Feedback Exterminator

[Mike Curtis <wd6ehr@xxxxxxxxxx>]

I've been using the Sabine FBX-901 Feedback Exterminator for about a week,
and it's absolutely incredible.  I used to get feedback like crazy.  Now,
maybe 4 times a night, I'll hear a little whimper - then it disappears! 

Using it is simple.  Connect it into your system like an EQ.  Put it in
BYPASS.  Adjust your stuff as you usually would, but don't compensate for
feedback.  Switch the FBX-901 in line, hold the RESET button 4 seconds (to
clean out last nights settings - it remembers these when powered down!)
and raise your master level until you hear a slight feedback.  After maybe
a second, the first LED will light and the feedback will disappear.  Do
this five more times, and you've filled the 6 "fixed" filters.  Back the
master volume off a little so it's not on the verge of feeding back and
you're all set! 

There are three more "dynamic" filters that look for stray feedback during
performances.  These can be changed to any ratio of fixed-dynamic.  I 
find the factory-stock 6/3 works just fine.

I first tried the FBX on my harp amp (a 6 watt all-tube Fender Champ),
which I mic into the PA.  It worked pretty well, but I would still have
problems with the PA feeding back.  When I put it on the PA, it fixed
everything.  On a PA, the FBX-901 needs to go between the preamp (which
mixes all mics into a single line) and the power amp.  This is the same
place you would put a graphic EQ. 

If you play through a big enough harp amp where you don't need to mic it
into the PA, you can use the FBX between the harp microphone and amp.  The
FBX-901 is designed for line level signals, and harp mics aren't nearly
that hot.  However, I didn't notice a noise increase (I roll off treble on
my harp.)

They list for around $650, but Guitar Center and all other local music 
shops have them for $380.  Not cheap, but if you have feedback problems, 
this unit will go a long way toward minimizing them.

The FBX-901 uses DSP to form 9 VERY narrowband notch filters.  These lock 
onto feedback and lower its level.  Because the filters are so narrow, 
they have no effect on the sound, other than to eliminate ringing caused 
by a system on the verge of feeding back.  I was concerned that it would 
interfere with my harmonica sound, but this has not happened.

Will this eliminate feedback under all circumstances?  No.  If you keep
cranking the amp until you "fill up" all 9 filters, then crank it more,
you can make it feed back.  What it WILL do is reduce feedback and allow
you to run higheer volume and more distortion before feeding back. 

I'm extremely happy with the FBX-901.  They also make an FBX-1801, a 
stereo version.  I _think_ it may have a couple of extra features.  This 
unit would be nice for PAs with a separate monitor system, or where you 
use a stereo board to supply mains and monitors separately.


 -- mike