Boss SD-2 Dual Overdrive mods;

[Bernardduur]

So, I modded my Boss SD-2; I got it for bass as it really nails that OD tone for bass on the LEAD channel but the CRUNCH channel didn't do much for me...........

So I took a look

The CRUNCH channel is very close to a Tubescreamer so I decided to mod it into a TS, adapted for bass. Here's what I did:

Mod A; more clarity;
Replace C34 / C13 / C9 / C18 / C43 and C22 with it's better quality replacements

Mod B; tubescreamer:

- Remove C36, C46, C47 and R49; replace this with an 1 uF NP cap (the start of C36 and the end of C46 are so close you can fit in a cap quite easily)
- Replace D4 with a silicon diode
- Replace D6 + D7 with one 1N400X diode
- Replace C28 with a 220 nF cap
- Replace R37 with a 4.7k resistor and run one end to Vref (which is on one side of R51; close. You can use the leftover traces of D6 / D7 to overcome the small distance without short circuiting
- Replace C12 with a 1 uF NP cap

PLAY!!

For guitar I would recommend the change of C28 to 100 nF

[nuttmeg1]

Hey man,

Do you have this schem?

Thanks,
Brian

[Bernardduur]

Here it is!

[nuttmeg1]

Thank you so much dude. I have loved this box forever but have had little use for the crunch channel. That's about to change.

Thanks,
Brian

[Bernardduur]

I also LOVE this pedal.....

But then only on bass

[Bernardduur]

OK, to add another mod;

I halved the gain on the second gain section of the LEAD mode; it makes the lower gain settings more alive and OD like without losing the distinct sounds on the higher settings.
To do this, replace R60 with an 100k resistor, C31 with an 10 nF cap.
On bass, I can get higher CRUNCH sounds from the LEAD mode so now the CRUNCH and LEAD do match each other.



Oh, btw, question;
I got one unit in from a friend and he asked me to do the same mods as I did as he LOVED my unit live. I saw this weird thing in his unit:
The unit has the same PCB as mine but there is a 1 meg resistor parallel to the C19 cap; the resistor is on the wrong side of the PCB and is put there by Boss I suppose (as it is the same sort of resistor used all over the pedal). If I remove the resistor (as I did; I expected it to alter the sound) the unit workds great until after 1 minute; then the unit gets all muddy and loses all OD........ With the resistor placed it has no trouble; can someone explain that to me??

[George Giblet]

So you gave up on the ODB3.

Thanks for sharing your results.  Looks like the Fat TS-9 configuration wins again for bass.

To simplify the mod you could probably just short C36, and short (or pull) C47.  That stuff isn't doing much with the mod.

> the unit workds great until after 1 minute; then the unit gets all muddy and loses all OD

So that effectively puts a 1MEG across the gain pot of the lead channel.   I have a feeling the gain pot is damaged or there is a cold joint on the pot (or pot wires if it has them).  When you take the 1M out the DC bias of that stage slowly shifts as the opamps input leakage charges/discharges the surrounding caps.  You could verify this by measuring the DC voltage on pin 7 of IC3b.  When it's good it will sit at 4.5V and when it's bad it will ride towards 0V ot 4.5V.   To fix it have a poke around for cold joints and perhaps measure the pot.  Try to buzz-out the pot and cables.

I'm surprised the gain pot works properly with the 1M in. You would think with the 1MEG is just sits at a high gain all the time (or drifts towards it at some point).

[Bernardduur]

Hey man!

The ODB is not from the scene; this SD-2 I have been using now for a long time..... the ODB just came in my life. We'll see!

> I'm surprised the gain pot works properly with the 1M in. You would think with the 1MEG is just sits at a high gain all the time (or drifts towards it at some point)

Dunno why but the potmeter just works like the one in my other unit; is functions brilliantly

[George Giblet]

> the ODB just came in my life. We'll see

OK.   After the ODB3 thread I was thinking of playing around with it.  When I thought you gave-up I wasn't going to bother - lucky I asked. 

It would be easy to go down the path of making the ODB-3 a TS-9 with a blend control.  I know that works (eg. Voodoo Sparkle drive, and the Sprinkle Drive),  but that's too easy!!!

> potmeter just works like the one in my other unit

Hmmm, something very weird is going on there.

[boyersdad]

Cool mod. I did a similar on the first channel, and also decreased the feedback resistor to get a little more poop out of it.

The crunch channel I made a few changes (clipping diodes and a copule RC's... can't remeber what off hand) but I found it was still hissy and just not awesome sounding. I'mma try modding it to an SD-1 (which I love to death; probably more than the TS).

[lynessmy]

sorry for digging up an old post....does any one still have schematic for SD2?
Please sent to j.ko@mailcity.com

[eddie84mx]

Hi, I have made the tubescrear mods of Bernardduur but now I have a small output volume on cruch channel...why???

HELP HELP PLEASE
bye bye