cafe latte wrote:Grado can hum on DD, idler and belt drive TT's as they can pick up EMF from AC motors or even from the turntables transformer if it is not well shielded. I am not convinced that the LP-120 has a shielding plate under the motor hemisphere that is connected to the platter like a Technics does so this is probably your hum. Also the mains transformer is likely to be not well shielded if at all so this will be another source of hum.
Could an amateur like me shield the AT LP120? What could be some simple and practical steps, materials?
Not easily no. EM fields are like water and are very hard to shield. I tried to shield the motor of a Lenco using a cart that hummed. I tried completely covering the hole on the metal chassis that the idler wheel of the lenco poked through after removing the idler wheel first and to my surprise I still had a hum. The em field was being deflected by the steel plate I put in (steel is a good material to shield EM) and by the steel chassis but it was leaking up and round the sides.
I dont know what causes the EM field in LP-120's but my guess is the transformer and the direct drive motor itself. The simplest way to eliminate EM problems from the transformer is to remove the transformer from the TT and put it in a box away from the TT (only attempt this if you know what you are doing though). If the DD motor is unshielded it is not so easy to fix. Remove the platter and look at the underside of the platter. You will see half of the motor attached to the platter, if the motor is shielded (I am fairly sure it isnt) behind the motor half you would have a circle of steel between the platter itself and the motor a bit larger than a record label would be. You cant just remove the motor and fit a shield unless you are confident you can get the motor EXACTLY back in its position that it is in factory. If you put it back slightly wrong you will increase the wow and flutter big time and it is already quite high on an LP-120 so unless you are confident you can get it right dont try it.
The LP-120 has more issues than just hum from a Grado, my advise is to live with the hum for now and save up for a better TT. For about what you will have paid for your lp-120 you can get a Technics sl1600mk2 which is the automatic version of the sl1200mk2 with a suspended sub chassis. You basically get a sl1200mk2 for a lot less money and you wont have any hum issues and they have far far far less wow and flutter too.