Moddjobbs

Vintage DOD Overdrive preamp 250 grey box repair 

I recently came into this pedal in non-working condition. All original 1978 grey box DOD 250  overdrive preamp

  
Bypassed signal was fine, but the unit had no drive output. Switch and voltages checked out ok, so I dug out my signal generator and oscilloscope. Trace signal was getting to the input of the op amp, but the amp had nothing on the output. 
I opted to add a socket when I removed the old UA741CP. This will make experimenting with different chips a lot eisier in the future! 
I replaced the op amp with an SK equivalent SK3552 (made in Italy) that I had on hand. Now this thing sounds awesome! Ready to rock for another 35 years

  
  

2 thoughts on “Vintage DOD Overdrive preamp 250 grey box repair ”

  1. I am troubleshooting a later, yellow (no led) version of the DOD Preamp 250, similar symptoms to your post: Fine in bypass but no drive control, and a reduced level from the bypass, even with the level on full.

    Admittingly a Noob here but can you explain or identify what the “OP amp” is that you replaced? Is that chip you mentioned making a socket for? Any help is greatly appreciated.

    1. Hello Kent,

      The op amp I replaced is the Rectangular silver component in the picture. (originally a UA741 in my pedal) I did choose to socket the replacement to allow for different op amps to be used in the future without pulling the board again.

      My Symptom was a bit different from yours in that I had no output at all. It sounds like you may have some, but It’s not what you’d expect out of the pedal.

      If you wanted to send some pictures over of your circuit board I’d be happy to give you a few places to look. Hit me up via the contact us portion of the site, and I’ll get my contact info to you. Thanks for your message!

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