Ring Modulator (dalek emulator)

[bizzlemedia]

Hi there,

The project I am working on at the moment revolves around a simple ring modulator circuit which I have built however I am having trouble deciding what to use as an onboard sin wave generator to act as the modulator signal (not sure If I have carrier and modulator mixed up). Basically, I have my microphone signal connected carrier input but I need something which I can include inside the same project box to produce a 30hz (aprox) sin wave to modulate the signal to produce a Dalek emulation.

555 timer chips are out of the question as I can only produce square waves with them. My analogue sin wave generation circuits look unnecessarily complicated and I need something small and simple.
I can produce a fantastic Dalek sound using my function generator as the modulator but obviously that can't be included in the finished project. Would a microcontroller do the trick? In a perfect work I would also like to be able to attach a pot to vary the frequency of the sin wave (between 5hz and 200hz)

Any suggestions would be greatly appreciated. Thanks

i

 

[Harald Kapp]

There are lots of simple sine wave generaators, e.g. this one. At 30 Hz the capacitors may become very big.
You could use a 555 followed by a low pass filter. You'd Need at least a 2nd order filter, better a 4th order filter. Here's one out of many available tools for designing such a filter. With an active filter you can keep capacitors small by choosing high resistor values. There's a limit to the resistance, however, because leackage currents will create noticeable offset voltages on high resistances.

 

[duke37]

Here is a low frequency phase shift oscillator from 'Transistors Theory and Circuits' byK.J.Dean 1964
This runs at 11Hz with 0.1µF capacitors.
It uses pnp in a Darlington configuation. I would use an npn Darlington (MPSA13) with reversed supply.

 

[bizzlemedia]

Hi guys, thanks for the fast responses. Would I be correct in understanding that both solutions would work at a fixed frequency? I really need to be able to vary the frequency between 1Hz and 300Hz. Thanks

 

[Harald Kapp]

If you can find an icl8038 that could be a useful chip.
Or the MAX038 (almost equivalent)

 

[KrisBlueNZ]

AFAIK the ring modulator sound is more closely associated with the voices of the Cylons from Battlestar Gallactica. The Dalek voices may use ring modulation as well, but I'm pretty sure their main characteristic is amplitude modulation with a sinewave at somewhere around 15 Hz.

 

[(*steve*)]

This is an interesting reference.

 

[KrisBlueNZ]

FWIW I think the distinctive Cylon voice sound is done using ring modulation with a carrier frequency in the audio band. I guess if you use a lower carrier frequency you get a Dalek voice.

 

[bizzlemedia]

If you can find an icl8038 that could be a useful chip.
Or the MAX038 (almost equivalent)

I've decided to use the icl8038 but it isn't proving easy. Mainly because this circuit requires a 15M (15 megohm?) potentiometer which I'm struggling to find. Am I reading the schematic incorrectly or is it a typo?

 

[kpatz]

On page 2 it explains what that 15M trimpot is for. It's to tweak the duty cycle to compensate for leakage. You could probably get by without it, or use a fixed resistor in the 10-15M range (try a few values until you get the desired result).

 

[Arouse1973]

AFAIK the ring modulator sound is more closely associated with the voices of the Cylons from Battlestar Gallactica. The Dalek voices may use ring modulation as well, but I'm pretty sure their main characteristic is amplitude modulation with a sinewave at somewhere around 15 Hz.

Bloody hell Kris is there somthing you should tell us lol

 

[Thedarkb]

Well with some code you can easily generate sine waves on any atmel AVR with analog outputs.

 

[Arouse1973]

Exterminate Exterimate. Sorry had to do that

 

[KrisBlueNZ]

Bloody hell Kris is there somthing you should tell us lol

Yes, but not what you think. I lost interest in sci-fi (and most fantasy, really) in my teens. But I remember helping a friend with a circuit called the "Cylon Voice". It was a project in a magazine, Electronics Australia I think, based on an XR2206 used as a ring modulator, with a carrier frequency in the audio range I think. It did a fair job of capturing the hollow rich sound of the Cylons.

The Daleks, from what I remember, had a harsh, staccato sound, not like that circuit at all. I guess that's because they used ring modulation at 30 Hz instead of using an audio-frequency carrier. A BBC article linked on this thread said that the Dalek sound was originally made using a tape loop!

 

[bizzlemedia]

Chaps, many many thanks for all your inputs.

One last little question, roughly how much current or input voltage is required by the ring mod for the function/sinewave input? I.e. is the icl8038's output strong enough to successfully carry/modulate the other signal input?

Sorry if my meagre understanding of these things makes what I'm trying to ask difficult to understand. Thanks.

 

[Arouse1973]

FWIW I think the distinctive Cylon voice sound is done using ring modulation with a carrier frequency in the audio band. I guess if you use a lower carrier frequency you get a Dalek voice.

I knew you would have the answer Kris