# EW/EM theremin build report

Posted: 11/10/2022 10:17:18 AM

Joined: 4/8/2020

That's incredibly useful, thank you very much. I'm a programmer myself and I have a little bit of experience building guitar pedals even following an schematic but my knowledge of circuitry is quite limited.Could you please indicate the values of those 4 capacitors and those two resistors? Also I see on the simplified schematic there are 8 capacitors while on the image there are only 4, I wish I could figure that out myself but you know I see you also used some fuse maybe? The thing the blue cable is going into.Also I live in Spain, here the wall plugs work at 220V, so I'm wondering if the same transformer will work in my case, since the stabilizers provide the 12 volts anyway and with only 10v difference the output of the transformer won't differ that much... I think?

The capacitors don't really matter that much, they just have to be big. The 4 electrolytic caps are 1000 uF rated at 35 V. The resistors are for the LEDs – use what's suitable for your LEDs or leave them out completely. You are also missing the four ceramic caps – these of course have much lower value and again the value can somewhat differ, but these are the super typical 100 nF.

The fuse is 80 mA rated for 250 V.

I'd recommend finding a transformer rated for your input voltage and the correct two output voltages. It shouldn't be too much of an issue.
If my quick math is correct, you'd be looking at 14.3 V on the output @ 220 V, and with the stabilizers being rated at 2 V of dropout voltage, you'd be riding very close to the edge.

Posted: 11/21/2022 9:45:08 PM

Joined: 11/7/2022

That's incredibly useful, thank you very much. I'm a programmer myself and I have a little bit of experience building guitar pedals even following an schematic but my knowledge of circuitry is quite limited.Could you please indicate the values of those 4 capacitors and those two resistors? Also I see on the simplified schematic there are 8 capacitors while on the image there are only 4, I wish I could figure that out myself but you know I see you also used some fuse maybe? The thing the blue cable is going into.Also I live in Spain, here the wall plugs work at 220V, so I'm wondering if the same transformer will work in my case, since the stabilizers provide the 12 volts anyway and with only 10v difference the output of the transformer won't differ that much... I think?The capacitors don't really matter that much, they just have to be big. The 4 electrolytic caps are 1000 uF rated at 35 V. The resistors are for the LEDs – use what's suitable for your LEDs or leave them out completely. You are also missing the four ceramic caps – these of course have much lower value and again the value can somewhat differ, but these are the super typical 100 nF.The fuse is 80 mA rated for 250 V.I'd recommend finding a transformer rated for your input voltage and the correct two output voltages. It shouldn't be too much of an issue.If my quick math is correct, you'd be looking at 14.3 V on the output @ 220 V, and with the stabilizers being rated at 2 V of dropout voltage, you'd be riding very close to the edge.

Thank you, that seems sorted out! Pretty much all components have been ordered but I'm having issues with the inductors. I tried getting them from Mouser but they ran out of stock of some of them, also the L11, L6 and L5 seem to be of a kind I'm not able to find, not sure if they are variable inductors or what. Do you know somewhere where I can get them? Even if it implies having them made on demand. Thanks again.

Posted: 11/22/2022 8:26:46 AM

Joined: 4/8/2020

Thank you, that seems sorted out! Pretty much all components have been ordered but I'm having issues with the inductors. I tried getting them from Mouser but they ran out of stock of some of them, also the L11, L6 and L5 seem to be of a kind I'm not able to find, not sure if they are variable inductors or what. Do you know somewhere where I can get them? Even if it implies having them made on demand. Thanks again.

Yes, they are variable inductors and it's very important that they are variable. They're what allows you to tune the instrument (not in the pitch sense of the word, but in the response sense – you set them once after your theremin is built).

I got them from a local amateur radio e-shop, but if I recall correctly, the original is from Coilcraft. I will try to find the exact original model in my notes. But in the end I ended up winding my own (got just the body and the ferrite screw from the e-shop and wound them myself – it was around 40 turns if I recall correctly, so nothing difficult).

