LUX - NLC - build notes - thermin

Some build notes for the LUX module.

This is a Nonlinear Circuits Eurorack module.

It's just 2HP 

Think optical thermin.

Four resistors, two photodiodes and a dual op amp. 

The simplest NLC module, so far.

Links:

+ Wiki

+ BOM

The photodiodes pick up changes in the light and convert this into control voltages.

I think its a useful module to have ... we can always use extra CVs 

Remember though ..   the closer your hand is to the photodiode 

the lower the output voltage.

-----------------------------

The photodiode i'm using is this one (recommended by Andrew F).

His notes:

"The 3rd ones I tried were 1540051EA3590 which

are my favorite so far, with a 1M resistor the output voltage sits at

about 8V in my shed at noon (I have a skylight), so it is easy to

play the module and get a 0-8V range."

Mouser No:710-1540051EA3590

Mfr. No:

1540051EA3590

THT stands for through hole technology

Photo diodes consume light , converting it to a current.

Of course you can try different photodiodes.

Experiment :-)

There are actually two identical lux circuits on this module so you could 

set up each differently to suit different conditions.

 dRANO Hotshot -- injecting drano ??

Not recommended - :-(

 

I think this is a lyric from the band "The Cramps"

New kind of kick...

https://mojim.com/usy123111x24x2.htm

 

 

 

Schottky, power

rectifier or 10R,

optional - for reverse

voltage

protection...or not

I'll use 10R only because I have lots of them.

 

The photodiodes produce current when light falls on them. This is

fed to an op amp which spits out a voltage that reflects the light

intensity. 

The design is really supposed to be an ambience and movement

sensor to reflect changing light conditions (if you were playing

outdoors for example) and it responds to your movements as you move

around tweaking and patching.

 

I'm started using 1M resistors with the photodiode.

This put out very low voltages .... approx 1V.

...........hardly noticable 

Then tested with 10M resistors ...the module put out voltages between 5V and 8V

...... much better .... though maybe a touch too high for euro ???

 This is the basic circuit

I think its worth experimenting.

At the moment, I'm only experimenting with the feedback (10M) resistor.

The (1k) output resistor may also be worth fiddling with.

next ... 4.7M resistors ...  --- between 4 & 5 volts

... I would refer  a bigger range

I'm in fairly well lit room.

This may be  very different in a dark room

6.8M

range 6.7 and 4.4V

3.3M

I'll stay with 3.3M for the moment.

In a fully lit room the output is about 4.5V

maybe different in a dark room

 

-----------------------------------------------------------------------------------

You can find more NLC builds here.

http://djjondent.blogspot.com.au/2015/03/non-linear-circuits-ncl-index.html

--------------------------------------------------------------------------------------

Thermin- part 3 build - completion

This is part 3 of the Thermin build.

The earlier parts are  here:

Part 1

Thermin - Silicon Chip 

Part 2:

 Thermin - Silicon Chip - build pics 2

 

This is the build so far.

Resistors, caps, IC headers, trimmers are in.

There are two types of Diodes:

1n4004 x 4

1n4148 x 2

+ Diodes - Basic Info 

.

The 1n4004 form a bridge rectifier.

 

 The power supply is a 12V AC  job.

These rectify the AC to DC.

 

 It can also be powered with a DC battery.

But don't use a 12DC switchmode power supply

 

 

 

 

 

 

 

 

 

 

 

 

 

These are replacements for the inductors used in the original schematics.

IF oscillator Coil.

Its commonly used in radio receivers.

These coils can be bought to different specs.

Usually colour coded

In this project a black and 3 white are used.

..

The IF coil  is also known as an inter-frequency transformer.

The basic characteristic of every coil is inductance.

Their inductance can be adjusted by stretching or squeezing the coil turns.

 

...

The metal casing contains two coils. 

The first coil on the left is connected to a capacitor forming an oscillator circuit. 

The second coil transfers the signal to the next stage.

Install the voltage regulator.

Its a 7809 delivering 9V to the circuit.

final components... volume pot, power jack, switch, etc

 

 

 .... first tests

 

 

The antenna.Volume plate.

Its made from 1mm gauge aluminium.

...

 

                                                                                          Pitch antenna

connect speaker.

..

Tuning

The T1 reference coil doesn't need much adjustment.

 

Thermin - Silicon Chip - build pics 2

Some build pics of the Silicon Chip Thermin.

 

This kit has been sitting in the bottom of a draw for about a decade and I only dug it out

after a friend asked for advice re building a thermin from the old Moog designs.

Though this kit isn't the same I thought I'd finally put it together to learn about thermins in general.

I think this old Jaycar kit is discontinued.

