Or more precisely – how to build a ring mod and light flasher.
The first step I took was to download the manual for the MoogerFooger and find out what all the knobs do. It looks to me like Nick Briggs uses a “secret Dalek factor” as the carrier and feeds this through a traditional ring modulator constructed from 4 diodes and 2 audio transformers.
Luckily there’s a great website that shows you how to build a passive analog ring mod here:
Follow the directions on the page and wire up the audio transformers:
and the germanium diodes
in the characteristic ring arrangement:
Your voice goes in on the red wires, the secret Dalek factor goes in on the green, and Dalek magic comes out of the yellow. (Actually connecting up in any order will make the RM work)
OK now to add the secret Dalek factor.
I don’t like to re-invent the wheel, so if there’s something out there that can *almost* do the job, I will hack away at that rather than design something from scratch.
The secret Dalek factor (as most of you know) is a 30Hz sine wave. So we need to find an audio oscillator that can provide what we need. Fortunately for us, (and Mr Hewlett, *and* Mr Packard), there’s such a thing as a WIEN-BRIDGE oscillator. Rainbow Kits sells a nice one for $not-very-much-at-all.
However, out of the box this kit does not do what we want. It oscillates at a fixed frequency that is too fast. After a bit of RC [1/2PiRC] math it turns out that we need to replace capacitors C1 and C2 with 0.1uF ceramic caps, and resistors C5 and C6 with approx 53.1KOhm.
Alternatively you can do as I did and get a dual gang pot (200KOhm) and turn this till the output reads close to 30Hz.
Great, so we’ve added the secret Dalek factor on the green wires, now we need to add the voice. For this we’ll need a microphone and a pre-amp. Velleman to the rescue here:
This tiny kit goes straight in unmodded.
All that remains is to add the speakers – for this I hooked up to 12v PC speakers to the red wires. Plug it in and hey presto – instant Dalek.
The sound can be improved greatly by feeding the microphone through an EQ effect pedal, boosting the mid-range and cutting the high and low.
Next stop – the light flashers…
This was tricky. The standard Schmitt trigger that’s on Dalek City is OK, but the lights can get stuck in the “on” position and you have to cough to toggle them off. Also inside the cockpit there’s no visual feedback to what the dome lights are doing. Also the current requirement to flash 2 x 20W halogen lights on 12V is pretty darned high.
Again, I’m just going to mod some existing cheap kits that are readily available. The first kit is the well-known Velleman MK103 sound to LED light flasher:
This works at a mic level input – great for us – and has high impedance so the signal is not really affected. It only light 4 LEDs though which is no where near what we want to power 40 watts of halogen grooviness.
Here’s a picture showing the basic mod:
I replaced the built in mic with two wires which is connected to the mic socket, and the last LED (4) has been removed. You can simply wire this output into an optoisolator (4n29) through a 1K resistor, then use a big power resistor to switch the lights (TIP142, or a Mosfet)
OR…. you can take the Rolls Royce approach and wire the output directly into this little beauty:
The fantabulous Velleman MK114 12v sound to light kit, rated at up to 50 watts at 12v and a brain tingling 100 watts at 24v!
You just plug it straight in and away you go…
Note – the MK103 really likes to be run at 9v, not 12 – so I added a 9v regulator to run it where it wants to be.
I like this solution, there are two parallel transistors and a nice big fuse. It really *looks* like it can handle the power.
So that’s it, your voice mod, light flashing device is ready to be installed in your favourite MkIII travel machine. The lamps I have plugged in are low power, as my PSU cannot put out enough current to drive the two 20w halogen bulbs I just bought. So I need a bigger PSU…
Of course, this is only half of the story.
To really sound like a Dalek you have to adopt the harsh staccato tone, and do a bit of acting…