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July 09, 2020, 10:52:36 PM

Author Topic: Very faint hum  (Read 1801 times)

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Offline Paul Birkeland

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Re: Very faint hum and ringing noise when adjusting volume
« Reply #30 on: January 24, 2020, 06:22:36 AM »
Yes, those are in the correct spot for the first test.

For the second test, move each clip lead to connect terminal 5 and terminal 10 on each output transformer together.
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 #31 on: January 24, 2020, 06:39:05 AM »
Is terminal 5 on the output transformer the tab with the red wire connected? In the manual it is showing that both solid red and solid blue wire are terminal 1

Offline Jimb0

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Re: Very faint hum and ringing noise when adjusting volume
« Reply #32 on: January 24, 2020, 07:48:18 AM »
PB the clips at terminal 5 and terminal 10 fixed the issue! No hum at all. I was also getting a louder hum at start up which would disappear after a couple seconds but that disappeared as well
« Last Edit: January 24, 2020, 07:53:37 AM by Jimb0 »

Offline Paul Birkeland

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Re: Very faint hum and ringing noise when adjusting volume
« Reply #33 on: January 24, 2020, 08:03:59 AM »
That didn't actually fix anything, it's just another test.

The next test is to disconnect the end of the 10uF cap that goes to the red wire leading to each output transformer, then check for noise again.
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 #34 on: January 24, 2020, 08:13:11 AM »
Lol yes I just found out I wasn't getting any sound.

Should I leave the clips there or remove them when testing the 10uf cap

Offline Jimb0

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Re: Very faint hum and ringing noise when adjusting volume
« Reply #35 on: January 24, 2020, 08:45:00 AM »
I think I did this right...

Offline Paul Birkeland

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Re: Very faint hum and ringing noise when adjusting volume
« Reply #36 on: January 24, 2020, 12:45:43 PM »
The clip leads should be out for that next test.
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 #37 on: January 24, 2020, 01:13:43 PM »
Thanks PB I'll be testing it now

Offline Jimb0

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Re: Very faint hum and ringing noise when adjusting volume
« Reply #38 on: January 24, 2020, 01:17:02 PM »
There is a hum when removing the side where there's a red lead going to the OT of the 10 uf cap. I think it also became slightly louder as well

Offline Paul Birkeland

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Re: Very faint hum and ringing noise when adjusting volume
« Reply #39 on: January 24, 2020, 01:26:04 PM »
Now you'll want to move the amp to see if that changes.

This, to me at the moment at least, indicates the output transformers are picking up some noise from somewhere.
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 #40 on: January 24, 2020, 01:38:17 PM »
The hum didn't change when I moved location

Offline Paul Birkeland

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Re: Very faint hum and ringing noise when adjusting volume
« Reply #41 on: January 24, 2020, 01:47:20 PM »
Well, I officially have no idea.  Do you happen to own a scope?  This might be a decent use of the repair service too.
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 #42 on: January 24, 2020, 02:46:36 PM »
I don't but I was planning on getting one if we couldn't fix it

Offline Paul Birkeland

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Re: Very faint hum and ringing noise when adjusting volume
« Reply #43 on: January 24, 2020, 03:44:08 PM »
The scope would be useful to quantify what you're hearing.
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 #44 on: February 02, 2020, 05:51:14 AM »
Just got the scope. I checked the regulated power supply. The 275v and the 215v and it looks clean. No obvious ripple.

50v per division
https://imgur.com/a/coqDaOB

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I put the scope on ground and on the output of the headphones as shown in the pictures

50v per division
https://imgur.com/a/CF0EFsr

The noise patterns are the same when amp is on or off. Also when headphone is plugged in or not.

Any other suggestions?