I need your expert help with an OD-3

[thejoe]

Hello fellas,
So, I've slowly been modding a new Boss OD-3. I had it pretty good but then I couldn't leave well enough alone and now it's not so great. I've noticed a faint hint of a really bad distortion under the whole signal. Like that awful Line 6 Insane distortion. Low but noticeable. I'm not sure how to fix it. If you all don't mind I'll give you all my play by play:

C28- .033mf
IC- TL071
D6- Silicon
D11- LED
C24- .1mf
C7- .056
R13- 1.5k

After all of this I got nuts. I tried to change R15, and R23 because I was hoping they would give the sputtery effect of being over or under biased. They might not have even been the right resistors.
I then thought circuit bending would be a cool idea. I had a wire from C13 that I was trying to bring back through the IC loop. I moved it all around (before R15, after R25, before or after R13). Nothing did anything I was hoping for. Somewhere throughout these last two bold endeavors I did get the sputtery effect but it was short and then stopped. i also don't remember what did it or if something was just shorting on another component or the case.
This is when I noticed that noise.
After this I did some more work moving with the diodes. I had a swtich hooked up and didn't notice much change between some of them. I then totally removed D6. Then I swapped a silicon for D11 and LED for D6 (which i don't like). I also put a JRC1458D in the IC thinking maybe that was the problem. And thats where it stands right now.

Sorry there was so much here. Any thoughts on where I went wrong?

Joe.

[ayayay!]

Do you have a schematic or this or are you just doing the "ready, shoot, aim" thing?  I'f you have a schem, please share.   

[thejoe]

Sorry, here's the schematic.
http://www.freeinfosociety.com/electronics/schemview.php?id=2299

I've modded lots of things before by following other people's ideas on the internet. But I got this pedal for free and just let myself get too wild.

[thejoe]

I'm going to try and take another crack at this today or tomorrow. I'm thinking it's either one of the electrolytic caps or one of the Jfets. Thoughts?

[thejoe]

Though I doubt anyone is tracking this thread, I did some prodding today with the audio probe. Everything sounds great until I get up to the collector of Q11. This is also, of course, the beginning of the overdrive circuit. I noticed that the emitter and base give no sound at all but R52 is still producing a dirty signal. Is that weird? Could the transistor be bad?

[HOTTUBES]

I'm going to assume you have an adaptor for your op amp , cause the factory op amp is an inline unit , where as the JRC is an 8 pin dip !




http://cimarrontechnology.com/ProductImages/smadapters/bd060301_7.jpg





have you tried putting the factory op amp back in ?

[HOTTUBES]

What kind of sound are you shooting for with this mod ??

[thejoe]

I don't exactly have that adapter but I made one on vero board. I'm still a bit green with mods. I was trying to make it sound like a more true overdrive. I knew that going asymmetrical on the clipping would help a bit. And I wanted it to sound real rock and roll like. It got to a point where it was a nice chimey overdrive, 70's sounding. I did notice that it wasn't as full on the low end though. So I was trying to add that and also thought I'd give a go at trying to get it sputtery which is where a lot of this went wrong.

[HOTTUBES]

Try this ....


1. reinstall the stock chip
2. remove C7 & C8 ( no jumper required )
3. C13 - 1 uf
4. C22 - .1 uf
5. C18 - .15 uf
6. C33 - 1 uf
7. C34 - .47 pf
8. D7 - LED and 4148 in series
9. D11 - LED


If the pedal is all stock  , this is a nice improvement !! 

[thejoe]

Ok thanks. I'll give this a shot. Any advice on what the crappy little under tones i was mentioning might be coming from?

[HOTTUBES]

Ooops !!   

Correction :   

C34 should read   470 pf   

Not .47 pf    !!!!

[HOTTUBES]

Question ?

If you hit a chord , and as the chord is decaying and fading out , do you hear the strange sounds at this point ??

[thejoe]

Question ?

If you hit a chord , and as the chord is decaying and fading out , do you hear the strange sounds at this point ??

Yes. The pedals main tone is nice but underneath is a really dirty, really fake sounding distortion. I'm noticing it mostly as the chord rings.

[HOTTUBES]

 

I have had this problem in the past as well , and it always ended up being in the clipping arrangement , i think it comes from clipping
a single stage to hard etc . To be honest ,i don't know the technical side of this stuff that well , but i have modded this pedal (OD3)
many times with good results , but they have all been in stock trim when i started the mod .

[thejoe]

Great. Well thanks for all of your help. I'll probably get around to this next week and let you know how it goes.