RE: Noisy A100

["Dallas Selman" <dselman@islandnet.com>]

----------
> From: ddillon@renaissance.cray.com (David Dillon)
> To: hammond@zk3.dec.com
> Cc: john@mars.skynet.co.uk
> Subject: Re: Noisy A100
> Date: Saturday, August 03, 1996 11:41 AM
> 
> 
> > Secondly, is it possible to remove the internal speakers, do I have to
> > put a dummy load on the amp? This is for reasons of weight as I would
> > love to gig with it ....
> 
> This depends on which Leslie model you have and how it's connected to
> your A-100.
> 
> If you have a balanced-input Leslie, such as a 21/22/31/122, driven by
> the G-G terminals of your A-100 preamp, you can remove not only the
> A-100 speakers but also the A-100 main and reverb power amplifiers,
> thereby saving even more weight.  (Note that A-100 reverb is lost.)
> 
> But if you have an unbalanced-input Leslie, such as a 47/51/147/251,
> driven by your main (and possibly reverb) power amplifiers, then you'll
> need to keep at least the main and perhaps the reverb amp, removing only
> the speakers.  It is _ESSENTIAL_ that those amplifiers have proper dummy
> load resistors.  Operating an amplifier unloaded (no speaker or dummy
> load) can destroy its output transformer.
> 
> Some Leslie models have built-in dummy load resistors.  But I prefer
> dummy loads in the A-100 console, regardless of the Leslie model.  This
> is so that an accidental unplug of the Hammond-to-Leslie cable won't
> leave the A-100 running unloaded, with attendant risk of damage.
> 
> Another option for an unbalanced-input Leslie is to convert its power
> amplifier to balanced-input.  After this conversion, you can get rid of
> both A-100 power amps and speakers, as above.  Write for details.
> 
> --
> Dave Dillon
> San Jose, CA, USA
> 
> Alternatively, you can do a simple mod to the A100 preamp which involves
lifting one of the 
the centre tap ground wire from the output transformer and jumpering one
of the "G" terminal
wires over to the ground terminal. Then the A100 preamp delivers and
unbalanced signal. The A100
reverb tank and amp can be driven from the 147 amp (or similar ) by
fitting 1/4" jacks 
at the output of the Leslie amp and the input of the reverb amp with the
reverb signal emitting from the 
A100 speakers.  In my case I put a 147 amp in a 710 which has 2 stationary
6 x 9 speakers, so I ran an audio
cable to and from the A100. I could have moved the reverb amp over to the
Leslie but its a bit of a squeeze.
I might make a small box for it and mount near the Leslie, (which we now
refer to as a 747).
> 
What happens if you pull the Leslie cable out of a B3 or A100 with just
preamp unloaded?
>