Many thanks for everyone's' replies to my enquiry about sudden appearance of hum following bi-wiring my Myryad MA120 amp to my Kef Reference Series Model 2 speakers.
When I was routing the second pair of speaker cables to the amp I accidentally pulled one of the inputs to the phono preamp. The preamp jumped off the rack, hit me on the bridge of the nose and landed, belly up, on the shag pile! I replaced it on the rack and only just managed to stop the blood dripping from the end of my nose onto the pale cream carpet.
Yesterday I reverted back to single cables to the speakers, replaced the links removed earlier and switched on the amp. To my dismay the hum remained.
I pondered that the only other change that had happened was the phono preamp's excursion onto the carpet. In desperation I turned off the power supply to the phono stage and the hum disappeared.
I checked all the connections to the phono preamp, particularly the ground connection, but the hum remained when I turned on the power amp.
In view of this, I am now looking for a simple, no nonsense, phono preamp. The current one is a HiQ, supplied by Nigel at Chantry Audio when he serviced my Ariston RD11S turntable in 2004.
Sorry to be long-winded but thought this might amuse some of you. Fortunately, I can laugh about it now.
Any suggestions or recommendations about a phono preamp would be gratefully received.