DOD FX50 (1988, NOT the "B" version)

[ubersam]

I have a DOD FX50 Overdrive Preamp that I wanted to revive and convert to be relay bypassed. I've searched for the schematic but the only ones I found are either close but is slightly different, or, schematics for the FX50-B, which is significantly different. So, I decided to just trace pedal myself. I have my traced schematic, the pic of the front of the board with component numbers added, and the flipped pic of the trace side of the board. They're all in here in case it could be of use to someone: https://www.dropbox.com/sh/8i99gntvkg5zsg2/AACUYgKHb32AZGCscdZvw54Za?dl=0.

[Rob Strand]

Thanks for posting.

I checked over it, it looks OK.
Didn't check the switch.  I remember most DOD effects use the same switch circuit.

Forgot to mention: Level Pot looks like a W taper (like a G taper), Distortion Pot is an Antilog (C taper)

[ubersam]

Thanks for the corrections. I updated the schematic with them.

[Ben N]

Nice, thanks. I have and love one of these, and have been meaning to trace it for years. Interesting that the bypass buffer is out of the sgnal path when the effect is on and the level pot is always connected to the output, or am I reading that incorrectly?

[ubersam]

You're welcome. You're reading it correctly, the level pot is always connected to the output. I've added a pic of the layout with the pic of the flipped trace side on top of the comp side if you want to double check. The bypass scheme is different from the Boss or Ibanez flip-flop method. As I understand the schematic, the buffer and the OD ckts are in parallel. In the 'overdrive' mode, the JFETs are 'open' and the buffered signal is cut off leaving only the overdriven signal at the output. In the 'bypass' mode, the JFETs are closed, the buffered signal is connected to the output, Q3 becomes a 'short' across R17 causing R16 & C5 to form a lowpass filter with a cutoff around 28Hz which 'mutes' the od signal leaving only the buffered signal at the output.