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In Reply to: RE: Sony ST J75 tranny(?) hum posted by ltman on August 23, 2023 at 12:31:06
Itman-
If the hum is present with the unit plugged into mains power, but NOT connected to an antenna, or preamp/system, then it sounds like a mechanical noise coming from the unit.
That being the case, you may be able to tighten the connection of the transformer to the chassis, and check the connection of the chassis parts to each other.
Before you do anything, unplug the unit from the mains power and let it sit for a day or two. This should provide time to allow the components to be deenergized.
Opening the unit carefully, take pictures if this is new for you, making note of orientation of the chassis parts-
once the cover / top is off, the transformer should be readily identifiable - gently try to move it to confirm it is loose.
A Toroidal transformer should have 1 connector thru the middle of the transformer to the bottom of the chassis - check to see that that fastener is tight (righty tighty). If it is an E-I or C Core- the transformer will be square in shape and may have 2-4 fasteners to secure it to the chassis.
Happy Listening
Follow Ups:
Mike Williams of Radio X Tuners put his ear to the case of one and heard a slight hum. Mike told us, "I did some isolation and dampened the transformer with soft-start resistors, which reduced the hum to almost nil, but it was still faintly heard. I have had several ST-J75s come through here since and all have had the same hum when you put your ear to the case.
10-4.
Will have a look at let you know.
thanks!
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