What to do with chassis ground wire on vintage Denon turntable

[dougi]

I have a vintage Denon turntable, which has two earth leads, tonearm earth wire associated with the RCA leads, and a chassis earth wire (with a small spade, like the tonearm earth wire).
I feed the turntable AC via a 240 three pin -100V two pin isolating step-down transformer, as Japan model being used in Australia.

The chassis ground appears connected to the bottom of the platter assembly. Below is a pic from the same model, with it highlighted. Given that I assume I can touch the platter assembly when on, this can't count as double insulated.

What is the safest way to deal with the chassis earth wire? I currently have it, and the tonearm earth, connected to the phono pre (Parks Audio Waxwing) ground terminal.

How I dress the chassis ground does make a difference to noise a bit, but I am more interested in what is safe?

Given I am using an isolation transformer, can I just remove it?

Are there risks leaving it connected to the pre (I don't know if the ground is earthed or not) or connecting it to an earth? (I assume I shouldn't as it would defeat the purpose of the isolation transformer).

Would it be safer to change the transformer to an autoformer and earth the chassis earth to it's earth?

 

[Chrispy]

Do you have some sort of ground hum using it vs not using it?

 

[dougi]

Do you have some sort of ground hum using it vs not using it?

Not exactly, no hum but noise is higher if not used (via the levels in the Waxwing and RME ADI-2 PRO which I use after it, but seems inaudible). I am more concerned with safety if something AC related comes adrift in the turntable and what is safest to do with it.

 

[Chrispy]

Not exactly, no hum but noise is higher if not used (via the levels in the Waxwing and RME ADI-2 PRO which I use after it, but seems inaudible). I am more concerned with safety if something AC related comes adrift in the turntable and what is safest to do with it.

Probably the only issue then is the noise rather than safety.

 

[xanalog]

The chassis ground appears connected to the bottom of the platter assembly.

but you are saying that you are using an isolation xfmr. The platter/chassis, therefore, is not at earth ground potential (re: AC MAINs 3rd prong) but 'floating'.

1) Why are you using an external xfmr anyways?
2) Is the "noise' you hear have any higher harmonic content to your primary AC Mains frequency (50Hz)?
3) Will running a 16gauge wire to the AC MAINs third wire remove the 'noise'?
4) Will tying the tonearm "earth lead" to platter ground (with or without (3) above, make a difference in the noise or AC hum?

 

[dougi]

but you are saying that you are using an isolation xfmr. The platter/chassis, therefore, is not at earth ground potential (re: AC MAINs 3rd prong) but 'floating'.

1) Why are you using an external xfmr anyways?
2) Is the "noise' you hear have any higher harmonic content to your primary AC Mains frequency (50Hz)?
3) Will running a 16gauge wire to the AC MAINs third wire remove the 'noise'?
4) Will tying the tonearm "earth lead" to platter ground (with or without (3) above, make a difference in the noise or AC hum?

1) To stepdown Australia AC 240V to the 100V the Japanese model needs.
2) I don't actually hear the noise, only see it differing via the pres displays.
3) & 4) I will try these but my may concern is if I now do ground the chassis via the ground wire whether it now creates a safety problem as it now bypasses the transformer isolation

 

[marin.weigel]

as it now bypasses the transformer isolation

It does not.

So, if it reduces audible noise - which you didn't specifically describe sonically - it's okay to use the grounding wire without any safety risk at all.

Your photo cuts off the most interesting part to the right, where the incoming two wire AC terminates into the internal transformer wiring.
I seem to see two red and two white leads, which would indicate the possibility to either parallelize windings for 110VAC or serialize them for 220VAC.
Maybe post another photo of the relevant detail.

 

[xanalog]

1) To stepdown Australia AC 240V to the 100V the Japanese model needs.

That was suspected; would you be better off replacing the internal transformer and do away with the stepdown that is external?

 

[Balle Clorin]

You cannot do this easily .Requires a custom transformer, see the schematic- the 100v version uses the AC from the line directly!