Pass Ono oscillation

Hi, I have built quite few years ago the Ono phono with the pcb bought from a group buy here. It has worked flawlessly until I had one of the 2 rcore transformers failure. Changed the trasformers to toroids but in one channel I have an oscillation, the sinusoid in not firm but moving insetself a bit up and down. The other channel is working properly. After much work I localised the problem in the mc preamp part, white background on the attached schematics. I have substitute all the components with newones even made a point to point version of it and implanted without success.
Any idea?
 

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Nelson Pass

The one and only
Paid Member
2001-03-29 12:38 am
OK, try operating it with no cartridge and set the loading at 1K.

If that doesn't do it, then put some resistance, say 100 ohms between the
Emitter of Q14 and the drains of the Jfets.

If that doesn't do it, put some resistance, again 100 ohms, in series with
the output capacitor.

:cool:
 
Hi Nelson, thank you for assistance but unfortunatly I tried all you suggested without success. I took semiconductors from working channel put them in faulty one but that was ineffective too. I took signal from jfets and attached to Q14 correct channel and output was correct. Again, if I attach the correct channel output signal in Q15 to output capacitor C10 faulty channel the output is clean. So problem is in the mc sub regulator.