Grounding techniques

[joecool85]

Should we worry about star grounding in some line-level audio equipment that doesn't produce high output currents?  Like some equalizer box or preamp or whatever.  Say it's made up half a dozen dual op-amp chips, all dual-supply, which are mostly at unity gain or very modest gain.  It's convenient to just run a single ground trace reaching all the places on the board which need a ground.

If you build it and there isn't any problems you are good and if it's noisy, then you'll want to try star grounding.  Unfortunately that is the only real answer.

[henry909]

I came to this forum looking for info to help solve a grounding problem with an old amp. And here the first thread I find is about grounding. But I am not sure whether I understand enough of the discussion above to figure out how to solve my problem.

Problem: I have an old Kay Model 780 SS amp. It has an old style two prong power cable, i.e., it doesn't have the third ground prong. The amp produces a lot of static and when you touch metal on the guitar , eg., the whammy bar or the bridge, you can hear static clicking through the amp. I suspect that the problem is the lack of ground on the power cable which goes through a grommetted hole in the chassis.

Can anyone give me an explanation of of how to add a ground to the power cable to see if that eliminates or reduces the static? Can I remove the chassis disconnect the old power cable. Then connect the two non-ground wires where the original power cable was connected and then simply screw the ground wire to the chassis?  Thanks.

[DrGonz78]

Take out your DMM and make sure what color wire is hot and neutral through the power cable. Then remove the cable and get a 3 prong type power cable. (Assuming you are in the US) Basically, you have answered the solution all ready in your post. Drill a hole in the chassis and attach a ground wire. It is really easy as you said in your post. Sometimes I find Black hot and other times white is hot...? Look at the function of the power cord in relation to your DMM. Adding a ground wire should solve your problem.

P.S. - Star grounding is something totally more advanced in my thinking in relation to just adding a simple ground wire.

[joecool85]

P.S. - Star grounding is something totally more advanced in my thinking in relation to just adding a simple ground wire.

Star grounding is normally used for audio signals, not power chain.

[flester]

Take out your DMM and make sure what color wire is hot and neutral through the power cable. Then remove the cable and get a 3 prong type power cable. (Assuming you are in the US) Basically, you have answered the solution all ready in your post. Drill a hole in the chassis and attach a ground wire. It is really easy as you said in your post. Sometimes I find Black hot and other times white is hot...? Look at the function of the power cord in relation to your DMM. Adding a ground wire should solve your problem.

P.S. - Star grounding is something totally more advanced in my thinking in relation to just adding a simple ground wire.

I am using a power supply with no ground so that no mains voltage gets to my amp. Any suggestions on how to add a ground wire to cut noise?

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[joecool85]

I am using a power supply with no ground so that no mains voltage gets to my amp. Any suggestions on how to add a ground wire to cut noise?

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Using a ground will not introduce mains voltage to your amp, so I am unsure what the concern is here.

[DrGonz78]

What amp is it? Does this mean you have a 3 prong power plug where the ground is broken off or something? Or it could be you have an old amp with a two prong, which involves some conversion. Or it could mean you have a modern amp with a two prong cable that is polarized and the manufacturer just did not utilize the ground plug option. So as Joe asked what is the concern here?

[phatt]

Maybe what was meant is;
He is using a plugpak/wallwart so there is no mains to the amp?

"IF" so and there is hum/buzz then the Q is valid but confusing.

@ Flester;
The term *Ground* can have many meanings.
Mains ground (EARTH) although related is quite different to the Ground or *Common* in your circuit.

If your Amplifier is as above, no mains in the chassis and powered via an external double insulated supply then you have have a local circuit ground issue.
Grounding back to mains EARTH probably won't solve much if you have a circuit problem causing hum/noise.

If it's hum, You most likely have a bad connection in the amplifier circuit common path somewhere.
If the circuit is very buzzy then likely there is too much gain somewhere with bad shielding.

Be aware that a lot of amps for modern higain thrash will all buzz when the distortion pots are maxed out and at bedroom volume it quite pronounced.
At gig level you would hardly notice it until you stop playing.
And yes,,, as *DrGonz* mentioned give us more info and clarify the problem so we can help.
Phil.

[flester]

OK let me clarify. In Ireland we have 240v AC mains with 3 pin plugs as used also in the UK. I am using a wallwart type power supply which has 3 prongs but the earth/ground pin is a plastic dummy, so the amp is not connected to 'earth'. My amp is simply a Kemo 40w audio power amp. There is slight hum which is OK, even with battery powered pedals but adding a pedal power supply gives unacceptable noise levels. The pedal supply works fine with a mains powered amp. When I connected the output negative to earth the noise went away ( using a mains plug). Is there another way to do this?

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[flester]

Ideally I want a wallwart with an earth connection if such a thing exists

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[Jazz P Bass]

I believe that you are missing the point of the Earth connection.

"Wall Wart" power supplies are typically rated as 'Double Insulated'.

Therefore there is no need for a connection to Earth Ground.

If you are having noise issues with the amplifier, I would look into why.

The power pack itself may be the issue, noise wise.

[phatt]

I believe that you are missing the point of the Earth connection.

"Wall Wart" power supplies are typically rated as 'Double Insulated'.

Therefore there is no need for a connection to Earth Ground.

If you are having noise issues with the amplifier, I would look into why.

The power pack itself may be the issue, noise wise.

Agree,, If one or both plugpaks are Switchmode type that can present problems with circuit grounding.
The older Iron/copper transformer Plugpaks were less prone to this.
Phil.

[joecool85]

If you are having noise issues with the amplifier, I would look into why.

The power pack itself may be the issue, noise wise.

I agree, most likely it is the power pack that is causing the noise.  Sometimes this can be filtered by adding power caps inside the amp.

[flester]

If you are having noise issues with the amplifier, I would look into why.

The power pack itself may be the issue, noise wise.

I agree, most likely it is the power pack that is causing the noise.  Sometimes this can be filtered by adding power caps inside the amp.

Thanks everyone. Power pack is not old but it was cheap so caveat emptor. I will look into using power filters though.

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[phatt]

Maybe post some pictures of what you have and that might help us to work out the issue.
Phil.