain fets biasing q1/q2 by ear using the following method:

Master volume cranked turning down normal channel volume until felt it was completely clean, (bright channel at zero). Normal channel biased at 6.5v it was fairly clean; above it, sound started fading away, so I started playing with its bias pot trying to find the loudest spot just before turning gated, farty etc... That was about 2.8v so I finally ended on 3.5v. I did the same with the bright channel, (q2).
Then started with q3 at 5v and found that at 3v, the thing still was clean, but louder.
Finally I cranked both channels and tuned q3 by ear, resulting on about 3.5v as well.
At this point, the pedal works great and sound very amp like with normal channel cranked and bright at about 75 percent, (bass about 10:00 o´clock, mids at  1 o´clock and treble at 9:00). If I lower the channels gains at about noon, it sounds too dry and stiff for my taste though...

Anyway, I think I will experiment lowering some resistors, (33k for input resistors, and 220/100k for the ones before q3, so this one gets hit harder), in order to get more gain.

Regarding to biasing q3 down to 19.4v: I´m going to up all trimmers to 100k, cause with 50k I just could go down to 25v coming from 28v. But, I noticed that with q3 at 25v, britte channel started to squelch and whine a little...

ok, time to work, I will post my results when I got something.
Cheers, Gilberto.

[traktop]

Ok, changed trimmers and rebias q1/q2 drains to 25.3v ad q3 to 19.4v, and now we´ve got a major whining party over here, and not only the britte channel but the normal as well. It happened from noon in advance on their respective volume controls.
So this is what I did:
Lowered both 470k resistors down to 100k, (the ones right after both channels volume pots and just before pushing q3), in order to get more gain. Then I powered the pedal with 9v and rebias q1/q2 to 6.5v and q3 to 5v, (initial suggested setting). Then activated the charge pump again to get 33v without touching the trimmers, and tried cranking both volume channels, guess what: Whining again...
Tried backing both channels volumes, and things got much better, but then I ended exactly at the same place where I started regarding to gain levels.
Anyway, if I go back to 9v with the "gain mod", this thing worked quite better; all of that with my stratocaster.

All of that was done at my night shift job, so when I returned home, and tried it with my girlfriend lespaul tuned to drop b, this pedal just came alive. Great, with lots of gain in 9v mode.
Powered with 33v sounded less gainy but this time the amount of clarity and detail was just amazing with a better detailed grain compared to 9v sound. All of this was done with the "correct" 9v bias, so I decided to play with the trimmers again to see what I get on 33v mode.

Super long story short: I finally got a good compromise leaving Q1/Q2 trimmers alone , (30.3v), and biasing Q3 down to proper 19.4v with no whining at all.


My conclusions:
My build don´t like my strat very much at 9v
My build likes my strat even worse at 33v
My build loves a thick-high output pickups les paul at 9v
My build wants to marry my girlfriend lespaul at 33 v

Now I need some sleep...