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I built the Boogie ’57 kit a couple months ago and I suspect somethings wrong given the way it sounds.
I have a couple other store bought and kit higher gain pedals to compare it to, and my build of the Boogie ’57 sounds a bit uncharacteristic of a high gain pedal. The best I can describe it is the notes seem to sputter out and decay quickly, I can record a sample if that would help.
I can hear some of the characteristic boogie chug when doing palm muted open e downstroke style stuff, but if I hold out a note longer than a second the gain drops a little drastically.Another symptom is that it seems a little light on the gain, I swapped out the gain pot for a 1M audio taper (I think I read it in this forum) and it did provide a little more gain but the uncharacteristic note decay persisted.
I tried biasing by ear, to 4.5V (Q3 wouldn’t go lower than 5.5V), 5V (same Q3 problem), and 6V, all of them kinda have the same effect. I sense theres some trouble in the Q3 area
If I put a LPB-1 in front of the pedal, it mitigates some of the sputtery decay, and if I put a Rat or a big muff in from of the Boogie ’57, the sputtery decay is hardly noticeable.
Its been a couple years since I played a mesa boogie amp but I recall the note decay being more “regular” than what I’m experiencing here with my build.
From the photo is there any obvious issue? I checked the resisters around the Q3 transistor in the schematic and they seem to be correctly placed.
Definitely sounds like your FETs aren’t biased correctly
Try biasing the drains to 5v you won’t get 5v on them all there is a post somewhere if you search boogie 57 where I’ve noted my voltages
Here it is found it, from the post;
My Q3 is biased at 8.4v and works fine the source resistance change will affect it a little, 1, 2 and 4 biased to 5v and Q5 to around 8v
You’ll notice Q3 and 5 have no source bypass cap so gain is set by Q1, 2 and 4 making them important to bias at 5v ish
The only thing I can see that’s incorrect in your build is R11 3K9 in the build doc, yours looks like 39K this would definitely affect gain especially if you’ve built it stock and used a 1M gain pot
What I’d do is make R11 100K use an A250K for the gain pot with a resistor to ground on lug 1 to stop it cutting out completely 8K2 worked for mine
If you look at the linked post youll see this makes the gain more gradual across the pot so you may as well kill two birds with one stone
The only thing I can see that’s incorrect in your build is R11 3K9 in the build doc, yours looks like 39K
Eureka! That was it!
I’ll need to practice identifying resistors by color band more quickly.
I didn’t have a 3K9 on hand (have some 3.3K and 4.7K) so I put in a socket for R11 to try both, and 4.7K seems to solve my issues with biasing Q3.
Now the decay is much more natural and musical, low E strings ring out in a distinctly metal way.
However, with the volume all the way up, it seems to be at least 6dB quieter than the bypassed signal.
And the A1M gain pot seems to not have much sweep at all, silent, then about an 1/8 of a turn gives me 80% of the gain. I’ll check out your suggestion re: the gain pots and dig further into the old threads.
Thanks for your help, Billy
Try the gain pot mod I detailed above if you check the link you’ll see I did a bit of work to get a nice range across the gain pot
It should have plenty of gain and volume make sure your volume pot has nice solder joints I’d suggest using an audio probe to see if you can find where the volume level changes or drops
I replaced the gain pot with a 250k and the 8K2 resistor to ground, much smoother gain sweep!
As far as the volume drop, with an audio probe I figured out the treble pot is shorting somehow.
When the pot comes into contact with the case it drops in volume, I looked at the schematic and it seems like none of the 3 connections for the treble pot are supposed to connect to ground.
As you know the enclosure itself will be grounded make sure none of the pot lugs are touching the enclosure causing a partial short to ground or you could try insulating where the treble pot goes through the enclosure with a thin piece of plastic or tape
I had a similar problem where when I tightened the pots up they moved and pot lugs touched each other
Yours look straight but you can’t always see if they move and touch something they shouldn’t
I can’t quite make out if all of your pots have the plastic covers on the rear if they don’t insulate the back of them so they can’t short on the solder side of the pcb
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