NEW UK DESIGNED & BUILT THEREMIN with volume loop & pitch rod etc

"Moving the pitch hand down, parallel to the rod and over the enclosure, causes a significant rise in pitch." - Gordon.

I suspect this is more to do with the case being effectively the theremins ground, or capacitively coupled to the "0V" or "ground".. (in fact, I dont just "suspect" - I am sure of this)

One gets this effect with any and every theremin where the hand capacitively couples to the circuit (board) and to the antenna.. Particularly if the theremin is not well grounded and the primary coupling from the antenna to the theremins ground is via capacitive coupling directly to the board / case.

The case being conductive acts as a good capacitor to any "ground" in the theremin - "ground" is an illusion - The theremin requires that there is a capacitor between the antenna and its "return point" - you form part of this capacitor.. If the "return point" is connected to "real" ground, then you can close the capacitive connection by (capacitively) coupling to any ground.. But if connection of this "return point" to "real" ground is poor, then direct coupling to the "internal" "return point" can be significant, and will increase pitch compression closer to the antenna.

Linearity and range / sensitivity requires the best possible grounding / earthing of the theremin.. Any theremin!

Fred

"Moving the pitch hand down, parallel to the rod and over the enclosure, causes a significant rise in pitch." - Gordon.

I suspect this is more to do with the case being effectively the theremins ground, or capacitively coupled to the "0V" or "ground"..

One gets this effect with any and every theremin where the hand capacitively couples to the circuit (board) and to the antenna.. Particularly if the theremin is not well grounded and the primary coupling from the antenna to the theremins ground is via capacitive coupling directly to the board / case.

Fred

Well if Gordon's LV-3 is set up as std, then the mic stand will screw into the epoxy drilled and tapped plate. This will in turn have the mic stand earth out on the casing. Mine though has been 'modified' by me with a clearance hole above the screw-in mic stand position as I thought this was better for stability (no, not pitch or sound quality but literally the stability of the theremin on the stand). The mic stand does of course NOT connect with any internal components and DOES clear the case as the hole is slightly larger than the mic stand threaded section. Does this have an effect? I'm unsure. I did clear the mod with the designer, John, first though!

Err, maybe the real reason is that my hand is smaller than Gorden's hand, so there's the answer......................I'll get my coat!

... and I just double checked. Seems I got it turned around in my head. Oops. Lowering the hand lowers the pitch. Earlier posting corrected.

I just received my new Lost Volts brand LV-3 Theremin today! Here's a mini-review for my theremin playing friends:

Out-of-the-box, and after installing a 9V battery, I found the pitch tuning knob was set to a non-usable range, with the zero beat zone too far away from the antenna, so I re-opened the cabinet while the instrument was mounted on a stand, and tweaked a variable resistor in the variable oscillator circuit. (I have a long history of breaking things this way.) As you might expect, the tuning with the bottom panel slid open was very different than with the panel closed. After about a dozen tweaks and tests I found a setting that worked for me, with a range of about 5+ octaves.

The timbre seems okay but not awesome. I like it better in the highest and lowest octaves. The middle range lacks brightness. It doesn't sound as good to me as more expensive and/or priceless theremins we all love, but I expected that. I don't care much for the overdrive capability of the volume antenna, but it may have some value I have yet to discover.

The good news is that the LV-3 works well on battery power when connected to my battery-powered Roland Mobile Cube amp. I expected a much smaller pitch antenna range, but there was almost no difference than when I plugged it into my grounded mains-powered guitar amp. So, I can finally play theremin in the great outdoors without a long, long extension cord!

The LV-3 is roughly the same size as the awful Gakken theremin, but it is a much, much better instrument. The antennas feel a little flimsy, but are much more sturdy than those of the Gakken. The blue LED power indicator is a nice feature.  I was pleased to find a mic stand adapter was included, so it will fit on the larger diameter U.S.-style  mic stands.

I think it is a good choice for beginning theremin players who don't care to invest a lot of money in their first instrument. Plus, the capability of running on battery power has obvious benefits for more experienced players who want to go (almost) cordless. I already have the excellent Moog Etherwave Plus and the beautiful Burns B3 Pro II theremins, so the LV-3 will be my third choice, but I can't wait to play it at some outdoor jam sessions (weather permitting.)

... and I just double checked. Seems I got it turned around in my head. Oops. Lowering the hand lowers the pitch. Earlier posting corrected.

