Moog Music Forum

Hi,

I just bought an etherwave kit and have spent the last few days building it. With great excitment I finally finished it today. Everything seemed have gone together just fine, but when I plugged it in and tried it the pitch circuit seemed way off. At first I thought something was somehow reversed as the pitch seemed to lower as I moved my hand closer to the antenna rather than rising as expected.

On closer inspection, however, I realized that the problem was that the zero beat point was at only 3 or 4 inches away from the antenna. On consulting the "Understanding, Customizing, and Hot-Rodding Your Etherwave Theremin" packet that came with the instrument I tried to make adjustments. Following the directions, I connected the two leads of the C28 capacitor. (This immediately resulted in an extreme reduction in the volume of the audio signal.) I then adjusted L6 slightly as instructed.

The next line of the instructions (on pg. 7) made me worry, however: "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." After reading this I thought this might be my problem since my L5 was clearly not all the way clockwise. So I gave L5 a couple big turns thinking that might fix the problem. Reading on, however, I saw that the instructions call for extremely small adjustments to L5, so I'm afraid that I may have made things worse and I don't know how to return it to the correct range.

Additionally, after removing the C28 connection I find that there is still hardly any volume to the theremin. I don't know if my coarse adjustment to L5 created this lack of volume or if something adverse happened from jumping C28 as instructed. I'm pretty much at a loss as how to proceed from here, so a ny help you can offer me would be greatly appreciated!

Thanks,

Ed

Hi, Edmond,

I built the kit, too.
At the very beginning, I had some similar problems, but I did not adjust anything inside the theremin to solve them. M;y problems where outside.

1. where do you place it?

If you place it on a table, the table itselve is a kind of capacitor. It sould be dry and should not contain any metal. (When I had it on a metal table - it seemed to be totally de-adjusted.) On the rack (stator (?), German: Ständer) it works fine.

2. The adjustment slightly changes when you close the case.

3. You can adjust the cero point (and have to) with the potentiometer. - But this is outside.

4. The case must be dry. (I painted it with watercolor, let it dry, and closed it, and nothing worked anymore. It was not dry enough. If you use the wrong color, it might be de-adjusted very hardly.)

5. If you place it too near a wall, it will be de-adjusted.

I'm afraid, you tried too much to modify the values inside. You need some kind of measurement equipment, to adjust the circuits again.

One hint: let somebody prove the wires, whether you made mistakes. (But I don't suppose.)

---

Re-tuning your theremin for ZERO BEAT

I’ve done this a number of times to my theremin in the past eight years. It will give you back a wide pitch range again and get ZERO BEAT in the optimum “TWELVE NOON” position when you set your pitch knob. You will be making very “fine tune” adjustments to the little “pots” on the tops of both the fixed and variable frequency oscillators.

Both of these procedures involves opening up your theremin to make adjustments with a little plastic tool that’s like screwdriver ( though I'm told the newer Etherwaves require an Allen key hexagonal tool). Exactly what to do depends upon what theremin you have. For a standard Etherwave, it can take about forty-five minutes. The trickiest part is getting the pitch knob to give you zero beat when positioned at about 12:00 rather than 5:00. It’s tricky because the lid has to be taken on and off repeatedly to make the adjustment.

If you’ve got a standard Etherwave, there are instructions in the manual, but they were written by Moogian Martians, so they’re a little difficult to understand.

As I mentioned before, you actually CAN get that setting straightened out, but to do it you will have to OPEN UP your theremin.

The primary reason to make this adjustment is that if you're currently at one extreme end of the pitch knob's position, over time you will be unable to get zero beat at all. If the knob is turned as far clockwise as it will go just to achieve silence, as the pitch "slippage" occurs -- and it will -- you'll be unable to adjust the knob. It may be okay now, and it may take months to fully slip, BUT it could easily happen INSTANTLY if you change location for a performance or something. Then you'd really be in a fix.

I've yet to have to make this adjustment to the Etherwave Pro, and the procedure will be different than the one described below.

BUT -- if you have a STANDARD ETHERWAVE, here's what to do.

If you have the standard Etherwave, you'll be adjusting the fixed pitch coil, L6. With the theremin turned off, you unplug the power supply, open the lid and place it aside. Plug the power supply back in. Now, turn the theremin on and turn the pitch knob to 12 noon. It's going to make a lot of noise.

Next, using a little plastic screwdriver, you turn the pot at the top of the L6 coil a little clockwise, or a little counterclockwise until you get zero beat. Make a note of the "hour" position of that little screw slot. ( five o'clock, three o'clock, etc.)

Now, place the theremin lid UPSIDE DOWN on the theremin. This is to simulate the lid being on. The position of zero beat CHANGES the second you put the lid on. So, to get things as accurate as you can without constantly having to take the lid on off on off on off, while plugging and unplugging the power supply, etc., you place it on top upside down. You'll notice that zero beat is no longer where it just was anymore. So, you need to compensate for what will happen when the lid is on.

Here's an example: The last time I made the adjustment, about a year ago (the second time in about five years), the hour LID OFF position of the screw head on L6 was 4:00 to achieve zero beat. The LID ON position of zero beat using the pitch knob was then about 10:00. I turned the knob back to 12, then I followed the trial and error described below, turning the coil screw counterclockwise a little more each time, until zero beat ended up at 12. Without a lot of fancy equipment, here's the only way to do it:

Take the lid off and turn the L6 coil screw just a little bit ( whether counterclockwise or clockwise depends entirely upon your theremin, so you may err on one side or the other until you figure out which direction to turn it ). The theremin will begin to make a lot of noise, but that's okay. Put the lid back on upside down and see where you get zero beat by turning the pitch knob. Chances are it will be off by hours. Note the hour you get zero beat. Determine whether you'll need to go clockwise or counterclockwise with the pitch knob to get either clockwise TO or counterclockwise BACK TO 12 noon.

Repeat the process by putting the pitch knob back to 12 ( the theremin will squeal, but that's okay ).

You're going to go back and forth with lid on, lid off, adjusting the coil gently either clockwise or counterclockwise, then putting the lid on, and seeing if you can get zero beat right at 12 noon with the pitch knob.

Be patient, this DOES work. Once you've achieved it -- and it can take about a half hour -- now comes the real task. Unplug the power supply, put the lid on fully (without screws ), plug the power supply back in, turn on the theremin, and see if zero beat falls at 12 noon using the pitch knob. I can pretty much guarantee you that it will not because even more of the lid is on, but you may be close within an hour or two. SO, you must now keep making the adjustments -- power supply out, lid off, power supply in, turn on theremin, adjust the coil to compensate, THEN power supply out, lid fully on, power supply in, turn on theremin, see if zero beat is at 12. you keep going until you've got zero beat with the pitch knob at the 12 noon position.

Sounds tedious? A lot of work? You're right. But it is the ONLY way. In the long run, it's well worth it. Once you've got it, that setting will hold for years. In addition, as you travel around playing in different places, the position of zero beat can change radically, but your pitch knob will rarely if ever have to be set to the extreme clockwise or counterclockwise position.

BE WARNED -- once you start with the coil adjustments, there's no turning back, you're committed. Never attempt this if you're pressed for time, in a bad mood, or you're unsure of the repercussions of messing around with theremin guts. It requires a lot of patience and a cool head. If in doubt, call tech support for advice or with questions at Moog Music BEFORE YOU START. My first time, I was very apprehensive, but it had to be done. That said, I have to add the caveat that doing this would be your own choice; I've described the process as carefully as possible, but the responsibility for the undertaking is entirely your own, as are any unexpected results.

GOOD LUCK!

-kip
www.performancekr.com/theremin.html