Yet another Dr. Boogey debug thread

Started by FiveseveN, August 17, 2009, 03:18:07 PM

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FiveseveN

I initially wanted to post this in one of the many Dr. B threads but I figured it may be a special kind of issue so I'd better not go hijacking people's threads.
So here's the deal: I built the usual gaussmarkov layout but skipped the tone stack (output taken straight from Q5's source via a .33-ish cap) since I'd be using it with cabsim and post-eq anyway. Here's the punchline: I can't get J201 here (or MPF102, or BF5457) so I used BF245 instead 'cause it was pretty much my only option. Yes, I am aware of the "reversed" pinout.
The issue: the circuit certainly has the "character" I'm looking for but with the gain pot maxxed only about a quarter or less of the gain I've heard in other Dr. Bs.
It's not an input signal problem (weak pickups) because my guitars have onboard preamps and quite high-gain ones, hitting the 12V rail when strumming hard. Oh and the Dr. B is also on a 12V supply (minus the diode drop of course). It's also not a biasing problem since I've tried both half supply and "by ear" for highest gain; the circuit sounds like it's working fine but it's just "as high as it goes".
Also tried halving the source resistors with no remarkable improvement. No real point in using a bigger gain pot bypass cap either since it's shorted with the pot pegged anyway. So I guess it boils down to this:
Should I keep trying to adapt the circuit to these FETs (even lower Rs maybe?) or just order some J201s and be done with it? I'm asking because I'd hate to go through the trouble only to find that it behaves the same with J201 and that the problem may actually lie somewhere else and I'm too much of a blockhead to figure it out.
Quote from: R.G. on July 31, 2018, 10:34:30 PMDoes the circuit sound better when oriented to magnetic north under a pyramid?

Ripthorn

Be aware that higher voltage supply will increase clean headroom.  Also, the only way to know exactly what a J201 will do is to them in there and see.  Where are you located?
Exact science is not an exact science - Nikola Tesla in The Prestige
https://scientificguitarist.wixsite.com/home

FiveseveN

I'm in the land of dark forests and ethnic food and great wine yet sadly no low Idds FETs  :icon_lol: (Romania). So yeah I guess I'll have to buy some J201 in the end.
As far as supply voltage goes, I figure the jump from 9V to 11.3 isn't a great big deal, certainly not enough to lower the saturation 5-fold!
Quote from: R.G. on July 31, 2018, 10:34:30 PMDoes the circuit sound better when oriented to magnetic north under a pyramid?

fpaul

I wouldn't count on the J201s completely solving this, although it's probably worth a try.  I used 201s and have the same problem with less gain than the clips I've heard.  Just my 2 cents.  Someday I'll spend some more time with it but have other priorities.  I'm guessing I have a problem with the board or may need to tweak the trimmers some more.
Frank