Component question on Electric Mistress

[Neal]

I'm used to tinkering on my tube amps, but I don't know much about solid state electronics. I recently fixed my old Deluxe Electric Mistress, and now I want to tidy it up before I put it back on the pedal board. On my EM, C5 is listed as 56pf, and is tacked on the back of the circuit board instead of the component side. The actual value in mine is 10 pf. I decided to replace the ceramic cap with a silver mica, and the closest value I had was 100pf. When I put the 100pf in, the flange effect was much less dramatic. I went back to a 10pf ceramic. This all leads to my question.... what exactly does this cap do, and why is it on the back of the board? Oscillation problems?
Here's the layout, courtesy of General Guitar Gadgets (I hope it's okay to post this link...) :
http://www.generalguitargadgets.com/...ms/dmistlo.gif

Thanks for any info!
Neal

[David Schwab]

It's hard to tell looking at the PC board like that, but it is after the TL071 op amp, so I could guess from the value of the cap it's to filter out very high frequencies... stuff like radio and the clock signal from the rest of the circuit. Replacing it with a larger value will filter out more high end... which is probably why the sound was less dramatic.

The fact that they tacked on a smaller value seems to indicate a change from the original specs.

I've seen a Deluxe Memory Man with a LOT of additional/replaced parts, tacked on the trace side of the board. These must be improvements they made after the circuit was finalized for production.

I'd just leave it.

[Neal]

Thanks, David

I appreciate the response. I had a signal generator going when I pulled the cap, and the flanger still worked, so a clock noise suppression cap makes sense. If I wanted to live dangerously, I'd leave it out altogether, but I don't think my old ears will hear the difference a 10pf cap makes. I'll just leave it.
I'm just glad to have it working again.... my pedalboard went through a car wreck 20+ years ago, and the broken pedals have been sitting in a box in the closet ever since. Last year I decided to resurrect what I could, and so far I've fixed a Morley Panner/Volume (including straightening out the chassis where the 1/4 jacks were pushed in), a script logo Dyna-Comp, a big-box Rat, and now the Electric Mistress. My Big Jam delay was too far gone, and way too noisy to miss. Now, if I still had the hair I had 20 years ago, I could rock and roll!
Neal

[StephenGiles]

Surely hair has nothing to do with rock n roll.

[Luijo]

Just ask Rob Halford!

Surely hair has nothing to do with rock n roll.

[Neal]

Buttoned it up last night.

Thanks, guys! Last night I finished the Electric Mistress up.... I put an on/off switch on it, replaced the footswitch (the old one was getting dodgy), put shielded cable on the input, and rigged a little aluminum shield around the power transformer. I cleaned up the case a little, put some Radio Shack knobs on it (the originals had gotten sheared off), and played "Barracuda". The cool thing is, it sounded exactly like I remembered... I figured I'd be disappointed when I finally got it done, but I wasn't.
I'd read about people having problems with a volume drop, and losing bottom end, but mine doesn't seem to have either of those problems. The board is labelled 5150 D, so apparently it's the 4th revision? The case is single-color black. I didn't bother to code-date the pots.
I'm a little jet-lagged today, from my trip down memory lane

I tell my wife that my baldness gives me super powers..... it makes me invisible to women!
Neal

[David Schwab]

I tell my wife that my baldness gives me super powers..... it makes me invisible to women! l

Out in these parts (NYC area) you see many guys with their heads shaved... women seem to like it just fine!

I always said if I started loosing my hair I'd shave my head!

[SlidePicker]

I kept mine shaved for a few years. A surprising number of young ladies would just come up and ask if they could rub my head, which I never refused.