[sdiy] Wallwarts and ground?

[Laurie Biddulph]

It is only GROUND when you call it that and/or refer it to your system 
chassis and/or an EARTH connection.
A single rail supply has a +ve terminal and a -ve terminal (current goes out 
one and in the other). When you connect one of these terminals to your 
systems COMMON, GROUND or REFERENCE rail it assumes the same identity. If 
you connect the +ve terminal to your system ground the other rail (-ve_ in 
this case becomes your systems negative rail. If you connect the -ve rail to 
your system ground then the other rail (+ve) becomes your systems positive 
rail.
For a dual supply you need 2 of these power supplies each connected with one 
of its rails to your system common.

To get proper dual rail output you need a centre-tapped AC plugpack. You 
can, however, achieve similar results with a single AC plugpack as shown on 
MFOS

Best Regards

(Mr) Laurie Biddulph
Phone: +61 (0)2 4340 0938
Mobile: 0400 257 645

Elby Designs
ABN: 70 022 727 605
http://www.elby-designs.com

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----- Original Message ----- 
From: "James R. Coplin" <james at ticalun.net>
To: "'SDIY'" <synth-diy at dropmix.xs4all.nl>
Sent: Monday, March 23, 2009 3:55 AM
Subject: RE: [sdiy] Wallwarts and ground?


>I think I understand where I'm getting confused.  A two wire 9v supply with 
>a + and - polarity is actually just delivering +9v and ground, not + and - 
>9v.  Is this correct?  If so, why do they call it negative instead of 
>ground?  Seems confusing to me...
>
> James R. Coplin
>
> -----Original Message-----
> From: Ray Wilson [mailto:raywilson at comcast.net]
> Sent: Sunday, March 22, 2009 8:39 AM
> To: James R. Coplin; 'SDIY'
> Subject: Re: [sdiy] Wallwarts and ground?
>
> If you already have +V DC and -V DC and ground (three wires coming out of
> the wallwart) you already have a bipolar power supply and you would not 
> need
> an MFOS wall wart board.
>
>
> ----- Original Message ----- 
> From: "James R. Coplin" <james at ticalun.net>
> To: "'Ray Wilson'" <raywilson at comcast.net>; "'SDIY'"
> <synth-diy at dropmix.xs4all.nl>
> Sent: Saturday, March 21, 2009 1:56 PM
> Subject: RE: [sdiy] Wallwarts and ground?
>
>
> 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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>> Synth-diy at dropmix.xs4all.nl
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>
>
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