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Dr Boogie oscillation

Started by Govmnt_Lacky, December 21, 2010, 11:27:09 AM

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Govmnt_Lacky

December 21, 2010, 11:27:09 AM
Just finished building the Boogie from the gaussmarkov layout and it sounds phenomenal!  :o

I... of course.... have one small problem. There is a mid to subtle oscillation in the sustained chords/notes  :'(

I biased the J201s to between 5.0 and 5.1V each. I also used shielded cable from jacks to switch and switch to board.

Should I try to rebis to 4.5V and adjust from there to try to get rid of the oscillations? Any other ideas from those who have had...and fixed this problem?  ;D

Thanks to all who help.  ;)
A Veteran is someone who, at one point in his or her life, wrote a blank check made payable to The United States of America
for an amount of 'up to and including my life.'

Govmnt_Lacky

#1
December 21, 2010, 04:11:16 PM
Bump... Anyone.... Bueller  ???
A Veteran is someone who, at one point in his or her life, wrote a blank check made payable to The United States of America
for an amount of 'up to and including my life.'

deadastronaut

#2
December 22, 2010, 07:58:56 AM
I always bias a boogie by ear....ive done it by dmm, with poor results...differences in gain on the fets i guess!...

i tend to turn my guitar right down and get the note coming through without any gating..then go from there...
https://www.youtube.com/user/100roberthenry
https://deadastronaut.wixsite.com/effects

chasm reverb/tremshifter/faze filter/abductor II delay/timestream reverb/dreamtime delay/skinwalker hi gain dist/black triangle OD/ nano drums/space patrol fuzz//

newfish

#3
December 23, 2010, 07:56:16 AM
Would an Audio Probe be useful here?

Tap into the signal as it leaves each gain stage, and adjust the trimpots to taste.
Happiness is a warm etchant bath.

Govmnt_Lacky

#4
January 09, 2011, 09:35:41 PM
Let me be a bit clearer on my description of what is going on. As I strum a chord, the initial sound is GREAT! Nice and tasty distortion however, as the note or chord goes into sustain, it begins to "wobble." Kind of like the volume of the note/chord fades in and out a-la a Phase 90.

I assumed this is what is meant by "oscillation" but I could be wrong which is why I am reposting.

Can this be tuned out by biasing one of the FET stages? If so, is there a particular stage/FET I should focus on or is it susceptible at ANY stage/FET?

Thanks for the help.  ;)
A Veteran is someone who, at one point in his or her life, wrote a blank check made payable to The United States of America
for an amount of 'up to and including my life.'

ayayay!

#5
January 10, 2011, 01:13:34 AM
First, let me say I feel your pain.  This is a tricky pedal.

I believe what you're hearing is the feedback oscillation that, as the chord fades, is fighting with the variations in the AC sig coming from your pickups.  Almost like they cancel in and out? 

I'm with dead astronaut here:  Bias by ear.  I had one of these I built where the first stage drain was like 1.6V!  JFET's are fussy. 
The people who work for a living are now outnumbered by those who vote for a living.

Govmnt_Lacky

#6
January 10, 2011, 08:03:51 AM
Quote from: ayayay! on January 10, 2011, 01:13:34 AM
Bias by ear.  I had one of these I built where the first stage drain was like 1.6V!  JFET's are fussy. 

So, would you suggest the first gain stage (1st JFET) as the one to bias and to try to tackle my "wobble" issues?
A Veteran is someone who, at one point in his or her life, wrote a blank check made payable to The United States of America
for an amount of 'up to and including my life.'
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