If the levels are OK without compression, but wander a great deal under compression, then it is caused by a slight displacement of the opto cells. On the stereo compressor the two opto cells (under the black cover) are close to and operated by an LED. By altering the distance of the cells from the LED you can adjust the balance. It’s tricky and takes a little time, but it works. The cells are normally about 1.5mm away from the LED, increasing that distance on one of them will alter the balance by reducing compression on that side only.
On pots, yes both the input and output pots on the P5 are 10Klog. Generally, the matching on log pots is quite poor and it’s common to get 2 or 3dB errors in the tracking.
Lin pots are very much better….. If you would like me to send you a couple of 10K lin ganged pots I can do that. they should fit the PC board OK. The only difference will be that the law of the control will be different, but still perfectly useable.
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