Two-chassis phono stage - grounding question

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Thermionic Idler
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#1 Two-chassis phono stage - grounding question

Post by Thermionic Idler »

So I have one metal chassis containing the phono stage circuitry with step-up transformers, and there will be another containing the power supply. An umbilical cable will connect the two with the ±12V supply.

The chassis with power transformer and power supply board will obviously be connected to safety earth because it will have mains cabling in it.

On the face of it, the chassis containing the phono stage circuit is all low-voltage and therefore, on the face of it, shouldn't need to be connected to mains ground. However, I was re-reading today about the issues Ant had with the Cole phono stage and the primary to secondary short that Nick discovered, and whether I should allow for that scenario and ground the whole lot to mains earth (and deal with whatever noise issues that may cause). How usual is it that mains finds its way onto a secondary winding?
Deck: Garrard 301 - Audio Origami PU7 - VdH Black Beauty
Phono: Pete Millett LR, Lundahl step-ups, AMB σ22 PSU
Linestage: AMB α24/LCDuino
Power amps: 'Newton' 300B PP based on a Lynn Olson design
Speakers: FF225WK 'Big Met' Metronomes c/o Cressy Snr
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Nick
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#2 Re: Two-chassis phono stage - grounding question

Post by Nick »

How usual is it that mains finds its way onto a secondary winding?
Once will do it.

Take the earth to the second box via a cable that can stand a few amps (15 I think for CE, 24 for USA). Earth both boxes, second one via via the umbilical. Connect the signal ground to safety ground via a 100R 3W resistor with 100nf cap across it at the output RCA's. Connect the Ground Terminal on the phono to the case ground.

At least that's what I do.
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#3 Re: Two-chassis phono stage - grounding question

Post by izzy wizzy »

I have wooden 2 box phono. I still take mains earth to the audio chassis for earthing/grounding purposes.
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Thermionic Idler
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#4 Re: Two-chassis phono stage - grounding question

Post by Thermionic Idler »

Thanks both.
Deck: Garrard 301 - Audio Origami PU7 - VdH Black Beauty
Phono: Pete Millett LR, Lundahl step-ups, AMB σ22 PSU
Linestage: AMB α24/LCDuino
Power amps: 'Newton' 300B PP based on a Lynn Olson design
Speakers: FF225WK 'Big Met' Metronomes c/o Cressy Snr
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