Note:
On the RS Illusion board leave all the Pots
mounted on the board. Once you have your own personal sound
dialed in you will not want to change them.
The Audio
Out
still needs a method of Volume Control
This simple CdS
Volume Control
works effectively but much better is the VAPP
board.
RS
Illusion board Pots:
1.
Audio Output Jack
- I would wire a 1/8"
stereo jack at the theremin for it's 3 wire versatility.
2.
Switch 1
for power on/off, this could also be mounted on the VAPP separate
volume stand using a stereo cord from the RS Illusion to the
VAPP board. See VAPP
webpage.
3.
LED 1
Panel mount this LED for a visual indication of the Null
Point or Zero Beat
LED 2 Leave this LED on the board, it adds
character to the sound by adjusting it from slightly off to
barely on.
Pot 1 –
Board mount 10k linear potentiometer. This Pot adjusts the audio
level into the TL082 Op. It can enhance the sound by driving the
audio at this point from a sine wave to a compressed peak sine
wave or a soft square wave. Start with this pot set to center.
Pot 2 – Board mount 10k linear potentiometer
controls the Audio-Output. This sets the level of the theremin so you could use a guitar or a keyboard
amplifier directly as a pitch only theremin. The VAPP
volume control board is connected here to give you maximum
advantage of creating the RS Illusion wave shape. Set this pot
to where the LED 2 is barely on.
Pot 3 – Board mount 1k linear potentiometer.
This pot
controls how much square wave generated noise is injected to the
audio to disrupt the natural sounding theremin sine
wave whistle. Add a little noise clockwise to create a more
violin or string like sound. Set this Pot about 1/4 clockwise or
less.
L2 – Coil
Oscillator board:
The best low
frequency wave shape is achieved when the L2
coil board is mounted with the coils in the same direction as
the L1 coils on the RS Illusion board. The
further away the L2 coil oscillator board is from the RS
Illusion board L1 coils and the antenna
is also better.
4.
The "CTB" Course Tune Brass screw
against the L2 Coil tunes the L2 oscillator to
match the RS Illusion board L1 coil resonant
frequency. The two oscillators match in frequency when you hear
the theremin whistle through an AM Radio or the RS Illusion
Audio-Out. A longer threaded brass can be used to stick of out the front panel for a
course pitch tuning knob.
5.
Pot 4
Panel Mount. This is used for setting the bias of the Q2
transistor which can also create a different low frequency wave
shape. This Pot also works excellent for course pitch tuning.
The L2 CTB screw will need re-adjustment with
any extreme repositioning of Pot 4. Start with this pot set
to center.
Pot 5
Board Mounted Thermal Drift Trim. This Pot 5 sets the voltage
across the Q2 transistors emitter to collector
junction; which also controls the transistors internal
capacitance. At the correct Pot 5 resistance the Q2
characteristics will more closely match the thermal behavior of the
RS Illusion board Q1 transistor. You can adjust
the Pot 5 resistance so the thermal drift is in either
direction. In your normal room temperature start with this set
in the middle of it's range. If the theremin Null Point moves
away from the antenna as the temperature rises then turn the Pot
counter clockwise slightly. If the Null Point moves closer to
the antenna as the temperature rises then turn the Pot 5
clockwise slightly. You are trying to find the ideal resistance
for this setting. Start with this pot set to center.
6.
Pot 6
Pitch Fine Tuning. This Pot 6 allows for very accurate setting
of the linear spread of the theremin notes. This is done by
moving the lowest linear notes to their proper location. At
higher audio frequencies above 200 hz this Pot 6 will appear to
do nothing! Use the CTB Pot 4 for course pitch tuning. Mount Pot
6 where its location is obvious on the panel layout so
none of the other panel control knobs won't be accidentally
changed. Start with this pot set to center.
The VAPP volume control board has two panel Pot controls 7
& 8
which could be mounted on their own stand with the VAPP board separate
from RS Illusion enclosure. The on/off switch
could also be
mounted at a separate VAPP volume stand using a stereo cord from
the RS Illusion to the VAPP board. See the VAPP
webpage.
Notes:
You may want to change some of the connections on the pc board using the
easy wiring terminals to solid soldered wires
on the board to prevent future intermittent loose wire problems.
These terminals are mainly beneficial when you're still experimenting and
don't want to have anything permanent.
I like to have my VAPP
volume control mounted on it's own stand separate from the main theremin.
This allows for better volume placement when you want to play
the linear very low notes above 30 hz.
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