OK i think I figured this one out. Back when I built it, it was around christmas time 2018 and once I got back to work I kinda forgot about it. Clearing out my cupboard, and I found my half-working pedal.
issues were, not much gain (light crunch at best), extremely woofy with tons of bass. Sounds like a bad doom amp.
I built mine based off Anders' layout on the previous page, copied here for reference:
I remember previously tracing this layout based on the hand-drawn schematic posted previously, copied here for reference:
I previously found no errors (except one I recently found, more below).
This is the Ampeg Vh140c schematic, again posted on the previous page:
there are several omissions on the hand-drawn schematic that may or may not make a difference.
1. at the input, 1N754 diodes (D1 and D2 on schematic) back to back, right after the 22k are omitted. I added them, no change.
2. C3 on the schematic, electrolytic 2.2uf, between the 1k5 resistor and ground. I added it, no change.
3. C23 (3.3uf) and C24 (0.22uf) are missing. I added C24 and it greatly improved the bass response, no more excessive low end. still not enough gain.
4. R38 is the wrong value in the layout, it is 100R in the ampeg schematic and the hand-drawn schematic, but 100k in Anders' layout. I changed this at the same time as adding the 3.3uf cap, and the gain level is greatly improved, about what I expected for a VH140c preamp. Death metal heaven.
Note that the 3.3uf in the ampeg schematic doesn't have polarity marked so not sure if its supposed to be polarised, the other caps 1uf and larger that arent electrolytic are specifically marked 'N.P.' on the schematic, so i'm not sure. I put in an electrolytic since it's what I have on hand. I put the positive end to ground, like the other electrolytics in the schematic.
5. the 22uf caps are backwards on Anders' layout (correct in both schematics). I flipped them but noticed no change.
6. C39 is missing, 0.047uf between IC5 and IC6. I haven't added this one yet.
7. Gain pot is wrong, Ampeg schematic states 100K audio taper but hand-drawn schematic shows 10k audio taper. hand-drawn schematic also omits 10k resistor (R48) after the gain pot. I added them but I don't think there was a change (I had a break between adding and testing so I can't say for sure).
Its late now so tomorrow I will give the pedal a go through a good power amp. Currently its late and I'm testing it half-open through a cheap class-d power amp board into a speaker cab. It oscillates a lot over 3/4ths gain, but the pedal is also open and my leads to the gain pot could be shorter, and shielded.