Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.2 9/18/84; site watcgl.UUCP
Path: utzoo!watmath!watcgl!dmmartindale
From: dmmartindale@watcgl.UUCP (Dave Martindale)
Newsgroups: net.audio
Subject: Re: power on/off sequences
Message-ID: <1100@watcgl.UUCP>
Date: Wed, 30-Jan-85 01:19:47 EST
Article-I.D.: watcgl.1100
Posted: Wed Jan 30 01:19:47 1985
Date-Received: Wed, 30-Jan-85 07:33:07 EST
References: <362@decwrl.UUCP>
Reply-To: dmmartindale@watcgl.UUCP (Dave Martindale)
Organization: U of Waterloo, Ontario
Lines: 33

In article <362@decwrl.UUCP> lauck@bergil.DEC writes:
>
>> Example:  my
>> power down sequence is the following: 1) preamp gain to zero,  2) power
>> off the amp,  3) wait 30 seconds,  4) power off the preamp.  Without the
>> delay or the zero gain I blow speaker fuses.
>> 
>My old preamp has a capacitive coupled singled ended output circuit.  It 
>generates about 10 volts DC on turn on or turn off.  My power amp is DC 
>coupled, with 1 volt for about 100 watts into 8 ohms.  It can output over 12 
>amps.  My woofer fuse is 3 amps.  Without the delay, loud sound, blown 
>fuses (woofer at least, sometimes midrange as well).  The "thump" scares my 
>wife who fears I am fooling with the system and promply leaves the room...
>
>The 30 second delay avoids the problem.  Perhaps I should get a better 
>preamp which has crowbar circuitry or better power supply rejection.

It seems that your preamp is built with the assumption that your power
amp will have some sort of circuitry to delay connecting the speakers
to the amplifier (many amplifiers have a relay for this) until the
amplifier is stable, and that this delay will absorb the preamp's
turnon/turnoff thump.  Conversely, it seems that your amplifier is
stable enough not to generate nasty transients on its own, and it assumes
that the preamp won't either.

Unfortunately, both assumptions are false in your case - this is just an
incompatibility between the amp and preamp.  It is probably best to
live with it, as you've learned to, or replace the preamp (since that is
the component you refer to as "old").

(All of the preamps and amps I've owned (two each) used direct-coupled
outputs and bipolar power supplies, and none generated turnon transients
large enough to hurt speakers.)