Finding the optimal Schematic

Hello Theremin World,

a friend of mine, who is a musician, asked me if i could build a theremin for him. i have experience in building effect pedals for E-Guitar, circuit Bending and some small IC-based synth projects. So, the last days were quiete exciting because i did research on the net for finding a fitting schematic and discovered thousands of theremin projects. its hard for me to find out which kind of theremin seems to be the best for a musician who maybe wants to use this apparatus on a stage with nearly clear sine-tones and not those poor heavily distorted sounds i heard in some youtube videos.

I found many projects (like art harrissons schematics or the theremin world database) which do not have a volume antenna. but my ideal would be a pitch-antenna (of course...) and a volume antenna, so i found the EM-Theremin. But i read about people who cannot find certain parts (mostly the TOKO-coils) even in the US. I'm living in germany, so i lost hope finding those parts in this country, nor europe.

My questions are:

-is there a schematic for a small volume and pitch-antenna-theremin (without tubes) that could fit my "expactations"

-is there a newer or altered version of the EM with findable (and payable) parts?

-any other advice for me in this case?

thanks for helping,

Tino.

I just discovered the "Silicon Chip Theremin". The sound is good and the transformers are normal 455kHz IF. I would try to build it on my own without a kit.

I read that the year 2000 version of the SC is much better then the 2009. True?

Is there a whole parts list with a description, for example which kind of capacitors i have to use?

Hi Tino,

Others here can likely help you find a schematic to get you going.

My advice, particularly if you intend to go down the Theremin construction road for any extended period of time, would be to avoid pre-made coils and transformers.  One way to do this is to buy a standard coil former (FredM pointed to some in an earlier thread) and add wire.  This way you can get a range of values and configurations, and the ferrite material might be better specified.

Or do big diameter air coils on phenolic or PVC pipe.  Single layer air core coils are fairly easily made to order with a simple jig, have high Q, low self capacitance (i.e. high self resonant frequency), and potentially low temperature dependence.  This makes them particularly attractive for use as the EQ coil (i.e. the series "linearizing" coil that feeds the "antenna").  It is an easy matter to add taps and windings to produce auto transformers and the like.  The main down sides are that you need more wire and volume to get larger values, and you can't easily "tune" them (resonant LC circuits with air core coils have to be tuned via variable caps).

For me one of the huge payoffs in constructing your own coils and transformers is in dispelling the "magic" associated with this class of components.

[EDIT] Sorry for all the scare quotes!  And as FredM pointed out in the following post, the Bourns 6300 series are quite nicely engineered.  Good luck!

Hi Tino,

IMO, The EM is one of the most reliable of the schematics on the web - and the inductors (and other inductors which can be used) are readily available.. Lots of discussion can be found here - I have used the 42IF106 (455kHz IFT transformers which do not have fitted tuning capacitors) - pins 1 - 2 of these IFTs give an adjustment of a little more than 44uH to 110uH - I usually fit two of these IFTS, one (wired between pins 1+2) in series with a fixed inductor (of about 68uH) and one wired in parallel with the fixed inductor for fine tuning (pins 1 and 3 wired across the fixed inductor - its adjustable between about 500uH and 1.0mH) and gives about 4uH trimming meaning that a 68uH fixed inductor "becomes" an adjustable inductor covering about 60uH to 64uH.. Total 'tank' inductance  is therebye tunable between 104uH and 174uH,

 There are enough tappings on the IFT to configure most required 'tank' inductances - you can, for example, use pins 4+5 for a series adjustment of between about 15u to 28uH, bringing the adjustment range down to about 75uH to 92uH.. A simple spreadsheet allows you to select the value of the fixed inductance and the IFT configuration to suit your requirements - I have not yet found any inductance and trimming configuration I was not able to achieve with a fixed inductor and a couple of 42IF106 IFTs - quite often only a single 42IF106 with either serial or parallel fixed inductor is enough.

As for the antenna inductors, the easiest IMO are the Bourns 6300 series.. and these are quite good - probably not as good as a well wound air coil though.

Thierry, on the thread linked above, gave details of available 'standard' tuning inductors which can be used - or if you can wait a couple of weeks, I have hundreds of tunable inductors I will be sorting (I am moving at the moment so cannot get to them) that I plan to package up and ebay over the next few months - drop me an email and I will send you details in a few weeks.

Fred.

Thanks everyone for helping.

I decided to go with the EM-Theremin. Of course i couldn't find the original TOKO coils, but i ordered some variable coils with almost the same values from a small german radio-seller. (here)
 For the Antenna Coils i use the Bourns 6300 series (Thx Fred.)

I finished it but the whole thing is not working. For troubleshooting (for which i need help) i opened a new thread.

Tino.