TOKO Inductors Needed for EM Theremin!

Posted: 10/5/2007 9:08:48 PM

From: Massachusetts

Joined: 8/18/2007

[i]Does it matter which guage wire I use for different components?[/i]

For this circuit no. For the T42-1 the 22AWG fits nicely in the side hole and the 28AWG fits nicely in the bottom hole.

[i]You told me the type of potentiometers you used for your theremin, and I think I'll go with them. However, the tolerance on those is 20%,
and the ones in the plans is 10% (the tolerance is not specified in the plans, but that's what it is on the Clarostat pots in the plans). Should the 20% work / did they work for you?[/i]

I did not have any problems with the pots on the pitch oscillator. I did not build the the volume oscillator but I would be surprised if the tolerance is a problem.

[i]I'm not quite sure what type of IC DIP socket I should get. The pitch of the LM13600 leads are 1.27 mm, but I'm not sure about any other of the specs. Do you know the serial number of the socket that you used for your LM13600? I think the 1-390261-4 may work ("with .300 center line ladder side"). Another with .600 center line is available, but I'm not sure which fits my IC- I don't even know if the pitch fits

Do not buy that type of socket. Since you only need one socket look for a socket with machined contacts. The machined contacts mate with
the pin on four sides. I did not use the LM13600 and all of my boards are SMD.

[i]What about that power supply? :)[/i]

That power supply will *NOT* work. You need an earth-ground (third prong) connection. Also I believe the etherwave transformer has a centertap. You need to look closely at the EM Theremin schematic and the power supply
transformer datasheet. Also look at the Hotrodding the Etherwave article.

[i]When you built your theremin, what did you use for the antennas/ rods?[/i]

I used an antenna from an old radio. You could use the pipes as called out in the article.

[i]Where can the knobs for the pots be purchased?[/i]

All ( * New ( * Digi ( * Mouse (

(* jcl *)
Posted: 10/5/2007 10:54:42 PM

Joined: 9/25/2007

I'm not sure what you mean about the centertap. Is all I need to do find a power supply with 3 prongs?

I don't know where or how to look for the correct type of socket...?

Do you know what the shaft size is on the potentiometers you used (296XD502B1N). The information and data sheet aren't listed on the internet.
Posted: 10/5/2007 11:06:34 PM

Joined: 9/25/2007

Could the 820A0062-03 work for a power supply? It's 850 mA, and can be found at Digikey.
Posted: 10/6/2007 9:49:44 AM

Joined: 9/25/2007

I looked at the specs of the DPA120020-P1-SZ power supply listed in the plans (it's out of stock now so that's why I'm searching for a subsitute), and it is just a two prong wall adapter. Shouldn't I be able to use a similar 2 prong adapter (like the Xicon one I mentioned earlier)?
Posted: 10/6/2007 10:38:04 AM

From: Massachusetts

Joined: 8/18/2007

I looked at the specs of the DPA120020-P1-SZ power supply listed in the plans (it's out of stock now so that's why I'm searching for a subsitute), and it is just a two prong wall adapter. Shouldn't I be able to use a similar 2 prong adapter (like the Xicon one I mentioned earlier)? [/i]

The EM Theremin works a lot better when the power
supply ground is tied to earth ground. Check the
Hod Rodding the Etherwave article. Also if you
look at the schematic in the article you will
see that the power supply output connector has
five pins (two pins are not used). On the connector there is an AC pin, a neutral pin
and an earth ground pin.

If you leave off the earth ground connection
the change in hand capacitance is much lower and
you will not get the pitch or volume range.

There is a discrepancy between the Hot Rodding
article and the EM article on the this issue.

(* jcl *)

Posted: 11/3/2007 1:10:56 PM

Joined: 9/25/2007

Hi again...

I've been really busy lately so I haven't been able to do much about my theremin. However, I did stop by RadioShack and looked for a power supply. They brought out an AC transformer (I think it was a transformer). To use it, I'd need to attach a wall plug to it and then buy a connector for the panel on the theremin. This is because it's simply a transformer with wires coming out of it. The guy at RadioShack said that he thought I was rectifying the voltage to change from AC to DC, but aren't I using the linear voltage regulators, not rectifiers? He said that if I was rectifying it, I'd need to get an input voltage of about 24 VAC to get the 12DC output. RadioShack offers a 24VAC and a 12VAC tranformer of this kind. What is the correct voltage for me? (I don't think the voltage is being cut in half by the linear regulators).


Posted: 11/3/2007 1:29:15 PM

From: Massachusetts

Joined: 8/18/2007

You need rectification and regulation.

You need to rectify the AC voltage which gives
you an unregulated DC voltage. It is unregulated
because the voltage changes with the amount
of current you draw. You need the linear regulators to provide a voltage that is stable
as you draw current.

You are correct that you shouldn't need 24VAC
to get 12VDC. Dropping that much voltage
across the linear regulator wastes power and
produces heat in the linear regulator.

That National Semiconductor article I referenced
in one of the prior posts should have the
details you require to calculate peak voltages
and capacitance requirements for your power

(* jcl *)
Posted: 11/3/2007 1:56:58 PM

Joined: 9/25/2007

The plans of the EM Theremin don't refer to any rectifiers. There is simply 12VAC input to the linear regulators. Do the regulators change from AC to DC as well as regulate the current?
Posted: 11/3/2007 2:07:55 PM

Joined: 9/25/2007

It looks like the 1N4001 power diodes might rectify the current. When I searched for these parts at digikey, a rectifier and a diode came up. Do I need the diode or the rectifier?

Doesn't rectification cut the voltage in half when switching from AC to DC?

What component in the circuit actually switches from AC to DC? Is it the diodes or the regulator ICs?

The plans call for a 12VAC power supply, so if I get the 12VAC transformer at RadioShack and follow the schematic shouldn't I have the correct values in my power supply part of the circuit, or do I need to do more than just follow the schematic?

Posted: 11/3/2007 2:13:48 PM

From: Massachusetts

Joined: 8/18/2007

Am I going to have to give you a homework assigment on rectification??? ;-)

I am looking at the Hot Rodding the Etherwave
schematic (which I believe is the same as the
EM Theremin schematic). D2, C19, D3, C20 perform
the rectification. U1 and U2 perform the

(* jcl *)

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