Path: utzoo!attcan!uunet!mcsun!ukc!reading!cf-cm!cybaswan!eegauthe
From: eegauthe@cybaswan.UUCP (o)
Newsgroups: sci.electronics
Subject: Re: Help to eliminate pre-amp power-up click
Summary: You need a good power supply
Message-ID: <1279@cybaswan.UUCP>
Date: 24 Nov 89 14:11:09 GMT
References: <184@vlsi.waterloo.edu> <2570003@hppad.HP.COM>
Reply-To: eegauthe@cybaswan.UUCP (Olivier Gautherot)
Organization: university College of Swansea, UK
Lines: 39

Hi,

The idea I'm suggesting here is not mine: I've pinched it from a
French magazine.  Anyway the result is impressive: I hardly see
my boomers moving at power down, not at all at power up, and
that's the most noisy!.  The secret lies in the power supply: it
is L146 based (LM723 clone, with a higher maximum voltage rating
and a slightly higher reference), using the frequency
compensation to slow down the rise at power up; big capacitors
supply the energy for a slow fall (I actually use the power
supply of the amplifier for the preamp as well, so 20mF on both
the +/-32V!).  It is designed to supply up to 6 Amp continuously,
which might be luxury for only a preamp (:->).  If you don't need
much current, 2x1mF might do.  Only the slow rise bit is
presented down here:

___________________________________________
 |					  |
 |	_________________________	  | 
 |	|			|	  /
 |	|		  V. out|-------|<
 |	|	L146		|	  v
 =10mF	|		f.comp	|	  |________________+32V
 |	|_______________________|	  |		|
 |			   |		  |		|
 |			   \		  = 10uF	|
 |			    >|___/\/\/\___|		= 10mF
 |			   v	   100k			|
 |			   |				|
GND			  GND			       GND

Good luck!
	Olivier

-- 
Olivier GAUTHEROT,// Postgraduate // Electrical Engineering Dept.
University of Wales // Swansea, SA2 8PP, U.K.	(+44 792 205678 ext 4564)
UUCP  : ...!ukc!pyr.swan.ac.uk!eegauthe    JANET : eegauthe@pyr.swan.ac.uk
	"A lovely girl in a hammock is a hanging garden."	A. Allais


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