September 12, 2016

"The Phoenix Ascended from the Ash and the Sun was Shining"

Rising Spirit of Theremin Breakout

Inspired by the YAEWSBM of Eric W. (dewster)  

In Memory of Fred J Mundell (FredM) & my friend Dana Abbott (Sewerpipe)

We reflect those who go before us... 

Christopher (oldtemecula)

Listen to my EtherWave Standard=> Mad Night.wav (channeling spirits)

1.9" x 3"

Purchase a finished EtherWave Standard board for $96, add my $50 modification and you will have a theremin better in design & sound than Clara Rockmore - That's Priceless

- Have the full range of classic theremin sound from beautiful flute to Clara to violin -

The Mixer Pot in the image above controls the RF level/blend across the mixer diode, along with the diode bias there is a sweet spot I adjust to. Another board the Harmonic Exciter is where the real vocal action happens. The third harmonic attenuation begins at the mixer diode to get that classic theremin sound. At the diode we have control over forward bias and RF mix.

Pull the C6 capacitor on the EWS and connect a Osc wire to each pad. The variable pitch side wire must connect to the Osc1, the other wire to Osc2 which is attached to the fixed oscillator. View this EWS Hot Rodding schematic.

The theremin breakout board will work with any two LC oscillators from 200 kHz to 1 MHz. The Harmonic Exciter board output audio is line level. (adjustable)

Mouser Parts List at Bottom of Webpage.


8.05.16  I will order 10 of the second PCB seen below next week, it is time.

7.25.16  Due to lack of interest I am in pause mode.

5.17.16 The Breakout PCB has been ordered. The Exciter board will come later.

5.11.15 Received the Mouser parts and most of the others.

5.08.16 Someone ask how the high pitch sound was, wish I could play tune  Sample.wav  1 Meg

A lot of parts on order, will order 10 of the first breakout PCB after I check out the parts.

Two switches could be used, one for Mute if wanted, one for a pure sine wave if needed for a sweet whistle.

5.06.16 I changed the potentiometer footprint to accommodate for more than one pot style.

First set of parts were ordered today from Mouser.

This second board is still developing

3.1" x 3.1"

LM386 Pitch Preview Amplifier Module

There is a spot on the board for home built theremin's to use a CdS photocell for a finger volume control in line to the main amplifier. Try this if traditional volume control is unavailable.

The Harmonic Exciter board on the left mounts on the wood shoulder by the volume control using a ribbon cable plugged into my other internal EWS breakout board.

There are four test points and ground on the left graphic. TP1 is the signal from the mixer diode, TP2 is a 3 volt audio signal sine wave, TP3 is ground and TP4 is a 5v p-p square wave from the 555 output in sync with TP2. TP5 is the final polished line level audio wave shape.

Another ribbon cable can be brought outside the box to drive a pitch preview LM386 ear bud amplifier with its own volume control knob, this also has a LED power ON indicator and a spot to mount a switch to Mute the theremin. The black power jack can output a regulated 5 volts or 9 volts @ low current to power something else like a pitch tuner, use a Y connector plugged into the pink 3.5 mm jack. The audio is pre-volume control. This extra external $3 - LM386 feature board is a luxury and not really necessary.

On the Standard the EWS Waveform pot is removed and set aside in the box, my Waveform pot will take its place. I might even replace the Brightness pot with my Exciter Gain pot.

Both EWS pots remain intact and connected, just removed from the panel and place securely aside inside the box.

On the EW Plus the Phoenix Exciter pots, which use a ribbon cable, could be dropped outside the box without drilling any holes so they do not interfere with the Plus panel potentiometers. 

Note: My Breakout board extends 1/2" (13mm) beyond the edge of the EWS PCB, it may not fit in the space behind the EW Plus custom board. Someone needs to experiment.

Find this Harmonic Analysis freeware program Here
Bypassing the Harmonic Exciter - Off Exciter On - This gives me the Clara sound I like
The two displays are in this recorded sound byte, about halfway I switch On the Harmonic Exciter
(right image), then OMG!

Switched on Clara.wav
Theremin Direct to Sound Card wav 3 megs

In the right image the third harmonic sits at 1-khz, this is the exact harmonic balance I try to dial in.

