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Thanks for the help!
The reason I’m asking is the repairs to this AV5000 amp are so close to being finished and I’d like it to be perfect before I button it up. The only issue left is channel 4 still has a very faint buzz. Originally the sound was more of a hum, but replacing C2 and C12 the V+ and V-, 100uF, 100V its now reduced to a faint buzz. There are 2, C1, C5, .12uF, film caps in parallel with C2 and C12 and since replacing C2 and C12 helped, could replacing the caps in parallel with them fix the issue? Attached is a copy of the schematic with the 4 caps inside the boxes.
I had this amp playing for most of the day today and it sounds very good, if I can cure channel 4’s buzz, it will be perfect!
Attachments
That 120 nF caps can not solve any buzz. Replacing them makes not much sense. If replacing the 100 µF caps solved the hum a little then the PSU should be examined I guess.
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On first diagnosis, I agree its somewhere in the power supply, but channel 4 shares its power source with the other 4 channels and they are quiet. To confirm it in the channel I swapped channel 4’s power plug with several of the other channel’s and the hum doesn’t move or change.
Any thoughts on where to look next would be appreciated!
1. Is is low frequency?
2. Did you already short the input to see if it changes?
3. Oscillation? Did you check with an oscilloscope?
4. The fact that it changed when the 100 µf caps were replaced maybe tell that all the caps should be changed?! How are the large filter caps?
5. Does the input wiring of channel 4 come close to a transformer ?
6. Please note that channels should stay equal so changes should be done to all channels.
* When you have found the issue please consider replacing C8 for film caps like 5 mm pitch Wima MKS2 and C10 for bipolar MUSE caps.
2. Did you already short the input to see if it changes?
3. Oscillation? Did you check with an oscilloscope?
4. The fact that it changed when the 100 µf caps were replaced maybe tell that all the caps should be changed?! How are the large filter caps?
5. Does the input wiring of channel 4 come close to a transformer ?
6. Please note that channels should stay equal so changes should be done to all channels.
* When you have found the issue please consider replacing C8 for film caps like 5 mm pitch Wima MKS2 and C10 for bipolar MUSE caps.
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