[AMRadio] Valiant modulation eedback


John Lawson jpl15 at panix.com
Fri Mar 17 16:46:24 EST 2006


Re: the discussion of acoustic/mechanical modulator feedback - my Valiant 
'talks' - and loudly - when I'm hitting it good.  I have a broadcast mike, 
preamp, EQ and compressor in my audio chain - all fed into the (as yet 
unmodified) Valiant input. (BTW, my buddy's Johnson 500 'talks' loud 
enough to heard in the next room - he also has to watch his mike 
placement.)

   Of course, when On The Air - the Valiant rings and howls - I have to 
move the mike, change the locations of various things - and quite likely 
put the Valiant on an acoustic absorbing pad of some kind. Lead-filled 
1/2" neoprene comes to mind - I've used that building theatres and 
recording studios - it's amazing what it sucks up.

   Another thought re: 'potted' vs. 'open frame' Mod Iron occurs to me 
(still with acoustic-designer hat on)...  isolating the offending 
transformer from the chassis might mitigate some of these feedback effects 
- maybe as easy as removing the mounting bolts and resting the device on 
hi-temp dense foam or even thick felt padding - something to break the 
close mechanical coupling between the transformer core and the chassis of 
tghe rig.   Maybe easier than re-doing the modulator, or even exiling tghe 
poor thing...

   I've done exactly this with building distro transformers of up to 100KVA 
- and in fact there are several commercially-available solutions for just 
this kind of thing...   hit the Big Breaker and half that end of the 
building goes hummmmmmmmmmmm.......  ;}


   Cheers

John  KB6SCO




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