SL-1210 mk2, audible hum from transformer

[Josey Wales]

Hi

I have disassembled and cleaned my SL-1210 mk2 and when I put it back together and powered up I could notice a slight hum coming from the transformer. It is audible if I put my ear to the platter without the mat on. I know that all transformers hum more or less, but should it really be audible this way?
If this is not normal any input on what the problem is would be much appreciated.

[adalbertuss]

Hi, are you sure, you didn't forget 3 rubber cushions which go under the trafo.

Regards
Wojtek

[Josey Wales]

The funniest thing happened.
I left it powered on and running at 33 speed throughout the night and this morning when I checked before going to work it was dead quiet.

[Trackside]

Transformers can hum more due to interference on the main circuit such as any DC from a poorly designed switching PSU connected to your mains can cause it.

[Josey Wales]

I tried four different outlets yesterday, being fed from from four different fuses in my main distribution box and the hum was constant when connected to either of the four.
Either the transformer coils got a bit warm and settled in place during the night or it was another electrical source of some kind that caused this issue.
Well, I guess I will never know for sure, I am just happy that it stopped.

[Mark E Smith's Dentist]

Although I can't hear hum from the trafo in my SL-120mk2, when I put a stethoscope on the plinth I was horrified. I've also got a stock 1200mk2 with a lesser cart for less well looked after records and there's much less hum through the 'scope with that one.

Can I get replacement transformer grommets? I'm wondering (hoping more like!) that the ones in my 120mkII have hardened.



JT

[Josey Wales]

According to Kevin at KAB older SL-1200/1210, manufactured before the early 1990's have a different type of transformer without welded laminations that can over time develop hum. Could be that the transformer in your SL-120 is of the older type.

[Trackside]

It's not difficult to remove the transformer and put it in a separate enclosure - it's even considered a tweak for better performance with a non bad stock PSU! The key issue is to measure the hum with a needle in teh groove and see if it's above the noisefloor of the vinyl (unmodulated inter track area on a good pressing or test record)

[Josey Wales]

I just checked the hum by pressing my ear to the platter, with the needle stationary on a reord and while playing and I could not hear anything so everything is alright now.
I am considering removing the power supply to an external box but currently I have a Dual 601 that needs some attention so it will have to be a future project.