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IC1 pin voltages?

A few things came to mind from your description: 1.) C9 isn't properly connected to ground via R11 (10K) and is storing up too much DC voltage by, instead of keeping Vref A steady. Ensure those solder joints and values (note that the cap orientation looks good). 2.) Vref A circuit (you...

Q3 buffers Q2 from being influenced by the impedance of the output circuit. It could (or might not) have an effect on the tone or reaction of the fuzz generated in Q2. If you like the result, you didn't need it.

Did you measure the values of the resistors which make up the Vref for Q3? R11, R12 & R13? Additionally the polarity and solder connection of C9? If Vref is too strong or weak, Q3 becomes an 'on-off' switch. Vref should be close to 50% of Vcc.

I appreciate you including the schematic, as it was not available on the PedalPCB website. That is a overtly complex circuit for a basic indicator LED. I personally would skip all the circuit between the R4 and pin #1 / column #2 of the 3DPT stomp switch, solder a 4K7 resistor to that lug...

Remember that the stomp switch sends the LED cathode to ground (lit) or open (not lit). I am fairly certain that PedalPCB does not utilize a switched (+) on any of their designs. In studying your pictures above, I may have found the issue. You have the LED anode (+) soldered into the...

The circuit is finding its way to ground somewhere. I'd suggest testing resistance to ground, of the 'switch' lug of the 3DPT stomp switch starting with a high DVM range, like 2M. Anything under 100K resistance continuity of cathode to ground will probably get the LED to light.

1/4" are too small. 5/16th would work. Do you have a preferred source?

I built one and used it for guitar and bass. I am currently making one for my neighbor. My build thread his here: https://forum.pedalpcb.com/threads/median-compressor-spirit-of-1776-functional-testing-update.22639/ IMHO, it is already to go for bass guitar. Its blocking R-C circuits...

I've seemed to run dry on sources for M7 internal-tooth lock washers, for use with 16mm potentiometers, commonly used on pedals. Any suggestions?

From your pin voltages, it appears that your Vref circuit has the wrong resistors in the voltage divider (R12 & R13). I am going to guess that you installed a 4k7 resistor for R13 instead of a 47K. All of your RC4558 pins, except #4 (0 volts) and #8 (near 18V), should be around half of Vcc...

Lots of good answers. Mine is simplified: it is a passive 3-band EQ which takes the full-frequency signal and passes specific frequencies to ground, via the filter cap on the Vref circuit.

I went with NOS T092 types for the same reason. The first SMDs I soldered directly, would not bias.

Great finish and nice build! I noticed you used adapters for the FETs. Was that to ease the process of auditioning / matching the FETS or did your SMD FETs not match the footprint already on the PCB?

Also check for a defective pot, by checking the continuity between all three lugs with an ohm meter DMM setting. It is rare, but I've encountered new defective pots.

My favorite, only because it was my second pedal ever, was a 1976 EHX Small Stone. My favorite in my collection now (and the only phaser) is a 1980 Ross 'Phaser,' which is extremely close to the MXR Phase 90 script. The only difference is they added a regenerate control topside, to allow for...

Check for proper FET orientation, if you have not already. Then and if you have a signal generator, throw a 1kHz sinewave into the pedal and adjust by sight and sound. You will be looking for a linear (smooth, not jumpy) reduction in volume as the 'Compression' control is turned to the right...

Where did you get your 2N5457 FETs?

Measure between pins 2 & 3 (Source and Gate), not gate to ground.

Good advice from @Robert. It is a trim pot that fine-tunes Q1 to behave symmetrically, allowing or disallowing the audio signal to be sent to ground. If you adjust the trim pot to its extremes, it while sending tone generator into the pedal or a guitar, you will hear the compression cutting in...