Xref: utzoo rec.audio:7521 sci.electronics:3468
Path: utzoo!utgpu!attcan!uunet!lll-winken!lll-tis!ames!oliveb!sun!gravity!klein
From: klein%gravity@Sun.COM (Mike Klein)
Newsgroups: rec.audio,sci.electronics
Subject: Re: Homebrew audio equipment
Message-ID: <61833@sun.uucp>
Date: 28 Jul 88 16:59:09 GMT
References: <1075@gethen.UUCP> <6315@bloom-beacon.MIT.EDU> <118@luna.UUCP> <5741@pogo.GPID.TEK.COM> <2627@kitty.UUCP>
Sender: news@sun.uucp
Reply-To: klein@sun.UUCP (Mike Klein)
Organization: Sun Microsystems, Mountain View, CA
Lines: 32

|	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...

More important than the ampere-hour rating will be, as for any power source
you are using, the output impedance.  Figure what your maximum current
drain will be at what frequencies, and see if the voltage drop on the power
rails will be acceptable to you.  If not, you are back to the original
problem with AC power supplies, which is how to reduce the output impedance
(although you do not have to worry about 120 Hz ripple).  The obvious
solution is to use capacitors as in the AC supply -- big ones to provide
lots of low-frequency current, in parallel with smaller (a few uF)
high-quality film capacitors to provide high-frequency current.

This is an interesting thought for a "transportable" power amplifier but
with simple design techniques and good grounding you can build, for about
$20-$40 if you buy at surplus stores, a very sturdy power supply for audio
purposes that will have plenty of reserve, a very small output impedance at
audio frequencies, and as good a 60 Hz isolation as you will need (the
ripple is actually 120 Hz since the negative half of the waveform is
reflected up by the bridge rectifier).  I have built a number of these, one
for a 100W single-channel subwoofer amplifier, another for a moving
coil preamp, all of my own design, and have had no trouble with any of the
above.  None of the parts required are high-tech and the cost is really
quite low.
--
Mike Klein		klein@Sun.COM
Sun Microsystems, Inc.	{ucbvax,hplabs,ihnp4,seismo}!sun!klein
Mountain View, CA