MXR Dynacomp (CA3080 Rev E. - 2006) noise fix  [SOLVED]

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lolbou
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Post by lolbou »

Hi, just reporting a repair on my 2006 MXR Dynacomp (rev E. with CA3080).

Problem was a "frying bacon" sound. I removed the socketed IC and audioprobed it. The noise was at both pin 2 and 3, so it was before the IC. Noise was also at the base of the first transistor, and up to the positive end of C2 (tantalum capacitor).

I replaced C2 with a good electrolytic, and noise is gone. Easy one, just make sure you add some leaded solder to the RoHS one before desoldering, makes it easier to desolder and clean.
For the record, here's the power supply and LED switching schem, the rest is just the classic schem.
MXR Dynacomp.gif
MXR Dynacomp.gif (266.33 KiB) Viewed 689 times
- Are you a mod or a rocker?
- Uh, no, I'm a mocker.

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YummyFuzz1
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Post by YummyFuzz1 »

Thanks for this post :)

I recently acquired a 1996 REV B MXR Dyna Comp with an LM3080N that had the rustling/frying noise. It was present at pin 6 of the IC, but not at pins 2 and 3. So thinking it was the chip, I replaced it with a new LM3080N, but afterwards, the noise was still present
(note - in this version I wasn't able to socket the IC as there was not enough clearance between the PCB and the bottom of the Sensitivity pot under which the IC was located).

So I removed the C2 tantalum cap and found it measured at 25pF, instead of the marked 105 (1uF). This meant the HP filter in this part of the circuit would have had a cutoff frequency of 6.3kHz instead of 0.15Hz. As you did, I replaced C2 with a good electrolytic, and now the rustling/frying noise is gone.

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