[sdiy] Power supply for Big Briar Etherwave Theremin

Sat Jul 2 00:27:31 CEST 2022

Hi Didier.  Yes, you want a center-tap on your power adapter.  The original
adapter most likely had a ground pin for a reason, no?  I sent you an ebay
link yesterday.  Did you take a look at that?  Since your power supply is
regulated you can probably use a more readily available 16 or 18VAC supply
found second-hand for pretty cheap.  Shouldn't be a big deal.

On Fri, Jul 1, 2022 at 1:38 AM Didier Leplae via Synth-diy <
synth-diy at synth-diy.org> wrote:

> Actually, I think the fact the Jameco supply is two prong might be a
> problem. In the manual on fdiskc there is mention of the importance of
> grounding.
>
> > On Jul 1, 2022, at 12:28 AM, Didier Leplae <didierleplae at yahoo.com>
> wrote:
> >
> > Yes, I am in the US, so mains voltage is 110-120. That Jameco supply
> might just be the answer!
> >
> > Also, yes, the power does go through some diodes and then smoothing
> capacitors before the voltage regulators.
> >
> >> On Jun 30, 2022, at 11:35 PM, brianw <brianw at audiobanshee.com> wrote:
> >>
> >> Great sleuthing. I assume there is a rectifier bridge and smoothing
> capacitors ahead of those voltage regulators. Just look at the voltage
> ratings on the capacitors, diodes, and check the specific model number of
> the regulators for their rated input voltage - both Absolute Maximum, and
> nominal recommended operating voltages.
> >>
> >> Also check how much will be dissipated by the regulators between AC
> input and DC output. The standard regulators like to see about 3 V, not too
> far below that (unless it's an LDO voltage regulator), and not too much
> more than that (or else the wattage rating of the regulator might be
> exceeded). The math may not be fun, but it should be straightforward to
> figure out (with full data sheets on the limits).
> >>
> >> If you find an AC output that doesn't exceed the ratings, then it
> should be fine.
> >>
> >> Brian Willoughby
> >>
> >>
> >>>> On Jun 30, 2022, at 1:23 PM, Didier Leplae via Synth-diy <
> synth-diy at synth-diy.org> wrote:
> >>> So, now I've opened up the theremin and it does indeed seem that pins
> 2&3 are connected to ground as indicated in the schematic from Fdiskc.
> >>>
> >>> The 14VAC is being converted to +12VDC and -12VDC with voltage
> regulators 78L12 & 79L12. So, I'd imagine going a little higher, to a 15VAC
> power supply wouldn't hurt anything.
> >>>> On Thursday, June 30, 2022, 2:25:14 PM CDT, Peter Pearson via
> Synth-diy <synth-diy at synth-diy.org> wrote:
> >>>
> >>>
> >>> Those are all DC supplies from the looks of it.  They're also barrel
> plug without a center tap.  You'll want a center tap.
> >>>
> >>> And yes, you're basically looking at a transformer that plugs in the
> wall on one end and has a cable going to your synth on the other.  If
> you've ever cracked one open, you'll see that that's what's inside the box
> part.
> >>>
> >>> https://www.youtube.com/watch?v=ue1-lnHVkpQ&ab_channel=FRY524
> >>>
> >>>> On Thu, Jun 30, 2022 at 3:11 PM brianw <brianw at audiobanshee.com>
> wrote:
> >>> Yes, they're still making them. Look for Triad Magnetics on Mouser.com
> >>>
> >>>
> https://www.mouser.com/c/power/power-supplies/plug-in-ac-adapters/wall-mount-ac-adapters/?m=Triad%20Magnetics&number%20of%20outputs=1%20Output&output%20voltage-channel%201=13.5%20V~~15%20V&instock=y&rp=power%2Fpower-supplies%2Fplug-in-ac-adapters%2Fwall-mount-ac-adapters%7C~Output%20Voltage-Channel%201
> >>>
> >>> I recently designed a phono (turntable) preamp, and I wanted to have a
> bipolar supply while avoiding 120 VAC. The AC output Triad Magnetics
> products work well. They have a wide variety of output voltages, and I
> bought an assortment to use with power supply design variations.
> >>>
> >>> They don't seem to have 14 VAC exactly ... only 13.5 VAC and 15 VAC.
> You'd have to look at the specific components in the Theremin to see
> whether either would be compatible (e.g. maximum voltage ratings, potential
> consequences of under-voltage, etc.).
> >>>
> >>> Brian Willoughby
> >>>
> >>>
