Grounding the armboard

[RochaCullen]

Hi,

I finally got around to installing my new RB301 on my SL1210. It took longer than I thought it would with all those screws and bolts. Anyway, I was a little disappointed when I fired things up given the level of hum, it wasn't very loud at my normal listening levels, but as I turned up the wick it got pretty bad. I know the RB300 and its successors ground through the left channel, but it seems I am missing something. I played a couple of records, turned off the TT and amp and was off to bed when I thought to myself, perhaps I should check about grounding the arm board.

Simply putting my finger on the armboard and a finger on the chassis of my amp dropped the hum noise considerably. So its obvious to me I need to run a ground wire from that. I also read elsewhere in the forum that grounding the pcb would also help things. I do recall when removing the stock arm it had a ground wire running to either the chassis or the board.

Anyway, so many folks on AOS have put different types of arms on the Techie I was wondering if other people had the same issue and how it was they overcame it.

Nathan

[CageyH]

I took an earth lead from the armboard to the PCB earth, which solved my problem.

[YNWaN]

Grounding the arm base may solve the issue, but a lot of armboards (most) are not grounded and in many cases they are made from a non-conductive material so can't be grounded. For example, in my case the armboard is aluminium, but it is anodised and anodising is not conductive, so the surfaces the arm actually bolts to do not conduct - then the chassis the armboard attaches to is a carbon fibre laminate and that isn't conductive either!.

[RochaCullen]

I took an earth lead from the armboard to the PCB earth, which solved my problem.

Hey Kevin,

I tried sending you an email based on a previous post of yours. You mentioned that you tried grounding the armboard alone and that did not solve it. So you are saying that you ran the ground wire from the armboard to the PCB and that cut the hum completely?

[RochaCullen]

Grounding the arm base may solve the issue, but a lot of armboards (most) are not grounded and in many cases they are made from a non-conductive material so can't be grounded. For example, in my case the armboard is aluminium, but it is anodised and anodising is not conductive, so the surfaces the arm actually bolts to do not conduct - then the chassis the armboard attaches to is a carbon fibre laminate and that isn't conductive either!.

My armboard is aluminium, and the bolts holding it to the deck seem to be conductive, given that when I touch them the hum drops significantly. I've painted the armboard, but the threaded holes will be bare aluminium.

[CageyH]

I have cleared my inbox now.

I also found the position of the earth wire to be quite critical.
From memory, I also ran a fly lead from the PCB to the phonostage, which sorted the problem entirely.

[RochaCullen]

I have cleared my inbox now.

I also found the position of the earth wire to be quite critical.
From memory, I also ran a fly lead from the PCB to the phonostage, which sorted the problem entirely.

Hey Kevin,

So you ran a lead from the armboard to the PCB, then from the PCB to the phono stage ground?

Thanks

Nathan

[CageyH]

Yes, I did.

I found my post from elsewhere:

So, after reading up about earth loops etc. I figured I would try an earth lead from the bottom left earth point of the SL1200 PCB to the phono stage. Earth hum gone.

[RochaCullen]

Yes, I did.

I found my post from elsewhere:

So, after reading up about earth loops etc. I figured I would try an earth lead from the bottom left earth point of the SL1200 PCB to the phono stage. Earth hum gone.

Thanks Kevin,

I'll give that a shot.

Nathan

[RochaCullen]

Magic. Got home from work. Laid claim to the kitchen table. Laid it all out. Ground wire introduced. Sorted!!!

Tunes were belting out until moments ago. Blasted beftime for the kids.

Thanks guys.