Etherwave Plus: mic stand interference and tuning tips

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Spider76
Posts: 3
Joined: Wed Mar 27, 2019 6:23 am

Etherwave Plus: mic stand interference and tuning tips

Post by Spider76 » Wed Aug 11, 2021 7:56 am

Hi everybody, I'm new to the forum and to the world of theremins: it always was a dream of mine and I finally realized it by getting one of the last Etherwaves I could find in EU (they're apparently discontinued now).

Of course I'm a total newbie but I've studied hard lots of manuals and tutorials before deciding the purchase. I know theremins are VERY sensitive to the surroundings, but what I didn't expect was the mic stand itself to completely mess the tuning.
In detail: when I set up the Etherwave on a wooden table, or even a metal X-stand (much bigger and heavier than the mic stand), everything works as expected: the volume knob actually regulates volume (turning it clockwise increases it, typical use setting around 1-2 o'clock), and the pitch knob fine-tunes pitch sensitivity (zero beat and more or less linear scaling when the knob is around 3 o'clock).

When I mount the theremin on a mic stand (straight single-pole type, with heavy round metal base), the behaviour is totally different. Pitch sensitivity is totally different, meaning not only that I have to turn back the tuning knob at around 12 o'clock, but also that scaling is different and pitch rises sharply when I stand back 1-2 meters from the instrument.
Also, the volume behaviour changes completely: adjusting the volume knob has basically no effect (it actually decreases a bit at maximum settings), I have to set it at minimum value, and instead of a smooth transistion, I hear a small "glitch" just before volume drops to silence.

The instrument is properly grounded, my music room is quite crowded but there are at least 4 feet from any furniture, keyboard or large objects. Just to make sure, I tried it in other rooms with more-less furniture, and the behaviour is the same, so I'm pretty sure it depends on the stand type.
I'm surprised I get these quirks on the mic stand and not on the X-stand, but that's how it is, and I know I will probably have to tune the etherwave.

Which brings me to the second part of my post: I'm a bit perplexed by the procedure. First of all, the manual that was included in my box is not the same as the one you can download from the Moog website. Mine is much more complete, with lots of information, circuit diagrams and the full procedure for building and calibrating the Etherwave (I guess it's the manual of the Kit version). The online manual does NOT include tuning instructions, which is a bit weird.
I couldn't find this version of the manual anywhere in pdf, but the text version is here:
https://translatedby.com/you/moog-ether ... /original/

This is what it says about tuning the pitch:
Using a clip lead or a temporarily-soldered wire jumper, connect the two leads of C28 together. (C28 is a small capacitor, about 3" to the left of the PITCH ANTENNA connection on the ETHERWAVE circuit board.) Then connect the instrument's audio output to headphones or a monitor amplifier. Now follow these steps to adjust L5 and L6:
Set P1 (the Pitch Tuning control) to its mid-position.
Grasp and hold the pitch antenna with one hand. With the other hand, adjust L6 for zero beat. Note: If the slug in L5 is fully counterclockwise, you have to turn it clockwise a turn or so in order to hear zero beat.) Then carefully turn L6 counterclockwise until you hear a pitch of about 3 kHz (3-1/2 octaves above middle C.
Let go of the pitch antenna. Slowly retract your hand from the vicinity of the antenna. You will hear the pitch go down.
If the pitch does not go down to zero beat when you've retracted your hand completely and stepped back, then L5 is set to too low an inductance. Advance the slug in L5 (that is, turn it clockwise) a small amount - perhaps 1 /10 turn or so - and repeat steps 2 and 3.
If the pitch goes to zero beat and then begins to ascend as you retract your hand, then L5 is set to too high an inductance. Turn the slug in L5 counterclock­wise a small amount, and repeat steps 2 and 3.
If the pitch jumps abruptly to a very different pitch as you retract your hand, then L5 is set to far too high an inductance. Turn the slug in L5 counterclockwise perhaps 1/4 turn, and repeat steps 2 and 3.
Eventually you will converge on the proper settings of L5 and L6. The idea is to achieve settings in which the pitch is at zero beat when you've stepped away from the theremin, begins to ascend when your body is about 24" from the pitch antenna, and is about 3 kHz when your hand touches the pitch antenna. Tap lightly on L5 and L6 as you converge on the proper settings, as this will stabilize the tuning slug positions.
I'm a bit perplexed by the need to "short" or temporarily solder C28...I have no soldering skill and certainly won't try that on a brand-new instrument. Is it really necessary? All the tuning suggestions I've read make no mention at all of this.
Also, this procedure doesn't talk about linearity: will I end up with a more less linear tuning, or is there some other trick required for this?

