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Lab Notes:
Replacing the original self wound L2 coil with two parallel choke coils works excellent using an adjustable ½” to
1" distance between them for tuning. Thermal pitch drift is
excellent using like combinations for the L1& L2 coils. Use your AM Radio tuned
to around 850 kHz to verify both Q1-L1 & Q2-L2 oscillators are working.
The distance and position of the L2-Osc board relative to the main RS Illusion board will affect
the low frequency wave shape sounds.
sound
byte (335k) The
audio wave shape is best if the board mounting allows the coils to all be in
the same direction.
You could get a really deep throaty low
frequency 25hz sine wave
if you enclose the L2-Osc board in metal enclosure for shielding and
maximum isolation between the two oscillators. Avoid
using this shielding if you can because it will encourage the thermal
drift. You might also try one side of the metal box for some
shielding.
Attach
the negative side of the power supply to the metal enclosure. View at Radio
Shack.
Tuning - the Q2-L2 oscillator board to match the RS Illusion M3 Q2-L1 oscillator.
Begin by hooking up the Lev antenna combo and set the variable antenna capacitor halfway. Set the
RS Illusion M3 board Pots 1 & 2 fully clockwise. Set the RS Illusion board Pot 3 fully counter-clockwise.
Set the three Pots on the L2 oscillator board to their center
position and center both
coils
L2a & L2b.
Have the L2 Oscillator
board connected to the RS Illusion M3 board.
Place an AM Radio about two feet from the RS Illusion M3
board. Power up your circuit boards and tune the AM Radio to find a quiet spot
on the dial between 700 kHz & 1100 kHz which is created by the oscillators. Move L2a back and forth with your fingers
and the theremin whistle should appear at some point in the movement. This coil
movement has over a 100 kHz sweep range. After
finding the theremin whistle use the L2b tuning screw for course tuning. If
you do not hear a theremin whistle over your AM Radio then read Troubleshooting
at the bottom of this webpage.
Visit Panel
Mounted Controls for proper setting of all of the RS Theremin board and
panel Pots.
RS Illusion
Sound
The RS Illusion has
four control Pots to
add character to your sound. The new L2 coil sine wave (68k) sound byte, the sound of
every theremin must begin here! I am using the VAPP
volume control board in the next sample. Raw RS Illusion
theremin voice, no outside affects or processing sinewave2.mp3
(155k)
Thermal Drift Trim! (Below
refers to the L2 tuning board in the graphics above)
Pot-5 10k with a 4.7 in parallel creates a centered
resistance of 2.5k where adjusting to either side of this resistance the pitch
will decrease or increase as the temperature
rises.
It is best when you adjust the Trim Pot 5 in what would be your
normal room temperature for playing.
Start with Pot 4, Pot 5 & Pot 6 set at their center point, adjust
your course tune brass screw so you are between 200hz & 300hz. Observe which direction the theremin pitch drifts over a
several degree room
temperature change. If your pitch rises with an increase in room temperature
(Null Point moves away from the antenna) then turn Pot 1 a tiny bit counter-clockwise to increase the resistance. If your pitch decreases as the
room temperature rises (Null Point moves closer to the antenna) then turn Pot-1 a tiny bit
clockwise to offset this. You want to center on the sweet spot!
Do not readjust the L2 board Pot 5 after
your ideal thermal pitch drift setting is found.
Pot-6 5k with a R22 1k resistor in parallel (0 - 800 ohm) is
a very fine low pitch frequency tuning control. The higher frequencies will
seem non responsive to this control. Mount this Pot on your theremin control
panel so it is obvious. Solder the unused Pot tab to
the center tab. This allows you to easily
adjust a specific outside lower notes distance to the antenna where by all the
other linear notes using the Lev Antenna LC tuning are precisely where you
expect them to be. Start with Pot 6 centered. Adjust your main
pitch frequency using the course tune brass screw on L2b. Also
minor adjustments on Pot 4 can be ideal for course pitch
tuning.
Parts List:
These
components are listed on the main RS Illusion parts
List.
100% Radio Shack
Iron-On
Printed Circuit Board
L2
PDF (216k)
Pot-4
10k panel mounted. Course
tune and wave shape
You could wire jump Pot-2
connection and put a 1k Pot in series with Pot-4 for very low pitch fine tuning.
Pot-5 10k board mounted. (271-282) Thermal
Drift Trim
Using a 5k board
mounted Pot without R23-4.7k mounted is good." (Not
at Radio Shack)
Pot-6 5k panel mounted. (271-1714) Low
freq pitch tune
Using a 1k panel
mounted Pot without R22-1k mounted is good." (Not at
Radio Shack)
R7 & R23 - 4.7k
R22 -1k
R5, R6 - 10k
R21- 47k
C21 -.1uf (272-1069)
C4, C9, C18 100pf (272-123)
C13 & C21 are not used
L2a & L2b RF Chokes
2 x 100 uh (273-0102)
All Hardware purchased at
Lowes Hardware Store.
Use an L bracket
or the four corner holes to mount board next to the RS
Illusion board.
The L bracket with the tuning knob is a brass 1/2" wide x
1 1/8 corner bracket found in the picture framing section of Lowes Hardware.
(BRAINERD 401XC) Mount this bracket so you can see how far above the board the
L2 choke coils need to mount for proper alignment.
Both items below are in the drawers on the nuts & bolts isle.
The T-Nut in the L bracket is a 1/4-20 x 5/16 (HILLMAN
H#880939) Use a dab of epoxy to secure it. When you enlarge the bracket hole
with a drill bit, clamp it or the bit will grab and damage your volume hand.
The brass screw has a snap on plastic screw cap which swivels over the
head of the brass screw. I drilled a small hole on both sides of the cap, fed a wire around
the choke and pulled it tight back through the cap.
(HILLMAN 1/4" H#881033) Purchase at Lowes Hardware.
The part # 's on
this original board do not match the graphic.
.
close-up
RS Illusion Theremin board
recommendations:
See Modifications
webpage for connections to the RS Illusion or Ultimate 2c board.
Leave all the RS Illusion Theremin board Pots 1,2,3 mounted on the
Illusion pc board.
Change RS Illusion capacitor C3-.001uf to
.22 uf (104).
D8 - IN914
With the new L2 and the main board at 9 volts the TLC555 diode noise injector is less
obvious in the sound or not at all?
It works good if the diode is turned around, stripe towards LED 1.
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