Ground problem! Noise disappear when i touch the chassis

[raza]

Hi,
Last week I finish 2 amps,

One Dumble style, and other 2 channel plexi.

In the two amps I have the same problem.

When I conect the guitar there are a low noise that change when I move the guitar, But when I touch some metal parts of the amp or guitar The low noise desappear. I test it with differents guitars and I have the same problem.

For wiring the ground I use differents bus
1 bus for all preamp grounds.
1 bus for all power suply grounds
1 bus for speaker outs grounds

Also Ihave other conections in the star ( Ct, the ground of the power chord, etc...)


What can I do? I have this problem in the 2 amps.


subirimagenes


sube

thanks!

[raza]

this are the buses


imagen

[darkbluemurder]

Assuming that the amp's chassis is properly grounded, what you describe is normal. As soon as you touch the guitar strings (which are grounded) your body becomes a shield to noises wanting to creep into the circuit. You will not have that with EMG equipped guitars because in those guitars the string ground is cut or - if the EMGs were factory installed - the string ground is non-existent.

Cheers Stephan

[coldengray]

You probably have ungrounded power in your house/apartment. I have the same issue with my old house and I am having a dedicated circuit put in for my amp area.

[neikeel]

A guitar amp is not like a motor vehicle, you do not want a star ground system.

Take the orange bus, the green bus and the red bus wires away from the central ground.

Ground the mains input to one dedicated lug only.

Ground the orange bus to the chassis near one corner of the amp beneath where you have drawn the long orange line, next ground the red bus to a dedicated lug in the bottom corner of the chassis (as it appears on your photograph) and the green bus to its own lug.

The chassis has a little impedence of its own and will provide a little resistance.

Star grounds are noisy.

Also guitars need good grounding and shielding too.

[raza]

I change the buses like you tell me and I have the same problem.


This is the scheme of I did


sube fotos

[neikeel]

Suggest you give the green bus its own lug in the corner.

Next, lift the heater centre tap wire from its ground and run a dedicated wire from the PT to the same ground point as the input jack.

Take the presence ground off the rest of the control bus and run dedicated wire to the PI filter cap node.

Are your heater wires neatly twisted?

Also worth checking that it is not a faulty ground in your house.

[DG45]

Did I miss any mention of whether this is only happening with the 2 builds and not with a factory amp? The guitar buzz thing is common, especially with single coil guitars but with humbuckers as well. I just shielded a dual humbucker guitar that was particularly offensive. Ar any rate, touch the string, buzz goes away or is greatly reduced ... common scenario (I never tried touching the amp chassis instead of the strings).

Also, is this happening with the amp in the chassis with shielding tape underneath the chassis? Or, is the amp outside of the chassis for testing?

I'm not real tech savvy (I keep saying that) but it's worth making the point, I think, that you be sure you aren't chasing your tail here.

[raza]

sorry for the delay, I've had a lot of work.

I understand that all amplifier is easy to make some noise.

But I have a "Custom Audio OD100Se +" not make any noise. On channel 2 with the full gain, I touch the metal chassis and the sound doesn't change

I would like to know the best way to ground a tube amp.
I have read many documents but in some cases are contradictory and which is not telling the truth.

Anyone have any reliable document?

[Carbia]

This is a pretty nice document:

http://www.valvewizard.co.uk/Grounding.pdf

I've done what he said multiple times and works fine

[raza]

I have tried multiple solutions to the problem of grounds. When I touch chassis or metal parts, the background noise changes for the better.

I'm desperate

As will those of Custom audio with this problem
What my Custom Audio makes it different?

[raza]

I tested the amp with a spectral analize, I put all controls at 12 o'clock. with the gain and volume at 12 oclock I have a very very loud sound.

This are the results


imag


What can I do? its posible that some value of some component make that my amp have this noise?