Introduction

The secret MXR doesn’t want you to know is that all three of these pedals share the same circuit board. I originally read this on several web boards and saw photos of both pedals side by side, so I asked MXR customer support to confirm. Guess what? They never replied. And they usually reply within a day or two. And I understand them, why would they want to tell people that Classic OD they sell for $40 through Guitar Center (I paid $30 with a coupon) is the same as the other two that cost $100. Sure, the paint job is not as nice, but who wants to give extra $60 for a stupid bullseye graphics?!

So what’s the difference between GT-OD and ZW, as they clearly sound differently? MXR put a small slider switch on the component side of the board that adds some components to the signal path, and they set to one position or the other when deciding how they want to label the pedal. The lame thing is that they put it where you can’t see it or flip it without disassembling the whole pedal.

I’ve seen people removing it completely and replacing it with a panel mount toggle switch, and that’s a cool mod. But here’s another idea that will save you time for drilling the enclosure and money to buy a new switch. Why don’t we just place the same switch where it can be accessed relatively painlessly? Here’s a step by step guide how to do it in about 10 minutes.

Step 1: disassemble the pedal

Unscrew both jacks, take all pot knobs off, unscrew the pot nuts and finally unscrew the bypass switch nut. After that you’ll be able to take the whole PCB out of the enclosure, just lightly press the bypass switch and pots at the same time. Locate the hidden switch in the top left corner of the PCB.

Step 2: desolder the switch

Using some desoldering braid will help. It’s a plated-trough hole PCB which makes it harder to lift a trace in the process. But it also means that after you’re done, the holes will most likely still be filled with solder that’s not easy to suck out (unless you have the right tool for the job).

Step 3: solder the switch back

Hopefully, you haven’t ruined the switch while desoldering (you can check with the DMM, it’s a standard SPDT, center pin is common), so we’re ready to solder it back on the other side of the board. Since the holes are likely filled with solder it’s going to be harder. I heated all three holes at the same time while inserting the switch and then added some solder to make a good connection. You don’t have to worry about switch orientation, since it’s symmetrical. Here’s how it should look like when done.

Alternatively, you can just solder three pins and use them with a jumper, like on hard-drives or motherboards.

Step 4: assemble the pedal

Repeat the step 1 but in reverse 🙂 Note that the switch tip will stick out of the enclosure for about 1-2mm, but it’s not a problem, when the lid is installed it won’t touch it…barely.

Step 5: test it!

Before screwing the lid on plug in the pedal to make sure that our mod went successfully and also make sure that you can screw the lid on without adding pressure on the switch. If the lid touches the switch make sure that the switch went all the way through the PCB. If that’s fine, you can always use a nail clipper (or some more professional tool) to shorten the switch tip. As far as the sonic test, you should hear the difference in sound between the two positions. One (GT-OD I think) is more natural sounding and the other (ZW) is a bit more defined in the higher mids and slightly louder. I think I prefer the ZW position, at least when driving a cleanish amp. It may be useful to have the natural mode when pushing an already good sounding overdriven amp into saturation without changing the tone. That’s why it’s cool being able to switch them easily 🙂

Conclusion

If you’re on the market for GT-OD or ZW pedal, just get a Classic OD in Guitar Center an perform this mod. If you already have one of these three pedals, it’s still useful to do the mod because it adds versatility. Both positions sound good, but differently. As said before, you can spend more time and replace the internal switch with the enclosure mounted toggle, or you can just re-position the switch and take the lid off whenever you want to play with it.