Electro-Harmonix Doctor Q

I have realised that since I started this blog I have managed to post every month, except for December. I want to keep going at this, so here's a quick cheater before the finish line.

I got this vintage EHX Doctor Q for fairly cheap, missing a battery door and "not working". The seller described some torn wiring inside. I thought this would be simple.

Graphics are actually quite clean for a pedal of this age.

I tried it out with a 1/8" power adapter in the DC jack and it worked just fine. It sounds pretty good too, and worked with weak single coils and humbuckers without having a sensitivity control. Range controls the width of the filer sweep, it has a fairly sensible & usable amount of variation.

Single sided PCB.

Opening it up, and the battery snap has broken off the power jack. Quick soldering job to restore it, and it works with a battery as well. It looks like EHX were not using the extra contact on the jack to switch the battery. The pot code is a CTS with a 1978 year of manufacture, so the pedal is probably that old as well.

Unfortunately it's hard to get the board out to take pictures as I don't have tools that can easily remove the round knurled nuts that EHX were using in this period. In the interest of not scratching things up I've left them along. The circuit is fairly simple, schematic is below.

It's pretty clear what happened to this one. With a missing battery door the 9V battery can just dangle out the hole in the chassis. The battery snap probably broke off when moving the pedal around. Sometimes I'm lucky.

I have a fairly complicated envelope filter build (maybe more on that in the future) so this one is surplus to requirements. Get in touch if you are interested in buying.