moog melodia

Fred said: “In fact, I almost enjoy destroying hypotheses as much as "solving" a riddle and coming up with an answer - there’s something sad about answering a question completely!”

Amen Fred that's why I keep it illusive, whether you’re a performer or designer there “is” something special about keeping a mystery shrouding ones theremin work, if it is playful & productive.

Good theremin sound is found in physical resonances and electronic feedback. I have two examples that have been posted at TW in the past. It does begin to sound microphonic at some point.

My funny antenna needs physical dampening to keep it from being environmentally responsive.

The other sound byte I called “Angel of Death” was a speaker in a large metal tub being fed by a multi-voiced theremin. The problem with this is resonant spikes are hard to control if you don’t have EQ equipment, which I don’t.  That particular sound byte may be incorporated into the opening of a rock song within the year by a family friend, guitarist Ryan Schuck. Move over Jimmy Page this is a theremin used more creatively.

Note: Angel of Death is what the angel was called at Passover, assisting Moses in freeing his people. As the wind blew there was a terrifying sound!  I am disappointed when the illusions of some bands glorify the demonic. Brian Welch known as Head in the band Korn recognized this and walked away to form a new band, still hard rock driven by a great guitarist.

Christopher

Hey Invisible  (-'

Fred said: "In the end, perhaps its all just about giving some "meaning" to life - its all a game really - but one doesn't usually walk away from a game if one is enjoying it.."

Your wisdom nailed it again as this ain't heaven. We all leave the game eventually.

What I find interesting is our conversations always seem to be like we are arm wrestling. LOL

Christopher

"What I find interesting is our conversations always seem to be like we are arm wrestling. LOL" - Christopher

Yeah - we have our own little game here ;-)  ..  Good friends often disagree more than they agree I think - can be quite nasty to each other,  and respect each other nonetheless! ;-)

Fred

ps - I think that you and I have a habit of hijacking threads with philosophical / religious stuff which has no relevance to the thread we are in - Some people (rightfully) get annoyed about this.

so I have moved my other comments to here:

http://www.thereminworld.com/Forums/T/28680/life-the-universe-time-space-fate-folly-and-everything-else?last=True

"Why not put a piezo pickup on the theremin box and feed that to another channel on the amp.I put my hand on my EW box when it was playing with the speaker close by..there was certainly vibrations there for such a pickup to process." - IJ

I think you may be misunderstanding the process a bit.. Its not that one actually wants the sound picked up by the box as an audio signal - one wants it as a modulation signal.

Here is where things are getting a wee bit muddy - its my fault - the mechanism involved with tubes in amplifiers is quite different to the mechanism involved with microphonics in theremins.

With a tube amplifier, the sound picked up by the tubes is mixed with the "audio" passing through the tubes - depending on the position of the tubes, their acoustic resonances, the phases of the respective electrical signals and sound waves etc, complex 'distortions' can be produced by this mixing - but it is all effectively direct mixing of sounds picked up by the "complex microphone" formed by the cabinet, tubes etc.

With a (solid state) theremin, the only way that microphonics can affect the audio output is through the mechanism of freqency modulation..

If one had a capacitor which was modulated by audio waves, and one had a fixed reference oscillator, and no other changes in capacitance, one would get a difference frequency which was changing in proportion to the changes in the capacitance due to the modulation... If the difference frequency was say 500Hz, and it deviated by 50Hz as a result of the modulation, and if the difference frequency was the signal used to modulate the capacitance, one would end up changing the waveform.. You would not get feedback in the same way as one does with an amplifier..

I am sure that a mathematician would be able to provide precise evaluation of the changed wave shape given centre frequency and modulation depth - But with acoustic feedback of the type I am talking about, where there are cabinet resonances and signal delays, I think it becomes more complex... Even if it was purely down to vibrating the plates on a variable capacitor, this component will have resonances etc which will hugely affect the modulation..

But - the primary difference is that the audio "itself" is not going to be picked up and transferred to the theremins output.. The only way this could happen would be if one had a frequency to voltage converter tracking the audio output frequency, and modulated the VFO with an audio signal - one could then probably get this audio from the CV output if the converter was extremely fast!

The other place that audio might appear is from the volume circuit - this is often a frequency-voltage converter.. But usually too slow to respond to AF modulation I would think..... But it might...... This would certainly change the wave shape or even possibly cause feedback at low frequencies and high volume levels.

Fred.

I just started building one of these, mostly because the project came out the year I was born!

The coils were a bit tough I had to rewind them 4 times! I have it mostly done but have to wait

for the antenna coils to come in next week. I got the coil forms from SurplusSales they were 

a bit expensive though....

I am told the Moog Trobadour is the same as the Melodia but in this picture I see

a Timbre pot. I wonder how it was configured in the circuit. I could imagine a pot 

and cap between the pitch oscillators to adjust the "pull". Anyone have one and

could trace the circuit?

I found this online somewhere. It seems t indicate you can use 15V to run the Melodia.

It seems funny you do not have to change some values...

Of course there is no values on here so maybe you do?

Here's the start of a box for the Melodia. I have all the parts now but have to "pull it all together"

Hello Bob,

"Of course there is no values on here so maybe you do?"

I am still trying to figure you out, two builds at once? I do like your MK2 schematic and would like a conversation eventually about the volume control section.

Everything I know is on a webpage somewhere.

Melodia NPN & PNP

Christopher

dew said: "Very little of this is spooky or unknowable if you take a systematic approach."

Oh come on dew did you see my final post in the EWS sound thread, something communicated mathematically, do you see it?.

Bob, are you doing any breadboarding or testing of the individual elements (oscillator, mixer, etc.)?  I think you could learn a lot by doing so.  LTSpice is also quite useful for gaining insight into what's going on with things that are difficult or impossible to measure on the bench (transistor currents, etc.) and it's a great way to quickly test out circuit variations without getting your hands dirty.  There's a ton of bad circuits out there, not necessarily saying the Melodia is poorly designed (though I'm not a fan of Bob Moog's later oscillator topologies), but at the very least one can optimize older circuits for newer components via Spice and breadboarding.

Oscillation is just feedback with gain, though any phase error can profoundly and negatively influence the voltage swing in the LC tank, and therefore at the antenna.  LC operating point and tank C / antenna C padding will dictate the roughly linear pitch range.  I've characterized antenna / hand capacitance a couple of different ways, and it's not hard to predict analog Theremin pitch performance via a spreadsheet.  Very little of this is spooky or unknowable if you take a systematic approach.