Calrec EQ - PCB re-design - Prototype phase


Well-known member
Jul 25, 2006
Reaction score
Cologne, Germany
Forget to update here:

In the meantime I've compared the PCB with the schematic and found some errors (e.g. three polarized capacitors had the wrong direction).
Corrected the errors ... and ...
no real difference. It even got worse because the Lo Mid +/- pot is now not working as a volume pot for the whole EQ anymore but fades to some sort of crackling now when turned left. :?

Yesterday I started checking the values of the capacitors and resistors which are all ok so far. I also checked the push buttons which are also working.

The next things which come to my mind are:

- exchanging the 5532 (from Reichelt) with NJM5532 from Profusion
- checking the pots

But maybe the problem lies elsewhere:
E.g. I don't really know how to check a capacitor, maybe one of them is dead.

And what confuses me most:
I always thought the polarization of capacitors is very important:
One of the caps with a wrong direction was a 22 uF cap as power supply bypass capacitors. Shouldn't this cap be exploded? (I exchanged this cap but outside it looks quite normal, no bubbles or such)

Edit: Forget to say that I don't have a real plan on how to debug a PCB. By now most of my soldered PCBs worked right away or the problem was in the cable management (connection to jacks & pots).