Hum left channel

[allthingsanalogue]

Anyone get a hum from the left when using a external psu on a sl1210?

It's very, very quiet but there, when i turn off the psu sr3-21 it goes away. Also when physically removing the arm from the deck but leaving connected to the Phono stage, even with the sr321 switched on it stops humming. As soon as any part of the arm touches the deck it starts again.

I've checked the pitch ground lead to armboard and it's fine, removing it makes no difference. I even completely removed the pitch from the pcb and it made no difference. It's a Rega arm.

I only first noticed it with headphones.

[CageyH]

When I had my Rega arm fitted, I had to run a separate earth lead from the main PCB to the phono stage to get rid of the hum.

[allthingsanalogue]

I tried that but it got louder, unless i connected it to wrong part on the pcb. I tried it connected to th same bottom left hand corner.

How loud was your hum? If i use a mutimeter and touch anywhere on the deck all the way back to the earth socket in the mains plugs i have continuity. I even tried disconecting the earth lead!

[CageyH]

[allthingsanalogue]

Should there be continuity to the earth socket in the mains plug from the chassis of the TT?

[CageyH]

My power supply only has +ve and -ve feeding the TT.
From what I remember, Rega arms are earthed through the left channel ground.

Try disconnecting the armboard earth, as the arm is grounded anyway.

[allthingsanalogue]

Done that, nothing changed. Only physically unscrewing the arm and lifting of the deck with hum stop?

I also removed the two resistors and capacitor 3 from the pcb as Paul advised.

[allthingsanalogue]

All fixed!

I ran a ground lead from the left hand point on the PCB to the phono stage, but the most important thing was to rewire the RB700 arm. I had to disconnect the ground wire from the left channel on the base of the arm and recconect to chassis of the arm.