Hum with B&K MC-101 and Spectral MCR cartridge

[centaurus3200]

hi all,

just bought a new (to me) toy, a B&K MC-101 preamp. i'm getting a hum on the phono stage, no matter how i ground my turntable (Technics SL-1600MK2). it was fine (maybe a FAINT hum) with my Yamaha C-70.

Hum is a lot less with my backup ADC XLM Integra MM cartridge and flip the input selector back to phono. virtually no hum.

i don't believe the MC-101 comes with any capacitive loading from the factory. you need to install the appropriate cap if needed. but i don't think resistive or capacitive loading has anything to do with the 60hz hum i'm hearing.

for reference, i'm using a technics SL-1600MK2 turntable and a super low output and impedance MC cartridge - Spectral MCR Signature (.2mV/2ohm). i'm starting to think the B&K is just plain poorly grounded and shielded.

i did move the TT around. no difference. if i unplug the TT's RCA's from the preamp's phono jacks (but leave the input selector on phono), hum goes away. if i put on the adc integra, hum goes nearly away. so, the preamp is getting some sort of ground loop through the cartridge?

NOTE: if i use my yamaha C-70 or my friend's Onkyo P-308 preamp's MC stage - DEAD SILENT with the same turntable/cartridge setup.

i even tried the preamp on a medical grade isolated power supply. still buzzed.

for reference, the MC-101 is pretty much the same circuit as the B&K Pro-10MC and the phono10a

Regards,
Robby