[sdiy] Power supply for Big Briar Etherwave Theremin

[Mr&MrsAccount]

I used to have a Big Briar Theremin and often ran it on a two-wire extension cord. That obviously negates any "earth ground" on the pin. 
I never had an issue with function, so maybe there are cases where an earth ground is essential... but I didn't find one. 
  
Harry Bissell 
  
   

-----Original Message-----

From: Peter <synth-diy at synth-diy.org>
To: Roman <modular at go2.pl>
Cc: synth-diy <synth-diy at synth-diy.org>
Date: Wednesday, 6 July 2022 9:21 AM EDT
Subject: Re: [sdiy] Power supply for Big Briar Etherwave Theremin

  
I looked at Didier's pic and yes the center pin specifically says "earth ground".  I'll admit that I got out in the weeds here, however the ebay link I had sent earlier also says GND on the center pin and has the added benefit of already being a DIN plug. 
  
https://www.ebay.com/itm/303827582131?hash=item46bd88fcb3:g:9D0AAOSweuFf6gew 
  
I fail to see how this is a worse option than cutting a barrel plug AC adapter and wiring it up yourself.  
  On Wed, Jul 6, 2022 at 4:55 AM Roman Sowa <modular at go2.pl> wrote: Exactly, it must be "grounded" in a sense of "earthed", and not 
"center-tap".
If you connect center-tap transformer there, it will not be grounded, it 
will be floating. And also it will be very hot, because ground pin on 
the socket is shorthed to one of AC pins.

You need a link from earth protect prong in your AC outlet to one end of 
your supply.
It all becomes so clear when you look at power input schematics on page 4

Do what Gordon says

Roman

W dniu 2022-07-06 o 08:05, Peter Pearson via Synth-diy pisze:
> https://manuals.fdiskc.com/flat/BigBriar%20Etherwave%20Service%20Manual.pdf 
> <https://manuals.fdiskc.com/flat/BigBriar%20Etherwave%20Service%20Manual.pdf>
> 
> Read page 8 of the service manual where it says - and I'm quoting here - 
> "*WHY IS THE POWER ADAPTER GROUNDED?*"
> 
> On Tue, Jul 5, 2022 at 7:04 AM Gordonjcp <gordonjcp at gjcp.net 
> <mailto:gordonjcp at gjcp.net>> wrote:
> 
>     On Thu, Jun 30, 2022 at 02:41:07PM -0400, Peter Pearson via
>     Synth-diy wrote:
>      >
>     https://manuals.fdiskc.com/flat/BigBriar%20Etherwave%20Service%20Manual.pdf
>     <https://manuals.fdiskc.com/flat/BigBriar%20Etherwave%20Service%20Manual.pdf>
>      >
>      > The schematic is here.  A DC supply won't work.  The theremin
>     might be
>      > fussy about grounding though, so you'll definitely want a
>     center-tap on
>      > your power adapter.  I wouldn't recommend trying to cheat a
>     barrel jack AC
>      > power adapter in there.
> 
>     If you look at the power input circuit, there are only two
>     connections.  There's nowhere for a centre-tap to go.
> 
>     It's a simple transformer fed into a pair of half-wave rectifiers,
>     same as the various crappy modular PSUs that are kicking around.
> 
>     Everyone is making this waaaaaaaaaaaaaaaaaaaaaaaaaaaaaay more
>     complicated than it needs to be.
> 
>     A 15V transformer will be fine.  It doesn't need a centre tap. 
>     Anything over 200mA will be fine.
> 
>     -- 
>     Gordonjcp
> 
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