Tracking down 60hz AC hum

[undefined_user]

Hello,

I finished my crack build recently and enjoyed the experience.

On the first time powering it up and listening to audio. Audio seems to work. Left and right channels both work. But there is a hum that exists at 0 volume all the way up through max volume. It sounds like 120 volts 60hz AC noise. Tried disconnecting every thing and hum is still there. Appears to be from the amp itself.

One question I had is was, is the transformer lid supposed to be electrically connected to the transformer plates? This transformer seemed to have a thick coat of laquer that the star lockwashers would not penetrate. The manual suggests tightening the screws to address this symptom but I dont think the lock-washers would cut through.


imgur album ending in a/Hz1LksI has a basic shot of the build

[Paul Birkeland]

You can post a link to the album and we can have a look at the photos.

Can you listen to a 120Hz tone and a 60Hz tone just to be sure you know which one you're hearing?  They each have very different causes.

[undefined_user]

This one maybe my fault.

I tested the amp last night with simple 45ohm apple earpods as its all I had at the time and I could hear the 60hz hum pretty well.

Only slight changes tonight including tightening down the screws on the transformer and adding a pair of 600ohm beyerdynamic 990's.

Now I can only hear the 60hz hum very slightly on the ear pods and not at all on the 600 ohm head phones.

Last night it seemed louder. If anything it seems mechanical in nature as the transformer on the unit itself is very slightly audible and that noise seems to be transferred into the tube.

Attaching an image of my build

[Paul Birkeland]

60Hz hum can be caused by things like a bad ground on your outlet or grounding issues between Crack and a source component.

120Hz hum can be caused by bad solder joints in the power supply not properly filtering noise. 

Did you double check by listening to test tones that you are hearing 60Hz and not 120Hz noise?

[undefined_user]

I went on youtube and listened to 60hz and 120hz tones.

The sound I'm hearing is closer to the 120hz tone.

Im familiar with the 60hz sound when you have different grounds on audio gear and the ac line noise likes to creep into the audio path. Ive never heard this 120hz tone before.


Attaching a few images of the underside.

I cant post links to external sites, but an album of the build exists at imgur.com/a/Hz1LksI

[Doc B.]

120Hz buzz means you probably have a connection somewhere that is not perfect, most likely a ground connection.

[Paul Birkeland]

A loose 220uF cap will also bring the 120Hz ripple way up.