My Cary PH 302 phono amp MM hum?

I have a PH302 and use the MM input with an external SUT. It has always been very quiet and hum free.

Maybe the transformer input of the MC input is providing a break in the ground loop - I'd still be suspecting a ground loop of some sort. Since I star earthed all my electronics off the same wall socket, I've had zero problems in this regard.

There is a ground lift switch on the rear of the PH302. You could try this, but it made no difference in my setup.

Is the hum in both channels or just one?
If only one, perhaps there is a 'dry' solder joint in the MM input. I've experienced this issue before with another preamp - resoldering a joint on a relay fixed the issue. If the hum is in both channels, this is probably less likely (ie there would have to be 2 faulty joints, you'd have to be unlucky).

Thanks for your reply. Sorry for my ignorance but what is an "external SUT"? Also not quite clear on a "star earth". I do notice a little more noise coming from the right speaker. And it seems less loud when I don't have the TT ground wire connected. I played with the fixed and floating ground and also found it made no difference. Thanks for the suggestions on the on the MM solder joints. I will check those.

A SUT is a Step Up Transformer, typically used for low output MC cartridges.

03-02-12: Sharpe
Thanks for your reply. Sorry for my ignorance but what is an "external SUT"? Also not quite clear on a "star earth". I do notice a little more noise coming from the right speaker. And it seems less loud when I don't have the TT ground wire connected. I played with the fixed and floating ground and also found it made no difference. Thanks for the suggestions on the on the MM solder joints. I will check those.

Definitely experiment with the turntable earth wire.
If you are using separate mains receptacles try connecting all components to the same socket.

Star earthed means all the earths wires are the same length and connected back to the same point. I have made all my (DIY) power cables conform to this and connect back to the same point on my dedicated line. The idea is that this will give the same (low) resistance/impedance in the mains earth leads and discourage stray currents from running over component interconnects etc. - forming ground loops. I have no such problems.

I still suspect a ground loop. I only mentioned the solder joints because I have experienced that issue and it resulted in hum.

Hello Tobes, I have the original PH-302 and I wanted to ask your advice on changing the tubes. I see that you're using Sylvania 1968 era. What do you think of Sylvania 1944 army military VT-229/6SL7 GT?

I imagine your Sylvania VT 229s would be a truly good tube for the phono amp as long as they were quiet. How do you like them this far.

Hi, Thanks for getting back to me regarding the tubes. I have not purchased them yet. I would need four and they're $80.00 each.

Hi Mechans, The tube are $80.00 plus tax and shipping. I need four $375.00. What do you think?

Sorry to reply so late. I was away. The tubes which frequently is still available as NOS in their military boxes thus NIB (new in Box) is a great choice but the price is daunting. I had thought the 6SL7s would cost less. It is a decent price for the more widely used 6SN7. Is this from a really good vendor? If so I might just hold my nose and accept the cost. They will last a long time and have (I hope) been properly screened and sort of matched. I add that "sort of" because it is really hard to find close matching in tubes that old and rare. I would ask the vendor to match as well as they can, but in your circuit it may not matter. Make sure they are returnable because you really do need quiet examples. Good luck.
Steve

GE GSL7/5691
ADZAM GSL7GT

I can get both matched. But not sure which one to get?