Technics SP15 ground hum

[Michaeld]

Hi all, First time post.

Got a frustrating hum problem with a relatively new (to me) turntable. It consists of a Technics SP15 in a custom granite plinth. Tonearm is a vintage 12inch Grace tonearm with Shure M97XE.

I recently rewired my 12inch Grace tonearm with Cardas silk wire and spent a bit of time getting the tonearm setup just right. It was sounding really good. Can home one day to find a visitor 7 yr old son had badly twisted the tonearm and completely destroyed the stylus.

Due to the tonearm being a 60's vintage it was very difficult to find someone capable of the repair. Eventually I found a jeweller (watch/clock repair place) who managed to fix the tonearm.

I have had the tonearm repaired and reinstalled. It seems to be fine however the TT has now developed an annoying hum which comes through the speakers. It is audible during softer parts of music and is very annoying if you crank up the volume (seems to make it proportionally worse - if that makes sense).

I have tried the following to fix but can't resolve the problem:

- I've completely rewired the tonearm.
- rewired the earth cable to the SP15 (when this earth wire is disconnected the hum becomes a loud buzz)- no change.
- added an earth wire to the chassis base - no change.
- tried a new cartridge - no difference. with the cartridge off hum is louder

hum stops when the SP15 power plug is pulled out of the mains?

connected another turntable to the phone preamp - no hum at all - v quiet.

Not sure if the hum is mains hum or hum from the Technics power supply?

Any help or advice greatly appreciated

 

[Enzo]

You installed a new ground wire to the chassis? But since the tonearm was taken out and was damaged, have you since checked continuity to the earth chassis ground from the tonearm itself all the way to the head shell?

 

[Michaeld]

I believe so. I have completely rewired it. Tried various combinations of earth wire of the tone arm, chassis, sp15 has its own earth wire from under the motor. all without joy??

 

[Pano]

Moved to Analogue Source. Should get more action here.

 

[sq225917]

My money is on lack of tonearm gnd, remember the base might be grounded, but the wand needs to be as well.

 

[Michaeld]

hi all, finally found a solution.

I bought new Cardas wire and rewired the tonearm from head shell to plug under the tonearm base. Also bought new RCA phono wire and plug at the tonearm base to phono pre amp. Also changed the Technics SP15 earth wire and cleaned and reseated the earth wire connection point on the SP15 base.

Also sprayed everything with deoxit. Spent the whole weekend on this and bingo hum was gone - still had a slight fuzz in one channel. After a bit of head scratching I changed the phase from 0 to 180 on the pre amp and the buzz disappeared? I don't really even know what that phase setting does?

So to celebrate have just ordered a new cartridge (clearaudio virtuoso) yay

 

[Michaeld]

thanks for your help