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10.03.13 

Theremin
Phoenix 
Volume Control Enhancements

Control Voltage on Steroids

PDF & Parts List

Center the board within outline when ironing, PDF face up. This tacks it to the board then flip over for final ironing.

PWM to control:

Volume Level with Step

LED Volume Torch Fade 
6v @ 200 ma

Pitch Preview Volume Fade
The Volume Enhancement board uses the Phoenix volume control's 555 pulsed PWM output to vary a super bright LED light source. Start with the Torch Terminal full On, fading down to Off in relationship to quieting of the volume control. 

J1 connects to a custom wiring of Out-2b jack on main board on the volume board. This board is powered with 9 volts on the jack Pin 5 the tip.  The output of the 555 pulse is connected to Pin 2 at the Out-2b jack and ground on the sleeve, jack Pin 1.

J2 connects to Y adapter off the J2 on the main volume board to get higher 12 volts which side steps the 7809. 

Normally with a theremin volume control, the outside pitch field quieting is insignificant. With this board you can set how much the first-step of detection fades in volume (5% to 50%) from your hand first being detected. This audio is taken from the VC-Enhancer Output-1 and not Output-1 on the Phoenix board.

This board also has an automatic Pitch Preview Fade as the main amplifier increases in volume. The preview jack on this board can have a resistor (1K?) placed across it to set the level of sound. This preview jack should drive a headphone amplifier.

R2- 300R & D1 sets the sensitivity and range of the U1 primary side internal LED.

R12- 47R  This could be a jumper wire, having it adds a bit more noise filtering.

Pot-1 Using a value of 2.2K = On/Off 100% change while 50K creates a minimal response 5% change in the first-step reduction, for both light and volume.

C1- 470 uf sets the first-step fade speed up or down for a natural affect, no abrupt On or Off.

C2- Sets first-step duration 1uf = 1 sec, .1= .1 sec.

Green LED-1 On, sound or light is at maximum.

Red LED-2 On = attenuation of brightness or sound is occurring while Pitch Preview increases in volume.

The Box  Mouser  box blueprint PDF    2.6 X 4.25 X 1.12    Date on PCB-PDF should be 9.23.13 or later

The TORCH output will drive a super bright LED flash light (6v @ 200 ma) to shine a volume controlled varying light on your performance.
The green wire passes the audio signal from the J2 Jack cable to the Vactrol circuit which adds in the first-step volume reducing effect then out to Output-1. Then to main Amp.

The purple wire passes the J2 Jack audio signal to the pitch preview Jack through U1 which auto fades when the theremin volume increases.

The red wire passes +9 volts to U1 which is a VO61A Opto Chip used for the Pitch Preview.

The blue wire passes the one shot 555 output to Pot-1 which shifts the volume level down a predetermined amount at the first detection of your volume hand in the loop field.

Notes:

The 555 PWM  normal level is +9v to just then pulses to ground when triggered. The responding circuits must also be powered by ground to +9v. The volume torch circuit works best powered by a separate 12 volts DC supply or J2 the input side of your 7809 voltage regulator. If using a single wall-wart this extra load on the transformer may add 60/120 hz hum in your audio sound.

Torch Driver: The PWM drives a TIP31 NPN transistor as a variable current driver at ~ 6v @ 200 ma. The 10 ohm 10 Watt power resistor is for short protection and drops the balance of 12 volts down to around 6 volts for powering the LED torch.

Pitch Preview: R1- 2.2k turns on U1 internal LED. It determines the intensity and when audio is heard in the ear-bud. Using a 4.7k causes a later response in the volume quieting.

First Step: The main theremin volume quieting uses a mono-stable trip circuit or missing pulse to sense the volume control first quieting PWM pulse breaking out of Null to have more initial volume quieting effect. 

R10 - 2.2k  (10K) holds Q1 PNP base positive so it is off.  Q1 is pulsed on through C3-.22uf  (.01uf - 1uf )

R100  100 ohm @ 1 watt located on the Phoenix Volume Control board protects the 555 output from shorting when an incorrect TS plug is plugged into the Out-2b jack or while the proper stereo plug is pushed into the Out-2b TRS Jack. The plug tip is +V, the Ring is PWM, the Sleeve is at ground.

Idea, maybe use a 3.5 mm male to a two 1/4" female Y so an effects pedal can plug into one side and reduce the playing level of sound 50% with a resistor value to ground.

The circuit board above uses these three circuits below to add extra features to an ordinary theremin volume control.


.
Perceptions of Increases in Decibel Level
Imperceptible Change 1dB
 Barely Perceptible Change 3dB
Clearly Noticeable Change 5dB
About Twice as Loud 10dB
About Four Times as Loud 20dB
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At Null theremin volume is max, as volume begins to quiet with pulses it turns on U1 and it begins to pass audio to the ear bud. So at maximum volume no sound is heard in ear bud.
The Phoenix R100 refers to a resistor mounted from Pin 3 on the main theremin board 555 to the Out-2b jack which you will custom wire. The 100 ohm resistor limits the short current as a stereo plug is inserted into the jack. The jack is wired to output  +9v, gnd and the 555 8 volt pulse to drive Volume Torch board.