Differential Reverb (better subject line!)

[Don Tillman]

   From: honcho at paia.com
   Date: Tue, 11 Aug 98 22:20:07 CDT

   >>Just to know if I got this right, you take two complete reverb 
   >>*tanks*, each with 2 or 3 springs, and connect them together?

This is a very interesting and clever idea.  I'm eager to hear the
nuances of the reverb sound as you subtract the signal from the second
tank.

Does Accutronics know about this?  I could imagine a high-end reverb
tank product from those guys with four separate reverb spring sets
(for stereo!) all mounted on a common subassembly mechanically tweaked
to fit in a 1-rack high unit.

Each of the current Accutronics spring reverb tanks, the higher
quality models, contains three spring pairs.  So this monster tank
would have 12 spring pairs!  For a better stereo sound make the
springs designated for one channel a little less delay than the
springs for the other.

   Credit where it's due, this is one of Craig's. It isn't at the site 
   linked to anything but I did put up a quick and dirty schematic a 
   while ago at www.paia.com/hotsp001.jpg .

   Note in particular, though, the reversal of polarity on the send 
   transducer(s) on _one_ of the tanks and that the tanks _must_ be 
   identical.

A couple of friendly suggestions for this circuit:

Invert the receive transducers instead of the send transducers; hum
cancelling for free!

Accutronics recommends using lots of drive current; more than an opamp
could provide.  Their application note has half-a-dozen drive
circuits.

  -- Don