This classic pedal has had a few incarnations along the years but most sought after seems to be the original “grey spec” version. Differences are subtle but they are there…
New reissue version is pretty close to the original and only few components are different. To get grey I changed the following:
1. Change opamp from 4558 to 1458
Original grey has LM741 opamp but 1458 is basically the same chip, just a dual version of it. Advantage of using a 1458 opamp is that it’s also pin compatible with 4558.
2. Remove 25pf
This was added to the reissues to smooth down the harshness of 4558 I guess…not in the original so I removed it.
3. Gain cap 56nF->47nF
This was 47nF in the originals. It limits the bass increase when turning up gain resulting from the ic clipping.
5. 100k resistor to 10k
This affects how “sharp” the clipping is through diodes, stock value in this one was 100k and grey spec is 10k. Higher values give smoother sound.
I also installed an on/off led and for that a new 3pdt footswitch had to be installed. And behold! A yellow grey DOD with a red eye! :)
Sound is tighter compared to the original but also has a nice edge which I like.