Bottlehead Forum

Bottlehead Kits => Mainline => Topic started by: Tabaia on June 24, 2025, 07:56:26 PM

Title: Buzz on left channel
Post by: Tabaia on June 24, 2025, 07:56:26 PM

Hi,

I turned on the mainline today.
Left channel now has a buzz in the signal.

What I have done:
1: Changed inputs - no change
2: unplugged input - no change
3: Changed headphone outputs - Balanced out has slightly less buzz
4: Plugged into different power out lets - no change
5: Listening without feeding audio into the unit I changed the volume pots - no change in buzz, it remains constant and no change in level.
6: Changing to high impedance increases the noise up a notch.
7: had a look through the the soldering underneath, nothing was immediately obvious to me.

Right Channel is completely silent.

What would the next step be?

Title: Re: Buzz on left channel
Post by: Paul Birkeland on June 25, 2025, 04:52:52 AM

If you tap pretty hard on the top plate, does the buzz go away?

Typically something like this is just a solder joint that isn't 100%.

Title: Re: Buzz on left channel
Post by: Tabaia on June 25, 2025, 11:21:55 AM

Did some tapping all around the top plate as well as gently lifting the whole unit and  tapping the whole unit on the  table. no change.

Title: Re: Buzz on left channel
Post by: Kris on June 25, 2025, 11:25:44 AM

Did you try different headphones?

Title: Re: Buzz on left channel
Post by: Tabaia on June 25, 2025, 11:29:36 AM

yes i did try different headphones

Title: Re: Buzz on left channel
Post by: Kris on June 25, 2025, 11:35:34 AM

Try swapping tubes too just to rule that out.

Title: Re: Buzz on left channel
Post by: Tabaia on June 25, 2025, 11:44:45 AM

Just swapped them - no change

Title: Re: Buzz on left channel
Post by: Paul Birkeland on June 25, 2025, 01:23:10 PM

Can you report the IA, OA, and OB voltages on both of the high current C4S boards?

Title: Re: Buzz on left channel
Post by: Tabaia on June 26, 2025, 09:57:47 PM

Here are the voltages
C4S Board A 
IA : 260.0
OA : 219.1
OB : 135.6
C4S Board B 
IA : 255.0
OA : 218.8
OB : 130

Title: Re: Buzz on left channel
Post by: Paul Birkeland on June 27, 2025, 06:04:16 AM

Do you hear the same noise with nothing plugged into the RCA inputs?

Title: Re: Buzz on left channel
Post by: Tabaia on June 27, 2025, 12:11:24 PM

Yes, the hum is consistent regardless of anything being plugged in or increases in the volume pots.
There is only a change when switching between low and high impedance, high increases the  hum.

Title: Re: Buzz on left channel
Post by: Thermioniclife on June 27, 2025, 01:45:34 PM

Clean the tube pins and if you can clean the socket receptacle's. I believe Doc B has a video regarding this.

Title: Re: Buzz on left channel
Post by: Tabaia on June 27, 2025, 11:48:51 PM

I removed and swapped the tubes, as far as the socket goes it should be ok as it is quite new.In anycase removing and resetting the tubes made no difference.
I think the issue may be elsewhere.
Thanks for the tip though, after looking at some other posts I gained some more knowledge on tube socket cleaning.