Volume Pot Hum - Marantz 2215b

[akadrhouse]

I have a Marantz 2215b that I just finished restoring. Usually when I get a hum from a unit, I can trace it back to grounding and fix it. In this case the hum is quite different.

• On AUX source - Hum is volume pot dependent - volume on zero -> no hum
• On phono - hum is similar except when at max volume, the normal background becomes more pronounced than the hum
• Volume to the middle -> loudest hum
• Volume to max -> no hum
• Left and right channels equally affected
• Might be related to Tape? Pressing the Tape Button dramatically increases hum even when turned to zero on the volume.

Just trying to trouble shoot. The fact that the hum goes away when volume is max is weird to me. I can't quite figure out why that might be. I've not heard of hum being caused by the carbon tracks but maybe dirty except on max? I am going to flush it out well with fader lube next (and deoxit the tape switch) to see if that fixes it, but open to other insight!



I want to avoid taking the pot apart and cleaning if I can. I've seen some videos, and it looks like a pita.

Thanks in advance!

 

[akadrhouse]

Well, happy to say that cleaning out all switches and pots with fader lube, and re-soldering the black wires onto the volume pot, and putting it back together made it as quiet as a mouse.
I always forget that if I don't put it back together, it often has hum that goes away after final faceplate and case :/

 

[akadrhouse]

Well, one other question. This was masked before I fixed the constant hum.

When you first turn it on, it has a hum that fades in ~ 3 seconds to inaudible.
Dead quiet afterwards. Any ideas?

The hum is independent of volume gain.
As in, same amount regardless of volume on zero or on noon.

Lastly it happens the same when unit is cold, or if you shut it off for 3 seconds and back on after hours of play.

 

[BeerLegs]

I think that's normal. Mine does the same thing.

 

[Bill S]

Well, one other question. This was masked before I fixed the constant hum.

When you first turn it on, it has a hum that fades in ~ 3 seconds to inaudible.
Dead quiet afterwards. Any ideas?

The hum is independent of volume gain.
As in, same amount regardless of volume on zero or on noon.

Lastly it happens the same when unit is cold, or if you shut it off for 3 seconds and back on after hours of play.

I had a power switch on a 2325 that got noisey before it finally crapped out. Not saying that's it but I'd keep an eye on it and be prepared to replace it if it goes.

 

[akadrhouse]

I think that's normal. Mine does the same thing.

Thank you! And for linking to make up for my poor searching skills