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FM-3 hum is back and question about impedances.

60hz hum is back. Installing the "RCA ground upgrade" eliminated audible hum along with replacing the rectifier tube. But only for a while; the hum has returned. I do play the tuner 5-10 hours per day...

The hum does not change amplitude when volume pot is rotated. And no change regardless of signal level input.

However, it only becomes loud enough to be audible about 20 minutes after power up. I am guessing it's the power supply quad cap.

I have a brand new replacement 40/40/20/20 . That will be next to-do I guess. Although I expect the dern boards are very fragile and getting that sucker out without damage to the board will be a challenge.

Has to be expected to replace that can after 50+ years, and the tuner does sound wonderful otherwise...

QUESTION: I now have the FOSI V3 amp in the system. It has a "pass-through" line out which can be used while the amp is playing normally. I have connected this pass-through to another Class D amp in another room.

Would this arrangement put any electrical strain on the output of the FM-3? Maybe lowering impedance the tuner sees?


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Topic - FM-3 hum is back and question about impedances. - ltman 08:20:43 03/09/24 (6)


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