Paia Theremax 9505 Assembly And Using Manual page 20

Tuning and Testing
First time tuning can be tricky because both the Pitch pair and Volume
pair of oscillators must be close to a null in order to hear anything at all. If
the Pitch pair are close, but the Volume pair are far apart you won't hear
anything because the Volume doesn't come on. If the Volume pair are
close but the Pitch pair aren't, you won't hear anything because of no
pitch signal. In either case, there's no clear indication of what needs to be
adjusted to hear a sound. You can eliminate this complication by tempo-
rarily disabling the heterodyne part of the Volume control circuitry and
forcing the VCA "on" while the Pitch pair of oscillators is nulled.
Use the clip lead supplied to temporarily connect the V+ line (the banded
end of the zener D1) to the "high" side of the volume control (lug 3 of
R83). When using this trick, it is very important to set the front panel
Volume Control to mid-range or slightly less. The V+ voltage is almost
double the normal maximum CV and too high a Control Voltage causes
the VCA to saturate and effectively turns it off. If you forget, don't worry,
nothing will be damaged by having the Volume set too high, you just won't
hear anything until you turn it down.
Set the Pitch Trim and Volume Trim controls on the panel to mid-range
and the Pitch CV, Timbre and Velocity controls fully Counter-Clockwise.
Turn the slugs of all the coils L1-L4 fully "out" (Counter-Clockwise) just
until you feel resistance - the coils can be damaged by applying too much
force while turning the slugs. From the fully "out" position, turn the slugs of
the two coils L1 and L4 one full turn "in" (CW). These coils will not be
adjusted again.
Plug the Tmax output into an amp and turn both on. During initial setup you
may need to adjust the volume for comfortable listening levels or to
prevent overload and distortion. Make these changes with the amplifier's
volume control only. Do not change Tmax's Volume Control from it's
mid-range setting until told to do so later is these procedures.
Nulling Pitch
Slowly adjust the slug of L2 "in" (Clockwise) while listening for the hetero-
dyne tones that slide down form a very high pitch then go through zero
frequency and begin to climb again.. If you have the gain of the amplifier
that you're using set high, you may find a couple of places where tones
can be heard, but as you adjust the slug continuously from one end to the
other you will hear one in particular that is very much louder than the
20 Theremax 062702