Goals for a TW Theremin

"I really dont want to see something "come to market" which claims to be a "RCA Clone" design, but isnt.. As it stands now, the fet designs produced to date could probably be part of a reasonable starter theremin - but to get a true RCA "sound and feel" alike is going to take a LOT more work!"

Fred

you mean something like this

"but its got an 'RCA' switch!"

I posted a question to them:

"Can we please hear some samples - someone playing this astounding, incredible, fantastic, superior theremin ??"

Man! - I doubt that even Lev would have bragged so much.. And with that price tag, the "thereminist" should have been included - LOL ;-)

Fred.

"And with that price tag, the "thereminist" should have been included - LOL ;-)"

NO Thanks!   -   there is an especially disconcerting "spectral" quality to the model in the photos that just completely creeps me out.  

talk about being 'pulled from the aether'!

I gotta say, I love this ad!  No matter how may times i see it, it is  ALWAYS hilarious w/  countless things to mock.... ( and so disrespecting towards anyone's sense of decency that I dont feel bad about tearing in...)

HA!....Just take a look at that sad, mis-shaped volume... um?... attenuator.  (cant really call it a loop, can we?)

"NO Thanks!   -   there is an especially disconcerting "spectral" quality to the model in the photos that just completely creeps me out. " - Chobbs 

Awww - Cmon.. Anyone who buys a PAIA Theremax for that kind of money, deserves to be creeped out ..

But yes, I agree with you, she does look, well, not "spectral" IMO, but bored and stoned, and like she has just been subjected to the blood-draining expierience of having to listen to a Theremax..

The advertisement:

http://www.ebay.com/itm/ULTIMATE-THEREMIN-Analog-Synthesizer-Synth-Controller-Theramin-/221132959353?ssPageName=ADME:X:RTQ:US:1123

My question:

"Can we please hear some samples - someone playing this astounding, incredible, fantastic, superior theremin ??"

The Reply:

Sorry, that isn't currently possible. There are many recordings of classic RCA Thermins, and more contemporary solid-state designs. The timbral subtlties do not lend themselves to computer speakers usually. The refinements in control, range, intonation, stability, etc. are available to learn more about from PAIA website and literature. Every suggested refinement has been made, and then some. Hopethat helps. Cheers!

Price on Ebay (Buy it now) LOL ;-) = US $1,495.85

OoooOoOOO.. lemme jump on this and buy it!!!! :P I have an extra $1,500 laying around doing nothing!

"Sorry, that isn't currently possible."

OMG, that is too funny!

"There are many recordings of classic RCA Thermins, and more contemporary solid-state designs"

IOW, go jump in a lake.

"The timbral subtlties do not lend themselves to computer speakers usually."

What if I listen via headphones?

"The refinements in control, range, intonation, stability, etc. are available to learn more about from PAIA website and literature. Every suggested refinement has been made, and then some."

It's been refined to the point where no one on the face of the planet is refined enough to play it. 

Reminds me of that special guitar in Nigel's collection that's "still got the tagger on it" (This is Spinal Tap) - you can't touch it, you shouldn't even look at it for too long.

http://www.moviewavs.com/php/sounds/?id=bst&media=MP3S&type=Movies&movie=This_Is_Spinal_Tap&quote=donttouchit.txt&file=donttouchit.mp3

How about absolutely inundating them with enquiries and requests to hear this "RCA clone +" ? Ask for a sample with the RCA switch closed (or open - whatever) - Ask what their returns policy is if it doesnt sound like an RCA, or if its unplayable.. 

After all, we need to know, dont we! If their claims are true, TW should be applauding this theremin.. an RCA for $1500 aint bad.

However - this is really off topic, on a really (IMO) important thread, so I will say no more about this astounding theremin here.. I personally dont think that any of the claims could possibly have any truth in them, as at its heart this is a Theremax!

Fred.

"It's been refined to the point where no one on the face of the planet is refined enough to play it. " - Dewster

LOL ;-)

Some things can be "refined" - some, however, cannot be refined without being completely redesigned - a polished turd will never be anything other than a turd.

"but its got an 'RCA' switch!"  - Chobbs

Ha ha!  That magic RCA switch is just so stupid on so many levels. 

And for that price I'd expect at the very least a new silk screened panel with a nice clean layout, not a bunch of drilled out, hacked up, crammed in extra controls.

