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First, I personally never qualify who or what I will learn something new and having been working on music electronics since the late 1970's, I never think I know it all. IMHO, Brian Wampler is a smart dude. Sadly, the one thing that would be hard to learn from him, is his incredible sense of...

I use a four conductor 1/8" plug into the phone's headphone + mic jack, which terminates to (4) RCA plugs, to which I use an RCA female to 1/4" male adapter. The app I use is called 'PA Tone', is free and will do all the audio frequencies and multiple wave forms, plus pink and white noise. I...

Yes. Digital Multi Meter set on DC voltage set to a range higher than 9V. Then you need a signal generator (I use a phone app) into the input and look at the sine wave oscilloscope, which is set to 1ms at .1 V on the AC setting. I check the input and out put of the devices, folloing the schematic.

I could not find anything glaring from the pics. I recommend checking and notating the pin voltages on the ICs, FET and Transistor, looking for anomalies (Vref not being in tolerance of half of the Vcc). Then I would throw a 1Khz sine wave into the input and trace it through each stage with...

There are trace levels of mercury in solder, especially before the 2000's.

Anything which creates negative pressure away from your nose and mouth, works. Sadly, I didn't start using one until this year. I wonder what 50 years of breathing lead, acid and mercury will do to me?

The single op-amp IC in a DoD 250 Overdrive, will eventually distort and contribute to the distortion sound, but only say one third. However, the 250 is basically a distortion, which gets most off its grit and compression from hard-clipping asymmetrical diodes and its character from the C3 + R7...

I repair music equipment and one of my clients tries things and flips them, letting me try them before they go. I've encountered effects like this and think I actually tried one. They are often clever and original, but like you - I struggle to find a musical application for them.

For reference, I have an early 1980's grey-box DoD 280 compressor. As I understand it, the DoD250 had tweaks in its evolution. I acquired this in 1992 (disassembled), from a friend and revived it / modified in the past few years. My Mods: - R5 is the resistor in parallel with the...

'Live at Pompeii' is a great recording! Yeah, an 1176 derivative is not squishy or noisy, like an OTA or VCA compressor. Studio engineers describe the 1176 as making the music jump off the page and when the effect is turned off, it is very noticeable that it doesn't sound as big. I built the...

A Strat into a Dynacomp (squishy and muted treble), into a 100w Hiwatt (stiff and wide dynamic range) sounds about right for early Floyd. 'Breathe' would be a good example. However, that was probably on a light setting enhanced by a Fairchild or a mixing desk studio compressor before tape...

My neighbor had one and I took a peek under the hood. Like the Wampler Ego 76 (Median Compressor on PedalPCB), it is a simplified Urei 1176 FET compressor.

RESOLVED: Thanks to @bean and @Erik S, I resolved the original problem. The short story is, the schematic was drawn incorrect. It had the (-) polarity of the 4.7uF cap facing pin #10, when it should have been facing pins #15 & #16. This corrected the pin voltages. The original NE571 compandor...

@Erik S , this would easily run on 18 VDC and I am guessing 40ma. Just undo the diodes and insert the 18 VDC in one of the holes, at the 470uF cap. Then just undo the AC clips, the strain relief and then use a plastic hole cover. I was thinking converting to true bypass, as it has tone suck...

@Erik S , one more thing: be careful of handling the lead wires. Many pedals of this era used aluminum wire and soldered with acid-rosin solder. It corrodes the wire at the joint and they easily break off, or look connected but are actually hanging by threads. I've found this same condition...

That is extremely helpful and ties into what @bean provided! Thank you! Indeed, my only problem appears to be pin #10 where I am over voltage by 8v to 9.5v. Per Bean's advice, I am going to rebuild the 33k resistors and 10uF cap at pins #10 & #12. I can tell from your gut-shot, that your...

Most appreciated. The device in question is the NE571 IC. A reading of DC voltage to ground for all the 16 pins would be extremely helpful, in conjunction with the info @bean kindly gave! I've had this pedal since 1986, as it was gifted to me by a friend who was terminally ill. One of those...

Is that from doing the math from the datasheet? Vout DC = (R DC1 + R DC2) / R4

My DoD Chorus 690 wasn't working. The LFO, Flip-flop SAD512D bucket-brigade chip and the compression half of the NE571 compandor was operating, but the expansion wasn't and the Vcc was about +14.2VDC (below the threshold of the LM78L15 regulator). I assumed the electrolytics were all bad and...

To mitigate eddy currents keep the signal circuit ground in a 'star' (emanating from one point), then connect that to 'earth' (chassis ground) via a very low ohms resistor (10 ohms works, I typically use a 5 ohm). It keeps the junction of the dissimilar metals of the enclosure (typically...