Problem with Boss OS-2 OD/Distortion pedal

[Chuck_Farlee]

I have a Boss OS-2 distortion pedal that makes a high pitched whine when hooked up to a Boss PSA-120S adapter. It doesn't do this with a battery. It sounds like some noise is coming over the line.

Here is a link to the schematic:

http://www.freeinfosociety.com/elect...es/bossos2.gif

Any ideas where to start?

I called Boss tech support and they don't provide trouble shooting of this sort over the phone.

I was thinking of replacing the two 100uF caps (C3 & C2) because I'm thinking the power coming out of the adapter may not be filtered enough.

chuck

[Enzo]

Usually with Boss pedals, if you use some other adaptor they get hummy due to lack of sufficient filtration. Try some other adaptor to see if this condition remains. Ignore any increase in hum for the test. That will tell you if the adaptor is involved.

You could increase C3 to 470 or more and make me happy.

Your link didn't work for me, try this one:
http://www.freeinfosociety.com/media.php?id=1894

[Chuck_Farlee]

Enzo,

Usually with Boss pedals, if you use some other adaptor they get hummy due to lack of sufficient filtration. Try some other adaptor to see if this condition remains. Ignore any increase in hum for the test. That will tell you if the adaptor is involved.

You could increase C3 to 470 or more and make me happy.

Your link didn't work for me, try this one:
http://www.freeinfosociety.com/media.php?id=1894

Thanks for the reply. I will try another adapter to see if that is the problem. I should have mentioned that I have another PSA-120s that I tried. I have two other OD pedals on the board and with one of the adaptors, I get a little bit of hum out of the other two and a lot out of the OS-2. With another PSA-120Sadaptor, I get no hum out of the other two and still quite a bit out of the OS-2.

chuck

[Enzo]

Wait, you already tried it with a different Boss adaptor? That is what we needed. Does it have the same symptom with both adaptors? Or does it bahave any different? I mean do you get the same noise either way?

Before modifying the circuit, I doubt this model came out with all of them acting this way using a proper Boss adaptor, so maybe the pedal has a problem. For example, the voltage across C2 should be half that across C3 - is that the case?

WHen it makes this noise, try all the controls. WHich controls have any effect on the noise, and what effect is that? In other words, it would be a clue if the noise was always present and the volume control turned it up and down. It would be a different clue if the noise only happened when the volume was over 5 or under 7 or whatever. Or if it changed its note as the control turned.

[Chuck_Farlee]

Wait, you already tried it with a different Boss adapter? That is what we needed. Does it have the same symptom with both adapters? Or does it behave any different? I mean do you get the same noise either way?

Pretty much the same noise with either adapter. What's weird is that with one adapter the other two OD pedals make the same noise, but lower in volume. The OS-2 makes the same noise with both pedals at about the same volume.

I have a few other adapters I can try.

Before modifying the circuit, I doubt this model came out with all of them acting this way using a proper Boss adapter, so maybe the pedal has a problem. For example, the voltage across C2 should be half that across C3 - is that the case?

I will check that tonight after I get off work.

WHen it makes this noise, try all the controls. WHich controls have any effect on the noise, and what effect is that? In other words, it would be a clue if the noise was always present and the volume control turned it up and down. It would be a different clue if the noise only happened when the volume was over 5 or under 7 or whatever. Or if it changed its note as the control turned.

There is always noise and gets louder when the volume control is turned up. The other controls don't seem to affect it, only the volume/level control.

Once again, thanks for your help.

[Chuck_Farlee]

Update:

I changed out C3 and C2 with 330uF/16v caps and that cleared up the problem. The stock 100uF/16v caps were very small. The new 330uF/16v caps were larger, but still fit inside the enclosure.

Thanks for the help, Enzo.

chuck