[sdiy] Wallwarts and ground?

[Scott Gravenhorst]

"James R. Coplin" <james at ticalun.net> wrote:
>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... 

Yes! correct!

It's called - because it is more negative than the other wire.

If you look at a dry cell, one side is labeled +, the other side is labeled -.  Same deal.


>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
>>
>>
>> _______________________________________________
>> Synth-diy mailing list
>> Synth-diy at dropmix.xs4all.nl
>> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
>
>
>_______________________________________________
>Synth-diy mailing list
>Synth-diy at dropmix.xs4all.nl
>http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
>

-- ScottG
________________________________________________________________________
-- Scott Gravenhorst
-- FPGA MIDI Synthesizer Information: home1.gte.net/res0658s/FPGA_synth/
-- FatMan: home1.gte.net/res0658s/fatman/
-- NonFatMan: home1.gte.net/res0658s/electronics/
-- When the going gets tough, the tough use the command line.