[sdiy] Power supply for Big Briar Etherwave Theremin

[3]

If you call or email Moog support they will sell you the correct supply. 

> On Jul 6, 2022, at 10:06 AM, Roman Sowa <modular at go2.pl> wrote:
> 
> "Why didn't they just" is a question that pops up in my mind everytime I see any kind of equipment.
> 
> Roman
> 
> W dniu 2022-07-06 o 15:47, rburnett at richieburnett.co.uk pisze:
>> As that document says, the Theremin requires a proper AC ground for the RF return currents so that it is able to react to the capacitance of hands around its antennas correctly.  For this reason the AC power adapter has one of its output lines connected to mains earth (ground.)
>> The document goes on to say that if the Theremin is also grounded via an audio amplifier/mixer/whatever then you might get a low-frequency ground-loop and experience some unwanted mains hum (>.<)  Which begs the question... "Why didn't they just AC ground the Theremin via a reasonable sized capacitor?"   A suitably chosen value would be insignificant in series with typical antenna capacitances (pico-Farads) and yet still present a sufficiently high reactance to limit the flow of low-frequency 50/60Hz hum currents.
>> -Richie,
>>> On 2022-07-06 14:14, Peter Pearson via Synth-diy wrote:
>>> 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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>>>>> 
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