How to determine where hum is coming from

[CrazyIvan]

PL 400 white oak cap kit, pl14 board, light upgrade, new output transistors, WA dc protection running quasi comp.
Upon power up, there is a hum through the speakers that changes tone and then lowers. Where should I begin trying to eliminate this? Isolate the transformer from the chassis? I have a fluke meter for test equipment no scope.

 

[Gepetto]

Pictures is where you should start...

 

[WOPL Sniffer]

I had a pair of test speakers I used in the shop, they hummed when I hooked up a WOPL to them. Took me 2 days of dicking around to figure out it was the speakers. Try the easy route first.

 

[WOPL Sniffer]

swap out cables, unhook unnecessary equipment, all easier that tearing open an amp until you HAVE to.

 

[Lazarus Short]

If your stereo hums...it's because it doesn't know the words.

 

[Gepetto]

Pictures is where you should start, you likely have a wiring situation inside that is causing a ground loop.

 

[CrazyIvan]

 

[CrazyIvan]

Video of the hum

 

[George S.]

Ivan, I assume you've built the control board quasi complementary along with the jumpers in Teflon tubing on the backside of the board?

 

[Gepetto]

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Would be helpful to have a view with the control board flipped out of the way. Is the input copper plate isolated from the chassis using the fiber insulating washers? Do you have an AC third wire in use or the original 2 wire cord connection only? You hum video has the hallmarks of a ground loop.

 

[CrazyIvan]

I never removed the copper input plate. I will unbolt it to see if it has fiber washers. If it came that way from the factory I'd assume they are there,

 

[Gepetto]

Would be helpful to have a view with the control board flipped out of the way. Is the input copper plate isolated from the chassis using the fiber insulating washers? Do you have an AC third wire in use or the original 2 wire cord connection only? You hum video has the hallmarks of a ground loop.

 

[CrazyIvan]

sorry , original 2 prong plug.

 

[MusicSteve]

First, does everything work except for the Bussing?
I did not look at the board wiring so it could be their also

I like to test just the amp first (ground loops can be a lot of things) I like to disconnect the Rca inputs and retest.
than . I also like to Flip the 2-Prong AC plug and see if their a different.
if theirs no buss than it upstream.
than I hook up the RCA only to the next component,,, (and this component upstream disconnected),,,, until I find were the buzz is coming from.
This is only one way to do it
Good luck

 

[MusicSteve]

Quick look at the board
Also might want to re-solder the Rt Bias Connecter (Looks like it not solder)
and also check the LT one

 

[CrazyIvan]

Ivan, I assume you've built the control board quasi complementary along with the jumpers in Teflon tubing on the backside of the board?

Yes , you are correct. jumpers have tubing installed.

 

[CrazyIvan]

First, does everything work except for the Bussing?
I did not look at the board wiring so it could be their also

I like to test just the amp first (ground loops can be a lot of things) I like to disconnect the Rca inputs and retest.
than . I also like to Flip the 2-Prong AC plug and see if their a different.
if theirs no buss than it upstream.
than I hook up the RCA only to the next component,,, (and this component upstream disconnected),,,, until I find were the buzz is coming from.
This is only one way to do it
Good luck

Well well well, the hum went away with no rca input connected, I use a schiit valhalla 2 as a preamp (for volume control) and an Audiocontrol C101. With C101 plugged in it hums! run just the Schiit. NO hum.

Thanks to everyone for helping diagnose this issue.

 

[George S.]

I see one issue with the control board screws being in backwards and protruding towards the back wall, but that's minor. I have issues with preamps picking up transformer hum from amps if they're stacked. So I keep them separated in the main system. The main system is dead silent.
Upstairs in my work room I keep them stacked due to space limitations and because the hum is very minor. Can't hear the hum when music is playing. Annoying, but really a non issue.

 

[Gepetto]

I see one issue with the control board screws being in backwards and protruding towards the back wall, but that's minor. I have issues with preamps picking up transformer hum from amps if they're stacked. So I keep them separated in the main system. The main system is dead silent.
Upstairs in my work room I keep them stacked due to space limitations and because the hum is very minor. Can't hear the hum when music is playing. Annoying, but really a non issue.

Well well well, the hum went away with no rca input connected, I use a schiit valhalla 2 as a preamp (for volume control) and an Audiocontrol C101. With C101 plugged in it hums! run just the Schiit. NO hum.

Thanks to everyone for helping diagnose this issue.

Glad you found the culprit. Enjoy

 

[Gepetto]

I see one issue with the control board screws being in backwards and protruding towards the back wall, but that's minor. I have issues with preamps picking up transformer hum from amps if they're stacked. So I keep them separated in the main system. The main system is dead silent.
Upstairs in my work room I keep them stacked due to space limitations and because the hum is very minor. Can't hear the hum when music is playing. Annoying, but really a non issue.

Agree, while minor, those internal tooth lockwashers will tear up the board and expose bare copper which is not what you want. Best to flip them around.