Equivalencies for Pop. Electronics Theremin

Fred wrote:

I have one question.. I do not understand what motivates people to select, out of the dozens of Theremin designs freely available, this particular Theremin (or, for that matter, the Glasgow Theremin).. It really puzzles me!

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I don't know about theremin builders but I suspect that like many aspiring players, they are frequently guided in their decisions by cost and by the apparent simplicity of design. They have little or no experience with the instrument and do not understand how vastly different the behavior is of the various available models.

The principle of the theremin is simple, and its EM interface is invisible, so people tend to think all theremins respond in more or less the same way. The subtleties of linearity and configuration are known only to relatively experienced theremin aficionados, and newcomers to the instrument often ignore the advice given to them and are guided instead by their pocketbooks (and sometimes by the mistaken belief that they already know).

If pianos had keyboards with linearity that resembled the configurations of some theremins, every note would be spaced differently from its neighbor. Could you imagine a keyboard where the bass notes were four inches wide, and the treble a quarter of an inch? Anyone could see at a glance that such a keyboard is not playable.

The theremin is invisible, and so are its pitfalls.

With the theremin, everyone is an expert. I have seen people give lessons in how to play when their instrument is barely out of the box it came in! This doesn't happen with traditional instruments but it is surprisingly common with the theremin.

Fred, could it be that the same false sense of understanding applies to the technical and design side of the wonderful world of the theremin?

[i]"Fred, could it be that the same false sense of understanding applies to the technical and design side of the wonderful world of the theremin?" - Coalport [/i]

From my personal expierience, it can.. I was fooled into believing (or fooled myself) that the Theremin was something which could easily be improved and was technically extremely simple... Yes, there is a lot more going on WRT Theremins than one first sees.. Also, the more I think I know, the more I am forced to realize that I dont know..

My puzzle is more about why people choose something like the 1967 PE design over a 2000+ design from Silicon Chip or similar.. I can understand that people may not know anything about linearity etc.. But suspect that most hobbyists know that older designs = more difficulty getting parts / support etc. The S/C designs are about equal to the PE in terms of linearity - but one can buy all the components, or a complete kit with PCB (http://www.jaycar.com.au/productView.asp?ID=KC5295)for < $60.. This is a 2 antenna "Theremin".

I suppose what is really needed is some easily accessible comparison table on DIY Theremins.. I cannot "blame" anyone for choosing the "wrong" kit if data is not available..

But, I think that people only really have themselves to blame if they make the "wrong" choice - An on-line search for their chosen Theremin, and a few HOURS of study of returned hits would show what problems others have had.. But then, mistakes are not always bad.. One learns more from them than from getting things 'right' first time!

The reason given [i]"this was the simplest two-antenna theremin I could find"[/i] highlights, I feel, the problem with assessing difficulty of Theremin projects.. It IS difficult to compare designs (even ignoring the musical aspects).. A design using a few transistors may seem simpler than one using transistors, op-amps and multiplier IC.. But, in fact, it often turns out that the more 'complex' design is easier to construct and get working than a 'simpler' design.

Fred.

Being half way through my first electronics project (yes, I finally cracked; I'm making an Art Harrison Cacophonator (http://electro-music.com/forum/viewtopic.php?highlight=cacophonator&t=40593)) I can see the appeal of a low component count. :-)

(It probably isn't helping that I made a few beginner errors; low power resistors come in batches of 100, so I went for the big ones that are sold individually. Consequently my little bit of stripboard looks like a scale model of Manhattan! This means that the little ABS box I bought is now just a bit too small, so the battery and one particularly large capacitor are now in a separate box (an Altoids tin) attached to the bottom.

I also now have a few specialist tools on my shopping list, such as a wire stripper - an hour and a half of preparing 24 wires to attach to off-board components with a Stanley knife convinced me of that.)

Welcome to the world of electronic construction Gordon!

[i]"Being half way through my first electronics project (yes, I finally cracked; I'm making an Art Harrison Cacophonator) I can see the appeal of a low component count. :-)"[/i]

And for making the first mistake! ;-) It is not the component count which soley determines a projects complexity.. The Cacophonator is much more complex than its component count would indicate, because it has so many "off board" components.. My rule-of-thumb is that every off-board component is equal to 6 on-board components, because one must place connection points on the board, cut/strip wires, fit connectors, and wire the off-board component correctly.. 6 is really too low a weighting!

[i]"(It probably isn't helping that I made a few beginner errors; low power resistors come in batches of 100, so I went for the big ones that are sold individually."[/i]

Maplin does small resistors as one-off, RS and Farnell sell them in multiples of 10.. I always have at least 100 of every value - if you ever have a small kit of resistors you require just email me the list and I will post them to you.

[i]"I also now have a few specialist tools on my shopping list, such as a wire stripper - an hour and a half of preparing 24 wires to attach to off-board components with a Stanley knife convinced me of that.)"[/i]

Hmm.. When I started (at about 12) a wire stripper seemed a needless expense - My teeth worked as a perfect wire stripper... looking back at how much I have paid in dental work, I recon a wire stripper would have been a lot cheaper and less painful!

Have fun with your new noise maker!

Fred.

I am having fun with it!

It worked first time, which is satisfying, although I suspect I'd have learned more about how it works if I'd had some debugging to do. It was a bit like painting-by-numbers. Still, at least I have learned how to solder so now I can repair cables and suchlike - which is cheaper and easier than replacing them. So that's good.

