This is what happens after a while

[aron]

I decided to fix my broken DOD 250 overdrive that I bought at the local flea market. I did a quick check and confirmed that the op amp was getting power when the unit was powered on.

When I plugged it in, the volume knob made hissing sounds so I immediately assumed it was a connection problem to the input of the circuit.
In addition the jacks were noisy and the switch was bad. So I changed the switch, changed the jacks to Switchcraft and nothing.... Same hiss....

I started tracing using my meter and pencil/paper. Using continuity and resistance testing, everything looked correct in terms of connections. Physically everything was fine.

I switched to DC metering and saw power 9V but the voltage divider VR was way, way off. What was going on? Luckily instead of trying to debug that too much, I measured the output pin and it was close to 8.5V+. Way too high. I deduced the op amp was blown.

What I couldn't figure out was why the biasing resistors were way different from the schematics and why it was using an MC4558 instead of 741 or 1458 etc....

I put a socket in there, plugged in an RC4558 and it fired right up - biased correctly etc... It sounded ok.

Then today, I was thinking of modding it to the DOD 250 grey spec and I looked at it again..........

uh..... It's a ROSS distortion!!!!! No wonder the schematics looked off!

[sshrugg]

Hah!  Nice.  Great news that it's working.  Sounds like you kind of lost the forest for the trees there 

[jakenold]

Cool stuff Aron - it's a great circuit for lower gain stuff like blues.

I found one in the new place me and my band reherse. The former owner said we could have everything in the place (really nice 65sq meters, two story with tall windows and tall ceiling) if they didn't have to clean up... and guess what I found: a Ross Distortion, a Ross Compressor, an 70's VOX wah, a JCM800 and a Big Muff 70's thing. None were working, but the faults were minor, and now I've got a KILLER rig for the price of swinging the vacuum around a bit. Score one for Jake!

We haven't got a great flea market culture here in Denmark, regarding musical equipment, so this ws really a great thing indeed!

Kind regards, Jake.

[aron]

When I first started on this hobby, I traded away a Fender Blender, Mutron V and Ross Phaser (mint!!!) for a Carvin 33 watt combo.

I wonder who got the better deal??