Help debugging Boss SD1 mod

Frequent questions about dead or faulty pedals. Whether you repair, mod or build pedals, debugging is important. Threads about general debugging problems irrespective of the circuit involved...
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alberto2000
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Joined: 27 Dec 2009, 23:57
Location: Zurich, Switzerland

Post by alberto2000 »

Hello

Changed R6 from 4.7k into 2.2k, tested, no problems.
Changed D4 and D6 from 1s2473 into 1n34a germanium & 1n4001 in series, tested, no problems.
Changed D5 from 1s2473 into 1n4001, tested, no problems.
Changed C3 from .047uf into .1uf AND changed LED from red to a green one, tested, and now there's a problem: some high frequent beeping tone.. which changes in pitch when turning around the 'drive' pot.. what could that be? Could it have to do with the LED or is it the capacitator? Any help welcome..

Cheers
r.

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5thumbs
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Post by 5thumbs »

Work is preventing me from giving this question any cycles right now, but here's the SD-1 schematic for reference. (That way, those of you without an SD-1 in front of you can play along too.)

Please, talk amongst yourselves. I'll try to pop back in later.
Attachments
BOSS-original SD-1 schematic
BOSS-original SD-1 schematic
Modding a DS-1? Please read 'Build Your Own DS-1 Distortion'.

"Other than a good first-in-line buffer/booster, using other FX to improve bad clean tone is like gift-wrapping garbage."

alberto2000
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Joined: 27 Dec 2009, 23:57
Location: Zurich, Switzerland

Post by alberto2000 »

5 thumbs up for 5thumbs :P
thanks

r.

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5thumbs
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Post by 5thumbs »

Well, thinking about it a little more, I doubt any of the components are to blame (at first.) From your description, it sounds like your pedal is oscillating a bit (the squeal.) You might want to check to see if the problem changes when you have the pedal: 1) open w/PCB in housing; 2) open with PCB pulled out of housing and 3) closed.

None of the component replacements you did should cause the issue you're seeing. That's why I'd first look at the wiring, which the above steps might help you identify a problem there. In addition to looking for a loose or frayed wire, pay attention to how they fit into the pedal when closed. Try to keep the wires away from the op amp (inputs, to be specific.) The high-impedance inputs of op amps can cause RFI, so it's a good idea to move away from them, if possible.

Of course, you might also try swapping the LED -or- capacitor back to their stock components. If swapping back to stock on either component fixes the oscillations, then you have your culprit.

Good luck!
Modding a DS-1? Please read 'Build Your Own DS-1 Distortion'.

"Other than a good first-in-line buffer/booster, using other FX to improve bad clean tone is like gift-wrapping garbage."

alberto2000
Posts: 30
Joined: 27 Dec 2009, 23:57
Location: Zurich, Switzerland

Post by alberto2000 »

Alright, thanks a lot, I'll try.
r.

alberto2000
Posts: 30
Joined: 27 Dec 2009, 23:57
Location: Zurich, Switzerland

Post by alberto2000 »

Solved by changing back to stock capacitor.

I'll try a 0.15uf capacitor instead...

r.

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5thumbs
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Post by 5thumbs »

alberto2000 wrote:Solved by changing back to stock capacitor.

I'll try a 0.15uf capacitor instead...

r.
Interesting. Did you have other 0.1uF cap available to try? I'm wondering if it's a bad cap showing some sort of microphonic tendency.

I'll have to open up my SD-1 at home to make sure, but I'm pretty darn sure I've got 2.2K in R6 and 0.1uF in C3. I don't have any squealing in my setup. The 0.1uF cap I used is either a Cornell-Dubilier CDE-series film cap or an AVX 63V boxed metal film.

Not sure what's going on, but at least you found what component is causing the squeal. Now it's just a matter of figuring out why that sucker is misbehaving.
Modding a DS-1? Please read 'Build Your Own DS-1 Distortion'.

"Other than a good first-in-line buffer/booster, using other FX to improve bad clean tone is like gift-wrapping garbage."

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