I've also learned a few tips about construction - like choosing the enclosure [i]after[/i] building the circuit when you can see how large it really is. Although I am pleased with the compactness of my finished cacophonator, and I think the Altoids tin pedestal that the main black ABS box sits on gives it a distinctive look as well as easy access to the battery. I certainly don't want to open the main box too often - my choice of using long wires to connect the off-board components and then cramming them all in to a too-small box at the end made for ease of construction but gives the finished product some similarities to a Jack-in-the-box. (Considering the sort of music it makes, the French name, [i]diable en boîte[/i], is probably more appropriate.)

That's a very considerate offer, Fred, but if I'm going to make more circuits I think it would be more useful to have a decent stock of basic components to hand. Do you know of a "starter kit" that I could put on my Christmas list?

Well done, Gordon..
Getting a working, bug free first project is worthy of congratulations.. Dont worry about missing out on the debug learning - you will get the chance to do this in future.. of that I have NO doubt! ;-)

Ok - Parts I would advise getting..
I recomend Rapid Electronics (http://www.rapidonline.com/) - There are cheaper (and more expensive) Ebay sellers, but Rapid are (in my eapierience) the fastest and most reliable supplier, and the prices are good.
--------------
MR25 resistor kit 13-0270 £10.56 1000
Ceramic capacitor kit 13-0206 224 £7.64
Electrolytic capacitor kit 13-0220 93 £5.28
1n4148 diodes 47-3309 10p ea or £8.20 for 100 * can be got cheaper
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BC547B NPN transistors 81-0468 6p each or 74p for 25
BC557B PNP Transistors 81-0474 9p ea or £1.83 for 25
--< Good general purpose transistors

Good opamps for general use where you want inputs and outputs to cover full supply range:
LMC662CN Dual R-R Opamp 82-0394 £1.29ea

Reasonably good opamps for audio signals:
TLO72 Daul FET Opamp 82-0050 39p ea

Fantastic low-cost opamp 'workhorse' (buy 25!):
LM358D Dual Opamp 82-0258 19p ea or 25 for £3.82

Regulators are essential for most circuits .. 5V regulator allows one to drive circuit from 9V battery and keep rail voltage constant as battery discharges - also vital if using unregulated power supply:

78L05 +5V regulator 47-3612 23p ea £4.40 for 25
79L05 -5V regulator 47-3616 33p ea
78L12 +12V.. 47-3614 29p ea
79L12 -12V.. 47-3618 29p ea
LM317LZ Adjustable +Ve regulator 47-3316 29p ea

A selection of CMOS gates I could not live without:

4093 Quad Schmitt NAND 82-0420 28p ea
40106 Hex Schmitt inverter 83-0482 39p ea
4070 Quad EXOR 83-0400 30p
4013 Dual FF / D latch 83-0332 30p

And THE ONLY 555 timer IC worth buying - this one is damn good, and can run up to 2.7Mhz.. it can with the addition of one resistor make a Theremin oscillator which is far better than those made from gates.

Dont be tempted to opt for dual versions.. you are best off with singles so that each can be decoupled.

TS555CN Fast CMOS 555 timer / oscillator 82-1048 57p or 10 for £4.23


Other ICs (like analogue multipliers, PLLs etc) are expensive in small quantity - If you need these, email me - I have stocks of components I bought for abandoned projects, and if I have anything you need I could probably supply it at <50% what you could buy them for..

Fred.

oops.. last in thread -> continued here (http://www.thereminworld.com/forum.asp?F=3&T=4604&cmd=p&p=1)

Hello everyone!!!!

Im working in updating theremin circuit with a new and modern PCB !!!!

Ive re-wroten the schematic and made a new board for same circuit :

-All standard and easy to find components including transistors , diodes and coils.

-almost all components are SMD

-board is a lot smaller 1/5 of the original

-it will be a lot more cheap and simple to build and debug

I have small question on some of the components , as i found some errata for some capacitors  , also some tips on the coils and coil position.

i will post an early version of the pcb tonight

Tips on the PCB are very welcome!!!!!

Cheers !!!

 

Almost no comment from my side, but:

a) I'd never, never use SMD coils because of their elevated temperature coefficients, but hand wound coils on a plastic former with a small ferrite core for fine tuning. The inductors must be variable to allow to compensate other component's tolerances.

b) The oscillators have to be geometrically spaced to prevent electromagnetic and electrostatic coupling, and interference. Thus, building the circuit on such a small board will either not work at all or give disappointing results.

Good day Thierry :   

>>a) I'd never, never use SMD coils because of their elevated temperature coefficients, 
>>but hand wound coils on a plastic former with a small ferrite core for fine tuning. 
>>The inductors must be variable to allow to compensate other component's tolerances.

Actually i havent made the choice for inductances , i will NOT USE SMD coils , this was only to complete the shematic and will be replaced by final coil choice.

i have some questions about the coils:

• I noticed that L3 & L1 must be in 90° to the PCB , can i still use shielded coils like this toko  5PNR-T1018Z ???
• will  "SLOT TEN-5-14" from Coilcraft  work ??

>>b) The oscillators have to be geometrically spaced to prevent electromagnetic and electrostatic coupling, 
>>and interference. Thus, building the circuit on such a small board will either not work at all or give disappointing results.

I replicated the exact same design from the old Board but only smaller  , all components are placed in same positon..

Thanks for your help Thierry , and when i get the boards ready i will be happy to send one to you...

Cheers..

In that special circuit, where the parallel capacitances to the inductors are relatively high, using shielded ones should not be a problem and there will be (thanks to the shielding) no need to place them at 90° as long as the shields are properly grounded.

I'd personally prefer the bigger (10mm) Coilcraft SLOT TEN inductors. The smaller (5mm) TOKOs have forcibly to have less windings and a smaller core with a higher AL value which can also lead to temperature stability problems.