Help with Allen & heath 1970s discrete mixer (quasi, mod1, mod2) recap mods

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Vyvyan88
audio school
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Joined: Wed Oct 13, 2021 12:51 pm

Help with Allen & heath 1970s discrete mixer (quasi, mod1, mod2) recap mods

Post by Vyvyan88 » Thu Oct 14, 2021 2:10 pm

Recently bought an early 70s Allen & heath quasi mixer, it's completely discrete with sowter 3379 input transformers 200 ohm primary and 7.2K ohm secondary. Turns ratio 1:6. I've been using parts and the frame of a Yamaha m 512 and m916 to build a custom console so I'm retrofitting these in there. So far I've added a switch for direct outs tapped from the 47uf cap post fade just before the panpots and I've recapped with mainly stock values. Change eq cap for wima (thinking of replacing with inductor eq using the the schematics for the jlm pm2000 eq mod) and replaced .22 input caps with wima on some channels and orange drops Sprague on others .

I don't have much knowledge of discrete circuits, so I was wondering if anyone can review the schematics and let me know if they see any areas that can be improved with different values or materials. Thinking of replacing the 10uf and 47uf coupling caps with polypropylene film is that doable? The wimas will fit as I have plenty of space inside the console frame. Is there a simple way to add an insert and return point apart from the echo send? I've put a Google drive link to schematics for the quasi and other mod series boards as they are nearly identical and there isn't much info online. Any ideas and suggestions will be appreciated

https://drive.google.com/folderview?id= ... lCtXSUg9Dx

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