Grounding vs interference question - buzz

[derekiseric]

Today I noticed a buzz with the volume set to zero on my Hoffman AB763 build that stopped when I touched the input jacks with my fingers while the chassis was out of the cab sitting on top. 

There was no guitar or cord plugged into the input jack.  I got the buzzing to stop when I put the chassis back into the cab and screwed it in (where it touches the foil shielding stapled to the cab top. 

I checked my grounds in the amp and they all seem to be ok with my DMM. 
Is this interference or signals being picked up or is there a grounding problem?

Thank you for any help!

[Ed_Chambley]

Not necessarily if you have for instance folurescent lights or microwave or even a cell phone. Just check as you have and insure earth ground is good.

[derekiseric]

Thank you for the reply Ed,

I’m getting 0 ohms between the amp grounds and the chassis.  I’m going to test the outlet in the house just to be sure. 

Also - the build is in a newer Fender Handwired 64 Deluxe Reverb chassis where Fender used the brass ground plate across the pots and soldered ground leads there - like the 60’s ones..  I’m wondering if I have a ground loop between my pot and input jacks bus wiring and the brass plate? 

[sluckey]

I think what you experienced is quite normal.

[Ed_Chambley]

It is normal for me and actually I have a old Telecaster (59) that will let you know how far from the amp you are.  It will also play the radio sometimes and the Ham radio guy in my neighborhood doesn't know I can hear his transmissions.


He wouldn't care, we are both nerds anyway.

[derekiseric]

Thank you both!  I’m going to triple check my grounds just to be sure.

If I wave my hand above the open chassis right around the V3 Reverb section the hum gets louder.  Also - if I put the chassis in the cab but don’t screw it in so it isn’t touching the foil sheet on the top - it makes the same hum when I touch the handle brackets on the top of the cab. 

I hate having phones, computers, etc always around. 

That’s an awesome telecaster to have!  I bet it sounds amazing.  - through my Deluxe Reverb you could get those Roy Buchanan tones! 

As long as the HAM radio doesn’t start talking back to you it should be ok. 

[PRR]

A guitar amp is a HIGH-gain system.

If it sits open, all the crap in the room gets in and is amplified.

High-gain audio should be in an enclosed metal box. Or when you must work "open", discount the stray buzz as something which should go-away when you close it up.

[derekiseric]

Thank you for the replies! It’s working great!