Wine Box Theremin Build

Hi everyone, just joined here today as I have currently just begun to build the Strange Apparatus Theremin AKA The Wine Box Theremin that I found in the schematics section of this site.

I'm building this Theremin as a project for college, as I am in my final year, this project is going to be very important.

As I will be mostly building in college, I will have various equipment at my disposal, PSUs & oscilloscopes etc.

I have been in touch with Adrian Bontenbal who wrote the Wine Box Theremin report based on his modification of the Strange Apparatus Theremin & he has been a great help so far. 

So basically, I'm just here to ask if anyone has built this particular Theremin in the past & has any useful tips, pictures, sounds samples or just any general information that they think could come in handy while I'm building it.

Any help at all is appreciated, thanks in advance!

Hello Conor,

Being at the start of a theremin journey is a very exciting place, for some even magical. There are several things about this theremin you chose I would question but it should get you to that special moment of heterodyning.

If I had simple advice to offer it would be to keep the pitch and fixed oscillators far apart from one another so they talk to the detector like two little twins whispering in the back seat. A distance of 4" (10cm) or more would be nice. To often theremin designs have these two oscillators in an uncontrolled scream so you end up with an audio wave shape that is a piercing sound rather than something mellow and sweet. Shielded coils are nice but not a must, also this extra distance allows for lower coupling. Instead of a Null unlocking above 200 Hz it can be more like 30 Hz which is desired by many.

A second thought is avoiding the use of all those variable capacitors, use coils that tune. Thermal Pitch drifting is the concern here. Under 1 MHz operating freq I have never found a frequency that works best though I think higher is better, just make sure both oscillator freqs are a match. I like being above 550 kHz so I can use an AM Radio for troubleshooting, even though I have all the proper tools. When there is no sound the radio is the first tool I fire up. If the oscillators are talking then the problem is further down the chain.

I wish you fun and a whole lot of luck, as theremins have lots of attitude.

Christopher

My own theremin website is down for the week while the web servers across the planet get word that my old domain has be released and now they can re-point to my new webpage location.

Hi Christopher , thanks for the reply, I can't wait to get this thing up and running. 

I have a question about the variable caps, first of all, what is their actual purpose in the circuit, I assume because they are dealing with very small values that they are for fine tuning, but what will tuning them change?

Also, say I found the perfect setting for those caps, would it be possible to replace them with a cap of  a fixed value ?

cheers!

Now that my website is down I do not have the daily exchange of theremin chatter, so here I am realizing the theremin over the years must have become therapy for me. LOL

Because I don't speak engineer-eeze I like to use terms like "scream" for the oscillators and what not. An engineer might jump in and try to convince me oscillators do not scream. I like to use these terms to get the overconfident excited. (-'

My explanations work for me yet many things in theremin design can have a different interpretation or be improved upon except heterodyning which is the basic fundamental a theremin is designed around.

Variable capacitors were chosen in the wine box design as a means to finely tune the variable pitch and fixed oscillators as their frequency must match perfectly, shifting one osc freq away from the other by the proximity of your hand is when the audio tone will show up. Use variable inductors instead.

Pitch thermal drift experienced by some people is caused by materials that expand and contract as the environment temperature changes. The two main places are the junctions of the transistors you choose to use all the way up to the physical room heating up that the theremin is sitting in, variable capacitors aggravate this also and that is why modern theremin designs wouldn't use any. Using a wall-wart and a voltage regulator thermally isolated from the oscillator circuits is extremely important to prevent thermal drift.

On my tube/valve theremin designs I use solid state or PN junction tuning to avoid variable caps. Likewise for transistor oscillator theremin tuning you vary the voltage across the transistor junction to vary the transistors internal capacitance for tuning. Your circuit does this off the base of the transistor, a bit rough though.

I can guarantee if you used all those variable capacitors indicated your wine box theremin it will drift so bad that you will go from musical note C1 to C7 in minutes by just staring at your theremin build and it won't be because you are psychic! I learned this the hard way and respect your designer's component choices in his early theremin journey.

The theremin will teach you a lot if you are able to listen.

Christopher

"I have a question about the variable caps, first of all, what is their actual purpose in the circuit, I assume because they are dealing with very small values that they are for fine tuning, but what will tuning them change?" - Connor

Hi Connor,

First - I am an electronics engineer, so my approach will be somewhat different - probably gruffer! LOL ;-)

You say "I am in my final year, this project is going to be very important." .. Well, the question " what will tuning them change? " is, IMO, a really bad indicator.. To me, it shouts "I dont have a clue about how what I am building actually works" .. This MIGHT be somewhat ok if you ar just a hobbyist building a kit - but its NOT ok if you are an electronics student doing your final year project!

