Grounding turntable simultaneously to AC power supply AND external phono preamplifier

Sean de Silva

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I want to get this right on the first go and avoid having to travel down the rabbit hole of a fiddly trial and error approach. I've been trying to figure this out but I'm in a quandary hence would appreciate guidance from our experienced FMs who might have been in a similar situation.
I'm considering replacing the stock 2pin power cable of my TT with Mr Murthy's high quality 3pin cable. He has advised that in order to connect the earth wire of his 3pin cable to the TT, I'd have to locate the TT power transformer screw, wrap and probably solder the earth wire to this screw which would then ensure that the TT is grounded to the AC power supply.
Here lies the abiding conundrum..
The TT already has a thin green ground wire soldered internally and connected to the ground terminal of my external phono preamp. This was done to eliminate that distinctive 100Hz buzz which it has successfully.
Hence, if I ground the TT to the AC supply as advised, would this introduce a problem that doesn't exist by creating a 50Hz ground loop hum since the TT and other gear would now be connected to the same AC supply and thereby risk introducing ground differentials between TT and other gear? i.e. TT grounded to AC power supply and to phono preamp simultaneously!
Taking all these factors into account,
Should I not ground the TT to AC earth but only connect L & N of power cable thus effectively reducing it to a 2pin cable? Or
Should I ground TT to AC earth and connect/ disconnect TT ground to phono preamp?
 
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G401fan

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Your TT tonearm earthwire has no business getting anywhere close to the AC power supply. And what exactly is the TT power transformer? Most TTs have no such animal. They may, at best, have a rectifying board to convert AC to DC, if the motor is a DC motor. Stick to the two pin power supply, if that was what the TT originally came with. Fancy power cords do not improve the sound of a TT. No point in second guessing the original designer.
 

Sean de Silva

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Your TT tonearm earthwire has no business getting anywhere close to the AC power supply. And what exactly is the TT power transformer? Most TTs have no such animal. They may, at best, have a rectifying board to convert AC to DC, if the motor is a DC motor. Stick to the two pin power supply, if that was what the TT originally came with. Fancy power cords do not improve the sound of a TT. No point in second guessing the original designer.
Thank you for the advice. Noted. As it ain't broke, I ain't fiddling around to fix it.
 

quad

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And what exactly is the TT power transformer? Most TTs have no such animal. They may, at best, have a rectifying board to convert AC to DC, if the motor is a DC motor.

Almost any TT with electronics in it, SL1200 for ex, have a transformer to step the mains AC to a lower voltage which is then rectified and regulated. This will not apply to TTs which run directly off mains AC like the venerable 301/401s, of course.
 

stevieboy

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You haven't mentioned which TT you have. The only suggestion I can make is try the connection and see. There's not one solution but generally a flow chart of try this and if you still have hum try this, type of advice scenarios for hum. Different setups seem to need different grounding configurations. Tons of examples littered all though the net forums. Me personally I've had a slight reduction in hum by running a second grounding wire from the grounding post of the phonostage to a screw on the front of the phonostage. I'm not electrically minded enough to figure out why that works but it does. So wire it up as a temporary connection as per Murthy's advice before soldering, listen and if you have no hum solder away!
 

Sean de Silva

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You haven't mentioned which TT you have. The only suggestion I can make is try the connection and see. There's not one solution but generally a flow chart of try this and if you still have hum try this, type of advice scenarios for hum. Different setups seem to need different grounding configurations. Tons of examples littered all though the net forums. Me personally I've had a slight reduction in hum by running a second grounding wire from the grounding post of the phonostage to a screw on the front of the phonostage. I'm not electrically minded enough to figure out why that works but it does. So wire it up as a temporary connection as per Murthy's advice before soldering, listen and if you have no hum solder away!
Marantz DD6170
 
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