Boss OD-1 Overdrive Mods By Analog Man

The Boss OD-1 was about the first OVERDRIVE pedal made, except perhaps the Ibanez Overdrives. But the early Ibanez pre-tube screamer OVERDRIVES were quite fuzzy and distorted, while the OD-1 is the first of the "tube screamer type" overdrive pedals. It was in the very first series of the Boss Compact Effectors. The OD-1 came out in 1977 and was discontinued in 1985. They were very popular in the LA metal scene in the mid 80s and the Japanese scene in the same time and much longer. The SD-1 took over from the OD-1 in the mid 80s but people still wanted that pure OD-1 sound. The OD-1 (and SD-1) use asymmetrical clipping, which Boss has a patent on, to give some thick overdrive with an edge. Tube Screamers use symmetrical clipping for a smoother, warmer, less edgy sound.

The original OD-1 was made with a QUAD OP AMP CHIP, seen at the left. This RC3403D chip has 14 pins. Some early ones (1978) used an NEC uPC4741C quad op amp instead. Later versions used a common dual op amp, with 8 pins. Usually a 4558 chip was used, and often the famous JRC4558D as seen on the right. But the sound of the later unit with the smaller chip was NOT the same as the original version. The oldest versions will have a metal thumbscrew and ink-stamped serial number in the battery compartment. But some with the small chip have those features, too (1980). So the only way to tell if you have the GOOD ONE is to look inside for the chip and see if it is the small one (8 legs) or the big one (14 legs = best tone).

In the BOSS BOOK, they say that they stopped using the big chip (made by Raytheon in the USA) because they had some failures. They switched to a Japanese made IC instead. I think it may have had more to do with cost and using Japanese parts, but for whatever reason, the circuit changed and I think in a detrimental way.

In early 2005 I finally sat down with older and newer pedals as I agreed to modify one for a customer. I found the main difference was capacitors, several smaller value capacitors were used, sucking away low end and making a thin tone.

Substutiting the old capacitor values helped a lot, it sounded almost exactly like the old one! Then I tried to install the larger chip in the new board, it did not look too hard as there was room for it. But it was very difficult as four of the legs had to go to different points on the board, and some bias resistors had to be changed to use a chip instead of the transistors that were used on the newer versions. These two transistors have to be removed. I was successful installing the large chip, and it sounded a little better but almost the same as with just the capacitor mods.

So we will offer the capacitor mods as a standard OD-1 VINTAGE mod, and add the chip change for a VINTAGE CHIP mod for extra cost for those who want the exact sound of the original. The VINTAGE CHIP mod will have all the capacitors changed from the VINTAGE mod, plus the chip and other changes to the 100% original circuit, using a JRC3403D chip which I have found is like two JRC4558D chips, awesome tone.

We were pleasantly surprised when we saw this picture of Radiohead's Ed O'Brien's pedalboard, with our OD-1 mod on it.

Here's an awesome demo by Joe Perkins Music!


Please fill out and send in our MOD FORM with your pedal, it has both of the options available. We can also mod your pedal for PSA (9v) adaptors if it is an early one made for ACA (12V) adaptors. Just put a note on the mod form for that, no extra charge. We can also install a bright LED of various colors, another option on the MOD FORM.

Thanks!!! Mike aNaLoG.MaN