DR Boogie oscillates and I don't know why!

[guillemdc]

I built not long ago a BSIAB which is quite similar and it simply worked. Now this one is killing me. It's the circuit marked as V2. I've biased everything at 4.5V and it squeals when there's silence. Once you play, it sounds great and all the controls are responsive and seem to do what they're supposed to. If you stop playing, there's this obnoxious BEEEEEEEEEEP that varies in pitch depending on how you use the EQ controls.

I tried to bias it lower to no avail. Now it sits at 4V but the beep is still there as strong as ever. The build seems ok, but maybe you can give me a clue of where to look at, since there's obviously something very wrong that I don't manage to see.

It seems that the mids is the most sensitive control to the beep and, once you put it at zero, it seems to almost disappear. However, the attack of each note has a weird resonance that doesn't seem to be present on the tail of the note, which sounds great.

BTW, you'll see the board is quite crowded, I used some very big caps in it that I had laying around and hence some components may be buried under those. Also, there's a small daughter board that I use to wire the grounds and hot wires. I believe the builds with this many pots end up slightly cleaner this way.






Cheers!

[fx-fidden]

It could be a power supply issue. My Boss PSU has it sometime with transistor circuit.
Did you try it with a battery?

[lasermonkey]

Whenever I build a dirt circuit that uses transistors, I always add extra filtering to the power supply, as I've had one too many that have whined with a mains adapter.
I nicked the one from the Rat- a series 47R resistor between the 9v input and the circuit, with a 47nF cap in parallel with the big cap to shunt the higher frequencies to ground. Seems to work every time.

[fx-fidden]

Thanks for the trick.
Maybe even a 100nF cap instead a 47nF could be ok, and I heard a ceramic one will be better in this case.

I had these kind of issue with some DIY circuits like an Echoplex Preamp and a Pharaoh Fuzz (but not with a Big Muff)... I remember these. I easily solved with a 47R or a 1N5817 in line.
While with the Woolly Mammoth, and especially the Ultimate Octave (Foxx Tone Machine variation) I just tamed a bit the whine with a diode in line.
With the the Ultimate Octave I tried an overkill electrolytic cap across the ground, a 47R, 100R, 220R in line with a diodes. I even tried a inductor because I heard that was the better method to solve the problem, but I can't silent it completely.
At least I know the problem is my old Boss PSU, because a Mooer PSU was ok.

[guillemdc]

Thanks a lot guys. I'm using a boss PSU so I'll try it this afternoon with a battery and see what happens.

However, I don't believe filtering is the problem. The circuit itself has those 5nF and 100uF caps going from the a bridge from the top row to ground, so adding more filtering seems kind of overkill, doesn't it?

@fx-fidden, when you speak about a resistor in line, do you mean the 100R that goes from 9V to the top row? I could try enlarging that one in case the battery does the trick since it should lower the voltage in the top row so it copes with PSUs that provide 9.5V. However, since I'm biasing the transistors with the trimmers... I don think that's gonna be the problem. I'm thinking more of a bad joint somewhere but I can't find it!

[fx-fidden]

 After the test with the battery you will know if the issue is caused by the PSU.
Yes, I meant that 100R resistor, that this layout has, indeed. Sometime a 1N5817 diode is more effective than a 100R and I guess drop less voltage. In case you can try even a 1N4001.

If you got the problem with the battery, so check your board: see if everything is in the right spot, look between the stripes and between the wires soldering, etc...

[guillemdc]

Thanks again for your responses.

I tried with the battery and again and it keeps on oscillating. I'm going nuts! I'll keep on retracing the circuit to see whether something isn't properly soldered. If someone knows which part could be causing it, please let me know!

[fx-fidden]

I have to build it, too. I know this effect is prone to oscillating, so it's not a whine caused from the PSU how I thought, but at least we know it, now.
Do you have a buffer or a buffered pedal like any Boss?
The idea is to put a buffer (or a Boss pedal disengaged) in front of the distortion and the oscillating should go away. It's a trick that usually works.

[Sensei Tim]

where did you source your j201's from?

[alltrax74]

Try a buffer in front of the boogie, that should solve the problem.
I have a Klon buffer in front of my pedal board, it solved all the oscillations I had with dirt (mostly high gain) pedals
Lately I built an Engl Powerball simulation pedal, with 5 J201s (I used SMD ones). It squeals like a pig, but with the buffer before in the chain, no more squeal (and it sounds amazing BTW)

[Sensei Tim]

I’ve built many dr boogie pedals using the layout here with no squealing.

I think it has to do with your biasing and/or the jfets themselves, or your wiring inside the enclosure.

Just setting the bias to 1/2 the supply voltage is usually a good starting point, but it’s not a set in stone value.  Try adjusting trim 3 and 4 and see if that helps.

On Sun, Jan 3, 2021 at 7:43 AM alltrax74 [via Guitar FX Layouts] <[hidden email]> wrote:

Try a buffer in front of the boogie, that should solve the problem.
I have a Klon buffer in front of my pedal board, it solved all the oscillations I had with dirt (mostly high gain) pedals
Lately I built an Engl Powerball simulation pedal, with 5 J201s (I used SMD ones). It squeals like a pig, but with the buffer before in the chain, no more squeal (and it sounds amazing BTW)

http://guitar-diy.jimdo.com/

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[guillemdc]

Alltrax you're a genius! I've put a boss pedal in front, not even turned on, and the oscillation is completely gone. I'm gonna build a little daughterboard with a buffer right before the effect and that should do it! I've changed half of the caps in the build and nothing seemed to change :S.

BTW, I'm using 475K dale resistors instead of 470k ones and a 33n instead of 30... maybe those little changes could have made it more oscillation prone, but they're within a 5% tolerance so I don't think so... Dunno, anyway, it works so thanks everybody for your help!!!

[alltrax74]

 Your Boss pedal must be buffered bypass
But don't try the daughter board thing, it mostly won't work. I tried it with a few high gain pedals and that didn't work. Buffer needs to be in a separate enclosure