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Help with tuning

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Help with tuning

Postby Neil » Wed Sep 09, 2009 10:49 am

I need some help. My Etherwave recently went completely out of tune, whcih could I guess indciate that something has actually gone wrong wit the whole thing. But, I have gone in and attempted to re tune it as per the instructions that came with it. I am struggling though. The first problem was that the manual tells you to turn L6 anticlockwise from the zero beat position to get a note 3.5 octaves above middle C, all while touching the pitch antenna. If I do this, and then withdraw my hand the note goes up, not down. Q1. Is this an error in the manual, should it be clockwise. or is my theremin busted.
Then, if I go for clockwise instead of anti-clockwise as suggested, I can get to a point where there is a high note when I am touching the antenna, and it drops to zero at around 24 inches. The problem I have though is that the dynamic range is now much narrower than it was when I bought it. Essentially, the note goes up barely at all until I get to within a couple of centimeters of the antenna, where it then climbs rapidly. This makes it unplayable. Therefore Q2. Have I dine something wrong in the tuning, or is my theremin busted?

Sorry this is long, but after 2 nights solidly fiddling about inside I'm completely lost! :(
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Postby mayidunk » Thu Sep 10, 2009 5:03 pm

Just off the top of my head, do you have the pitch tuning knob on the front panel set to the proper position before tuning L6?
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Re: Help with tuning

Postby wolf2112 » Fri Sep 25, 2009 11:22 am

Neil wrote:Sorry this is long, but after 2 nights solidly fiddling about inside I'm completely lost! :(

Two nights? I've been at it for nearly a week! I picked up the kit only last week, assembled it and started tweaking as per the manual... knobs set 1/2 way.

So, I got the volume pot (L11) adjusted with a voltmeter with no trouble, but I basically am having the same issue as Neil with the pitch pots (L5 & 6). However, I've pretty much finally got it to the point where I have a decent, usable range with my right arm, up to the requisite 3KHz as stated, but when I step away, it's still squealing like mad, i.e. not getting zero beat.

Any help is greatly appreciated... I'd like to get it working and play with before my field upgrade kit arrives in like six months. :lol:
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Postby chinard » Mon Nov 16, 2009 2:13 pm

i'm in the same boat.
I've tried the tuning procedure many times and it just makes no sense.
I think i posted about it here before and was basically told to RTFM.

c'mon ppl..
SOMEONE here must have some useful info for tuning!
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Postby Amos » Mon Nov 16, 2009 5:59 pm

Here is my technique for tuning the volume circuit:

Set the volume knob on the control panel to 3 o'clock. Stand as far to the right (pitch side) of the unit as possible, so you are away from the volume antenna. With the unit powered on and hooked up to amplification, reach over with the trimmer tool and start turning L11 through its range. Somewhere in the middle, you should hear a sound start to be audible, reach a maximum loudness, and then die off again. Turn the lug back to the point where the sound is loudest. This should put it in the correct range, to where the sound is silent when your hand approaches the antenna and them becomes louder as you draw away; additionally the Volume knob should be set correctly such that it controls not the actual volume but rather the hardness or softness of the volume curve; meaning how quickly the sound reaches maximum loudness as you draw your hand away. At the clockwise extreme it should have a brighter, sharper attack and at counterclockwise the volume should increase smoothly and slowly as you draw your hand away from the volume antenna.


Tuning the pitch circuit is really an art in itself. Roughly speaking, L5 controls the "top end" or the highest pitch you hear when you are touching the pitch antenna, and L6 controls the range, or how far from the antenna the zero point (zero beat, or silence) is located. I perform the tuning using a special wooden cabinet top with holes drilled above the variable inductors, because the presence or absence of the top influences the adjustments. It is more difficult when you have to perform the tuning with the cabinet top completely removed, and then listen to it again with the top in place to see if the tuning is still correct. Generally I find the top seems to influence the pitch downwards from what you hear with the top removed; if so in tuning it helps to "tune high" by a bit and then set the top in place to see if it falls into range. Here is my procedure.