Posted: 11/22/2022 9:02:07 AM

Joined: 4/8/2020

Thank you, that seems sorted out! Pretty much all components have been ordered but I'm having issues with the inductors. I tried getting them from Mouser but they ran out of stock of some of them, also the L11, L6 and L5 seem to be of a kind I'm not able to find, not sure if they are variable inductors or what. Do you know somewhere where I can get them? Even if it implies having them made on demand. Thanks again.

Toko 10EZ series is what is used in the Build the EM Theremin by Robert Moog in Electronic Musician February 1996, but they seem to be discontinued.

If you can get your hands on Coilcraft SLOT TEN, that's what I believe is in the original EW theremin. (https://www.coilcraft.com/en-us/products/rf/tunable-rf-inductors/vertical-mount/slot10/)

Posted: 11/22/2022 5:17:06 PM

From: 60 Miles North of San Diego, CA

Joined: 10/1/2014

EWS is a solid design. There is little difference in what frequency or inductors are used, you want a clean audio sine-wave at first to distort into the sound or timbre you want.

If I was doing this project to only use Mouser, change the oscillating frequency to 500 kHz instead of 286 kHz. Then use the 455 kHz adjustable IF transformers (ferrite shielded best) with two 10 MH chokes in the series antenna tuned circuit, I like this dual 10 MH choke.

Christopher

Posted: 11/22/2022 8:32:22 PM

Joined: 11/7/2022

Thank you, that seems sorted out! Pretty much all components have been ordered but I'm having issues with the inductors. I tried getting them from Mouser but they ran out of stock of some of them, also the L11, L6 and L5 seem to be of a kind I'm not able to find, not sure if they are variable inductors or what. Do you know somewhere where I can get them? Even if it implies having them made on demand. Thanks again.Toko 10EZ series is what is used in the Build the EM Theremin by Robert Moog in Electronic Musician February 1996, but they seem to be discontinued.If you can get your hands on Coilcraft SLOT TEN, that's what I believe is in the original EW theremin. (https://www.coilcraft.com/en-us/products/rf/tunable-rf-inductors/vertical-mount/slot10/)

I took a look on these Slot Ten inductors but their measures don't seem to match with the pcb layout you provided, which I already sent to print and have just here. The measures seem to match perfectly with the Slot Seven and I think these are the ones I'll be getting... though the shipping costs are quite expensive.
If I'm not wrong, the 7M3-437 are the ones I'll have to get, right?
https://www.coilcraft.com/en-us/products/rf/tunable-rf-inductors/vertical-mount/slot7/

Posted: 11/22/2022 8:52:39 PM

Joined: 4/8/2020

Thanks again for your help!I took a look on these Slot Ten inductors but their measures don't seem to match with the pcb layout you provided, which I already sent to print and have just here. The measures seem to match perfectly with the Slot Seven and I think these are the ones I'll be getting... though the shipping costs are quite expensive.If I'm not wrong, the 7M3-437 are the ones I'll have to get, right?https://www.coilcraft.com/en-us/products/rf/tunable-rf-inductors/vertical-mount/slot7/

You're probably right the ones I have are likely smaller. You probably mean the 7M3-473 (not 437), and yes, that would be the one.

Posted: 11/22/2022 8:56:49 PM

Joined: 4/8/2020

EWS is a solid design. There is little difference in what frequency or inductors are used, you want a clean audio sine-wave at first to distort into the sound or timbre you want.If I was doing this project to only use Mouser, change the oscillating frequency to 500 kHz instead of 286 kHz. Then use the 455 kHz adjustable IF transformers (ferrite shielded best) with two 10 MH chokes in the series antenna tuned circuit, I like this dual 10 MH choke.Christopher

That's a smart design change. The 455 kHz adjustable IF transformers seem more common. But when I was building mine, I was mortified to change anything