🚀 go-pugleaf

   From: francis@cs.adelaide.edu.au (Francis Vaughan)
   Date: 18 Nov 1992 03:25:51 GMT
   Organization: Adelaide Univerity, Computer Science

   Another alternative is possible.  Rather than use passive
   attenuation to set the output level, why not run the signals
   to the power amp at the line levels of the rest of the
   system and then vary the gain of the amplifier?  This
   presupposes an amplifier designed using a fairly normal
   feedback system.  

Here are my thoughts:

  1. With typical feedback amp designs, just getting the amp stable at any
*single* gain (over the usual assortment of load impedances) is difficult
enough as things currently stand.  Having the amp stable over a wide range
of closed loop gains would compromise the design a lot.  

  2. To get the volume down to zero you'd be forced to run the amp in an
inverting configutation (non-inverting gain can't go below 1.0).  Not a
biggee.  In fact preamp-level volume controls have been proposed
implemented with the input and feedback resistors within the pot just to
take advantage of the lower noise and cool attenuation curve.  (And the
popular Baxendall tone controls certainly work this way too.)

  3. There isn't a heck of a lot of noise contribution after the volume
control. 

  4. A well implemented low-volume switch solves the problem in a better
way by bypassing the recovery stage after the volume pot.  (Ie., it's
better to eliminate a stage than to apply lots of feedback to it.)

  -- Don