Earthing issues

arduino based linestage using 12B4 tubes

Earthing issues

Postby Ludwig » Sun Jun 07, 2015 10:19 pm

Just in the final stages of testing my Budgie and I notice that there's a nasty buzz when there's no CD player or source connected. Do I need to ground the -Ve side of the 24v supply to the signal ground?

EDIT: Actually I just noticed the grounds are connected. Could it be that my 24v power supply doesn't have an earth pin? Once I connect an earthed source the buzz disappears...
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Re: Earthing issues

Postby Ludwig » Mon Jun 08, 2015 8:36 pm

I did some more testing last night – potentially the issue is with the power amplifier, the IEC socket earth pin is not connected to the chassis or to the input signal ground!

If the power amplifier is on without anything connected (no Budgie, no source), it is silent.

Then, I add the Budgie, no source, just the RCA interconnects from the output of the Budgie to the RCA input of the power amp. Wild hissing happens which gets louder if I put my hand near the tubes or touch the chassis of the Budgie.

If I swap the power amp for one which does have the earth pin connected to the chassis and the input signal ground, then there is no hissing.

What would be causing the hissing?
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Re: Earthing issues

Postby 20to20 » Tue Jun 09, 2015 7:25 am

Ludwig wrote:
If I swap the power amp for one which does have the earth pin connected to the chassis and the input signal ground, then there is no hissing.

What would be causing the hissing?


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Re: Earthing issues

Postby Ludwig » Tue Jun 09, 2015 8:34 am

Indeed, very odd. The power amp doesn't seem to like the fact that the budgie is not grounded to the house earth. Presumably I either need to; 1) make a connection between the signal ground and the mains earth in the power amplifier, or 2) connect the -ve of the DC 24v supply of the Budgie to the mains earth somehow.

Or...just use a CD player or DAC which has the mains earth connected to the signal ground and just leave it at that!

On a positive note, I changed to another pair of 12B4A and the buzzing reduced significantly! Still plenty of noise if I touch e tubes, but presumably that is normal?
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Re: Earthing issues

Postby Shannon Parks » Wed Jun 17, 2015 6:41 am

Ludwig, what 24V supply are you using? Yes - you need a 3-prong earth grounded supply.

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