More Design Preferences for Keppinger

Pitch preview: Do you prefer front or back? 1/4" or 1/8" jacks?

Line out: Rear
CV out: Rear
XLR out: Rear

Are these okay in the back, or do they need to be in the front?

No spring reverb....

Inquiring minds want to know.

Philip Neidlinger

Pitch preview - I would think it would be best on the "players side" of the instrument. If it requires additional amplification to be useful, it would probably be best to go with the standard 1/4" instrument jack. Such units are generally geared towards guitarists. The jack would also need to be flush with the outermost surface and well clear of any obstructions (knobs, etc.).

For a performance instrument, I would think it best not to put the other inputs and outputs on the audience side of the instrument. However, for most "box" theremins, there really aren't any other easy options.

I personally wouldn't need the pitch preview, but if there will be one, it should be on the front side. 3.5mm (1/8") jack.

All other jacks and cables should be on the rear side.

My further request for a theremin which I would buy are the same as in my own design ideas:

6 to 7 continuously playable octaves (4 above middle C, 3 below) with equal spacing of 7.5cm (3") each. That means that I'd like to get ~4200Hz at 1 cm (0.4") from the pitch rod and ~32Hz at 53.5cm (21.4").

Absolutely no additional distortion in the lowest register (i.e. due to coupling effects).

Constant amplitude and waveform over the whole range.

Wave shaping sweepable between pure sine wave (no harmonics) and linear triangle wave (decent odd harmonics).

No interference when placed directly besides an Etherwave Standard (because this is the most common problem during workshops).

I would suggest that if the final product will be the typical horizontally-oriented rectangular box, it might be best to run the line out and CV out, out of the bottom. There are combination XLR/ 1/4" jacks that allow either type connection. I would suggest 1/4" for these bottom connections since these connectors are more robust than 3.5mm.

With this arrangement, the cables can be neatly velcro'd to the stand to keep them out of the way without crimping the connections into a tight 90 degree bend.

The Pitch Preview out should be a 3.5mm jack on the front panel, since almost all headphones these days have the 3.5mm stereo plug.

Don

"No interference when placed directly besides an Etherwave Standard (because this is the most common problem during workshops)."

I think this is a near impossible request for any Theremin.. My evaluation of the circuit leads me to think that this new Theremin will CAUSE less interference on adjacent instruments, but probably be more susceptible to interference from adjacent instruments..

The nature of interaction will, however, be completely different to what one gets from having 'normal' Theremins close to each other.

Avoiding interference with EW Standard should be not too difficult:

- Choosing oscillator frequencies which are neither equal nor multiples of the EWs oscillators.

- Minimize ERP by keeping by keeping the antenna voltages low. This could be a problem in Marks amplitude-detection based design. In my "classical" design I would have reduced the Antenna voltage still below the actual 1.8Vpp but then I had problems with the oscillators starting and with the amplitude stabilization.

"Avoiding interference with EW Standard should be not too difficult"

You may be right in what you say, and I may have been doing some things terribly wrong!

I have no proven theory to explain it, but I have found that the higher the P-P voltage on the antenna, the better the performance.. My first Theremin prototypes had low voltage and small sensing range, and I found that increasing voltage leads to greater range, stability (less noise susceptibility) and even reletive linearity.

As for keeping oscillator frequencies spaced for non-interference with other adjacent Theremins - is this REALLY practical? It can be tricky enough getting frequencies of pitch and volume oscillators on a Theremin set up so as to never produce 'birdies' without limiting the available spectrum to frequencies which will not be used (or corrupted) by any other adjacent Theremin.

One thing interests me.. Back in the good ol days of valve RCA's and the like, when Theremins had (I believe) extremely large voltage swings on their antennas, concerts were held where many Theremins were played.. Pictures I have seen show these Theremins in quite close proximity..

Did these Theremins interact with each other? Was each Theremin individually tuned so as not to interfere with the adjacent instrument? Would it have been possible to have concerts like this if the transistorised Theremins had appeared first? ... Am I an idiot who is missing something obvious? .... Probably!

Wow, sorry I'm late finding this.

As far as jacks for preview, audio, CVs, ect go, I would perfer to see both the audience, and player sides kept as clean as possible.

In the case of a mic-stand mounted, or RCA replica instrument, I would actually prefer the jacks be mounted through the bottum.

This would keep the instrument looking less cable cluttered to both the player, and the audience.