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Dalek / Cybermen voice changer

A simple ring-modulator circuit which can change your voice to sound like a Dalek or Cybermen from Doctor Who

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Using this simple analogue electronics project you can make your own Doctor Who inspired voice changer to sound like the Daleks or Cybermen.
I have been throwing this around for a while and need to go over everything to document it. The final goal is to retrofit a portable guitar amplifier as a self-contained unit, so you don't have to be constrained to your desk.

Building blocks of the project:

  • Microphone amplifier
  • Signal Generator - A sine wave with frequency depending on character and era (~30Hz)
  • Ring modulator - Combines a generated frequency with a voice input, making the effect.
  • Output Amplifier and Speaker
  • Fading light effect (Optional)

electret-microphone-amplifier.sch

KiCAD schematic for an electret microphone amplifier circuit using an LM386

sch - 9.03 kB - 11/05/2020 at 11:38

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electret-microphone-amplifier.png

Image of a KiCAD schematic for an electret microphone amplifier circuit using an LM386

Portable Network Graphics (PNG) - 40.84 kB - 10/30/2020 at 10:32

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ring-modulator-bg.png

Image of a KiCAD schematic for a ring modulator

Portable Network Graphics (PNG) - 40.39 kB - 08/20/2017 at 21:29

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dalek-ring-modulator.sch

KiCAD schematic for a ring modulator

x-kicad-schematic - 4.44 kB - 08/20/2017 at 21:19

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led-vu-meter.png

Image of a KiCAD schematic for a single LED VU meter using an LM386

Portable Network Graphics (PNG) - 21.44 kB - 08/18/2017 at 22:57

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  • 2 × Vigortronix VTX-101-1604 Signal transformer with centre-tap
  • 4 × 1N4148 Signal Diode (Don't worry about Germanium)
  • 2 × LM386 Low voltage audio power amplifier
  • 1 × Various capacitors and resistors Check out each schematic for parts
  • 1 × Speaker 8Ω 0.3W

  • New transformers tested and working

    Sproket12/16/2020 at 11:59 0 comments

    The 1:1 +C.T. transformers (Vigortronix VTX-101-1604) have arrived and seem to work well once soldered to some strip-board. Powering this board using the existing microphone amplifier and an external sine-wave source gives the desired result. It seems as though a buffer amplifier is required on the output due to signal drop through the ring modulator. Can always use that as a volume control for the speaker output. Nearly there, just being held back by another project deadline.

    1:1 Ring Modulator on strip board
    1:1 Ring Modulator on strip board

  • ​Some considerations and findings

    Sproket11/20/2020 at 10:42 0 comments

    The LT700 transformer is readily available, relatively cheap, and can be used in a ring modulator circuit. Many people including myself have used it successfully to create a Dalek / Cyberman voice changer. However, it is also less than ideal. The transformer is primarily designed to be used as an output stage for driving a speaker. Which is kinda okay for the output half of the ring modulator, however, the input half is effectively using the transformer backwards. Driving a signal into the very low impedance output of the transformer (especially with a large step-up in turns ratio) is a bit tricky. The ever popular LM386 power-amp IC is supposed to drive loads of at least 4R, unfortunately the transformers single-winding has a resistance of nearer zero (ignoring transformer load relationships for simplicity). Ideally an audio isolation transformer with a turns ratio of 1:1 should be used. From the usual retailers these can easily cost £10 GBP or $13 USD single quantity, so an online 'auction' website may be the way to go for ~half the price.

    TLDR: The LT700 should be replaced with an audio isolation transformer with ratio of 1:1 so that the LM386 can drive a more suitable load.

    UPDATE: I have managed to find a suitable 1:1 600R isolation transformer with a centre tap for £4 single quantity. Shall hopefully have some Vigortronix VTX-101-1604 transformers arrive next week for testing.

    Shame.. I have a bag full of LT700 transformers and now don't know what to do with them.


    I very quickly designed a PCB for the ring modulator using Easy EDA, unfortunately the footprint I used didn't have large plated through holes for mechanical support. This is being corrected and will be designed in KiCAD with a custom footprint as one doesn't seem to exist.

    Ring modulator PCB top
    Mechanical through-holes need to be added to the next revision, but looks neat.
    Ring modulator PCB bottom
    Soldering is a mess due to a dirty board. The copper idents turned out nicely though.

