Tuning Barb's Theremin

Posted: 8/30/2007 7:43:25 PM

From: Undisclosed location without Dick Cheney

Joined: 2/21/2005

Hi Folks,
I received email from an enthusiastic Theremin newcomer who asked me to post her questions for her because she has been unable to successfully sign up with ThereminWorld. Her name is Barb, and everything in this post after this paragraph is by her except the note I inserted in square braces.


After reading (many times) the excellent posts on the forum about tuning, and
opening up my theremin and messing around, I realized that, not knowing
anything about electronics really, I Need More Data. I like to understand
enough to know some cause and effect. I don't need technical terms, because I
probably won't understand them. I do understand what you are saying about it
not being necessary to get zero beat before playing, but for internal tuning
purposes, there are references to zero beat below because the instructions call
for it.
I have an Etherwave standard and a 15 watt Behringer amp. Yes, it is a guitar
amp, but it seems fine to me. I bought this theremin USED. The board says Moog
Music Inc. 11-211C and the layout is slightly different from the diagram in the
manual but I can find everything OK.

Before I practice too much, I want to make sure the internal tuning is as good
as I can get. To me, this means having a fairly wide range available, at least
2 octaves, maybe more. I think I understand well that the theremin needs to be
away from all solid objects because they will always affect ... everything. I
am assuming 2 feet clearance is enough since the power cord is not much longer
than that.

I have read and experimented with both the tuning instructions in the hotrod
manual and the posts on thereminworld forum. This is what I think I understand
about tuning:

Tuning the instrument internally (as opposed to tuning before playing only
using the pitch knob) has to do with adjusting L5 and L6 and the pitch knob.
The manual said to connect the two posts of C28 with a clipon lead, but
schielenkrahe's post says nothing about this. What is the reason to "short
circuit" C28 or not? (I've tried the methods with and without the clip lead.)

The tuning done on L5 and L6 are two variables that are related to each other
somehow. How? Does one regulate the lowest end frequency that will be available
and the other the range of pitch? I have messed with this A LOT. I decided I
would have to "go back to square 1" which according to the manual is to raise
L5 all the way up and then turn it clockwise about 1 full turn till zero beat,
then start messing with L6.

I decided I should use schielenkrahe's method because it is "in the real world"
(i.e., takes into account putting the cover back on!), but still, I have
trouble getting both a zero beat (or really low tone) when stepping away AND a
good range of pitch to play thru.

I believe if I understood better the relationship between the effects of
changing L5 and L6, I would be able to do the internal tuning much better.

Then, after the INTERNAL tuning is adequate, I use the pitch knob to change the
RANGE for each piece I play? But if I started out with a 3 octave range, it
will still be a 3 octave range? Like, I started out with a C4-E6 range, I turn
the knob up and now I have about an F4-A6 range?

Related questions: do I have to use a plastic tool on L5 and L6? Guess what? I
didn't. I used a metal screwdriver with a plastic handle, and nothing blew up.
Is this a really bad thing to do? [note from Tom: I replied that yes, it's really bad.]

And ... you are all saying, I believe, that once the internal tuning is done
well, you don't find the need to retune it that way for years?

After I resolve this, my next project will be investigating adding a pitch
preview. But one thing at a time.
Posted: 8/30/2007 8:25:06 PM

From: Croxley Green, Hertfordshire, UK

Joined: 10/5/2005

Hi Barb.

Before you go fiddling with the innards again, how is the field size and range as it stands?

[i]Can[/i] you stand a couple of feet away and tune it so it is at zero beat with your arms by your side? How high is the highest note you can play - right close to the rod. Very high?

If so, I'd say don't worry about trying to tweak it more until you have a feel for the instrument. If not then some idea of the extent of the problem would probably help.

And, no the pitch knob controls the size of the field, and hence the position of zero beat, but it does not vary the number of octaves the instrument can play, simply how widely spread the notes are.

You must be logged in to post a reply. Please log in or register for a new account.