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The pitch & volume boards are connected together
through the J2 TRS jack. 12 volt
power can go to either board power supply setup. The regulated 9 volts
goes through J2 TRS
jack to the other board. All this from a
single 12 volt AC transformer with earth ground.
Amazon
Parts not on 3.04.20
board are marked in red, blue are part value changes. Pot-2 & purple
line not defined yet and not needed, still experimental.
- Click on Board to Enlarge -
View is of top of board looking through it -
- This board
is used for both Pitch or Volume with minor component changes -
| Static Discharge protection with the Phoenix is accomplished by using a high voltage wire within the loop but no direct connection to the loop.
Static discharge maxes out around 12kv. A static spark to the loop is dissipated in the
metal loop and absorbed back to the atmosphere. Static discharge is not quite DC but the
DC resistance of the loop circuit to ground when using the L4
inductor is about four ohms. The voltage pressure on the
metal loop bypasses the volume control circuits. This lack of
static discharge preventive
measures has destroyed many Theremins when grabbing the Volume loop. |
vol-buffer
8.24.20
- I will post an actual picture of my 3.04.20 board with this mod, the
Volume Board copper foil must be cut by C21.
| 8.25.20
- The above and below board wires for Volume Board pre-amp section
is a bit confusing, will be working on it.
On the Volume Board
R28- 10k
lower right corner can remain on top, also the Out-2 TRS jack is
not needed.
On the Pitch Board R28
is moved to the bottom of board so the
TRS jack at pin 5 can be the output for a Pitch Preview ear bud.
The copper trace above pin-5 needs to be cut. Better picture
coming. I
will first draw this pre-amp section schematic so the connections
make sense. |
Special wiring
of the 3.04.20 board to add in a volume buffer section using U2A with a
3:1 gain. The green lines are wires, the blue represent a
component. x marks parts not mounted on Volume board only. The
track needs to be cut above the RCA jack. The latest board date will
have this better laid out.
This is the
latest board with volume pre-amp corrections
The parts with
a pink x
should not be on the volume board. Pot-5 10k is on the updated board but
can be fashioned onto the 3.04.20 board, U3 is not mounted which allows
C25- 10uf to be used. The pink wires are for the Pre-Amp U2a to be used to
feed the Vactrol audio in.
Audio
Section
Volume
Section of the board
9.06.20
I will put these images here until I find a better place.
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-
The last components stuffed in the Audio section on both
boards -
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The R39- 10k, D3- 1N914, C37- 1uf, C32-.1, D4 & D5 1N4007 are
only needed on the Volume Control board. R38- 10k
is on the back side of board using the R32 pads.
View
Schematic
of this Mod
Using
the TRS jack for AC power input on the Pitch Board solder
the green wire to the bottom of the board
|
freq-to-vol
The two 1N4001
diodes drop circuit voltage to 8 volts, this worked better for the volume setup.
Scope0 -
Compare to sample below
.
Scope0
- In this sample I reversed the direction of the L2 coil from the
sample above. Interesting shift in phase.
The
board for my Pitch has a real nice round wave shape not pointy as
above.
Over
the AM Radio I can hear a nice sine wave from this pointy wave
above so the detector diode may have more influence than I
thought. A rounder wave shape is better for the theremin vocal
sound.
Need
to study if an increase in detector diode current might round out the
wave shape.
|
Scope2 -
Output Pin-7 of LM358 to 555 trigger, Pin-2 using .1 uf input
.
|
Scope1 -
This is control signal at bias Pin-5 of LM358, Input 1uf or 105
With
bias fixed at ground no signal the Scope2 LM358 output is a square
wave that follows the input frequency. This shuts off volume as
the Pin-2 signal is High too long. With the 555 Pin-2 chopped by
the Pin-5 of LM358 signal the duration of being High at 555 Pin-2
is reduced so not all the way off.
Notice
in sample below the above control wave shape is imposed up side
down onto the wave shape. This is good as it reduces the time of
the 555 is High quieting the sound. High input to 555 output goes
Low which drains C9 diming the green LED or quieting the sound..
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|
Scope2 -
Output Pin-7 of LM358 to 555 trigger Pin-2, Input 1uf or 105
This
wave shape above is what I feedback on the Pitch Board to add grit
to the sound. This is added through a 50k potentiometer with build
in switch to turn off the added effect. experimental
|
Scope2 -
Output Pin-7 of LM358 to 555 trigger Pin-2, Input 1uf or 105
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Use
the inline volume control from the pitch preview jack to the
ear bud.
The
yellow wire on board can have a switch inserted to Mute Sound
The volume
response can be on/off or adjusted out to 18" of fade window
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Caution:
Touching the
Phoenix volume loop
could turn the sound back
on
| It
overwhelms or stalls out the sensitive variable volume oscillator. To prevent
this
do not use a direct connection to the metal loop... feed in
about 8" of insulated wire, then check the overall response, adjust if needed.
For solid loops see below.
- Using high voltage wire also "protects" against static discharge -
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If your
Volume Loop is a solid rod then wrap insulated wire on one end for gradual
build up of capacitive
coupling. Keep wrapping until grabbing the loop stalls out the volume
oscillator and the sound comes back on, then remove a few wraps until
stable. I have not
tried the one below.. so experiment.
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