GHR Audio

Those 2.5 - 6 -1.2s might be dual time constants like release time position 5 & 6 in Fairchild 660 viewtopic.php?p=37#p37

Yes R18 is attack resistor and R19 release resistor. I connected 6 position rotary switch with different resistors and capacitors to J10 & J11 to change the release time. J10 & J11 marked TC on the board connect parallel to C9 & R19. R18 could be made variable too without any ill effects.

Gain and ...

6BA6 is essentially equivalent to 6K4P. Only somewhat significant difference is that in 6KP4 suppressor grid is internally connected to cathode. Difference in internal connections won’t matter since tube pins 2 & 7 are connected together on the board. Any vari-mu pentode with same pinout as 6BA6 or ...

It’s just hot glue to keep the tall capacitors in their place during transport or rough handling. Definitely not needed if the unit just sits in a rack in a studio.

Gerber files now available for everyone.

viewtopic.php?t=104

Read this read if you plan to build one
viewtopic.php?t=69


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Gerber Files

GroupDiy Thread
https://groupdiy.com/threads/mic-preamp ... ers.81364/

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Gerber Files
viewtopic.php?p=266#p266

Both sidechains, gain reduction meters, volume controls and switches on the same board.

Schematic

New version with even less transformers coming soon.

Layout Front panel