You need to understand how the theremin operates - about having two HF oscillators tuned close together so that, when mixed (heterodyned) they produce an audio beat frequency, how one of these oscillators is fixed frequency, and the other is variable - with antenna capacitance changing this frequency - so that, as this frequency changes, the heterodyne (audio) frequency changes...

Oh - thats what the variable capacitors are for - to tune the oscillators - they will change the operating frequency (resonance) of the LC circuit of the oscillators .... And Christopher is, IMO, right - far better to use tunable inductors.

Good luck - but get your nose into the theory before you start building.. You should not need to ask a question like the above!

Fred.

Hi Fred, cheers for getting involved!

I'm not strictly an electronics student, it's AV technology to be exact (but electronics is one of my many classes) & the project is another whole class in itself. 

I understand how the Theremin works (although this is my first time dealing with oscillators & specifically these Colpitt's ones) it's just that I was unsure of what tuning these capacitors (especially considering they are such a small value) would change. 

We recently covered mixers in my Digital Communications class so I understand how the mixer will give me the difference between the oscillators to produce my audible tone.

On Thursday I built & tested the variable pitch oscillator & it's oscillating roughly where I need it to (~167KHz) although I plan to replace the trimmer caps (unless you know of a reason not to) with fixed value caps. Using a 68pF cap gave me a frequency of ~169KHz but I need 172KHz so I will be buying more smaller value caps soon. 

In regards to the tuneable inductors, do you mean like these (http://tinyurl.com/q9tflr5) & would they simply be able to be put in in place of the variable caps?

Thanks for the help lads!

  Dude, I would not start out by replacing parts  (Do not  replace the variable caps/ fixed coils!)  Build the circuit as it is drawn,  get everything working , then start messing with changes to the design if you still see fit.  You will be in a world of  frustration if you go messing with stuff and  replacing parts before you are sure everything else is 100% functional.  Has anyone even built or seen one of these wine box theremins?  There is probably a good chance that this is an amateur design and like many others out there,  drawn up and posted online before the project ever even progress beyond the simulation stage.   I think that you'll have your hands full just getting this mother to work as it is drawn.  

 really I doubt there would be any noticeable difference  between using variable caps vs variable coils anyway. 

The article upon which the Wine box theremin is based can be found here - as far as I can see its an identical copy of the "Strangeapperatus" theremin except its built into a wine box rather than a large RCA style enclosure.

http://www.strangeapparatus.com/Theremin.html

To me, the unusual thing about it is the large tank inductance (1mH) vs the small tank capacitance (220pF).. to me, this looks like a poor choice for a theremin employing linearizing inductors.

But apart from that its a fairly bog standard set of circuits.

With regard to Charlies (Chobbs) comments "I would not start out by replacing parts  (Do not  replace the variable caps/ fixed coils!)  Build the circuit as it is drawn,  get everything working , then start messing with changes to the design if you still see fit.  You will be in a world of  frustration if you go messing with stuff and  replacing parts before you are sure everything else is 100% functional. " - I would generally wholeheartedly agree.. But with this circuit I think it quite likely you will have more difficulty getting it to work in the presented form than by altering it first - This is my reason:

The large inductances (1mH) give rise to a large potential for variation in inductor values (say 10% or 5% if you are extremely lucky) combine this with the large potential for variation in capacitor (220pF) values (say 5%) and it is highly likely that one will be unable to tune the two oscillators correctly using the 60pF trimmers.. Chances are you will need to tack extra capacitors onto one oscillator during calibration.. The trimmers will provide a large frequency shift, and may give enough adjustment - but this comes with a price anyway, in that the tiniest adjustment will give a large frequency shift - I suspect that tuning this theremin will be highly difficult and frustrating.

If one replaces the inductors with a 42IF106 IFT wired to give about 1mH (search here for 42IF106 - I will place a link ASAP) and remove the trimming capacitors, you have several turns of adjustment (rather than 1) on each inductor and its a lot easier (and more stable).

Fred.

>> Cannot find data on 42IF106 I posted before - but they can be bought from Mouser, and to get maximum inductance, connect pins 3+4 together and you get about 940uH across pins 1 and 6, this can be adjusted lower or to a little more than 1mH..