The tuning of the volume knob seems much simpler:
B. Adjusting L11 without a voltmeter:
Remove the temporary shorting connection across C28. Install the volume antenna. Position your ETHERWAVE so that the volume antenna is at least a foot from furniture and other large objects. Follow these steps to adjust L11:
Set the VOLUME knob to its mid position.
Carefully turn the slug in L11 counterclockwise until it is out as far as it will go. Then turn on your amplifier and set its volume control so that the theremin tone will be audible but soft.
Slowly turn the slug clockwise. At some point you will hear the theremin tone. As you turn the slug in L11, the tone will get louder, reach a maximum loud­ness, and then get softer. Turn the slug back to the maximum loudness, and notice how loud the tone is.
Slowly turn the slug counterclockwise until the tone is about half its maximum loudness. You should then notice that bringing your hand near the volume antenna lowers the volume, and the tone is complete silent when your hand is two or three inches from the volume antenna.
This completes the tuning of the Volume Oscillator. In performance, the exact volume tuning is achieved by adjusting the Volume Tuning control.
I hope this makes sense to experienced users, if you have any commment or advice to give me before I embark on opening up my new theremin, all tips&tricks will be VERY welcome!
Thanks!

mfl
Posts: 32
Joined: Wed Dec 09, 2020 4:39 pm

Re: Etherwave Plus: mic stand interference and tuning tips

Post by mfl » Sun Aug 15, 2021 2:54 pm

I hope the etherwave has not been discontinued, seems like it's just a rumour (at least based on a quick google search). The claravox is indeed a limited edition and there seems to have been problems with the deliveries because of pandemic electronic component shortages that seemed to have also affected the production and availability of the etherwave but no information confirming it was discontinued.

Moog seems to have stopped distributing etherwave kits (along side slightly raising the price of the pre-assembled ones) a few years ago without any announcements but I'd be surprised if they would go as far as discontinuing the whole etherwave line (leaving only the theremini) without any public statements or at least move the etherwave to the 'legacy' section of their product list on their website.

Now some random information / tips about ethewaves calibration.

First, shorting C28 before adjusting the pitch is optional, no need to solder anything. It does make it easier and faster but it's not mandatory. Otherwise, you simply need to keep readjusting the volume circuit along side adjusting the pitch antenna (instead of only adjusting the volume once after being done with the pitch).

If your 'phones' output is set in 'preview mode' (outputting the pitch without the volume being affected by the volume antenna) then shorting C28 is completely unnecessary as all it would do is make the main 'audio' output behave the same way.

About linearity, unless you're trying to go for a very unconventional range, the change in linearity caused by adjusting the variable inductors should not be noticeable. If you end up with noticeable linearity changes, I'd suggest also trying messing with the capacitance (distance between the pitch antenna wire and the aluminum plate bellow it) but this should not be necessary.

I noticed changes in linearity trying to adjust my theremin for a range much bellow the 'standard' C2 lower limit but inside the C2-C7 range, it seems to always remain fairly linear.

Adjusting the volume knob is indeed much simpler but I have to insist on starting with the slug in L11 as far out as it can go. Depending on how the pitch is set, it's possible to have more than one point in the L11 variable inductor were the volume seems ok but the deeper ones are hell. Setting L11 to far in can cause the volume antenna to start interfering with the pitch and that's frightening when it happens without understanding why.

I've personally only used mic stands like the one you're describing and I don't have the time right now to double check how setting on a table would affect my theremin but what you're describing make sense and adjusting the internal variable inductors should be the correct solution.

One last thing, the wooden case that you have to remove to access the variable inductors has a significant impact on the adjustment that can be hard to take into account at first (black etherwaves are a lot worst). That basically mean that once you get a good adjustment with both the pitch and volume potentiometers in central position without the case, putting it back will mess that up a bit. At this point, your adjustment should be close enough that redoing a final adjustment with the potentiometers positioned to compensate the offset the wooden top added should be enough.
Etherwave+ > Eurorack > [CV cables] > Minitaur , Sirin < [USB cables] < Bidule < nanoKontrols

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