First, listen to see if the pitch goes higher or lower as you draw your hand away from the pitch antenna. If it goes higher, adjust L5 so that the pitch descends through the zero point and then starts rising again; now it should be in the right direction. The next step is to grasp the pitch antenna and adjust L5 so that the frequency you hear is in the neighborhood of 3.8 kHz. L5 and L6 interact, so there will be a decent amount of back-and-forth between the two adjustments. Once you have the top end around 3.8 kHz, move your hand away and see where the zero point is located. It will likely be too close (too short a scale range); to adjust, stand at arm's length from the pitch antenna and reach over from the left to adjust L6. You want to adjust it so that the zero point is about an arm's length from the pitch antenna. Generally this involves turning the lug in L6 in the same direction as you adjusted L5 to get the top end.

NOTE: if the top is off the unit, you actually want to hold your right hand just about at the front edge of the wooden cabinet (~3 inches away from the pitch antenna) and adjust L6 until zero beat falls where your hand is, only 3 inches from the antenna. In my experience, this translates to about an arm's length when the top is put back on. The top kind of "stretches" the pitch field response by a large factor, which is part of why this whole tuning business is so difficult.


The first time you dial in zero beat, it will probably drive the top end higher than you wanted it to be, so go back to grasping the pitch antenna and turn L5 in the appropriate direction to get back in the neighborhood of 3.8kHz. Notice which direction it went (higher or lower) as a result of setting L6; and overshoot in the appropriate (opposite) direction to cut down on the number of times you have to go back and forth between the two adjustments.
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Postby Gordon Charlton » Tue Nov 17, 2009 12:09 pm

Thank you for posting that, Amos. I have so bookmarked this thread ready for the next time my pitch circuit starts to wander.

:D
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Postby wolf2112 » Wed Nov 18, 2009 3:21 am

Indeed, thanks for that, Amos... I'm definitely going to try this in the next few days!
The volume circuit is actually quite easy to adjust... the pitch can be a real trial, though.
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Postby Bryan1980 » Tue Nov 24, 2009 5:01 pm

:idea: That could be partly why I'm having so many problems playing the durn thing. My Etherwave might not even have been in tune when it arrived and since I obviously can't read the print manual (although I do now have a PDF version), I never even thought to try tuning. Of course I'll need to get an electronics savy friend to help me determine if we need to actually open the cabinet or if it's just a matter of fiddling with the pitch and volume knobs. Then of course the cluttered space I'm living in probably doesn't help matters any. I have to actually move my sofa in order to be able to be able to get far enough away from the instrument and to let the fields expand enough so I can play in the lower octives. Not to mention if you don't have enough space you can get some really whacky effects when you so much as twitch a finger, and by that I mean more than usual, where you might not get a sound until your hand gets really close to the pitch antenna, then squeals when you so much as move a finger.
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Postby Gordon Charlton » Mon Dec 07, 2009 8:40 am

Finally I got around to retuning my etherwave (*) - and thanks to Amos's instructions it was quicker and easier than the previous times I have dared to remove the top of the cabinet. :D

Amos wrote:NOTE: if the top is off the unit, you actually want to hold your right hand just about at the front edge of the wooden cabinet (~3 inches away from the pitch antenna) and adjust L6 until zero beat falls where your hand is, only 3 inches from the antenna. In my experience, this translates to about an arm's length when the top is put back on. The top kind of "stretches" the pitch field response by a large factor, which is part of why this whole tuning business is so difficult.


I note that 3.8kHz is between A♯7 and B7 in case knowing that helps anyone.


(*) I bent the stiff wire connecting the circuit board to the pitch rod closer to the foil sheet beneath it as an emergency measure to adjust the pitch field at a gig some time ago, and had not got around to putting it straight again.
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Re: Help with tuning

Postby Lance » Sun Jul 08, 2012 4:56 pm

Amos, thanks so much for your post. Like others here I did read the manual but this was a great help. I thought I'd assembled my kit wrong but it now works perfectly.
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