How do I distort thee, let me count the ways ...

It's a question of imagination. The problem of us "technicians" may be that we rarely meet this question. Our daily bread in RF mixing is either the case of two sine waves (which have no harmonics) or the XORing of two square waves (which is not a linear 4-quadrant multiplication). Out of that we have normally to do with mixer circuits which are far away from ideal multiplicators and thus adding more harmonics than expected.
The next is the phase question. We often meet frequency-depending phase shift which makes it difficult to identify the waveform visually. A ramp signal may mute into a "pregnant" sine-like wave without changing the harmonic content...
That's why I don't rely too much on visualisation.

Best regards from the country of Fourier!

[i]"A ramp signal may mute into a "pregnant" sine-like wave without changing the harmonic content..."[/i]

Yes - This is true and on real circuits (as opposed to simulations, where one can set the phases of the input waveforms to whatever one wants)it frequently occurs..

As you say, this is where visualisation can let one down.. I saw (on the 'scope) that the output waveform differed from the input waveform - but I (wrongly) assumed that this was due to input waveform phase differences. I have a PC 'scope capable of FFT, but it does not have good resolution - Running a harmonic analysis using my ancient HP333A distortion analyser gives much better results, but it takes a lot of effort to plot each harmonic independently - so I seldom do this.

What I really need to do is get my maths books and master this language - But right now, getting my Theremins to market is a higher priority.

Thank you for your insights, Thierry - They are a great help!

Best regards from the land of Darwin. ;)

[i]But right now, getting my Theremins to market is a higher priority.[/i]

There are people who could help you by promoting your theremins - if they only had already seen at least the prototype which was announced for last September...

[i]"There are people who could help you by promoting your theremins - if they only had already seen at least the prototype which was announced for last September"[/i]

Yes.. I know! :<

This last 8 months has not gone to plan.

hi guys!!
one question... the Etherwave´s oscillators are Hartley´s oscillator, aren´t they? how can i get the transfer function of this circuit..? the transistors form a diferential amplifier or not?
thank you

No, this are push-pull oscillators with two transistors. A third one is there to modify the working point for frequency fine tuning.

A Hartley oscillator would use a grounded tap of the coil in order to reverse the phase.

Transfer functions for oscillators are bit tricky. You could spend a whole lot of time modeling all the nonlinear aspects involved with starting the oscillator.

Steady-state is a bit easier, but I am not sure what added-value anyone would have with a precise model for a theremin oscillator circuit.

The fun part is the empirical "tweaking" that you do to see how you can affect the sound in a musically interesting way without killing the stability. "Dead oscillators" aren't very much fun ... oscillating amplifiers are more interesting, but are generally more annoying since you are trying not to create an oscillator!

Don

The variable pitch oscillator of the Etherwave is easy to stop. Increase the value of L5 (turn slug 2 full turns clockwise). Sometimes oscillation will now stop when you move away from the theremin (> 6ft) and will only restart when touching shortly the pitch antenna.

While tuning my Etherwave in order to get 7 almost linear octaves, I discovered some of these small side effects.

Another effect is that the oscillators output amplitude increases with increasing L values which gives (thanks to clipping effects in later stages) a brighter audio signal. The first harmonic, that means two times the base frequency, increases now mostly at the 3 o'clock position of the waveform knob. With the brightness knob at 1 o'clock I obtain a clean treble recorder sound in the higher register.

At least 1 advantage of this dirty diode mixer...

Hi guys!
I´ve been looking for some information about the push-pull oscillator, and comparating them with the etherwave´s one, I don´t really understand how it works. the frequency of oscillation will be given by the variable coil and the fixed coil in parallel with the capacitor, isn´t it?
if you can explained how it works it would be great...
thank you!

the problem that i found is that the push-pull oscillator are based in a common collector structure with the two bases connected to the coil or whatever is oscillating, and oscilation comes because one transitor does the positive half and the other the negative part.
following these structure, I can´t find the relationship between this and the Etherwave.
I do really need that somebody can explain it to me!