Ok - ;-)

Lets get back to the TW theremin..

My examination of the RCA front-end, and the fact that Chobbs has built an oscillator based (I believe) on the schematics presented here, proves that the simulations are functionally correct.

My further evaluations of the Lev oscillator in combination with the Lev (RCA) antenna equalizing circuit, leads me to believe that these (oscillator and antenna) circuits are an ideal basis for a theremin which would be easy to construct and calibrate, and which would give exceptional linearity and reliability.

I believe it is the split-inductor series configuration of this oscillator, with the antenna resonant circuit only acting across 1/2 of the total tank inductance, which makes the RCA a good theremin (linear) in terms of playability - although what I say here is not, I must add, from any personal expierience ! ;-)

There is also the added benefit that, as the antenna circuit can only act on 1/2 of the tank inductance, it is far less likely to suffer loading problems close to the antenna resonance frequency - I think the effect of this will be much greater stability at the bass end of the playing range. (Rob "w0ttm" has also, I believe, simulated the osc/antenna configuration and come to the same conclusions regarding loading)

Every benefit usually carries a price tag - The price one pays for this increased stability and linearity is (I think) that one will be limited to about 4 playable octaves.

Building a theremin using the Lev Oscillators and antenna circuit will not produce an RCA or Claramin - That goal is still being worked on.. But I believe that a modular design using the Lev "front end" as its core could be interfaced to any standard mixer circuit .. then, when a Lev / RCA "Clone" mixer (and any  other required processing)  has been developed, this could be added.

While on the subject of modularity - There is absolutely no reason why a theremin should only have one mixer.. If one has buffered oscillator outputs, you can feed these to several mixers to emulate several common theremin topologies simultaneously - You can drive a diode mixer (as per EW) and a true multiplier (AD 633 or MC1496) to emulate theremins (S/C Enkelaar and others) which use these, or any other mixer such as that used in the Melodia - and can follow these independent mixers with whatever processing circuity you choose (for example, follow a diode mixer with an LM13700 and copy the EW distortion mechanism)..

The outputs from each of these mixer 'sub circuits' could be switch selectable or combined in an audio mixer.. (the above is not hypothetical - I did exactly this with my H1 instruments, having a standard MC1496 analogue mixer as one "voice", and logic level mixed-signal heterodyning subsystem with shaping and sub-octave as a seperate "voice", all of which were combined to taste through an on-board audio mixer.)

Earlier I posted that I did not see a role for this "RCA Clone" as part of a modular system - I was wrong.. I now think that at least the front-end has a place and could be ideally suited to the TW theremin.

As I see it, the only thing which really needs to be done before this "front end" module can be put "into production" is to evaluate available inductors / transformers which can be bought off-the-shelf, and to design the module using these.. I am playing with this using a solderless breadboard at the moment :-( .. but have obtained a small choke / transformer costing <£1 and using two parallel IFTs to trim the inductances (£1 each) and can get the required individual and total inductances using these - I have other chokes on order which I believe will allow a single IFT to be fitted for fine tuning.. If this goes to plan, there would be one trimming inductor for the VFO, one for the REFO, a couple of chokes, and the antenna inductors - all easily available.

I would not use variable "trimmer" capacitors - I hate them! I  also would not have any user tuning control - I would use my screw adjustable length antenna for tuning.. I would advise that if a tuning control is required, this should be a good quality variable capacitor  (like the 5M11 part shown in the previous link) connected between the antenna and ground via a small (something like 2.2pF NPO) series capacitor (this would add 1.17pf to the antenna when set in the middle, 0.4pF at one extreme, 1.5pF at the other extreme)

.. Adding this capacitor will make the tuning control non-linear - From centre to minimum will change the capacitance by 0.7pF, wheras changing from centre to maximum will change the capacitance by 0.36pF, so the tuning capacitor should probably be set to about 1.8pF (a little more than 1/3 of its rotation from minimum) when first tuning the theremin. 

Once set for optimum linearity, the ONLY way to maintain this linearity is by changing the antenna capacitance or equalizer inductance (as in, bringing the antenna resonant frequency back to its correct value at the null point).. Adjusting either the VFO tank or REF frequency ALWAYS changes the operating point and therefore the linearity.

Fred.