Here
are never done before Phoenix Theremin concepts
1. The Becker Electrodeum is a parallel tuned electrode
or Pitch Antenna for ideal Pitch Field Linearity.
2. The
use of the L3 - 3.3 mh
choke with tickle wire is to sense the RF from
the L1 & L2 circuits.
This approach eliminates the need for buffer components with more
control over the final audio wave shape. (L3
may not be needed)
3. The use of
the VO618A opto-isolator driving the 600 ohm 1:1 transformer to create a
better wave shape with brightness in the sound.
4.
Thermal Drift Control - This is done with Pot-3 by balancing the
voltage drop across both transistors and balance the reactance of the oscillators.
Most drift comes from the PN
junction capacitance as vacuum tube theremins drift much less even
though hot.
5. Theremin
design would benefit from a small internal 12 volt battery @ < 100 ma
draw backup for critical performances to avoid when the power line
voltage briefly goes below the regulator minimum voltage, like when the
lights in the room blink. This does not have to be rechargeable as it
most likely is rarely if ever used. You could use the least expensive uninterruptable
power supply.
6. The
theremin oscillator design could be fashioned into an earth ground
quality tester.
Latest Up
to Date Notes:
2.09.21
While experimenting 9
volts can be applied
at the green terminal near Pot-3. Make sure earth ground is attached,
maybe to the negative side of your bench power supply. The audio
enhancement section uses a 5
volt regulator.
2.09.21
In the oscillator graphic above the use of L3 3300uh may not be needed.
The tickle wire length picking up the RF determines how much signal is
fed into the following circuits. This approach keeps the two oscillators
completely isolated from one another so it breaks out of Null or Zero
Beat below 30 Hz. The oscillators locking onto one another is actually
not a desire effect.
2.09.21 Substituted
Parts - 600:600 Audio
Transformer (original,
replacement)
3300 uh choke (original,
replacement)
2.09.21
It is best to have the Power
Supply components on
the Pitch Board for easy testing of the first board build. Also
this prevents any poor connection effects getting into the sound cause
by the board to board TRS jack connection.
- The
Power Supply parts are installed on one board only -
2.09.21
If Pitch & Volume boards are place in a EtherWave Standard box the Power
Supply needs to be on
the Volume Board so it does not get in the way of the EWS front panel
knobs.
2.10.21 If
the 10uf tantalum capacitor next to the 555 is mounted backward it acts
like a delayed short circuit.
2.10.21 The
220 ohm resistor in parallel with Pot-3 1k in the oscillator section
reduces the current through the Pot to less than .5 ma, also the
Pot behaves as an audio taper fashion which is desired.
2.04.21
Experiment: Replace
C17 & C19 with 3300
uh chokes in parallel with the IF Transformer to drop frequency down
to around 300 kHz and see if the Electrodeum Pitch Antenna works off the
third harmonic of the oscillator. This will further reduce thermal drift
and could have other benefits worth study.
2.04.21 A
device like
this could be used for remote Pitch Tuning when the theremin is
mounted in a sculpture or used in other applications.
2.03.21
If using IF transformers the secondary is not used so the copper trace
to one of the pads
of the secondary
on at each transformer must
be cut so the
secondary does not short out the oscillator circuit.
2.03.21
The Pitch Board must use the recommended IF Transformers or you will not
get a frequency that breaks out on Null or Zero Beat below 30 Hz. These
IF are not necessary on the Volume Board.
2.03.21
There are two methods of creating a signal that properly turns off the
Vactrol which is normally On so sound can pass. The most sensitive
method is seen in this
video. The oscillators are more tightly coupled breaking out of
Zero Beat around 1 kHz with a 5 kHz range. This needs more explanation
Working on List of what I can send:
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PCB x 2 I will cut the 4 pads to secondary so it does not short
IC sockets x 6
Vactrol x 1 For Volume Control
Vo618 Opto x 1 Enhances Sound
600:600 Audio Transformer Enhances Sound
3300 uh chokes x 4 , had to substitute as no Mouser stock
IF Transformers x 4 , I purchased 40 of these as they are excellent
IF tuning tool
Pot-3 1K thermal drift reducer
Match hFE of Transistor MPSA42 NPN x 6 also have a characteristic I like
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Wire Jump
Pot-1b terminal
Tantalum 10uf Capacitors
TRS Jacks needed
Do R31-100k mod at R2-220k
Add extra 3300 uh chokes, TRS Jacks, 5mm Terminals
Mount 7805 regulator none
in stock
Replacing C19
in the L2 oscillator section with a 5 pf variable capacitor
makes tuning or centering the heterodyning effect much easier. Used 10pf
not as good but better than adjusting the IF Transformers over and over.
Add a piece
of screen for folding the Pitch Board Oscillator shielding.
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I will solder the parts to boards for convenience.
This will all fit in a 6" x 10" bubble pack envelope.
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