TOKO Inductors Needed for EM Theremin!

Just to clarify, do I need a center-tapped power supply? Does this mean that there is a center-tap wire?

[i]I haven't been able to find any AC to AC transformers/adapters with 3 prongs where I could have access to an earth ground...they all
simply have 2 prongs for the input. [/i]

Me neither ;-) If you do find one please send me the Mfg/Mfg PN.

[i]From what I see in the diagram, the earth ground is then attached to one of the other wires. Is it the line or neutral?[/i]

*** Neutral ***. Mixing up the wires can be dangerous. You should have your teacher help
you with the power supply construction.
I would recommend that you place the power
supply in its own separate insulated box
so that dangerous AC voltage is not present
on your main circuit board.

[i]Just to clarify, do I need a center-tapped power supply? Does this mean that there is a center-tap wire?[/i]

It is not the power supply that is center-tapped it is the transformer. For the EM Theremin you do not need a center-tap transformer.


(* jcl *)

So a 3-prong is what I need?...or at least any type of transformer with a neutral, a line, and an earth ground?


I think that a 2 prong was used for the early EM theremin, but as you have said, it works better with the earth ground. This doesn't make sense that the power adapter didn't have an earth ground, because in the original EM theremin schematic, a ground is listed. Where is this coming from?


Thanks for all the feedback!

The transformer is unlikely to have an earth
ground. You need a line and neutral. The
earth ground will come from the third prong.

On the specific transformer as well as the power supply construction you should talk with your teacher. It is difficult to assist with this remotely.

The ground symbol is different from the earth
ground (or chasis ground) symbol. The ground
symbol in the EM and Hotrodding schematics are
used to define zero-volt reference points. In these circuits I believe the intent was to tie ground to earth ground. The schematic could be drawn better to show this.

I am not sure where the earth ground connection
is made in the EM Theremin. The only place I could think of is the output jack which connects
to an amplifier. I am not sure.

(* jcl *)

So if the transformer doesn't have an earth ground, and I by a plug to attach the wires to that has 3 prongs, will I need to run another wire from the third prong?

I'm going to RadioShack today and I'll take some pictures of the transformer to see what I'm dealing with.

I would recommend purchasing a connector like the Qualtek 703W-00-52 and wiring it according to
the Qualtek documentation. This will let you use
a standard removable AC cord.

Mouser sells the Qualtek part. There are other
manufacturers of similar parts.

http://www.mouser.com/search/ProductDetail.aspx?R=703W-00/52virtualkey56210000virtualkey562-703W-00/52

(* jcl *)

I went to RadioShack and got a "12.6 Volt AC, 450mA Power Transformer 120VAC input, center-tapped secondary"

I talked to one of the guys at RadioShack about the grounding. The transformer comes with 2 input wires- I believe 1 neutral, 1 line, and the output has the line, neutral, and secondary center-tap. I'd get a 3 prong plug and attach it to the input of the transformer. Since there are only two wires on the input, I'd add another wire coming from the third prong of the plug (ground) and then ground that to the case of the transformer. Would this serve as the adequate earth ground that I need?

If I need to continue the earth ground to the circuit, I could continue it from the third prong and ground it somewhere in the circuit. So that part of the theremin would be attached to earth ground. This is what I need to do, correct? As in, is this the ground that makes the theremin work better and allows for a better potential difference in capacitance? I'm slightly confused between the ground symbol on the schematic and earth ground. What I'm trying to ask is, it is in fact an earth ground that the theremin needs...?

Do you recommend having the actual transformer in or out of my theremin's box?

Also, on the schematic, there are a lot of the ground symbols, and they don't lead to anywhere specific. Where are all these grounds attached to on the circuit? Are these associated with earth ground. On the circuit, when one wire needs to be run to a different part of the circuit, they use a number and then the -< <- symbols to show they fit together. How do I know where to attach the grounds that have the ground symbol when there is no -< <- or number?

Great thread! I am also building the Etherwave clone from EM magazine.

Grounding:

An often used means of grounding a prototype is to create a grounding 'rail.' So, you just reserve one row of holes in the prototype board for grounding. Mostly, this simply keeps things more organized and reduces the chances for error. The green line at the bottom of the image linked below is my own ground rail. Just below that, I have the -12V rail. The +12 V rail is a little more hodgepodge, but you can probably surmise how that one will go together.

http://img86.imageshack.us/my.php?image=dsc5055thereminstepasp9.jpg

[URL=http://img86.imageshack.us/my.php?image=dsc5055thereminstepasp9.jpg][IMG]http://img86.imageshack.us/img86/8116/
dsc5055thereminstepasp9.th.jpg[/IMG][/URL]

hope this helps,

-Rick

Thanks for the feedback!

Rick,
I've had trouble finding the proper inductors. What have you done about that? As written in the thread, the Coilcraft SLOT-TEN inductor is a substitute for the 68uH Toko inductor and a different one that's available from Digikey substitutes the 100uH Toko. I was planning on getting the JW Miller inductors from Newark, but they are recently out of stock. How are you getting around this problem of unavailability of inductors?

Also, what do you plan on using for the power supply- just a 12VAC wall transformer? I've mentioned a RadioShack transformer in this thread, and I'm not sure if that'll work or not:

[i]"I talked to one of the guys at RadioShack about the grounding. The transformer comes with 2 input wires- I believe 1 neutral, 1 line, and the output has the line, neutral, and secondary center-tap. I'd get a 3 prong plug and attach it to the input of the transformer. Since there are only two wires on the input, I'd add another wire coming from the third prong of the plug (ground) and then ground that to the case of the transformer. Would this serve as the adequate earth ground that I need?

If I need to continue the earth ground to the circuit, I could continue it from the third prong and ground it somewhere in the circuit. So that part of the theremin would be attached to earth ground. This is what I need to do, correct? As in, is this the ground that makes the theremin work better and allows for a better potential difference in capacitance? I'm slightly confused between the ground symbol on the schematic and earth ground. What I'm trying to ask is, it is in fact an earth ground that the theremin needs...?"[/i]

Will you run an earth ground to the circuit or not? I think it's evident in the thread that I'm still quite confused about the different types of grounds and whether or not I need an earth ground, and what serves as each type of ground. I'd really appreciate any help.

Thanks,
Dan

Dan,

The inductor chase is the problem, isn't it? :)

I plan to purchase Digi-key part numbers TK2414-ND and TK2412-ND. The inductance values are not the same as the circuit calls for, so I plan order different fixed value inductors so the sum of the inductances add to 100uH or 68uH. I am working from Moog's schematic from his article on 'Hot Rodding Your Etherwave,' which is available from the Moog 'site.

If you're doing this for a grade or some such, be very wary of your supplier backordering parts -- it may be eight weeks until JW Miller finishes a batch!! I reworked a few items to make sure the parts arrived in a timely manner.

The Theremin does need an earth ground, so find a way to bring everything back to the wall plug somehow. There exist plans on the 'net for battery powered Theremins, all of them have some sort of ground you either plug in or step on. Mine certainly will take the ground straight from the third prong on the wall plug. Per the schematic, the power supply section ends in points 3, 4, and 5. Point 4 is where all the grounds in the circuit will connect. In my circuit, my ground rail ties to point 4, and everything ground goes to that rail.

I (against JCL's better guidance) am simply placing a transformer right on the board next to the power supply circuit. If my Theremin only plays a 60Hz tone, I'll let you know!

-Rick