1176 Mod board - True bypass and HPF sidechain MC77 based

[dmnieto]

Hi all, i have been working on a MC77 sidechain mod for my stereo 1176. It was supposed to provide:

- True bypass and buffered metering.
- Sidechain send/return.
- Sidechain HPF.
- 24V power supply (relays and led)

I received the prototype boards and well, they were a total bust:

1) i screwed out the footprint pinout of the relays (d'oh)
2) Error in the biasing of the meter buffer.
3) wrong orientation

I also believe that during testing I may have killed the second TL074. I measure 24.3v between ground and all the signals pins (5,6,12,13,10,9,2,3).

Attached are the schematics for the first version and the second that I am preparing to build next, do you see any clear mistakes?

I also dont like how I am selecting the switches for the relays, I think I need to add some resistors, also the idea of having to route the +24V in/out to the switches in the front panel... I dont like it. Do you think I could use some PNP as switches?

Thanks!

 

[dmnieto]

And this is the schematic for the boards I currently have