Completely newbie planning to build EM theremin

From: "What to build? EM or the Etherwave?" :

>>

I wonder what theremin should i build: the EM or the Etherwave (from "Understanding, Customizing, and Hot-Rodding..." pdf), since this last one is newer.

What do you say? Do you see the Etherwave more difficult?

PS: I took the schematics from the pdf so it's easier to see.

I guess another way to ask this is: is the Etherwave better or just slightly different?

<< - -Hazel

Answering here :

Both are nearly identical..

The EW has a few differences which are probably worth doing IMO, but you would be well advised to look at all Thierry's postings about the EW as the schematics you have linked to are not exactly like modern EW's - Antenna EQ inductances for example have changed a bit.

"is the Etherwave better or just slightly different?" - I think the EW is slightly "better" - Areas you need to be particularly looking at are the inductors (both the fixed and variable ones) as you will probably be using those you can get rather than the exact ones used on the EM/EW.. Again, you need to look over all the past postings to make informed choices. The topology of both EM and EW are identical - An EM could be modified to become an EW quite easily, but it is probably simpler if you find all the pieces and incorporate the changes in your first build.

I would also advise you to replace the transistors with ones having higher current handeling and dissipation ratings - something like the ZTX650.. I cannot vouch for this particular transistor in the EM/EW application, but it is my "standard" BJT and I have used it in theremin oscillator circuits - I think the 2n3904 is far too puny to be safely used in oscillators connected to loading components such as EQ inductors and antennas.

Fred.

'I would also advise you to replace the transistors with ones having higher current handeling and dissipation ratings - something like the ZTX650.. I cannot vouch for this particular transistor in the EM/EW application, but it is my "standard" BJT and I have used it in theremin oscillator circuits - I think the 2n3904 is far too puny to be safely used in oscillators connected to loading components such as EQ inductors and antennas.'

Fred.

Fred, by 'far too puny...' I'm assuming that you mean they'd just cease to work?
Do you know if there are equivalent replacements for 2n3906 transistors and would they (the replacements for 2n304/6) be directly replaceable without the need to alter component values around the transistors?

Thanks

Roy

"Fred, by 'far too puny...' I'm assuming that you mean they'd just cease to work?" - Roy

I have not actually had a 3904 fail in an EW oscillator - But I havent built many EW oscillators, and most I have built I used beefier transistors anyway - I can see from simulations that the 3904 can get into operating close to destructive levels if the resonance peaks..

To be honest, I never observed this until Thierry mentioned that one can destroy the 3904 if one upgrades to the new EW circuit (particularly I think if one reduces the antenna inductances as the new EW's have) - I checked this with simulation and found he is right!

Any transistor having a similar specification to the 3904 but having higher IC and dissipation will do the job without any other modification AFAICS.. There is nothing particularly special about the requirements - its what is sometimes called a TUN - Transistor Universal Npn.

The MPS2222A and ZTX650 are two of many which should work - they have the same pinout as the 3904, so if you put sockets in your board you could just use 3904's and swap to something beefier later.. Re sockets.. Buy a pack of these (or similar turned pin sockets strips) - they can be used for ICs and transistors.. I usually put sockets in my prototypes - when everything is working, it is easy to solder the transistor into its socket to make the build more robust... The ability to easily remove parts makes debugging a lot easier! - even if the part is not in question, it allows one to do tests which are not possible with the part in place.

I only mentioned the above because you are new to this - you are likely to make mistakes when setting things up, and your chances of blowing things up are higher than average!

One thing the 3904 has is low input and output capacitance - but I have never found higher Cobo or Cibo figures caused a problem - capacitances at the tank circuits (oscillators) are quite high anyway -

                                 3904:       MPS2222A:        ZTX451:

Vceo                            40              40                    80

Vcbo                            60              75                    80

Ic(mA)                         200            600                 1000

PD(mW)                       625           1000(?)            1000

hfe @ 2mA                    >50           >50                  >50

fT(MHz)                        300           300                  150

Cobo(pF)                        4               8

Cibo(pF)                         8              25

I personally like the ZTX parts, I have used them for years and found them to be reliable and their specifications spot on.. Yes, they are a little more expensive, and do not, by comparison to others, always represent the best value for money.. until one factors in the cost that one sub-standard transistor can actually work out at once one calculates the time and bother it causes!

 You may find this helpful : http://www.aoc.nrao.edu/~pharden/hobby/HG_DS1.pdf

Hi!

For now what I'm doing is writing down everything I read in the forum about each component (links, properties) in my EW's part list, so I'm making sure to buy the right ones. I'm also making the schematics of each "module" in the gEDA and noting my doubts.

But I'm reading so much that i'm thinking of giving it up, this last couple threads i read are overwhelming: http://www.thereminworld.com/Forums/T/28594/antennas-antenna-coils-for-em-theremin?Page=2 and http://thereminworld.com/Forums/T/28530/antenna-tuning?Page=3

I wish it were easier! I was excited! :(

Yeah -

Dont get too worried about those two threads - not stuff you really need to fully understand just to build an EM! - Some of that is probably 1st year engineering degree stuff.

