Feedback blew my phono stage?


Ok....I don't know what's going on here but here's my set-up
HALCRO
On the right hand side is my 'nude' Victor TT-101 DD turntable supported on spikes surrounded by 3 three tonearms on separate solid bronze armpods.
The 3 arms are connected separately to the Halcro DM10 preamp's phonostage via 2.5 metre long balanced Cardas Golden Ref phono cables.
With MM cartridges (I have around 30).....there are no problems.
With LOMC cartridges however......if I rest the stylus on the record without the motor turned on......I can induce a low frequency feedback through the speakers if I turn up the volume sufficiently?
Nothing I did to support the turntable differently.....could eliminate this problem so I have simply been playing MM cartridges through this turntable.
Recently.....I mounted an Acutex 420STR MM cartridge on the SAEC tonearm and discovered that it produced the same feedback symptoms as the LOMCs?
In experimenting with differing support methods for the Victor.....I forgot to turn the volume down before hitting the 'mute' button to 'OFF'....and an almighty noise knocked out my phono stage and tripped the protection on the left channel Halcro monoblock.
The 'Balanced' XLR inputs for the phonostage now produce no output whilst the RCA inputs produce a feeble output in the right channel only.

Any Gurus here with some ideas for the cause of this problem would be much appreciated?
Incidentally......no such problems with the 3 tonearms on the Raven AC connected to the same preamp inputs....even with LOMCs?
128x128halcro
Atmasphere, is that true even when a feedback loop is in effect that amplifies rapidly? I've never heard this on a turntable but certainly on a microphone and on a guitar pick-up. It gets loud very fast.
I received the repaired DM10 back from Adelaide and re-inserted it in my system.
I must admit that even before testing it.....I was 90% sure that the turntable 'ground' to one of the DM58 Monoblocks was indeed the problem?
All the symptoms fitted including the 'coup de grace' when I placed the solid copper 1.8Kg Micro Seiki Cu180 'mat' under the TT-101 in direct contact with the metal base of the cage.
Without understanding electrical theory........I assume the potential voltage difference was increased enormously by this action which explains the fact that when I turned on the preamp........there was an immediate 'explosion' (even though the volume was turned down) which 'blew the chokes and capacitor?
I disconnected the 'ground' wire and placed the LOMC FR-7f cartridge and turned up the volume gradually.
Although there was a low 'hum' as the volume increased.......there was no 'feedback loop'.
I then connected the devilish 420STR, placed it on the vinyl and gradually increased the volume.
No hum and no 'feedback loop' even when the volume was at maximum!?
Problem solved.......and as so often occurs.......I was the problem!!? :-(
Dear Halcro: Good to hear you are happy again!.

regards and enjoy the music,
R.
Aigenga, Yes.

Halcro, good to hear things are up and running! Hard to be without tunes...
Pretty quick turnaround by Halcro. Do you live across the street from the factory?