Glasgow digital Theremin

Posted: 4/10/2012 3:48:39 PM
Flub

Joined: 6/12/2011

Hey there,

I gave up the analog circuit from the glasgow university page. now i try to get this one working : http://www.theremin.us/Glasgow/schematic.gif

 

I only need the variable dc level part.

instead of the three nand gates (4093) I used two of them and used one of the four free gates in the second 4093 for U4A.

The problem is that the output A is always at maximum and has some wavy form, when i turn the trimmer the brightness and the wavoform changes a a little bit, thats all what happens.

has anyone built this circuit here?

Do I have to use 3 differnent quadruple 2 input nand gates?

Another thing which is different in my circuit is that I have 1000 instead of 820 pF for C4.

 

regards,

Flo

 

Posted: 4/10/2012 10:22:52 PM
dewster

From: Northern NJ, USA

Joined: 2/17/2012

I'm looking at the TI datasheet for the CD4098BE and they say R3 shouldn't be below 5K ohms.  Just based on that this circuit strikes me as rather suspect.

The -3dB point for R2/C3 is ~340kHz, which is probably too high, causing the monostable to retrigger too often.

Posted: 4/21/2012 4:16:50 PM
Thierry

From: Colmar, France

Joined: 12/31/2007

Both Glasgow circuits, the analogue and the digital are pure academic projects. The circuit examples shown in the paper (whose theoretical part is much more interesting) are there for illustrating construction principles rather then being approved and tested DIY circuits. 

A successful approach could be to take these circuits just as simple design examples and to re-engineer them almost from scratch based on today available parts and exact calculation.

Posted: 5/2/2015 2:50:21 PM
AngelLaHash

From: Newark

Joined: 3/18/2013

i did build two and one of the chips blew up...

Re-Reading it, asks for a 4070 Xor but it has a Icon of a nXor (4077)

http://www.theremin.info/-/viewpub/tid/10/pid/65

 

 

"The minimum value of external resistance, RX, is 5kΩ. The maximum value of external capacitance, CX, is 100µF. Figure 9 shows time periods as a function of CX for values of RX and VDD."

T= 0.5 x Rx x Cx = 0.5 x 1000 x 0.000'000'000'820 = 0.000'000'041seconds

Now if you want to keep the time and Rx cant be below 5K then

Cx = T / ( 0.5 x Rx ) = 0.000'000'041 / ( 0.5 x 5000 ) = 0.000'000'041 / 2500 = 0.000'000'000'164

Cx = 164pF

 

Also 
"Please Do look carefully at the updated digital theremin schematic. It corrects a few mistakes and omissions in the original circuit. Zener Diode is drawn incorrectly - Be aware that the "2V7" diode should be symbolized as a Zener, with the cathode up, not down, as shown. (It is a 2.7 volt Zener diode.) Thanks to Art Harrison for this tip!"

Posted: 5/2/2015 3:27:31 PM
oldtemecula

From: 60 Miles North of San Diego, CA

Joined: 10/1/2014

Angel said: "i did build two and one of the chips blew up..."

I had a capacitor explode like a firecracker once, makes wearing glasses a good idea. I can't stand the suspense, let us hear the sweet sound of your theremin improvements.

Do you recommend the Glasgow?

Christopher

Posted: 5/2/2015 4:49:29 PM
AngelLaHash

From: Newark

Joined: 3/18/2013

Ive never got it working yet... 
There is so many bits, i have to do it in stages and by the time i get around to a 2nd stage ive forgotten .. need more Note Writing i think :(

The bit that blew up on me was one of the chips, and you just hear a Crack Pop sound and then your got SILCON in the Roof..

 

Im making a OPEN THEREMIN with a Aurdino (however you spell them)

Posted: 5/3/2015 8:46:38 AM
Thierry

From: Colmar, France

Joined: 12/31/2007

As I said, the Glasgow circuits are just proofs of concept, not blueprints for building working and playable instruments. The only thing which is really of interest is the theoretical section of the Glasgow paper.

Building an Arduino based Open.Theremin is a ways better idea, it has already proven to work and to be playable.

Posted: 5/3/2015 7:26:01 PM
AngelLaHash

From: Newark

Joined: 3/18/2013

As I said, the Glasgow circuits are just proofs of concept, not blueprints for building working and playable instruments. The only thing which is really of interest is the theoretical section of the Glasgow paper.


I keep trying because of this wording, to me it says it works

"The design has proven very successful in recording, where the signal-to-noise is of HI-FI quality, and also in playability, since the tuning and volume offset is easily trimmed by adjustable knobs on the front panel. The pitch control circuit has been revised and can easily replace the original circuit. (Designed and built by Lindsay Reid and Brendan Dougan for a final year project )"

http://www.theremin.info/-/viewpub/tid/10/pid/65

Posted: 5/3/2015 8:01:06 PM
Thierry

From: Colmar, France

Joined: 12/31/2007

Yes, you will most probably get it producing a sound. But il will not be playable because of a very incoherent tone spacing (un-linearity) and a sluggish volume response. A guy in Germany is producing theremins based on that circuit and selling them on ebay under the name "Golem Theremin".

I've seen many of these "instruments" and many people who were completely disappointed by these, because (even after an extremely long warm-up time and meticulous adjusting) only one single octave in the middle of the pitch range was playable with the established aerial fingering techniques, while the tone spacing was ways too wide below and ways too small above.

Before building whatever theremin circuit or buying whatever instrument, have a look on platforms like youtube or vimeo and check if one of the renowned classical theremin players has used it for a professional recording. If not, keep your fingers away and don't rely on the testimonial of high school students or even engineers without any (at least semi-) professional musical training if you don't want to end up with only a fancy gesture controlled sound or noise generator. Technical data like a pitch range from 20 to 20,000Hz are impressive, but don't say anything about the usable and playable pitch range. If the tones are not widely enough spaced in the high register, you'll never manage to hit a specific tone with precision and a decent vibrato will be impossible because the slightest arm movement will result in a 3 or 4 tones shift.

Remember that the instrument which Leon Theremin built himself for the great Clara Rockmore had "only" a pitch range of 4.5 octaves (from 65 to 1,700Hz), a signal to noise ratio of only 45dB, and a distortion factor of > 10%, thus far below any "hifi" specification, but her playing (technique, expression and timbre) in her recordings are still the reference for every aspiring thereminist today.

Posted: 5/3/2015 8:04:15 PM
oldtemecula

From: 60 Miles North of San Diego, CA

Joined: 10/1/2014

Angel said: "I keep trying because of this wording, to me it says it works"

A person "learns more" when his build does not work. If the Glasgow worked they would have furnished a sound byte for analysis somewhere. TW has followed the Glasgow over the years and no one has ever provided a sound sample, I may be wrong. You might be the first and I hope you break the spell. These are students going for a grade only or else they would have improved the design by now. The theremin has taken down some of the brightest engineers.

I have always said before someone selects a theremin design to buy or build get a sound sample to verify if this is what you want. This does not demonstrate everything but it is a good starting point. I often post samples for this very reason, even if it sounds like crap, this helps separate me from people who's talk is just intellectual bad gas.

Christopher

 

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