SD-1 to OD-1 Specs Conversion

(http://www.erikhansen.net/?page_id=91)

There were two versions of the old yellow Boss OD-1 Overdrive; the early 14-pin quad opamp version and the later dual opamp version. The quad opamp versions go for pretty high dollar these days and are more sought after but the dual opamp versions are still good pedals.

A Boss SD-1 Super Overdrive can be changed to the later (dual opamp) OD-1 specs fairly easily. The tone control needs to be removed from the circuit and the input to the opamp after the clipping stage needs to be changed to go to the inverting input (pin 2) rather than the non-inverting input (pin 3). There are a couple of other part changes necessary as well.

First let’s look at the differences and then the conversion process.

Differences:

SD-1 Part No. / Value R1 – 10k C2 – 0.018uf C6 – 0.01uf 2nd 1/2 IC – Pin 3 R11 – 22k

OD-1 Part No. / Value R1 – 1k C2 – 0.0047uf C4 – 0.018uf 2nd 1/2 IC – Pin 2

Conversion:

• Lift leg of R7 closest to the top of the PCB.
• Disconnect wires from pad 5, 8 (see next step) and 11.
• Solder a short wire in to pad 8 or desolder the wire from lug 3 of the tone pot (and leave wire attached to pad 8).
• Solder wire that leads to pad 8 to lifted leg of R7.
• Change C4 to 10k resistor.
• Change R1 to 1k.
• Change C2 to 0.0047uf.
• Change C6 to 0.018uf.
• Remove and jumper R11.

Ok, so what about the sound differences between the quad opamp OD-1 and the dual opamp OD-1? They do sound different, no doubt about it. The later dual opamp versions are a bit brighter sounding. Many prefer the sound of the quad opamp version. If you have the dual opamp version, you can get 90% of the tone of the quad version by making the following changes (thanks to Analogman for this).

• Change C1, C6 and C7 from 0.047uf to 0.1uf.
• Change C2 from 0.0047uf to 0.047uf.

diystompboxes.com thread discussion

*Please note, the 4 changes above pertain to the OD-1 part locations. For SD-1 part locations, read on.

Now that we know this, we can take our now converted SD-1 and make these same changes.

• Change C1, C8 and C9 from 0.047uf to 0.1uf.
• Change C2 from 0.0047uf to 0.047uf.

There are a few other part differences between the quad and dual versions. The SD-1 uses the same values as the dual. These changes are as follows (SD-1 part locations).

• Change R4 from 100k to 10k.
• Change R16 from 1k to 470 ohm.
• Change C10 from 1uf/50v to 10uf.

I noticed that these last three changes gave it too much of a tube screamer like quality so even though those are the quad version values, it sounds more like a quad with the stock values, to my ears anyway.

Once finished, tape down the disconnected wires that lead to the tone pot to the inside of the enclosure so they stay out of the way.

This is an excellent mod, in my opinion. It sounds very close to the old OD-1 after this, as well as it should considering how the two circuits are so similar.