I noticed when I had my instrument open, that the little screw next to the blue power LED indicator is connected to the LED and to the circuit board.  That could explain the effect of the cabinet on the tuning.

"... and I just double checked. Seems I got it turned around in my head. Oops. Lowering the hand lowers the pitch. Earlier posting corrected." - Gordon

Ok - thats strange! ;-) ... Because either way, if the case was "linked" to the antenna (which its not) or if the case was "linked" to "ground", increasing capacitance (getting closer) should lower the frequency of the VFO and therefore increase the pitch.

So, well, I dont know! ;-) .. The only obvious was of lowering the pitch by proximity that I can see is if one was somehow lowering the reference frequency by doing this.. With an uncased theremin board, I can accept this possibility - but through an aluminium case? (in fact, the reference osc should not be so prone to interfering capacitance that it changes - should only be noticable if one is deliberately using a finger near the board for crude debugging).

"I noticed when I had my instrument open, that the little screw next to the blue power LED indicator is connected to the LED and to the circuit board.  That could explain the effect of the cabinet on the tuning." - Rick

If the case is not connected to "ground" but is connected to some other circuit point (by mistake?) then, well, anything is possible..

Looking at the photo, there obviously is a deliberate connection to the aluminium on one of the LED leads - I assumed this must be a ground connection.. There is (AFAICS) no other obvious connection point - the jack socket (one usual way of coupling ground) is a plastic insulated type.

Pitch going lower with proximity, combined with a deliberate galvanic connection to the case, shouts to me that something is badly wrong! - Yes, the case should be connected to the circuits ground or "0V" - but the effect of this connection should not be what Gordon is seeing!

Fred.

*there is one way that could explain the behaviour - that would be if the case was being deliberately driven with a shielding signal, so approaching it could, in fact, reduce capacitance... But I think this is unlikely - Unless John has been telepathically looking at my recent design (or me at his, LOL ;-) and the LV-3 is quite different to anything conventional.

This might help a bit Fred. The pitch rod post is on the LHS with the LED centre bottom.

I have added a section of black plastic tube to the pitch rod to allow easier finger tightening as can be seen in the photo.

http://i1181.photobucket.com/albums/x423/TheKRU251/DSCF2144_zps0a02f72a.jpg

"This might help a bit Fred. The pitch rod post is on the LHS with the LED centre bottom." - Chris

Thanks Chris, yes, I have a photo - but yours gives a better perspective WRT the antennas..

I strongly suspect that the LED lead connected to the chassis will, or should, go directly to the -V battery / supply, connection (and that this is the internal ground).

In fact, anything else would surprise me.

Which leaves me thinking something is wrong! ..

And I wonder what the operating frequency of this theremin is - probably quite high I guess.. And whether there is an (unintentional) inductance or some coupling between the LED/chassis connection point and the supply - perhaps due to the track position / thickness or whatever (ground to chassis connection should be at a the main ground "star point" in any HF design), and whether perhaps this is affecting the reference osc....

But whatever - it should not behave in that way! Of that, I am almost certain!

Fred.

(the above is no criticism - This theremin has been designed and built with price as the focus - And this obviously includes the cost of development and evaluation / testing, which I am sure has been minimal )

"This might help a bit Fred. The pitch rod post is on the LHS with the LED centre bottom." - Chris

Thanks Chris, yes, I have a photo - but yours gives a better perspective WRT the antennas..

I strongly suspect that the LED lead connected to the chassis will, or should, go directly to the -V battery / supply, connection (and that this is the internal ground).

In fact, anything else would surprise me.

Which leaves me thinking something is wrong! ..

And I wonder what the operating frequency of this theremin is - probably quite high I guess.. And whether there is an (unintentional) inductance or some coupling between the LED/chassis connection point and the supply - perhaps due to the track position / thickness or whatever (ground to chassis connection should be at a the main ground "star point" in any HF design), and whether perhaps this is affecting the reference osc....

But whatever - it should not behave in that way! Of that, I am almost certain!

Fred.

(the above is no criticism - This theremin has been designed and built with price as the focus - And this obviously includes the cost of development and evaluation / testing, which I am sure has been minimal )

Just tried the hand-parallel-to-the-pitch-rod movement on my modified Moog EW.

Same effect in terms of pitch change at the top or bottom of the pitch rod.............and that has the wooden case too!!!