Complete Phoenix Pitch/Volume theremin just two mouse clicks - Mouser Parts - about  $80 June 2018

Read how to get the free PCB board 
Two boards are needed for the complete project.

Note: The commercial pcb needs a center dimple drilled at each TRS jack to accommodate a metal tab and level the jack (View jack in middle of this page)

Do Not Install these parts initially - Pot-5, V1, VTL5C1, C9, LED-1, Q4, S1 & S2, U3 and all parts crossed with symbol "/"  R1, R18, R23, R25, R26, R29, R30, Rx, C6, C12, C21, C25, C26, C28.  The Pitch & Volume boards use a different combination.

Step #2   The Rest of the Parts

The ground plate is used under the Pitch Board only after the board is aligned in the enclosure and the stand-offs are glued into place, it is not used with the volume control board setup. It may not be necessary at all.

Connect 12 volts dc power to T6 or plug into the Jack with a positive tip. This connection is diode protected against reverse polarity.

The audio signal for testing is at the Out-2B jack. Use a stereo cable to your computer sound card input.

If needed revisit View the 3 x 3 Stuffed This test works the same except output the audio through an amplifier or sound card.

LED-2 (red) works as a tuning indicator, it will be Off at the Null and On if it detects the heterodyne audio signal even in the range is above human hearing. (ultra-sonic)   If L1 & L2 are "way out" of tune LED-2 will also be off.

Connect the two boards together, if you stuffed two, with a 3.5 mm TRS stereo cable plugged into the J2 Jack on both boards. Only one board needs 12 volts power connected directly to it. This power is passed through the J2 cable to the other board. Audio will only pass to the Volume Control board after the Harmonic Enhancement components and white wires are installed on the Pitch board.

* In the next Step #3 and Step #4 the Volume Board will need to be tuned 100 kHz lower than the Pitch Board which is about 800 kHz. An analog AM Radio will come in handy here for verification of frequencies.

Add this mod if desired only after everything is working perfect. A very faint birdie from LED-1 can occur, adding R32 on the modification webpage eliminates this plus really spreads the quiet side of the volume response.

The retuning of L1 is always necessary with any 3 x 3 section circuit or antenna change.

Connect the Phoenix to earth ground and the Lev Antenna. Once the L1 & L2 adjustments are finalized , only Pot-4 is used for tuning. The Lev Antenna has two mysterious features, first it give a perfectly linear pitch field and second where the wire connection is made it will compensate for thermal drift caused by the environment.

The Phoenix is "thermal drift resistant" as a bird she was born from fire and rose from the ashes.

Latest Board Modifications Found Here

Step #3   Pitch Board Only

Install:  Pot-5 -100k, C9 = .1uf

Remove the jumper wire at T1 C-D  from both boards and install Pot-5 = 5k on the pitch board only.

Extra power supply filtering is recommend on the Pitch board at the +9v Jumper wire. (See Mods) R31 & C29

LED-2 can use connecting wire so it can occupy the wood box hole drilled for LED-1 which is not use on the Pitch Board. LED-2 can be any type or color, LED-1 is critical and must be on the Volume Board only.

Install the Audio Enhancement parts for the best sound.
This audio is passed through the J2 cable to the Volume Control.
C6-1uf  C21-1uf  C25-1uf 
R1-1K  R18-10K  R26-2.2K  R29-2.2K
V1-Transformer with P facing towards Pot-1, this is the same area the Vactrol V1 mounts on the Volume Control Board.
U3- VO618A Opto, dimple to #1

Note: Mount C25 & R29 with longer leads above the board so they can be clipped and resoldered for testing for the best effect.

Install the two (white) Jumper wires for Audio Enhancement activation (See Mods)

The main reason not to have a ground under the L2 side is that it could interfere with inside pitch linearity of the Lev Antenna.

Out-2B is used for a pitch preview on the Pitch board. Custom wire in an internal headphone amplifier in the box or use one side of a stereo Eq-Pre Amp to prevent any loading distortion on the Phoenix audio signal.

For Perfect Pitch Field Linearity use the Lev Antenna concept and for Volume Control anything metal works. You want to avoid direct contact with the volume side antenna so insulate it with a plastic sleeve or run an insulated wire inside the loop.

