Phone II hummmmm

Hi, all.

I've recently changed the MC transformers (from the standard 1:20 WAD) in my Phono II as I needed a bit more gain on my new cartridge (Goldring Eroica Elite).

I've fitted some Lundahl LL1678 configured for 1:32 step-up. Apart from that the amp is as per the original design.

Now I'm getting quite and audible hum which increases if I touch the headshell on my Rega Planar 3. The Rega earthing is supposed to be via the shield on the phono cables and the set-up as it was with my previous cartridge which didn't have any audible hum.

The hum decreases if I touch the headshell and the body of the pre-amp at the same time suggesting that the earthing from the deck to the amp isn't working. I've twisted the input wires to the transformer (as per the original WAD installation) and I don't think the hum is being picked up there.

Has anyone else had a similar problem with the Rega arm/deck? Would it be ok to create a seperate earth from the deck to the amp and does anyone have any suggestions on where is the best point to attach it on the deck?

[John Caswell]

Hi Ed,
If you have changed the transformers and you are now getting hum it implies that the wiring/earthing of the transformers is not correct,
Check with a DMM that:-
1) The cartridge earth wires ie green and blue get to earth
2) That the TX primary gets to earth
3) That the TX secondary gets to earth
4) That the TX screen and case get to earth.

John - Dr John

[Guy Pettigrew]

Hi Ed

You might also like to know the standard WAD Phono 2 transformers were 1:10.

moving to 1:32 might do all sorts of odd things, but John Caswell could advise there.

Guy

I should get home tonight and I'll try to test the connections tomorrow.

The gain I'm getting from the Pre-amp is about right I'd say at 32:1. I'm not positive, but I thought the Pre II had 20:1 step transfofrmers? Going from the original step ups to the current 32:1 should have been a fairly large jump in volume if they were 10:1 wouldn't it?

The specs for the Lundahl transformers are here:

http://www.lundahl.se/pdfs/datash/1678.pdf

I think the problem is that the primary side of the transformers don't have a specificied earth (green) like the WAD transformers do, and I don't have the solder tags of the phono sockets on the inputs specifically connected to earth either.

So changing the transformers has "lost" my earth connection to the input phono sockets. As the Rega P3 is earthed via the phono sockets by design, I have no earth on the deck.

I'll try earthing the input phono sockets and see how that works.

Back with results in 15 mins

Ok, that has sorted it. The only hum I have now is the normal (barely audible at full volume) one. Thanks Dr J, spot on as usual!