Hello all - I'm new here.. was pointed to the site by Frank Van Alstine during an email thread with him about his well-known Grado Longhorn mod.
I just mounted a new Grado Prestige Gold on my Thorens TD-166 MkII table and noticed a significant hum in the background when the the volume is up past mid-point on my receiver - an old Harman/Kardon 430 (twin mono power blocks). Poking around on the web for "grado hum" I came across a lot of info about grado hum problems, all pointing to incompatibilities between Grado carts and particular turntables. I didn't find anything specific about my Thorens, but went through a lot of trouble trying to find the problem with my TT - tonearm wiring, connections, cabling, motor shielding.. the whole nine yards. Nothing I tried would change it - the hum was still there and would change as I moved the tonearm back and forth - i.e. changing it's position relative to the motor, which also jibed with lots of the info I found online.
But then I realized something that might have seemed obvious but wasn't: the hum was the same whether the platter was turning or stopped. WHAT??!!!! Hmmmm, maybe the problem *isn't* the TT. A little more thinking... and then...
Maybe it's the amp. The TT is mounted on a shelf about a foot above the HK - plenty of space, right? Uh, NO... not with the Grado. Sure enough, I lift the table up slowly and the hum gets quieter and quieter until it is about 2 ft. away from the HK and the hum is gone.
So - it ends up that the Grado is picking up radiation of some sort not from the turntable's tiny electric motor, but from the HK's large twin mono power transformers. Testing this further, I mount a crappy ancient AudioTechnical cart, and then a more recent Ortofon TP14 and neither cause hum at the TT's original position. Mount a different, older Grado Z+ cart, and the hum comes and goes exactly as it does with the new Prestige Gold. Problem solved.
I wanted to post this here because the finding made me wonder just how many folks out there dealing with the famous "Grado hum" and assuming it is an issue between their TT-motor and Grado cart when it's actually their power amp.