 

This looks like a very easy project that

is great for beginners.

All through hole components.

This is part 2 of my Thermin notes.

The first part of the build notes are here:

• Thermin - Silicon Chip

More links:

https://www.siliconchip.com.au/Issue/2018/January/Make+your+own+Theremin+%E2%80%93+then+make+music%21

 

I'll discuss the circuit as I build the synth.

All Thermins start with this same basic circuit.

 

The basic circuit comprises 3 oscillators (reference, pitch & volume).

In this case they all operate at 455kHz.

Each oscillator is essentially identical.

They comprise a JEFT (junction field effect transistor) and a pre-wound IF (Intermediate Frequency) transformer. 

The JFETs are all 2N5485.

In this case the Reference oscillator = Q1 & T1 

The Pitch Osc = Q2 & T2

Vol Osc = Q3 & T3

 

The original Moog circuit used 2N 168 & 2N1086 transistors.

These are old GE  intermediate- and high-frequency transistors intended for use in radio receiver circuits.

I reckon these would be difficult to find today. 

 

+ Transistor - Basic info  

 

T1,T2 & T3 are the pre-wound IF (Intermediate Frequency) transformers.

These are a modern substitute for the inductors used in the vintage circuits.

Looks like you can buy these on Aliexpress, etc

 

The Tone Oscillators (ref & pitch)

The Reference & Pitch Oscillators are mixed in IC1 (called the product detector) to produce a audible tone.

IC1 = MC1496

It's a balanced modulator/mixer.

You won't find this in the original Moog circuit where the two oscillators are mixed through two capacitors and rectified through a diode.

 

Its a pretty common chip .

Pretty old ... dates I think from the 1970s. Easy to find on Ebay.

The MC1496 is used here as a mixer.

The signal inputs are on pins 1 & 4 .

Carrier inputs are pins 8 & 10.

Outputs are pins 6 & 12.

 

The deeper I compare this circuit with the original Moog circuit, the more I realise

how components have changed over the last 70 years.

I guess this is to be expected.

I wonder if its practical finding all those old vintage parts if you wished to stay true

to the original schematics.

Anyway, back to the build.

The VR2 trimmer looks like an new addition to the original circuit..

I think this is a basic wave shaper ???

It varies the coupling between the pitch & reference oscillators that produces the final voicing

& adds some waveform distortion. 

The addition of this shaper circuit changes the final timbre.

It can now be varied from a pure sinewave (which is not characteristic of a Thermin) to  a much deeper sounding square/ramp tone, which I think has a lot more harmonic content.

 

The output from IC1 is fed into IC2.

IC2 is a LM358 op amp.

It acts like a low pass filter.

Again, you won't find this in the vintage Moog Thermin. 

That circuit has no ICs. Its all transistor based.

 

The output from the filter is applied to the power amp (IC3, LM386)

 and this drives the speaker.

 

IC 3 = LM 386

IC 2 = Lm 358

IC 1= MC 1496

The Volume Oscillator.

This is made up of  T3 & Q3

The secondary winding of T3  is connected to the base of Q4 (BC548)

The collector of Q4 is  attached to T4 (and its capacitor).

T4 is another IF coil.

To be continued ......

Thermin- part 3 build - completion

 PS: do let me know if there are any mistakes or omissions. Cheers Jono

Thermin - Silicon Chip

 Some pics of a build... the Silicon Chip Thermin.

https://www.siliconchip.com.au/Issue/2018/January/Make+your+own+Theremin+%E2%80%93+then+make+music%21

This kit has been stuck in a draw for over 10 years ??

This design is from 2009.

A friend recently asked for some help in building a thermin  using Bob Moog's design.

In the 1960s Moog had 4 designs :

The Vangard, (Vacuum tubes)

The Professional (Transistors)

The Melodia (Kit & built vesions)

The Troubador

http://moogarchives.com/moogth2.htm

The Melodia could be purchased as a kit.

I though before I embark on that project I'll build this and see what I can learn.

This is the inside of a Melodia.

This old instrument seems to be made up of transistors, oscillators, coils and wires which create electromagnetic fields around the instrument's two antennae. 

Thermin's rely on the human body's capacitance. When you move your body in and out of that electromagnetic field, you change the frequency of the oscillating circuit.

You are actually making a variable capacitor with your hand being one plate, and the antenna, the other.

What a thermin contains are basically two primary circuits:
1) a pitch circuit.
2) volume circuit.

These two circuits are connected to individual antennas.

Vol antenna is on the left. pitch on the right.

The antennas need to be separated by at least 20 inches & be about 3.5 feet from the ground.

According to the build guide these antenna coils are machine wound by a special method called

"progressive universal" and cannot be duplicated by hand wiring. 

