This is the Barton Musical Circuits BMC21 Full Wave Dual Rectifier in Kosmo format. It’s built using a PCB I bought from Barton, behind a panel I designed and had fabricated.
It’s a kind of wavefolding circuit. An input waveform is AC coupled, a DC bias is added, and it’s rectified, so anything below 0 V is “folded” upward to a positive voltage. Then the output is also AC coupled. There are two rectifiers, so you can use it on two different waveforms, or you can connect the output of the first to the input of the second (it’s normalled that way) for another order of folding.
I used the Barton PCB, but I did make some changes. As usual with Barton modules, I used 100 nF instead of 10 nF for the bypass caps, and I replaced the 10R series resistors on the power rails with 1N5817 Schottkys for reverse voltage protection. I got the diode orientation right on the second try. I also changed a lot of the resistors. The input and feedback resistors on the input op amp stages need to be 100k, for proper input impedance, but the following stages don’t need such high resistances, which can drive the noise floor upward. I reduced their 100k and 200k values to 10k and 20k. But that affects the RC time constant of the filter that does the output AC coupling, so I increased the associated capacitor from 100 nF to 1 µF.
I was having trouble plugging one of the ICs into its socket, and then I took a closer look:
Two problems there. One is the white box capacitor on the left; that’s one of the 1 µF I used instead of 100 nF. It’s larger than the footprint provided. It and the grey cap barely fit between the sockets, but they interfere with the ICs which overhang the ends of the socket — I could get one IC in but not both. I ended up removing the white cap and replacing it with another one mounted on top of the grey one. Was I starting to feel like changing the resistors was more trouble than it was worth? I might have been.
The other problem was pin 9. Something was in that hole blocking it up. I’m about 75% sure it wasn’t solder. I did try heating that pin and it didn’t seem to want to melt. Even if it was solder, and even if I could get it to melt, it would have been hard to get it out. Maybe with a good solder sucker, if there were such a thing and I owned one. Maybe not even then.
Unsoldering the socket would be possible in principle. It’d be difficult and chances would be high of damaging at least one pad. So instead I bent pin 9 of the IC out and soldered a purple bodge wire to it. Then I discovered pin 8 did go into the socket but did not make reliable contact, so I soldered a green bodge wire to that. And… I think it’s working now.
Panel design files, Gerbers, and documentation in GitHub repository at https://github.com/holmesrichards/frontpanels/tree/main/Barton_Dual_Rectifiers.