[sdiy] Wallwarts and ground?

[James R. Coplin]

What if the wallwart is already putting out +/-9v *DC* how would I hook it up?  I think it would be easier to deal with the AC as I understand how to get DC and a relative ground from that, I'm just not sure what to do if I already have a supply with +/-9v DC. 

James R. Coplin

-----Original Message-----
From: Ray Wilson [mailto:raywilson at comcast.net] 
Sent: Saturday, March 21, 2009 2:34 PM
To: James R. Coplin; 'SDIY'
Subject: Re: [sdiy] Wallwarts and ground?

Hi James

The MFOS wall wart supply board does supply a ground. The supply is relative 
to itself and supplies +V, -V and ground (which is the center potential of 
the 2 voltages). If you measure from the board's ground to either supply 
output you get the appropriate voltage. It does not supply a connection to 
"earth ground" since that is one of the benefits of using a wall wart which 
is essentially a transformer with the line side (primary) connected to the 
plug prongs and the secondary connected to the two wires that come out of 
it. The MFOS wall wart supply uses half wave rectification (which is all you 
can get from a non-center tapper secondary) to take one side of the 
secondary get + and - voltage with two diodes, while the other side of the 
secondary becomes the relative ground of the output.

The page explains the whole idea behind the design too.
http://www.musicfromouterspace.com/analogsynth/WALLWARTSUPPLY/WALLWARTSUPPLY.php

Hope this helps.

Ray Wilson


----- Original Message ----- 
From: "James R. Coplin" <james at ticalun.net>
To: "'SDIY'" <synth-diy at dropmix.xs4all.nl>
Sent: Saturday, March 21, 2009 10:24 AM
Subject: [sdiy] Wallwarts and ground?


> So, I’m helping a friend finish up his MFOS Sound Lab project and I want 
> to run it off of a 9v wall wart instead of batteries.  The power supply 
> delivers +/-9v but no dedicated ground.  I guess I never thought about it 
> as I always just use the power supply for my modular so voltage and ground 
> paths are always there.  What do I do to provide a ground with the 
> wallwart supply?
>
> James R. Coplin
>
>
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