> >>>>> On Jun 30, 2022, at 11:58 AM, Tom Wiltshire <tom at electricdruid.net>
> wrote:
> >>>>
> >>>> +1 agree. An "AC supply" in this case is called a "transformer",
> surely?
> >>>>
> >>>> I know they're a bit out of fashion, but I *think* they're still
> making them, so it can't be that hard to find one that'll get you from your
> local mains voltage to 14VAC. 200mA is basically nothing, so that's not
> going to be the hard bit. It looks like it needs a centre-tapped output,
> but those are common too, so it isn't difficult.
> >>>>
> >>>> HTH,
> >>>> Tom
> >>>>
> >>>>> On 30 Jun 2022, at 18:56, brianw <brianw at audiobanshee.com> wrote:
> >>>>>
> >>>>> I may be oversimplifying, but the vast majority of AC output
> "supplies" are nothing more than a transformer.
> >>>>>
> >>>>> If you live in the 220 VAC 50 Hz part of the world, then you'll need
> a transformer rated for 200 mA that can convert 220 VAC to 14 VAC.
> >>>>>
> >>>>> If you live in the 120 VAC 60 Hz part of the world, then you'll need
> a transformer rated for 200 mA that can convert 120 VAC to 14 VAC.
> >>>>>
> >>>>> It's possible to design a power supply circuit that actually
> generates a 14 VAC sine wave at the proper frequency, with 3 W of output
> power, but I somehow find it doubtful that Big Briar did that. The Apple II
> power supply was renowned for synthesizing a 60 Hz wave, with feedback to
> increase or decrease the frequency depending upon the correct output
> voltage. This is why the Apple II made an audible chirp when the power
> switch was flipped. But that power supply was a lot larger than the
> Etherwave, and certainly more expensive.
> >>>>>
> >>>>> Brian
> >>>>>
> >>>>>
> >>>>> On Jun 30, 2022, at 10:10 AM, Didier Leplae wrote:
> >>>>>> I would imagine what’s indicated on your power supply must be
> correct. I also found another image online of a power supply and it had the
> same pinout. Perhaps the schematic has an error or perhaps there was
> another version. I should be able to open up the theremin and see if pins 2
> and 3 are both connected to ground.
> >>>>>>
> >>>>>> Now, does anyone have a suggestion for building a 14vac 200ma power
> supply? Or if I could find something with those specs I could put a 5pin
> din connector on it
> >>>>>>
> >>>>>> On Jun 30, 2022, at 11:33 AM, Ben Stuyts <ben at stuyts.nl> wrote:
> >>>>>>> Oh bummer. Let me know if you want me to actually measure it.
> >>>>>>>
> >>>>>>> Ben
> >>>>>>>
> >>>>>>> On 30 Jun 2022, at 18:00, Didier Leplae <didierleplae at yahoo.com>
> wrote:
> >>>>>>>> Interesting because the pinout shown on your power supply is
> different than indicated in the schematic in the manual on fdiskc. There
> pin 1 is connected to power and pin 2&3 are connected to ground. I wonder
> if that means there were different versions?
> >>>>>>>>
> >>>>>>>> On Jun 30, 2022, at 10:43 AM, Ben Stuyts <ben at stuyts.nl> wrote:
> >>>>>>>>> Here’s a photo of mine. Funny, the MIDI warning on the label.
> >>>>>>>>>
> >>>>>>>>> The connector on my Etherwave is a 5-pin connector, so the power
> plug can be either 3-pin or 5-pin.
> >>>>>>>>>
> >>>>>>>>> Ben
> >>>>>>>>>
> >>>>>>>>> <PSU_Etherwave.jpeg>
> >>>>>>>>>
> >>>>>>>>> On 29 Jun 2022, at 22:46, Didier Leplae via Synth-diy <
> synth-diy at synth-diy.org> wrote:
> >>>>>>>>>> I have an opportunity to buy a Big Briar Etherwave Theremin
> from a friend for cheap. The only problem is it is missing the power
> supply.
> >>>>>>>>>> Searching online, I find a lot of Moog Etherwave power supplies.
> >>>>>>>>>> Does anyone happen to know if these are compatible?
> >>>>>>>>>> The power plug on the Big Briar unit is a 5-pin midi style
> plug.
> >>>>>>>>>> Pictures of the Moog power supply look like 3 pins.
> >>>>>>>>>>
> https://www.bigcitymusic.com/products/power-supply-115v-us-for-etherwave-theremin
> >>>>>>>>>>
> >>>>>>>>>> I’m wondering if they just simply removed two pins and the
> three fit in the midi style plug.
> >>>>>>>>>> If not compatible, does anyone know where to get a hold of the
> Big Briar supply?
> >>>>>
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