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July 10, 2020, 12:01:04 AM

Author Topic: Very faint hum  (Read 1808 times)

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Offline Jimb0

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Very faint hum
« on: December 27, 2019, 07:13:13 AM »
Getting a very faint hum on both channels. Isn't affected by volume. Also getting a ringing like sound when I'm adjusting volume up and down.
« Last Edit: February 08, 2020, 02:44:38 PM by Jimb0 »

Offline Paul Birkeland

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Re: Very faint hum and ringing noise when adjusting volume
« Reply #1 on: December 27, 2019, 08:50:56 AM »
The ringing sound is completely normal and normal with 6C45P operation.

Does the faint hum change in magnitude when you switch impedances?  If you listen to a 60Hz and a 120Hz tone, does it sound like either?
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Jimb0

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Re: Very faint hum and ringing noise when adjusting volume
« Reply #2 on: December 27, 2019, 08:57:20 AM »
No differences between low and high impedance as far as I can tell

Offline Jimb0

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Re: Very faint hum and ringing noise when adjusting volume
« Reply #3 on: December 27, 2019, 09:23:52 AM »
Definitely a 60 hz tone

Offline Paul Birkeland

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Re: Very faint hum and ringing noise when adjusting volume
« Reply #4 on: December 27, 2019, 09:40:11 AM »
If the impedance switch doesn't change anything, what happens if you unplug all your sources?
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Jimb0

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Re: Very faint hum and ringing noise when adjusting volume
« Reply #5 on: December 27, 2019, 09:53:12 AM »
it's still there PB

Offline Paul Birkeland

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Re: Very faint hum and ringing noise when adjusting volume
« Reply #6 on: December 27, 2019, 05:56:57 PM »
What headphones are you using?  Is this the new Mainline with the universal power transformer? If so what is your wall voltage?  How tight is the hardware on the power transformer?
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Jimb0

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Re: Very faint hum and ringing noise when adjusting volume
« Reply #7 on: December 28, 2019, 07:56:36 AM »
Using HD 650's, older version with 120v. I was missing a screw for the power board but it has been replaced. I will try retightening them and see what happens

Offline Jimb0

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Re: Very faint hum and ringing noise when adjusting volume
« Reply #8 on: December 28, 2019, 11:42:23 AM »
I've retightened everything but still getting hum

Offline Paul Birkeland

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Re: Very faint hum and ringing noise when adjusting volume
« Reply #9 on: December 28, 2019, 06:19:46 PM »
Can you double check your voltages to be sure they are all in line?

Have you tried the Mainline in a different room to be sure the source of hum isn't perhaps something close by with a power transformer that just happens to be perfectly aimed?
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Jimb0

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Re: Very faint hum and ringing noise when adjusting volume
« Reply #10 on: January 23, 2020, 05:13:53 AM »
I rechecked the voltages today and they checked out okay. Also tried moving to a different location but the hum is still present

Also I forgot to mention that I had to extend one of the wires from the CAT-5 going to the XLR output. I just used some extra wire and soldered both ends together. Is it possible that this is causing the issue?

Offline Jimb0

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Re: Very faint hum and ringing noise when adjusting volume
« Reply #11 on: January 23, 2020, 05:19:13 AM »
Pic
« Last Edit: January 23, 2020, 05:23:32 AM by Jimb0 »

Offline Paul Birkeland

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Re: Very faint hum and ringing noise when adjusting volume
« Reply #12 on: January 23, 2020, 06:24:59 AM »
You could try this modification:

https://forum.bottlehead.com/index.php?topic=11676.0

Extending that wire as you did is unlikely to cause hum issues, but I would cover up the exposed solder joint with some nail polish or RTV.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Jimb0

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Re: Very faint hum and ringing noise when adjusting volume
« Reply #13 on: January 23, 2020, 07:49:11 AM »
Thanks PB will do

Offline Jimb0

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Re: Very faint hum and ringing noise when adjusting volume
« Reply #14 on: January 23, 2020, 09:04:52 AM »
Tried the mod but to no avail still getting that hum