[AMRadio] Valiant modulation eedback

Rick Brashear rickbras at airmail.net
Fri Mar 17 16:56:15 EST 2006

Thanks John.  I hadn't thought of isolating the xfmr from the chassis.  
I do that with near fields in the studio all the time to get a flatter 
response.  You may be on to something big here, thanks!


John Lawson wrote:

> 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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