# simple theremin issues

Posted: 4/14/2007 6:22:21 AM

Joined: 4/14/2007

http://www.thereminworld.com/pics/schematics/simple.jpg

in this schematic it shows 2 4093 op amps, but isnt the 4093 a quad chip n therefore already contains 4 op amps in it??

also I've been working on this particular circuit and I found that using such small capacitors (100 pf).

I'm intending on using this theremin circuit in an installation artwork and hope to have a large sensitivity range from the antenna, around 1 and a half feet. Is this possible???
Posted: 4/14/2007 6:24:19 AM

Joined: 4/14/2007

I didnt finish one of my sentences there, I meant to say that using 100pf capacitors makes the theremin extremely unstable.
Posted: 4/14/2007 6:52:31 AM

From: France

Joined: 4/8/2007

I've noticed it in my topic, and i'm working on it to find a way to use only one chip:

http://www.thereminworld.com/forum.asp?F=3&T=2505&cmd=p&p=1

then you can find something like this on www.thereminvision.com

What do you mean by unstable?
Posted: 4/14/2007 7:04:31 AM

Joined: 4/14/2007

i've used one 4093 chip, connected it up like you would 2 chips, using 8 points on 1 chip as opposed to 4 on 2 chips. By unstable I mean, the frequency is supersonic all the time. I'm not sure if this is an issue with the 100pf capacitors or is it to do with using just one 4093 chip?
Posted: 4/14/2007 8:29:30 AM

From: France

Joined: 4/8/2007

You used 3 NAND gates to make the 2 oscillators, and the "mixer"? and the 2 remaining leads were Vcc and grounding?

Hum actually i'm not sure that "mixing" the two signals with logic gates is a good thing.. I've done the maths with square signals, both results with a NXOR gate (original circuit, 4077) and with a NAND gate (3rd quarter of the 4093) are erratics, and don't have anything in common with an audio signal..

About unstability, it can be the result of too much close oscillators (in the same chip there)..

Did you try the circuit as pictured? with separated 4093 and a 4077 mixer chip? it works?
Posted: 4/17/2007 2:22:51 PM

Joined: 4/14/2007

no i just used the 1 4093 chip and then used the 4077 too.... I havent tried it as it is exactly in the diagram. does it work?
Posted: 4/17/2007 3:48:00 PM

Joined: 3/4/2007

I'd like to build this thing as it looks so simple.

what is the 1N component?

has anyone seen this circuit working?
Posted: 4/18/2007 2:28:41 PM

From: France

Joined: 4/8/2007

[quote andyl222] does it work? [/quote]

I don't know, i didn't try yet..

[quote rheo]
what is the 1N component?
has anyone seen this circuit working?
[/quote]

The 1N component is a 1nF capacitor.

Posted: 4/18/2007 5:21:46 PM

From: Australia

Joined: 1/21/2006

I have made that circuit but found that it wasnt very good distance wise (5 - 10cm control room) here is circuit i found easy to make. It has a better range and sounds allot better.

http://i4.photobucket.com/albums/y125/tatems/simple_digital.gif
Posted: 4/19/2007 2:51:17 AM

From: France

Joined: 4/8/2007

Thanks a lot Tatems!

Hum control room is set by the frequency of the fixed oscillator if i remember well, a higher frequency can cause unstability.. But 10cm room is enough for me (it's just for having fun)..

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