Hotrodded Gakken Mini

Just for curiosity:

Shorten the amp input cable and see if it picks still up that noise...

It was already the shortest cable I have! Only about 3 feet. I was thinking a possibility is because my workbench amp is a battery-powered Pignose. Maybe something that plugs into the wall would be better grounded or something.

Also discovered that I need top go back to the internally hardwired handle because the external plug-in version doesn't do the signal-expanding bit of grounding I'd hoped for...which really was the whole point originally.

I was not able to download the pictures - so may have the wrong idea about what you are trying to do (email me the pictures and I well be more able to help).. But ..
If you are trying to regulate (or turn on/off) the volume, an attenuator is probably what is needed.. just breaking the signal is not ideal - amplifiers can have extremely high input impedences, and signal leakage through a switch is often enough to to be heard..
1.) Put a resistor between the side connected to the amplifier (the 'output') and ground (the cable screen).. The value of this resistor will depend on the output drive capability - start with 10k, and reduce it if required (dont go below about 1k).. You may even find that a 100k resistor will significantly reduce signal leakage.

2.) Put a spring-loaded potentiometer (Log 10k 'pitch bend' 'joystick' or similar) between the signal out and the amplifier in (connect the potentiometer wiper [centre terminal] to the amplifier side, ground to left terminal of potentiometer [knob facing you] and signal to the right terminal.. This should give hand operated volume control..

But I am only guessing that this is what you are trying to do.. may have it completely wrong!

They're not downloads, they're links to Imageshack pages. You should be able to just click over.

Thanks, I'll try the resistor method...hope it works!

As far as the volume pot, what I'm looking to do is not so much control the volume as be able to cut it in and out, like a staccato effect. So it needs to be an on/off type switch.

But I've been thinking about adding a volume pot also, but I'm not sure where I'd put it aesthetically. It's designed so the whole thing closes up into it's own box, and the output jack and on/off switch are recessed so's not to interrupt the smoothness. The only way I can figure to add a volume control without having a big knob sticking way out like a sore thumb is to keep it inside the box, which isn't really ideal.

Thanks a bunch for your tips. Man, fifteen years ago, who would have imagined I'd be modifying something I got from a Japanese magazine, with help from some British guys?

"As far as the volume pot, what I'm looking to do is not so much control the volume as be able to cut it in and out, like a staccato effect. So it needs to be an on/off type switch."

There may be a real neat solution to this... One can get "Force Sensing Resistors"(google this or http://www.interlinkelectronics.com/force_sensors/technologies/fsr.html)
also "Quantum Tunnelling" compound or "pills"http://www.maplin.co.uk/module.aspx?moduleno=44202..

it may be possible to construct a simple attenuator using these - it certainly is possible to use the FSR with a VCA to control volume as a function of pressure.

Output from Theremin ---->[FSR/QTC]---->OUTPUT<----[Resistor]---->Ground.

The above is a schematic!
The FSR/QTC could be configured either for on/off (switch) or as a variable resistor. One could also use any membrane type switch.

" Man, fifteen years ago, who would have imagined I'd be modifying something I got from a Japanese magazine, with help from some British guys?" - Yeah! Every now and then I get that feeling of utter awe, thinking back at how everything has changed.. I was not even able to watch the moon landings live, as there was no TV in the country (S.A.) at the time.. and a teletype was sophisticated (and extremely expensive)'texting'.

Saw the pictures - still dont understand the "doesn't do the signal-expanding bit of grounding I'd hoped for" though!

I believe Peter Pringle wrapped kitchen foil around the tip of his thumb and forefinger as a switch.

Having just watched a video of someone playing a pencil by drawing with it, (http://www.youtube.com/watch?v=gDaj3tBSM2M) it occurs to me that you could inlay a pencil lead into your box as a volume slider. (I guess using a similar principle to the device in the video to control volume would be easy enough.)

Kitchen foil !? Ye gods! Get some interesting 'crackly' effects perhaps, with nice bursts of 50Hz ....

How about a magnet on one finger and a reed (magnetic) switch on the other? Could be fitted to elasticated glove fingers, and the switch could be screened with aluminium foil.

Discussion so far has been about interrupting the signal.. There is another way, which is to feed the signal through a (say 10k) resistor, and use the switch to short this to ground at the amplifier side.. Doing this will give a massive attenuation of signal when the switch is closed..

Example - Amplifier input Z = 500k (say).. Feed Resistor = 10k .. Switch closed = 10 ohms ... Signal attenuation with switch open = 0.98 (insignificant, << 1db). Signal attenuation with switch closed = 0.00099 (-60db) with an extremely poor switch.. 1 ohm switch, gives -80db, and usual switches (100mR or less) better than -100db..

An easy clean and "distortion free" method to achieve a volume control with staccato is to project your Audio-Out through a super bright LED and demodulate it using a hand held solar cell.

Visit this webpage to understand better what I am talking about.

Volume Control with Staccato (http://www.oldtemecula.com/theremin/ultimate2b/volume/index.htm)

Christopher
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Force sensing resistors...pencil lead volume sliders...solar cells...boy, y'all got no problem taking a simple problem and coming up with complex solutions! I'm gonna stick with the simple "add a resistor" idea. Scrounging around my workbench I wasn't able to locate a suitable one but I'll pick one up. So if I'm reading this correctly, it goes into the ground wire, right?

I have a bunch of those solar cells sitting in a drawer, salvaged from driveway lights...so much potential!

Oh, and the "doesn't do the signal-expanding bit of grounding I'd hoped for" is specific to this Theremin/toy...if you're not familiar with it, one of the tricks they recommend is to run a strip of aluminum foil from the battery ground to the exterior, so when you hold it in your hand, you serve as the ground and suddenly the playable range becomes significantly better. Or something like that. So the original idea was to have a handle with metal on the outside to contact in your palm so you're not limited to holding the theremin itself or a strip of tinfoil in your hand.

[i]boy, y'all got no problem taking a simple problem and coming up with complex solutions![/i]

Isn't that the very essence of a thereminist though?

Problem - design an instrument that can play one note at a time.

Solution - takes [i]years[/i] to master basic skills.