Its the more down to earth stuff you need to know.. A few quick questions you should be able to answer :: Given a resistor with a voltage across it, what power is it dissipating and what current is flowing? :: Given a capacitor charging through a resistor connected to a given voltage, and given that the voltage across the capacitor was 0V at start, calculate the time it takes for the voltage across the capacitor to get to 30% of the final voltage :: Can you explain the basic operation of a NPN transistor? :: Can you explain the basic operation of an inductor? :: Can you explain the basics of LC resonant circuits?

If you can do the above, you have IMO probably more than enough theoretical knowledge to get you going - and all you need to develop is construction related skills.

Many good engineers started with only basic understanding, perhaps less than the questions I asked.. They learned from soldering bits together and evaluating the reasons for the smoke - LOL ;-) .. Some gave up, others then went on to Uni or studied the theory some other way...

And one can be lucky! - I sure was! - I never understood anything when I bought a big tube communications reciever and fixed it at about the age of 11 - and by 12 I had started my first synthesiser without any real understanding about what I was doing.

I still think starting with something simpler would be wise - But sometimes luck seems to favour the brave!

Considerably patience can be considered as an entrance ticket for a project like this. Getting done the circuit board is a question of discipline IMHO. Other than e.g. a finished guitar effects device a theremin might work only somehow at first. Finally bringing it to life is the trick. Simply start. Or not. Or order a jaycar kit. Or..

Dominik is right, at least w/ a pedal -it'll either work or not.  Theremins are 'haunted'

However, if you are  making individual 'module' pcbs for each part of the circuit - just start with just the pitch part... Actually, start with the Power supply.   When you get that working,  make the pitch circuits -reference and variable oscillators.  If you include the 'detector' part and you can even play it thru an amp (assuming you get it working.)  When you are bored of pitch-only and you feel brave,  then tackle the volume/vca.  

Also start preparing a cabinet now.  You are gonna want  things mounted securely with no floppy wires.  Theremins are obstinate beasts on the bench.

'Dominik is right, at least w/ a pedal -it'll either work or not.  Theremins are 'haunted'

However, if you are  making individual 'module' pcbs for each part of the circuit - just start with just the pitch part... Actually, start with the Power supply.   When you get that working,  make the pitch circuits -reference and variable oscillators.  If you include the 'detector' part and you can even play it thru an amp (assuming you get it working.)  When you are bored of pitch-only and you feel brave,  then tackle the volume/vca.  

Also start preparing a cabinet now.  You are gonna want  things mounted securely with no floppy wires.  Theremins are obstinate beasts on the bench.'-Chobbs

How true is this!

No time to loose...more later...

Roy

Fred, thanks for your info and the link to info on transistors-for me the learning curve is fairly steep but I'm getting there, albeit in the knowledge that I'll never in the short term assimilate all of the electronics theory to fully understand what many of you here talk about.
It doesn’t stop me listening and asking questions though!

The ‘Theremin Circuits Scratchpad’ forum is quite a good read and I find myself ‘kind of’ following it in it’s ideas if not in the theory.

A long time ago I dabbled in electronics, the highlight being a fully operational ‘Electronics Today International’ sound-to-light unit...woo hoo...Disco wasn’t dead!
That was then and my next electronics project was many years later when I decided to make an Arthur Harrison 145 theremin: primarily this one because it was a pitch and volume theremin and also because the accompanying construction details seemed to be comprehensive.

So I made this, connected it to a battery and failed at Point 4 in the 35 point test and calibration procedure. Checked my connections, couldn’t find anything wrong, checked again...eventually e-mailed Art asking for any advice and he suggested that I check a few things. To my shame I found that I’d missed a link and from there went almost effortlessly to Test point 23, where I stayed even after some help, for some time. I have to mention that Art was really helpful with his suggestions but I kind of lost heart and also had other more pressing projects on the go.
Eventually (after mothballing the project for a few years) I had a look at it again and after checking voltages and so on found the faulty component and upon replacing it was utterly amazed that I was able to work through to the end and had a fully operational theremin.

I guess the point of me rambling is to give an outline of how things might not work out in the first instant but with perseverance will get there.
Also, for myself, I had to learn some of how the circuit worked for me to know why it wasn’t working, which is good.

As for Chobbs comment, my theremin acted very differently once it was in a box and away from the bench surrounded by wires and metal things. It's amazing how much of a different beast it became.

I’m pretty happy with the instrument and am having so much fun with it, even trying to learn how to play it properly!

The thing is that now I’m bitten and I’m gazing at the EM/EW with a view as another one, have not discounted the PAiA and even have had more than a passing thought about a valve theremin; the valve thing is probably because I like the nostalgia of the valves and also because I think that the sound will be closer to the RCA since it is valve technology, although I know that in reality the sound from a solid state will probably be just as satisfying!

OK, rant over...many apologies!

Roy

"The thing is that now I’m bitten and I’m gazing at the EM/EW with a view as another one, have not discounted the PAiA and even have had more than a passing thought about a valve theremin" - Roy

My opinion on PAiA is well known..  IMO its a pile o crap - in fact, everything PAiA ever "designed" is.

- And if I was a newbee, I would wait a little longer - The TW theremin (or a RCA clone type) will be published within the next 6 months I would guess, and already a few blocks have been built and worked - IMO this theremin will be better than the EW, and simpler. (I have gone a bit quiet on the RCA clone stuff because I am doing the physical building / testing / modifying at present - I suspect others are doing likewise )