  • Microphone amplifier

    Sproket11/05/2020 at 09:26 0 comments

    An electret microphone amplifier circuit using an LM386 has been successfully tested. With an additional capacitor between pins 1 & 8 for 200x gain, the amplified signal is a bit overkill. A potentiometer wired as a variable resistor will need to be included for setting the correct gain. This gain value could be fixed, but when using a microphone inconsistent input volume is to be expected.


    Microphone amplifier schematic



    Microphone amplifier on breadboard.
    Using a speaker for output testing there is lots of feedback, especially when C4 200x gain capacitor is fitted.



    Printed Circuit Boards.
    This etched board shows version two of the layout with a corrected IC footprint and addition of component idents on the top copper layer. Components are on the bottom layer due to it being a single-sided PCB. Kicad can get confusing with idents being pushed to a different layer than the footprint, but it is workable.



    First revision of PCB. Assembled and working.

  • Frequency generator

    Sproket08/30/2017 at 12:55 0 comments

    Using an LM386 low voltage amplifier I made a simple resonator to see what the output would be. A 470uF capacitor with the load of an 8Ohm speaker gave a useful frequency of 40Hz. Unfortunately instead of resembling a sine wave the lower frequencies became more of an asymmetrical square wave. This is still usable to an extent but not ideal for recreating an authentic sound. It would be best to make a more accurate sine wave generator to drive the amplifier and ring-modulator in tern.

    Direct digital synthesis of waveforms is entirely possible, cheap, flexible, and compact using a microcontroller. But since I have the transformers and amplifiers at hand, and the Radiophonic workshop wouldn't of had microcontrollers, I want this project to be entirely analogue.

  • And it begins - Documentation

    Sproket08/21/2017 at 12:24 0 comments

    After a lot of hassle with editing build instructions and a lot of re-uploading of images; I have the start of this projects documentation. I now have images of a couple schematics, breadboarding, and soldered vero strip board. A link has been added to the BBCs research page for the Radiophonic Workshop ring modulator, and a schematic where I found the light-organ / LED VU meter.

    Other modules to come soon.

  • Document and finalise

    Sproket08/19/2017 at 11:13 0 comments

    For a while now, since coming across a whole pile of signal transformers. I have been making various building blocks to retrofit a portable guitar amplifier as a Dalek/Cybermen voice changer.

    I have all the parts working, almost. This is an attempt to document my works for the hopeful benefit to myself and others.

View all 6 project logs

  • 1
    Download, check, purchase, prepare

    I have recently started finding all the modules used to make this project, and if I am lucky the schematics or references for them. Documentation is still a work in progress so not all steps are there just yet.

    1. Download the KiCAD schematic files and/or the PNG images of the circuitry.
    2. Check the BOM (Bill of Materials) and make a list of parts which the project requires.
    3. Purchase the parts from your favourite online or otherwise-based electronics retailer.
    4. Prepare for what is to come.. Board layout, soldering, testing, thoroughly annoying anyone who doesn't appreciate what you have created.
  • 2
    Prototype

    Stick prongy-leggy things into a breadboard anywhere you like, as long as you follow the dot-to-dot schematic. Try each section at a time, and try again.

    1. Electret microphone amplifier. Showed directly connected to speaker for testing.

    2. Sine wave generator - Future Update
    3. Ring Modulator
    4. Speaker & Amp - Almost identical to the microphone amplifier - Future Update
    5. *LED fade-effect or light-organ. Operates much like the light emitting from a Dalek's plunger (** *Optional) (**Optional)

    Probable Tip: If you haven't got any testing gear you could make the amplifier first and use it to test the noisy parts individually. Or just stick a speaker on the output seeing as though the LM386 is usually happy with that.

  • 3
    Don't get too excited, it will all fall apart.

    So hopefully your rats-nest works and is gleefully exciting you. You have probably noticed bits constantly falling off. It is time to painstakingly recreate each part ALL OVER AGAIN but on [Vero] strip board. It's a good thing though, it shouldn't fall apart again if you do it well.

    Don't try to follow my examples precisely, I have a habit of using boards which look alright at the start but instantly become too narrow.

    PICTURES OF SOLDERED STUFF

    The light-organ or single LED VU meter.


    The Ring-Modulator. I used 1/4" TS Jack plugs on mine for testing. Not entirely necessary but it was fun using a keyboard/PA amp much to the bemusement of everyone present.


    More to follow...

View all 3 instructions

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