OV560 MKII (Neumann OV60 in API500 format)

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[silent:arts]

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I often get asked for standard API 500 compatible DIY kits, so I decided to offer a MKII version of the OV560 HiZ.

[ original schematic | original data-sheet ]

OV560mkII-4387.jpg


#OV560 on Instagram

Full kits are available in the White Market (limited quantity)
 

patrik.horat

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Jul 7, 2021
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Location
Zurich, Switzerland
Hi everyone,
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).

Thanks for your help!
 

[silent:arts]

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Look for a bad solder joint at R21. It is the only different component in the 10dB setting compared to 20dB.
 

patrik.horat

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Joined
Jul 7, 2021
Messages
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Location
Zurich, Switzerland
Thanks for the hint. I checked R21 and it should be fine as far as I can tell.
Could the solder joints at S1 be a problem as well?

To clearify the noises I am getting, I attached 3 audio files. one at 10dB, one at 20 and one at 30dB, turing the "adjust" knob (starting at -10).
10dB: View attachment OV560 Horat 10dB ADJUST -10 to 10.mp3
20dB: View attachment OV560 Horat 20dB ADJUST -10 to 10.mp3
30dB: View attachment OV560 Horat 30dB ADJUST -10 to 10.mp3
Could there be a problem at "output" as well?

I might have to add: the white noise (rauschen) isn't really there at -10db (adjust), it starts slightly after I begin to turn the adjust knob.
 
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[silent:arts]

Well-known member
White Market Member
Joined
Jun 4, 2004
Messages
5,139
Location
Berlin, Germany
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.
 

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