After making the 250 true bypass, I went ahead and did a few fidelity mods:
I removed the stock 4558 dual op amp, which sounds like ass, and replaced it with a 1458. The 1458 is essential a dual version of the 741 op amp, which was the chip in the original 250 ODs.
I removed the stock clipping diodes (I forget what they were) and replaced them with:
two 1N914 switching diodes
two 1N4004 rectifier diodes
no diodes
All of which I put on a SPDT on-off-on switch. I forget which on-side is which pair of diodes, but the middle (off) is the no-diode setting.
I bought the notoriously bland, famously on-the-edge-of-being-a-great-overdrive DOD 250 on the cheap recently. I picked it up with the sole intention of modding the circuitry. There are some great mods out there:
For instance, Analog Man has a page up giving a brief explanation of the circuit, and the differences between the reissue and the original pedal. It’s a good place to start for modding this pedal.
Also, a quick Google search will turn up half a dozen or so forum threads like this one, detailing people’s trial and errors with parts replacement.
I decided to start with true bypass.
One of my favorite things about this pedal is the use of a pin connector to easily separate the PCB from the actual hardware in the pedal. It’s a feature that will make it a hundred times easier to modify and test the circuit on a trial/error sort of basis. One snap of the connectors and I’ve got the circuit in my signal chain. An easy separation and I’ve got a stand-alone PCB to play with on the bench. Cool.
The signal path coming from/going to the white, female side of the connector is as follows:
From left to right, looking down on the opened enclosure.
Black: – output from circuit, coming from the second pin of the level pot.
White – ground
Green – positive
Grey - output
I’ve been kept busy during most of my free time by a lot of things, but my favorite has to be the new effects pedals I’m building. In this picture, the finished pedal (burgundy, lit LED) is the rehoused BMP from my previous post, fitted with a feed-back loop and noise gate. I then made it all pretty-like.
Tomorrow I’m going to capture a few clips of the pedal in action. This thing can generate everything from the standard BMP swarm-of-bees or bass-scraping to 8-bit-motorcycle revving. It’s a touchy little beast, with some odd settings combos leading to illogical results. For instance; the noise gate acts as normal with the feed-back loop off, quieting the pedal noise floor as its resistance is increased; but with the loop on, the gate acts as a way-around the loop, letting more clean-signal (though still colored by the BMP) through.
Anyway, it was a good experiment in pedal modding, and has given me more than a few ideas for future distortion projects. For now it’s secured a permanent spot on the pedal board.
The all-black pedal next to it is my EA Tremolo clone waiting for final wiring and lettering. I’m also about to begin work on a Green Ringer clone, which should be fun when combined with the FUZZ . .
