Special page for Ignacio

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Phoenix Pitch Board

Parts List Phoenix EWS


- My original theremin design is not easy... only because we are human and make mistakes -

- This is ready, will be mailed out around Feb 22 when my assistant picks up my meds -
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Features:  Null-Tuning,  Mute Switch, Pitch Preview, Adjustable Timbre (sine to vocal), using the Electrodeum Antenna/Electrode the Pitch Field Linearity will be similar to the E-pro. 

Pitch Drift is suppressed with Pot-3 (seen as blue Pot below) balancing the two transistors PN junction capacitance along with the reactance of both oscillators.

This is the actual Pitch Board as of  9/19/20 - Breaks out of Null below 30 Hz Smooth

Click on image to enlarge

View Ignacio Boards Under Construction


Note:
On the 3.04.20 board the two secondary IF Transformer pins should be cut off or not soldered.
Or
Cut one of the traces to the IF Transformer secondary


This ferrite cup type of IF Transformer is a " Must" to shield the two Inductive Fields from each other


The Oscillator is Colpitts in design, C17 & C18 could be replace with an Inductor to go much lower in frequency which might better reduce thermal drift. Another idea is to replace C19 with a 5pf variable capacitor to make aligning the frequencies for heterodyning easier.

The Pitch Antenna L4 circuit needs to resonate for ideal linearity, a lower harmonic might work.

Red X are parts not needed, Left oscillator side blue lines = R8- 3.3k, R20-3.3k, R25- 220, parallel C29 with a .1uf capacitor on the bottom of the board to bypass high frequencies.

* The blue line under the ICl 555 on right side of board is a 100k resistor connected at R2- 220k to top of R31- 33k   C5- 1uf lower right needs connection relocated.

U2a is used as a 1:1 signal buffer for the Pitch Preview & Audio Out through J2 TRS Jack

   unmod-pitch - Press Ctrl-F5 to update image to 2.09.21 -  

The two parallel yellow lines are the signal out from the transformer to the 1:1 gain LM358 buffer and back to C6-10uf cap which feeds Pin-2 on the TRS Jack by the 7805 above which connects to the Volume Board. The board 9 volts dc is also transferred here. 

TRS Jack     Tip= +9 volts      Ring = Audio      Sleeve= Neg

Both images are looking through the board from the top side, not a bottom view

- Click on image for clear enlargement -

A few parts are not needed on this board seen with the red X

Near C41-1uf the short yellow line on the Pitch Board is a needed solder bridge across the pads for 1:1 gain

2.09.21 Notes

At long blue line mount a 220uf axial capacitor across for Pitch Preview signal at TRS J3.

Once everything is working good it would be more solid to solder parts directly to the board that are in a terminal. The Oscillator Section would be most important.

The Phoenix Electrodeum board uses less than 35 ma. You want the minimal working voltage across the 7809 for it to still work properly 11.5v to 12v. This keeps unwanted heat at a minimum in the box.


The ideal Pitch Wave Shape, the droop is throaty, the upper skew is even harmonics.

The above waveform is this webpage which is the original Timbre circuit heard in all 2020 YouTube video's

I should organize and put all notes in a Printable PDF file

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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