Xref: utzoo rec.audio:7506 sci.electronics:3459
Path: utzoo!attcan!uunet!kitty!larry
From: larry@kitty.UUCP (Larry Lippman)
Newsgroups: rec.audio,sci.electronics
Subject: Re: Homebrew audio equipment
Summary: Alternative power supply suggestion...
Message-ID: <2627@kitty.UUCP>
Date: 27 Jul 88 14:46:55 GMT
References: <1075@gethen.UUCP> <6315@bloom-beacon.MIT.EDU> <118@luna.UUCP> <5741@pogo.GPID.TEK.COM>
Organization: Recognition Research Corp., Clarence, NY
Lines: 39

In article <5741@pogo.GPID.TEK.COM>, darrellm@pogo.GPID.TEK.COM (Darrell McGinnis) writes:
> 
> 	I've got one comment on power-amps when rolling-your-own.
> 	In the power supply, the bigger the caps you use the better
> 	the ripple filtering (60Hz stuff) BUT ALSO the bigger the
> 	current surge through your rectifying diodes.

	While I have not as yet tried this myself, I have a suggestion as
to a power supply method which will totally eliminate any possibility
of AC power line hum - use batteries!  The problem of having large
filter capacitors, inductors, etc. is also eliminated.

	Now, before you laugh, consider a reasonable method to implement
the use of batteries: use two banks of gel cells, with one bank being
charged while the other bank is in use.  Consider, for example, an
amplifier rated at 100 watts RMS requiring + and - 24 volt supplies.
Conservatively speaking, 8 amperes per supply should be more than
sufficient to assure full output power.  Gel cells are readily available
in 30 ampere-hour size, which should provide at least 4 hours of
operation at full output power.  More realistically, a 30 ampere-hour
gel cell for such a 100 watt amplifier should last much closer to
8 hours of normal listening since one is hardly going to deliver a
continuous 100 watts RMS.

	I would use a manual switch to change each bank of batteries
from charger to amplifier.  In fact, the charger should be capable
of charging both banks of batteries simultaneously, say during the
night, in order to increase listening time.  I would also use a
voltage comparator/alarm circuit to warn of low battery condition,
so as not to run the risk of inadvertently listening to distorted
sound resulting from abnormal supply voltage.

	The above methodology, can, of course, be applied to preamplifiers
and other audio components.

<>  Larry Lippman @ Recognition Research Corp., Clarence, New York
<>  UUCP:  {allegra|ames|boulder|decvax|rutgers|watmath}!sunybcs!kitty!larry
<>  VOICE: 716/688-1231          {att|hplabs|mtune|utzoo|uunet}!/
<>  FAX:   716/741-9635 {G1,G2,G3 modes}   "Have you hugged your cat today?"