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

Showing 3 responses by sarcher30

There is no music playing and you get feedback? Do you live next to a busy street or some other source of vibration? You could just move the TT temporarily to a different location and see if the problem goes away.

Is it low frequency feedback? You could also try a rumble filter.
One possible explanation for why it is occurring mostly with MC's and not MM's is most MM's are high compliance and most MC's are low compliance.
I agree with Onhwy61. TT's in corners is a no-no. In that room I would buy an isolation rack or two and locate them between the speakers. In the same plane as the speakers. Then put both TT's and your front end gear on them. If you get them short enough they won't block the TV. If you had room I would locate the whole front end of the system to the side wall but it does not look practical in your case.

Sorry to hear about you preamp. Halcro is no longer in business that I am aware of. Hopefully you can find someone that can repair it.