Please help.... Grounding issue, and 60 Hz hum

[PaulHilgeman]

I have recently built a preamp, 4 gainclones and a separate power supply.

I have included a rough schematic of the whole deal.

There are a few issues. There is a soft Hum when it is on. It does now change with the POT or the input, and the amps dont get hot, so I doubt that it is oscilation. Besides, it sounds like 60 Hz.

When I have all 4 amplifiers powered on, and have all 4 connected to the preamp, there is a hum. The buzz sortof depends on which of the amplifiers is connected. Since there are 4 of them, that leave 16 possiblibies, I did not try them all, but it changes depending on which ones are plugged into the preamp. I am guessing this is some sort of ground loop issue.

Also, if I connect the grounds of the two power supply circuits together, the hum gets louder.

Also on a side note, when I turn a fan on, on the other side of the room, I get a decently loud click through the speakers, and also when I turn the whole thing on, I get a pretty loud click as well.

If anyone could help, I would be very apreciative.

[ashwin]

Hi Paul,
regarding the click on turn on, a 100nf cap (X2 type) across your power switch should solve it.
As for the clicks due to turning on other appliances, I had a similar problem. I tried the common mode supply filter mentioned here
and I found that it reduced the click quite a bit. But I had to power both the amp and the source (in my case a discman) through this filter. I used an inductance of about 2mH (calculated, not measured), and I guess a higher value would have gotten rid of the click completely.

Hope that helps.

- Ashwin

[PaulHilgeman]

Thanks for that, I am going ti build the double. Parts for it arent all that expensive either.

Anyone else on the hum?

-Paul

[Mattyo5]

Have you tried lifting the ground from the wall? Thats an easy thing to try and the first thing that comes to my mind.

-Matthew K. Olson

[PaulHilgeman]

Hey matt, thanks for the tip.

I am not sure what you mean by it though. If you mean taking the earth connection on my AC input module and connectiing it to both the ground connections on the amplifier supply and the preamp supply... I have tried that, and the humm got louder. I will try again, but I am not sure if it will work.

Please specify if you meant somthing else...

Paul Hilgeman

[Mattyo5]

no no...uh there are 3 connections in the all plug. The bottom one is the ground. Use an adapter to make sure that the ground connection never gets into the wall socket. ie...only the 2 "hot" prongs from the power plug actually get plugged into the wall.

http://www.partsexpress.com/pe/showd..._ID=3050&DID=7

use something like this...its the fastest way to try it

-Matthew K. Olson

[pinkmouse]

Originally posted by Mattyo5
Have you tried lifting the ground from the wall? Thats an easy thing to try and the first thing that comes to my mind.

And also possibly the most dangerous

Removing Earth bonds from equipment should not be required to eliminate earth loops. They are there for yours and others safety, and such actions could result in death or serious injury.

Please do not make this suggestion again.

[Mattyo5]

Sorry Paul, only trying to help. I had a problem w/ ground stuff too in my gainclone a while back. MOAMPS suggested that try something.... is your hum more like a buzz or a hum? b/c I had a 120hz buzz i think...wasn't loud.... what I had to do was ground everything at 2 "star" grounds... this ended up being grounding the gainclone at the ground point on the power supply caps ...the 1kuf ones that are attached to the chip. Then I took 1 wire off of there and went to chassis...this is where the ground met w/ the power supply ground coming off the main power supply caps. In your case, if you aren't using big main ps caps, i think the ground would come from the middle of 2 bridge rectifiers. Anyway, i don't know if this'll help... hope its not as dangerous as lifting the ground from the wall.

-Matthew K. Olson

ps...i'll find a link for ya to that diagram

here

Gainclone trouble

[moamps]

Originally posted by pinkmouse
Removing Earth bonds from equipment should not be required to eliminate earth loops. They are there for yours and others safety, and such actions could result in death or serious injury.

Hi,

let's not exaggerate, please. Lots of commercial equipment with all required safety certificates have two-wire mains plugs (even metal chassis).


Regards

[EC8010]

Originally posted by moamps
Let's not exaggerate, please. Lots of commercial equipment with all required safety certificates have two-wire mains plugs (even metal chassis).

Indeed, they do. But they are rigorusly tested to make sure that they meet the safety requirements. If you're not absolutely certain which tests are required to legally meet double insulated requirements, you don't have the test gear or knowledge. Earthed eqipment is much simpler.

Edit: This is serious. Don't ever remove earth bonds.