[sdiy] Blocking audio at power off

[Philippe Derenne]

Hi Justin,

You can get the AC voltage from the main transformer (assuming your device 
is AC-powered...), go through another rectifier bridge (or a simple 
rectifier diode). Then put a little capacitor (like 100 µF) between the + 
an - outputs of the bridge, and use this DC voltage to power up a little 
relay. When you shut down the power, the little capacitor is quickly 
discharged through the relay coil, before the main DC voltage disapears. The 
relay goes back to standstill state.
You use a contact of this relay to open the signal line, and maybe another 
to put the input to the ground...
I use this system to disconnect speakers from my amplifier, but with a timer 
to connect them 2-3 seconds after power-up.

Just a simple idea...

Phil.

----- Original Message ----- 
From: "Justin Owen" <juzowen at googlemail.com>
To: <synth-diy at dropmix.xs4all.nl>
Sent: Monday, September 08, 2008 3:46 PM
Subject: [sdiy] Blocking audio at power off


> Hey all,
>
> Probably hoping for too much here - but what's the absolute simplest way 
> of blocking an audio signal through a circuit when it is powered down.
>
> I'm getting signal from the audio input of a circuit going through a 
> transistor straight to the output after I've turned it 'off'.
>
> When I say simple - I mean simpler than adding another transistor set up 
> as a switch, an IC or a hardware switch...
>
> ...any such thing exist?
>
> Thanks much
>
> Justin
>
>
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