Using a pot you can sweep the range from a bland EWS to Hello Clara, how do engineers Model that in software?

Most diodes for mixing seemed to work ok, the 1N914 worked the best for me. I like the germanium diode 1N34A but I can find no extra benefits. I tried a germanium 1N60 and it did not work as good for the 3rd harmonic issue. I tried an old germanium transistor base/collector and it worked outstanding. Serendipity 

I also tried a 1N4007, it sounded a bit like Donald Duck singing. This breakout circuit board allows for a terminal to be mounted in place of the mixer diode so you can experiment with different diodes.


Clara wave shape from the Mixer Diode (top) to the Harmonic Exciter output (bottom)

Top = 1-volt per grid-line, Bottom = 2-volts per grid-line @ 400 Hz

Exciter output uses a potentiometer feeding back to the EWS VCA

The key to the authentic sound of Lev Sergeyevich Termen is the lazy bottom in the waveform. This is what generates the throaty vocal sound. This is created by having a minimum bias through the RF mixing diode. Full bias creates the ideal sine wave. 

The skew on top in the bottom wave shape develops by using an audio transformer, this generates the even harmonic overtones.

The above RCA wave shapes are from master builder Andrew Baron's RCA Registry webpage. 
Read what he states creates a beautiful sound.

Notice the RCA 880 Hz wave shape against my 400 Hz, the RCA 220 Hz flat bottom creates the buzz.

My sound bytes reveal this schematic is more than engineer Modeling bluster.

Most theremin builders want to build with substance not theory. I created this webpage because there is just too much intellectual engineering gibberish going on and very little demonstration of hands on practice.

Feed two Vacuum Tube RF Oscillator signals through this buffer and the spirits will be channeled, I have done it.

Pull the C6 capacitor of the EWS and connect a wire to each pad. This isolates both oscillator signals from one another. The variable pitch side wire must connect to the Osc1, the other wire to Osc2 which is attached to the fixed oscillator. View this EWS Hot Rodding schematic.

Pulling C2 instead of C6 will effect linearity, this may be better but needs study.

R1-100K & R10-470K instead of Pot 1M a simple switch or pin jumper can be used. 
Open = Clara, when Closed = sweet sine wave.

gnd--jmp if jumped allows this buffer board to be used with other single supply theremin design's.

gnd is a connection between +12v & -12v along with earth ground.

The bottom right side terminal is the audio straight from the Phoenix Harmonic Exciter board back to the EWS VCA. This signal level is pot adjustable.

Diode D2 & D4 help prevent accidental reverse power connections.

Diode D3 replaces the diode removed from the back of the EWS board for the Breakout installation.

Q1 & Q2 emitters are deliberately lean on current ~1 ma, for the lazy wave shape, to me the sound is better.

This buffer board outputs an ideal sine wave whistle (.2v p-p) not using the plug-on Exciter Board and by placing a pin jumper across the two center In-Out pins at the 4-pin Buffer-Breakout strip. The buffer board by itself is not the sound I am after.

Buffer Breakout Parts  
Buffer Breakout
  Harmonic Exciter
Harmonic Exciter Parts

Mouser Parts List:

Mouser Parts List For Buffer & Exciter Boards  $35   8.15.16   Parts are for both boards the Breakout & Harmonic Exciter (this needs update)

Supplied by oldtemecula, the PCB's, the cable between boards, the 2x .1" 4-pin strip, 2x 8 pin dip socket, the 10K waveform pot which replaces the original EWS pot and a LM386 finished pitch preview amplifier module.  Added a CdS cell to experiment with manual volume control at  FV.

Валерий я не забыл тебя.

9.12.16   I have a handful of Harmonic Exciter project sets to give away to EWS owners at no cost. This is experimental and your success is dependant upon your skills to follow directions and soldering the tiny pads properly. Only C2-15pf is removed from the EWS. If you can not get your build to work properly simply remove the build and tack the extra C2-15pf on the parts list back to where it was and no one will ever know. If it does work.......WOW!

Your EtherWave Standard could sound like this.
Notice the Interesting Harmonic Spread

My decision on who gets this package is based upon your sharing a photo and description of your past electronic accomplishments. I will create a new webpage with more construction details if there is any interest in my research. This is not a beginner build.

Post your interest in my Chat Forum