Minimum Theremin - is it working?

[earthtonesaudio]

Hi,

I just breadboarded the minimum theremin, and I think it's working, but I'm not sure.  Normally it just makes a ton of noise, white noise plus a lot of low frequency components... lots of content below about 700Hz.  This noise will also change in amplitude as my hand moves closer or farther from the antenna. 
When I touch either the ground, or +V part of the circuit, the noise stops, and I can hear a really quiet "theremin-type" tone that responds to hand/antenna interactions.  But it's just barely there.

Some possible problems:
-I have a tiny breadboard (about 2" by 3") and all the parts are crammed in there, with jumpers all over the place.
-I didn't have any 270k resistors, so I used 3 100k's in series.
-Also didn't have any 27k, so I used 33k
-my "antenna" is a long bit of wire from the breadboard, going to a big sheet of aluminum foil.
-I'm using an LM317 regulator, and it seems to get better signal to noise adjusted for 6 volts instead of 5.
-my CMOS inverters (4069UB) keep popping out of the breadboard. 

While fiddling around with it, I've found that I can coax a little more theremin type tones out of it by just touching my finger to random leads on the breadboard.

I know Theremins are kinda left-field for most people, but I figure y'all have more experience debugging on breadboards, and might know what's going on with mine.

Schematic:

[birt]

my best advice is to build it on perf. a theremin is a very sensitive circuit and breadboard is just not suitable for that in my opinion.

the normal sound of this circuit is a pretty clean theremin sound. if you move far enough there should be silence. the zero calibration is also pretty important. the procedure is described on Harrisons website.

[Paul Perry (Frostwave)]

+1 on comment by birt.

You really need every connection soldered & rock steady, to have any chance at all.
Your resistor substitutions should be OK.
I haven't built it myself, but I've built very similar things, and I have never been very impressed.

[birt]

well i have built this one a couple of times. one was even used in a contemporary classical performance in Vienna. the output was fed to an ugly face, then to a volume pedal and then to the main mix.

this is one of those minimum theremins:

[earthtonesaudio]

Thanks for the feedback!  I'll build it "for real" then.  I'm glad someone else has built this successfully.  Birt, did you build this from the kit, or DIY?  If the latter, did you use a 4049, 4069 or similar?

Never mind, I checked the Harrison website, and they use 4069 chips.  Looks like I'm good to go.

By the way that bear is cute.

But here's a question for ya: did you mount the circuit in a metal enclosure?  The site says that doing so will give a more "sinusoidal" tone, but I'm not sure what they mean by that.

[birt]

it's definatly not a metal bear :p

and since i run iot trough effects i don't care for a really clean tone. to my taste the cleanest theremin tones are kinda wimpy :p

[earthtonesaudio]

Well, I gave it another shot and it worked!  I didn't worry so much about the parts values, just used what I had that was close enough.

On the breadboard, with wires going every which-way, and the 2 cmos chips just 2cm apart, I got "obviously working" Theremin behavior.
Also: Antenna is about 10cm square (folded up aluminum foil) and max sensing distance is probably about 15cm.  Not spectacular, but fine for just messing around.
Either I got lucky with the layout, or this simple design really is quite robust with respect to stray capacitances and interference.  Good to know!

[frequencycentral]

I built a simple theremin using a 4093 and 4077 (and just a very few extra parts) a few years ago.

My experience was that it had to be calibrated whenever it was set up in different location.

Things like proximity to walls, distance from the floor, if it was set up on a metal legged table etc. all had an effect on it.

I ended up using a 1K multi-turn trim pot in series with the 10K trim pot.

I also used a proper telescopic radio style antenna, the length of which you could adjust for fine tuning.

I still have the board, but it was a bit of a blind alley for me - I seem to remember that I found the calibration irregularities quite frustrating.

Fun though, and reading your thread makes me want to dig it out again!