If the Lev Antenna is not desired, a 3.3 mh coil is on the parts list to test in series with a regular 18" rod antenna.

After the enclosure has its holes drill and the PBC standoffs are glued into place, the Pitch board will need a 2" x 2" ground plate with a 2" wire soldered to it under the L1 half of the 3 x 3 section of the board. 

Have the ground plate copper side away from the solder connections under the L1 half of the osc board. Hold this in place with double adhesive foam tape.  (See Mods)  

The ground plate wire is connected at the terminal T1.  The ground at D is variable using Pot-5 for a more adjustable effect or just use C which is a fixed ground connection.

Step #4   Volume Board Only

Install:   Vactrol VTL5C1, green LED-1, C9- 1000uf, C6= 10uf on left side of Vactrol
Input-1 & Output-1 TRS Jacks, &  R34-10K (See Mods)

C17 & C19 only on the volume board 3 x 3 should be 100pf to move the frequency away from the Pitch Board frequency.

The Volume Control "will not" work without the green LED-1 installed.

See Modification R32-2.2k  (See Mods)  This is for expanded shading on the quiet side.

R33-4K7 was added on the volume board only. This quiets a hiss sometimes heard at low volume. (See Mods)

Pot-5  100k trimmer is installed on both the Volume and Pitch boards. 

A 100K (68k?) resistor is installed from B to Ant2 at the ABCD terminal to get the proper wave shape for volume.
Do not do this at first, try the ABD wiring method like on the pitch board, tune Pot-5 100K for wave shape. see here

Make the volume loop antenna connection at the Ant- terminal not Ant2 or which works best.

Note: Some sound cards display this wave shape inverted when it is not! If you really have a pointy up wave form with your volume response will be more on/off, with little or no shading. 

See the Volume Wave Shape webpage. This covers how to get the proper wave shape.

Volume Control needs a spikier waveform in the negative going direction. This can be scope viewed on the right side of C1 as a upward spike 0 to 500 hz  1 volt  p-p. You could record the signal into Audacity out Out-2B and spread it out to view. 

NPN Transistor Q3 flips the upward spike downward for proper operation of the 555 trigger pin-2. 

Almost any thing works for the volume side antenna. You could fashion a Loop or use a straight rod. I have considered using a paint roller metal rod. View Roller Rod .jpg 

The best volume antenna would be a rubber coated wire, feed this through a metal or plastic loop or other form.

With the Phoenix board used for volume control, the board indicator red LED-2 will “turn off” at the Null Point which is the loudest volume, and green LED-1 will be at it's brightest. 

If green LED-1 is Off no sound can pass to the main amplifier. The Mute switch turns off green LED-1.

The green LED-1 might be mounted so it is visible to the Thereminist.

Use the Phoenix volume control with any pitch only theremin or change that righty to a lefty. You can position the Phoenix volume control anywhere around you for comfort, especially for left handed playing. Using the Vactrol is a true resistive volume control and it adds no distortion to the original sound. (Keep signal level below 1v p-p)

Note: The Vactrol overdriven will flatten the audio signal peak; which adds distortion in the sound. This can be easily viewed in Audacity recorded from the Volume Control Output-1 TRS stereo jack. Turn Pot-1 on the Pitch board down a bit, CCW, this solves the flattening.

Mount the PCB's in their enclosure and connect the antennas. Retuning of L1 & L2 will now be necessary. You want the pitch board to be around 900 kHz and the volume board around 750 kHz.

Use your imagination to set the Phoenix up, mount the enclosure if using two on their own tripod or base.

Earth Ground is so important to the proper theremin sound that I advise using a power receptacle strip that has a green LED ground indicator. The LED should light steadily. Everything should plug into this one power strip. 

Connecting the Phoenix Output-1 to a  power amplifier which uses a three prong power plug is one method to get ground. 

Visit the Black Box ground for the Phoenix. Output-1 on the Volume Control board can be reconnected to use the Out-2B Jack so no 1/2" holes need to be drilled in the side of the box, just the bottom.

My method to avoid ground loop hum is shown on the graphic of the cable layout on my Phoenix Cables webpage. Using the ground loop isolator and the shortest cables are good ideas.

theremin@oldtemecula.com
Design by Christopher