Ground loop/hum after unplugging / plugging back on

[Entrigo]

Question on ground loop - turntable and external phono stage.

I unplugged and replugged my phono stage and turntable today (Vertere Phono1 mkiiL and Technics SL1500C) and when I plugged them back in, I got a pretty loud ground hum.

This disappears if I connect the ground cable to the "Signal ground" post on the Vertere instead of the "Chassis ground". It had always been connected to chassis ground and never had any hum.

Also - if I connect the ground wire to the ground post on my Rega Elex amp, no hum.

Ideas? I am fine with it being connected to the Signal ground but:

1. The Vertere has three grounding settings and these don't seem to make any difference when connected to the signal ground - I feel there was a slightly lower noise floor when connected to the chassis ground.

2. I simply want to understand how that happened, since it had worked the other way until now...

Thanks.

 

[abacus]

The central ground point should be on your phono stage or amp (Depending whether the phono stage is built in or not).
If your turntable has more than one ground point (Unusual but some turntable might be like this) just connect them to the central ground point until the hum goes away.

Bill

 

[Gray]

The unplug / replug part might be the key.

In your position I would be checking the signal return (screen) continuity between the disconnected* cartridge pins and both RCA plugs bodies.

(Wiggle the cable at the RCA end a bit to check for intermittency - but not enough to cause it!)

* A multimeter uses a voltage to test continuity.
Isolating the cartridge pins avoids any chance of you accidentally putting that voltage through its coils.

 

[Entrigo]

The central ground point should be on your phono stage or amp (Depending whether the phono stage is built in or not).
If your turntable has more than one ground point (Unusual but some turntable might be like this) just connect them to the central ground point until the hum goes away.

Bill

It is. The turntable only has one. The phono (external - Vertere) has two - a "Chassis group" and a "Signal ground".

The thing is, it was connected exactly the same before unplugging - to "chassis ground" and no hum.

 

[Entrigo]

The unplug / replug part might be the key.

In your position I would be checking the signal return (screen) continuity between the disconnected* cartridge pins and both RCA plugs bodies.

(Wiggle the cable at the RCA end a bit to check for intermittency - but not enough to cause it!)

* A multimeter uses a voltage to test continuity.
Isolating the cartridge pins avoids any chance of you accidentally putting that voltage through its coils.

Thanks Gray.

So, in baby steps (tech philistine)... Do I disconnect the leads from the cartridge pins, then wriggle the leads (not the RCA at the back), correct?

 

[Gray]

Thanks Gray.

So, in baby steps (tech philistine)... Do I disconnect the leads from the cartridge pins, then wriggle the leads (not the RCA at the back), correct?

Well if (big if) there's any intermittent screen connection in your phono cables - then it won't be at the cartridge end (because that remains undisturbed - unlike the plug / unplug RCA end).

Might be a bit fiddly holding meter probes at either end, while wiggling - crocodile leads would do the holding for you.

Bit of a shot in the dark, but it's worth checking if you can - just to confirm that all connections from cartridge to plugs are continuous and solid.

 

[Entrigo]

Well, I started by unplugging everything and plugged everything back in after cleaning terminals. I now get a hum only in position 2 on the Vertere - which is a "ground lift", whatever that is. No hum either on hard or soft ground as well as no hum on signal ground. That'll do...

Now I'll do a bit of testing to see which one has the lowest noise floor and I am good to go.

Still none the wiser as per what happened, how and why. Ghost in the machine and juju I reckon...