 

It looks like though the original circuit is quite simple, its full of hard to find parts.

The most difficult to obtain being the inductors.

More about inductors are here:

+ Inductors, ferric beads, noise reduction methods, etc

 

Inductors are also called coils or chokes.
They are passive two terminal components.
Like capacitors, they store energy.

However, in this case, energy is stored as a magnetic field.
They are usually made up of a insulated (copper) wire, wound round a core (magnetic ... iron or ferrite).

 

 

The schematics indicate (L4) 10mH volume and (L1) 75mH pitch antenna inductors.
These are wound coils that I think were only available only from Moog.
I can't find any manufacturer’s part number.  
They might be custom-made for Moog ???? 

 

According to the vintage DIY manual:

"satisfactory substitues for the antenna coils can be made by connecting

three 25mhy ferrite chokes in series

and

for the volume: connect two 10mhy chokes in series. 

It seems like the rest of the inductors (the 4 within the metal case) can be hand wound.

The pitch circuit used two oscillators:
A variable oscillator and a fixed oscillator.
The variable oscillator produces a range of frequencies and is connected to the vertical antenna.
The fixed oscillator generates waves at a static frequency.
 
Signals from the fixed and variable oscillators were mixed together
and then amplified and output as sound.

The second circuit (the volume circuit) controls the volume of the pitch circuit.
To do this it uses an oscillator connected to an antenna.
Disrupting the electromagnetic field around this antenna changes the volume of the tones from
the pitch circuit.

---------------------------------------------------------------------

Some Links:

https://technitoys.com/building-a-replica-moog-melodia-theremin/

how to make your own inductors

https://youtu.be/d-E12DlzGGc

 

https://youtu.be/awyLYgu6ODM

 

 This webpage is really useful:

https://rimstar.org/science_electronics_projects/coil_design_inductance.htm

 

 https://www.cs.nmsu.edu/~rth/EMTheremin.pdf

 

--------------------------------------------------------------------------

I'll start the silicon chip thermin build in another post

 

Diodes - Basic Info

The name diode is derived from “di–ode” which means a device that has two electrodes. 

These belong to the world of "semiconductors". 

Semiconductors are usually broken up into positive or P-type, and negative or N-type. --- this has nothing to do with the poles of a battery. The two types are joined together.

Orientation

A diode is a two-terminal electronic component that conducts current primarily in one direction; it has low resistance in one direction, and high resistance in the other. Wikipedia

They allow current to flow in one direction.

See the arrow.

A PN junction is the simplest form of the semiconductor diode.

 

 

 Semiconductor diodes are the most common type of diode.

 

Different Types of Diodes

• Small Signal Diode. ...
• Large Signal Diode. ...
• Zener Diode. ...
• Light Emitting Diode (LED) ...
• Constant Current Diodes. ...
• Schottky Diode. ...
• Shockley Diode. ...
• Step Recovery Diodes. (Snap-off)
• PN Junction Diodes
• Tunnel Diode (Esaki)
  
• Varactor diode (Varicap)
  
• Photo diode
• PIN diode
• Lazer diode
• Avalanche Diode 
• Vacuum Tube diodes
• Crystal rectifier (crystal diodes)
• Gunn Diodes
• Thermal Diodes
• Stabistors or Forward Reference Diodes 
• Gold-doped diodes
• Super barrier diodes
  

 Common Diodes you will use are Schottky, LED, Signal, photo and Zener

Schottky Diodes

Very commonly used in Synthesizers.

The main application area of Schottky diodes is in switching power supplies which are intended to work with frequencies over 20kHz.

They are also known as barrier or hot carrier diodes. 

They have their own symbol.

It has a low forward voltage drop and a very fast switching speed.  

The forward voltage drop is substantially less than that of the conventional silicon pn-junction diode. 

 

 

A silicon p–n diode has a typical forward voltage of 0.6 – 1.7 Volts, while the Schottky's forward voltage is 0.15– 0.45 V. This lower forward voltage requirement allows higher switching speeds and better system efficiency.  

 

 

These are all different types of Schottky Diodes

..

-----------------------------------------------------------------------------------

Photo diodes

A photodiode is a PN-junction diode that consumes light energy to produce an electric current.

It's designed to absorb photons.

 They are also called a photo-detector, a light detector, and a photo-sensor. 

Photodiodes are designed to work in reverse bias condition. 

Typical photodiode materials are Silicon, Germanium and Indium gallium arsenide.

In the NLC Lux module, its used to make a "optical thermin".

Links

+ http://sequence15.blogspot.com/2009/06/electricity-for-synth-diyers-diodes.html