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Old 5th November 2002, 09:04 PM   #1
basil is offline basil  Canada
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Cool diy phono preamp grounding ?

I am finishing a op-amp based phono preamp and was wondering how I should connect the ground from the turntable to the preamp and wether or not I should continue that ground to my line driver/preamp.
To be honest I am not completely clear on how to proberly gound a tunrtable.
Thanks.
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Old 6th November 2002, 06:12 AM   #2
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Try connecting it to earth ground.

Jocko
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Old 6th November 2002, 06:56 AM   #3
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You must ground the turntable (or the tone arm) somewhere. There are no absolute rules. If you get no hum, it's sufficient.

Start with your amp's chassi (which is connected to the signal ground in some way. You can also try connecting the ground cable directly to the signal ground.
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Old 6th November 2002, 01:38 PM   #4
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One thing you might want to try while playing with grounding schemes, is to reverse the polarity of your AC line cords. Depending on how the primaries of your power transformers are wired, the leakage currents could be lower if you change polarity.

Jocko
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Old 20th November 2007, 11:30 AM   #5
Giaime is offline Giaime  Italy
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Hello all,

I found this old old topic while searching before posting a new topic.

So since it's related, I'll ask it here.

The question is the same: where do I connect the ground lug of my turntable (the ground wire, NOT the signal grounds of RCA connectors).

I'm in the process of building a solid state preamplifier. Its ground scheme, from AC plug to phono input ground:

mains earth - returns of mains Y2 filter caps - small ferrite choke - chassis - 10nF capacitor in parallel with back-to-back 1N4007 diodes (to prevent ground loops) - PSU ground - wire to the phono PCB - phono input ground.

Where in this path shall I connect the turntable ground wire? I think that I must separate it from the input signal ground, but I can't connect to mains earth or I will short circuit the diodes (that won't work any more). So I think I have to run a wire up to the PSU ground.

What do you think about? Thanks in advance.
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Old 20th November 2007, 12:30 PM   #6
AMV8 is offline AMV8  United Kingdom
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Hi

I agree with peranders who advises;

quote
Start with your amp's chassi (which is connected to the signal ground in some way. You can also try connecting the ground cable directly to the signal ground.
unquote

I then connect the pre amp chassis to mains ground and the pre amp signal ground to the pre amp chassis via a 5w 5r resistor or a thermistor.

Make sure the ground lead from the turntable earths both the arm and the turntable. T
In my experience the arm tube is sometimes difficult to ground and is often the cause of the hum that prople hear. A unipivot arm usually grounds itself to the arm base and turntable ok but a knife edge bearing between arm and arm base often does not earth the arm tube and you may need to ground the arm.

Don

Don
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