PRR-176 Rev 1 Compressor Discussion (Reboot of lost forum subject)

[emx]

Seems the original forum for the revision 1 of the AC Sound PRR-176 was lost or deleted from the forum so, if no one minds, I would like to recreate it here. Surely there are a few of these boards and probably un-operational units still laying around other than the one I ran across and picked up. I believe there are a handful of error corrections that were not stated listed elsewhere and I have some further errors and build tips I wanted to share should I ever get this unit operational. I'll be sharing everything I ran across when I can.

 

[Script]

Ever got it operational?

Here's the BOM for v1.1

 

[duantro]

I got a v2 one off of the black market that I got working. Good luck, It;s really difficult to decipher all of the revisions, etc. Mine sounds great, but oscillates if I use a 1731 and gain it up. might be something goofy with the opamp though.

 

[living sounds]

I got a v2 one off of the black market that I got working. Good luck, It;s really difficult to decipher all of the revisions, etc. Mine sounds great, but oscillates if I use a 1731 and gain it up. might be something goofy with the opamp though.

Make sure the tubes actually get 6.3V heater voltage. It may be necessary to use thicker wire for the heater as well. I had motorboating issues in mine until I got that part right.

 

[emx]

Ever got it operational?

Here's the BOM for v1.1

@Script, I got a bit overran with a new job there and burnt out on DIY for a bit after doing a lot of Eurorack synth and other builds but I'm going to be finishing this one off hopefully soon. I've got it about 4/5'ths done so far.

 

[Script]

Boards are from 2011, I think?

Rev 1 had three issues, if I remember correctly:

- a missing via in the input section (I think, but could be a later version)
- noise induced from the PSU (better placed off-board)
- noise pickup from interstage transformers (if unshielded)
- Also wiring never seemed intuitive on those boards.

But it's all long ago and I could be mistaken. [[Never got down to building it, cos I built the original PRR unit at that time modding the hell out of it.]]

I think it would be best to get the board pass clean audio first. And look at everything side chain in a second step.

 

[living sounds]

Make sure the tubes actually get 6.3V heater voltage. It may be necessary to use thicker wire for the heater as well. I had motorboating issues in mine until I got that part right.

I ran into thumping/motorboating issues again that manifested themselves after longer running times. It turned out that I had the secondaries for the +/- 18V and the heater switched. The heaters use a lot more current than the op amps, it looks like my trafo went into thermal shutdown. Luckily nothing was damaged. With the russian NOS tubes I use in the PRR 176, thumping is a lot lower than my Sta Level clone and my trafoless vari-mu.

I've read that people have modified the heater power setup to parallal. This does indeed allow for a better heater voltage matching between both tubes. However, with the +/- 18V trafo this also taxes the resistor of the CR filter before the regulator as well as the regulator itself excessively, things get dangerously hot, so it's not a good idea.

 

[emx]

Anyone know how hot the meters can get before having issues or melting? Talking about the the ones below that"fit" the Collective cases enclosure.

https://www.hairballaudio.com/catalog/parts-store/panel-meters/8027-wf-1ma-meter

The backs look to be made of nylon. With as much as the Collective cases are a claustrophobic cramped nightmare I'm likely going to have to put the front tube about 3CM away from the back of a meter if I want to use the transformer options I'm looking at along with the wider revision 1 PCB.