I cannot see any details regarding the proposed inductors in the article - this is just asking for trouble! IMO

The IFT above and some 6300 series bourns inductors is probably the easiest and safest way to have this circuit operational without a lot of hassle IMO.. You cannot just go out and buy any old 1mH and 10mH inductors, stick them into a circuit like this, and expect it to work! - Alas though, if details and warnings are not given, those who do not have expierience with RF or theremins may well not realise the critical importance of these components.

Hello all you lurkers,

There is something valuable for you in this writing. (-'

When I look at the schematic of this wine box design, it would work but could be simplified and get the same results. This is what the learning curve is all about, we all start somewhere.

My main question is why do theremin designers like to use the frequency of operation they choose? When I see all those chokes added to the pitch side in this particular theremin I wonder if they were thrown in just because they saw it somewhere else?

In my language of electronic thinking this reminds me of the old days when CB radio was popular at 27 Mhz. Someone wanted a 12" antenna on top of his car and so someone else spends a huge amount of time calculating the use of tuning coils to make this work, it never matched the response of just doing the obvious, increase the frequency of operation, but they were restricted.

In theremin design we have no restrictions on home built personal designs. Why is this theremin using 172 MHz?  Also what I have noticed is that I run my theremins 922 MHz and they have the same sensitivity as a theremin at 286 kHz, there are no extra octaves in the pitch field even though I am at triple the frequency.

I often use the term "happy theremin" and every designer knows this response by the sweetness of the sound.

There are advantages at going higher in freq, it would not be modifying this design to bring the operating frequency up to 572 kHz so it could be monitored over an AM Radio for learning. This monitoring also works for an EtherWave Standard but interestingly best at 858 kHz which is triple the fundamental frequency.

Using a "digital" AM Radio tuned to 860 kHz is an excellent method to set the L5 IFT coil to match the EWS choke network for ideal linearity. Grabbing and holding the end of the antenna still has me baffled and smiling. (-:

Christopher

"My main question is why do theremin designers like to use the frequency of operation they choose? " - Christopher

"like" has little to do with things IMO, its physics which determines suitable frequencies given the constraints - these being both physical and financial..

The "physical" constraints and "financial" constraints are closely related - yes, it would probably be possible to create a theremin running at 922MHz (although I think you meant 922kHz ;-) but there would be real problems - a short length of PCB track acts as a big inductive attenuator at this frequency, your antenna would be the size of a pencil, and the cost of mixer etc could be high... Anything above about 10MHz is silly..

The practical and financial factors probably limit practical frequency range to between 120kHz and about 3MHz - below 120kHz one starts to have severe problems filtering away sum components adequately so that they dont appear on the audio.. Above about 1MHz one starts to get into "real RF" territory .. As a general rule, the higher the frequency, the more expensive components to handle the operations become - the higher the frequency, the more care needs to be exerted over layout - capacitances and inductances of tracks become more significant, and the difficulty of manufacture and testing is increased..

So between 120kHz and 1MHz is the reasonable size of the pond..

Now we need to think about the wanted antenna dimentions , which of itself determines the shape of the field, the sensitivity, and even to an extent the linearity..

At the next stage of evaluation we get onto the antenna circuit, and the conventional (Lev invented) method of linearization and sensitivity amplification - this is an area we strongly disagree on, so I wont go into detail - except that Lev's design was IMO clever for several reasons - one of which being that it allowed the oscillator to be built with little sensitivity to capacitive change in its components, but moved the required high sensitivity to the antenna - so that the demands on the layout etc were greatly reduced.

"When I see all those chokes added to the pitch side in this particular theremin I wonder if they were thrown in just because they saw it somewhere else?"

Perhaps some "designers" do it for this reason - And this StrangeApperatus theremin may well be one of these - In my view, following the reasoning behind Lev's designs, the values for the tank L+C are ill suited to the antenna network of this theremin.. << in my past life, a few months ago, I would probably have entered this design into my simulator or even built it - I cannot be bothered anymore - so I may be wrong in my assessment >>

But for designers who understand Lev's design (Designers like Bob Moog) and implement their theremins on the principles derived from his designs (even if their understanding or implementation is imperfect) there are GOOD reasons for the operating frequencies they choose.

There are two main theremin topologies - those (like Lev's and Moog's) which use a series antenna inductance, and those (like the Jaycar S/C and yours) which dont.. I am not saying either are superior or inferior - The Tvox does not use a series antenna inductor and is a wonderful theremin..

But for those who choose the Lev (Moog) topology, lower operating frequency has some big advantages which tend to make operation in the 150kHz to 500kHz the most likely band the designer will choose.

Fred.