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Do these gyrators work with the resistances tied to ground? I've seen it done that way, but I think in those circuits we might have been looking at a dual supply.

Since this is a single supply, shouldn't those go to Vbias/4.5V instead? I think that ground connection is going to screw it up.

A Ling ?

May I also suggest that someone starting out learn how to properly use their DMM?  For measuring resistance, voltage, and current at minimum.  It is a little *boring* to take the time doing this basic thing, but it's VERY likely to pay off big time later!    Youtube has many videos you can find.

And make yourself an audio probe.  This is just a regular guitar cable, but the phone plug is removed at one end.  An alligator clip is connected to the ground lead, and a capacitor with a nice stiff lead is connected to the other end.

What's it for?  You can plug some audio source into the pedal circuit board, connect the cable alligator clip to a suitable ground connection and then use the free end of the capacitor to probe different informative parts of the audio path to hear if there is signal passing.  The capacitor block any DC from reaching your amplifier.

It's not the be-all and end-all of troubleshooting, and is not a replacement for things like using your meter to measure voltages at critical locations, or continuity (both of which can be applied after a preliminary probe).  But it can be VERY helpful to know you have signal at this point, at that point as well, but it stops at THIS point in the circuit.

With less than full Range, Manual has an effect. Thanks @ElectricDruid.
The Bias trimmer has effect on the thumping, but does not dial it away, but rather change character between clicky and thumpy.
I still think I should be able to find out what causes the thumping problem, and then hopefully the sound will also be more "flangy".

I manage to buy one CD4007, one CD4049 that I tried in, but no change.
I also tried a new 78L15, but no change either.
Then I was going to try changing the 2N5457, but it is a bit more costly in my shop for a random swap test, so i googled that (among others) BF244A might be a replacement, and that was cheap enough to try.
And now the thumping went almost all away, but quite a murkier sound. So clearly not a 1-1 replacement in this case.
I got an SMD 2N5457 and I have some adapter I will try later on, or just buy the TO-92 one. So a bit more hopeful, although it might well turn out to be the same problem with a proper swap of the Q1.
Strangely, the pinout says DSG, but my meter has it GDS and that would not have fitted on the PCB without twisting some legs around in either prepared slot.
And it seems to work as the standard pinout (DSG).

>  pic of those caps?

Not just "gum". Adams Chiclets.