Technics SL-1200MK2 internal grounding

[MartinConnolly]

I have recently bought a pair of 1988 Technics SL-1200 Mk2 DJ turntables. All original components inside and all still work!
But, they have been 'internally grounded' which is a common mod that some DJs do which removes the ground wire and just connects the turntable chassis to one of the sheilds on the RCA phono cables.

Now, Technics say this shouldn't be done because the outputs from a phono cartridge are balanced positives and negatives, not unbalanced signal plus ground.

So, I plan to remove this mod.

However, looking at the back of my chosen cartridge - a classic Stanton D680AL, there is a 'ground strap' connecting one of the negative pins to the metal chassis of the cartridge.

I'm confused. Isn't this doing the same thing? The metal of the cartridge makes contact with the metal headshell and tonearm, so Isn't the whole chassis of the turntable grounded through this strap?

Your thoughts please?

[MartinConnolly]

Re: Technics SL-1200MK2 internal grounding

I may have just answered this myself. The Stanton is supplied with threaded plastic spacers for the retaining screws, so it becomes electrically isolated from the headshell. I still don't see the point of the 'ground strap' on the back though.

[redwire]

Re: Technics SL-1200MK2 internal grounding

It's a battle between the turntable's earth-grounding, and the phono-preamp's earth grounding. Who has or does not have it. At least/most one end needs it.

The tonearm, chassis, cartridge's headshell can pickup mains hum and noise, and require to be earth-grounded to make an electrostatic shield.
Older turntables (2-prong power cord, no PE ground) can't do this so require a chassis ground connection through the loose ground wire at the preamp.
Newer turntables with 3-wire power cord, they (tonearm, chassis) are earth-grounded, and you can verify with an ohmmeter.

Ultimately, a cartridge's audio outputs are isolated/floating. They usually get some form of ground reference when plugged into the RCA's at the phono-preamp end.

You don't want a ground-loop between the audio ground and the earth ground, which will happen if you do the DJ mod/Stanton ground strap (on a 3-prong TT) AND the phono-preamp (RCA's) is also earth-grounded (3-prong power cord). Does the preamp have a 2-prong or 3-prong power cord, you can check ohms between the RCA jacks and 3rd prong PE ground on the power cord.

So at least 4 permutations of turntable grounding to understand.

[MartinConnolly]

Re: Technics SL-1200MK2 internal grounding

Both the turntable and mixer are 2-prong power. No earth, with the box-within-a-box double insulated symbols.

I must say, it sounds stunning, with dynamics and balance that put my cheap Numark CD players to shame, so there's a lot of 'if it ain't broke don't fix it', but at high volume, when I hold the headshell I can hear a faint crackle from my body static leaking into the output, which I assumed was because of the internal grounding.