E-Pro range switch- howzit do?

I'm terribly curious: has anyone with a good EE background cracked open their Etherwave Pro and figured out how the range-switch works?

If the diagram in the owner's manual is correct, the range switch acts upon the detector, and for the life of me I can't see how this might work.

When I first read the spec I assumed that range-switching was done by changing the BFO by powers of two, but then I recognized you'd have to shift the resonant Fc of the pitch antenna, as well. Then I downloaded the manual, saw the block diagram, and became even more confused.

Anyone able to straighten me out?

Not sure how they implement the frequency division in the detector.

Have you noticed that the range switch affects the tone quality, too? Particularly in the high range position, the tone is a bit darker (mellower) than in the other positions.

RE: range switch/tone quality-

I think that has less to do with the range switch 'affecting' tone quality, and more to do with the switch introducing frequencies in that range into the formants-if-you-will built into the machine itself.

It's typical for acoustic instruments to be mostly upper harmonics in their bass range, middle harmonics in the middle of their ranges, and mostly first and second harmonics (darker) in the upper range.

This is a well-known characteristic that I'm sure Uncle Bob had in mind when he was designing the EW-Pro.

If you'll remember the Etherwave _Standard_ had a few capacitors right before the output jack to do just that- to roll off some of the upper harmonics.

And with the EW-Pro, don't forget where you may have left your filter settings, and that the waveshapers are connected to the pitch-to-voltage circuit.

But still, the question remains... how do they do the range-switching with the detector? Or is the diagram a sneaky way of misleading us to throw off any industrial espionage? ^_^

Studying the block diagram and checking the various outputs gives a little insight into the internal organization of the Epro. I believe the "Register switch" arrow should point to the "wave shaping" block rather than the detector block"...

1) The range switch and and tone-controls only affect the phones and main audio output.

2) The main "mute" switch only affects the main audio out (this is not in the diagram).

3) The pitch CV and the tuner output are NOT affected by the range control. Note too that the tuner output ALWAYS plays in the upper range and is taken off the detector. This suggests that the native tuning of the Etherwave Pro corresponds to the "high" range. This also confirms that the range switch does not change the frequency of (say) the reference oscillator (if it did, then the range switch would affect the pitch output and pitch CV).

4) One can then deduce that the register switch is, in reality, a function of the wave-shaping block -- to move the Register Switch input to the Wave Shaping block seems to correct the discrepencies between the block diagram and the Epro's operation.

I don't know how the wave shaping, etc... is implemented in the Epro. Since the range switch drops the pitch by octaves (that is, by an intregal amount: 1:2) one can deduce the presence of a frequency divider function. Don't know if the Epro divides via digital or analog circuitry.

The user's guide suggests using a digital tuner with the pitch output however a headphone works, too.

EXCELLENT observation & inference, man!

This begins to make a bit more sense, then- let's guess a Schmidtt trigger right after the detector, then the Fc/er, then the waveshaping?

As for response, then, I'm guessing the procedure is this: set to five-octaves, set for zero beat, then as you switch to higher ranges, zero beat keeps moving behind you?

Actually, the zero beat position does not change with the range switch. Rather, the lowest playable frequency (before zero beat) shifts downward with the range switch. Also, the highest playable frequency shifts downward in the same manner.

The pitch output range is always the same -- the frequency divider function simply shifts the pitch lower by one or two octaves depending on the position of the range switch.

The easiest way to observe this is to connect your audio output to a speaker and connect the pitch output to an "open air" headphone then try out the theremin at different settings of the range switch.