New theremin? Nano from Poland...

There does not appear to be an obvious way to take the cover off to look inside.  I'll make some test recordings and take some close-up photos later today.

I made an easy modification today.  I replaced the volume antenna's velcro mounting bracket with a spring clamp.  It's much quicker and easier to mount the antenna now.

Here is a link to some photos (with and without my modification), along with an mp3 file of the unprocessed audio output, recorded directly from the line out jack.  

https://www.dropbox.com/sh/00q3sd7e2v9egsk/AABAgFxf6WnTVNv71Q0G-Bs5a 

The audio file contains:

1-  smooth voice sweep with standard pitch range

2- smooth voice sweep with extended bass

3- smooth voice - some random notes

4- harsh voice sweep with standard pitch range

5- harsh voice sweep with extended bass

6- harsh voice - some random notes

Yesterday I mentioned that I found the volume antenna easier to play if I tilted it toward my left arm, rather than positioning it parallel to my shoulders.  I just found a diagram of this playing position on the Nano theremin website.  http://assec.pl/position.gif

Thanks rickreid!  I'm trying to figure out what the heck those fasteners are on the main foot unit?  They look recessed somehow.  Are those just paper cutouts with all the lettering and stuff on them?

I can see some non-smooth pitch change, and can definitely hear it with the brighter voice (bottom).  But it maybe doesn't seem quite as bad in this regard as the file submitted by assec.

That volume pad is real interesting - Am I correct in thinking its a sandwich with a hard inflexible top surface on which the Nano box is mounted, and a flexible rubber base? - as in, when the pedal is compressed, the Nano is actually moving a bit? This would be quite clever, as a FSR mounted on this inflexible 'panel' could be wired directly to the Nano and its wiring (or tracks if PCB) wouldnt be stressed.

Gordon - This could be an easy way to implement your requirement - and the FSR output could be inverted electronically quite easily. (ok, im making big assumptions about the Nano here - but whether this is how the Nano pad operates or not, it could be a cheap easy way to do the job)

Rick, thanks for these pictures and sound files, and I feel bad asking for more ;-) .. But could we have one really slow sweep, and one slow sweep where the volume is slowly and repeatedly modulated (min to max) by the volume antenna ?

It is starting to look like the (IMO) awful artifacts I heard / saw in assec's samples might have been from connected stuff and not from the Nano - and clearly the audio from the Nano isnt being produced by any heterodyning process, so its probably unlikely that these artifacts were due to poor filtering of HF causing aliasing at the external (digital) equipment.

I like the core (chopped ramp) waveform - its actually great for filtering / processing and acts well as an excitation signal for formant filters - and its easy to produce by heterodyning two square waves in quite a simple logic configuration.. I suspect this waveform would be ideal for feeding into a TM or similar.

Fred.

"I'm trying to figure out what the heck those fasteners are on the main foot unit?  They look recessed somehow. " - Dewster

They look to me like some kind of 'caged nut' insert - as in, they are tapped to accept a thread from the other side - I suspect that to open the box one would need to remove the rubber pad on the underside of the box to access the screws... They look like some Ikea furniture fittings, only smaller..

Looking at the whole thing, I would not be surprised if there was one circuit board for the whole lot, pedal and all.. the way the 'rubber' has been cut away to give access to the 3 pin connector makes me think this connector is probably soldered to this boards 'underside' and that the Nano box isnt 'complete' - its 'lid' being replaced by the board, and alternative means of keeping it all together being implemented with these strange fasteners.

"That volume pad is real interesting - Am I correct in thinking its a sandwich with a hard inflexible top surface on which the Nano box is mounted, and a flexible rubber base? - as in, when the pedal is compressed, the Nano is actually moving a bit? This would be quite clever, as a FSR mounted on this inflexible 'panel' could be wired directly to the Nano and its wiring (or tracks if PCB) wouldnt be stressed."  - FredM

That is interesting.  So: thick rubber on the bottom, stiff board in the middle, controller box and thin rubber on the top.  If you look at picture 5 you can see copper on the top of the stiff board in the middle, which leads me to believe it is PWB material.  This project seems rather cleverly cobbled together from parts on hand so that in itself could mean nothing.  But it could also mean that there are traces etched into the copper under the thin rubber on top, and that it functions capacitively.

The pitch preview jack looks kind of like a fragile afterthought, with that notch to accommodate it.  Going by the serial number it seems you have the 12th one made!

Hi Dewster ;-)

We are thinking similar again! .. I was updating my prev post while you were doing the above. I doubt the pad is capacitive, and I think it was declared resistive on assecs web site... But I do think its likely to be a PCB.. Simply because this would be the simplest / easiest to implement.. Lets hope its at least 1.6mm good quality FR4, (really needs to be thicker) because over time, boards which are repeatedly stressed can get troublesome cracks in their traces..

Fred

ps - Many thanks for those great photos, Rick!

"Looking at the whole thing, I would not be surprised if there was one circuit board for the whole lot, pedal and all.."  - FredM

Doh!  I didn't think of that.  That makes too much sense for it not to be the case.

The pressure pad is very rigid.  There's a thin top layer that feels like hard rubber.  It is stiff, but not shiny-smooth.  The thicker bottom layer is a hard, porous plastic material of some sort.  I am assuming there must be a piezo-electric component somewhere in the pad.  The pad does not flex or give in any noticeable way.

There are two recessed screws on the short end shown in photo number 8 that are for course tuning of the two oscillators.  I happened to not fully extend the pitch antenna, which affected the tuning, of course.  I tweaked these screws and was able to re-tune the instrument.  I found the distance between the bottom of the pitch antenna and the end of the volume antenna affects pitch tuning as well.  Mounting the volume antenna an inch or two lower on the microphone stand probably would have eliminated the need to adjust the course tuning.

Dewster,

The adhesive label materials feels like heavy paper, but with sort of plastic feel to it as well.  I am not sure which it is.