1972 mini mixer

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1972 mini mixer

Postby Jim Williams » Mon Sep 19, 2016 10:05 am

I have a 1972 era mini Calrec in with 8 PQ10S-242 modules and 8 RL22S-241 modules. I'm restoring/fixing it up as the owner complained of excessive noise.

They are hissy at 40 db of gain. The hi boost adds even more. These are Neve-y like designs, all discrete transistors, mostly BC184's with some BC214 PNP's and some 2n parts.

After examining the designs I removed those transistors and used 2SC3329BL and 2SA1084's for the PNP's. El caps were replaced with larger values, Panasonic FR series was used. Some of the mic pre tantalum signal coupling caps were bypassed with Wima .01 polyprop film caps to let the air out.

I replaced the 160 hz bass EQ caps with Wima .1 uf, that brings the depth down for a deeper bass range. The hi shelf was .01 mylar film, too middy for me. I used Wima FKP-2 .0056 uf, perfect.

Now this little console is silent, really quiet. The noise is gone even with full boost of hi EQ. The tops are now open and breathy, really nice and full range. The 100 pf input roll-off caps were changed to 47 pf to allow an extra octave of top end response.

Now, does anyone have any documents on this? I'm pretty good at reading circuits but the roadmap would be helpful for one module that is cranky.
Jim Williams
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Re: 1972 mini mixer

Postby GJC Designs » Sun Oct 02, 2016 5:39 pm

Your best source of a schematic will be Calrec themselves.
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