I just finished building a MIG VPR Eleven-Space Rack and a OV560 MKII (my first builts ever). I had the VPR Floor Box PSU Bundle (Two DC Cable)assembled by Volker.
The first testing was okay, everything seemed to be fine. After moving it to another place I had trouble with phantom power so I noticed that the fuse broke. I replaced it and now it's back working (both the Midas 502 I bought and the OV560 MKII).
I noticed some "scratching" and "humming" noise:
- when the gain is set to 10dB (lowest) and the dB adjustment is to -10 I hear some kind of humming or interfering noise
- when moving the db adjustment I noise decreases and I can hear some kind of scrating noise when moving the knob
I can't hear these noises when the gain is set to 20dB or higher.
Any ideas what I might did wrong. (I suppose that the rack should be fine since I don't have these problems with the Midas 502).
Ah, I re-read your post and found my misunderstanding (I read the noise is only at the 10dB setting).
Ok, let us forget about R21 (only relevant for the 10dB setting).
I guess you calibrated the DC offset with R23.
Your noise can either be from a broken or bad connected C8, or the potentiometer itself.
I won't be in town for the next two weeks, but if the problem persists, send me your OV560 after Aug 8th and I'll take care of it.