some years ago I built a Forsell Opto with the TommyTones board, but never got it going properly. I put it aside to revisit someday, which I now have. I found the TT board pretty hard to work with so here I set out to make things as simple as possible:
JLM ac/dc power supply - but any reliable +/-15 to +/-18vdc will do
the sidechain pcb direct from Fred Forsell's site - I uploaded the gerber to easyeda.com and 5 boards arrived a few weeks later
mnats meter pcb - although I have redone it it use a header for connecting to a meter bar
no input or output amps
Pleased to report this is now working just fine.
I thought I would have problems finding the OPA2604 specified, but an email from Fred clarified that this ic is only necessary if using +/-24vdc. OPA2134 or NE5532's @ +/-18vdc work fine. Also that is fine for the meter's LM3916, which the schematic shows as having +24vdc.
The only problem I had was a solder bridge on the mnats meter pcb - the labeling is on the copper side and "com" is awfully close to the trace and the meter input pad. When shorted, no metering.
Next steps are
- put a JLM 10k rev log wired in parallel to make a proper 5k rev log for the ratio
- add a JLM regurgitator for make up gain
Assuming that works, I'll make another unit and rehouse it all as a stereo unit with a link, and use the nice front panel design (I don't recall who did it). If I was to balance the input, I'd use the little that board from
https://www.diyrecordingequipment.com/. Not sure on that yet.