Double insulated vs earthed amp and turntable (Rega) hum

plymman

Active Member
I'm posting this just out of interest to see if anyone can give me a bit of background.

I have a Rega P1 that had the dreaded hum issue. I sent it back and it was returned with two modifications.

1. A ground wire was added the RCA connection that carries the earth/ground. This had no effect.

2. They gave me a ground wire to attach to the amp that terminates in a 3 pin plug. This completely fixed the issue.

Just by connecting the grounded plug my hum has gone and the turntable is perfectly silent, to say I'm happy is an understatement, the Rega sounds absolutely amazing for the money. While it was being fixed I was loaned a Project Essential 3A which didn't come close to the Rega and made me appreciate it even more.

I know some people are affected by Rega hum and others aren't (mine didn't hum at all while at the store) and I've not understood why, could the answer be below?

They said its partly due to Regas grounding system and the type of amp it's connected to. They said there's no issue if connected to an amp that is fully earthed but can be a problem if the amp is double insulated. Both my amps that have hum are double insulated.

What is the difference between an earthed amp and a double insulated amp and why would the ground cable to 3 pin plug fix it?

This could be a very easy fix for anyone that gets a humming Rega in the future but I'd like to know why it works.

Thanks.
 

Gray3

Active Member
What is the difference between an earthed amp and a double insulated amp and why would the ground cable to 3 pin plug fix it?
An earthed amp has its metal casing earthed to the (top) earth pin of its mains plug.
A double insulated amp doesn't need its case to be earthed at the mains socket (note that both your amps will have 2-core mains leads).
The earth wire they've given you is connected to the earth pin in the plug - so by using it you're earthing the casing of your unearthed amp.

Glad you're happy now.
But you see the potential for harm here though I'm sure......someone buys a plug to make their own....but connects the wire to the live, rather than the earth pin....leaving their entire metal casing live :eek:.
 

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