[sdiy] Wallwarts and ground?

[John Blacet]

--Yes, somewhat confusing! But you've got the idea.

> 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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>
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-- 
John Blacet