Voice Modulator Circuit Ideas

[JMAntonucci]

Hi... I'm a beginner electronics student who needs to create a final project that involves basic AM and FM modulation. I want to be able to speak/sing into a microphone and feed the signal into an amplitude modulation circuit in which I can control the amount of modulation with a potentiometer, and then through a frequency modulation circuit in which I can control the amount of modulation with another potentiometer. Then the modulated signal will be fed through a 8-ohm output speaker. So, I have the concept down, but being a beginner, I'm having a lot of trouble trying to figure out the best/simplest way to do this, all the parts I need, etc.

Please, if you have any idea how to create this project in the simplest way, basing it off basic electronics theory (can't use Integrated circuits or anything... I have to create my own circuits to show that I know what's actually going on in terms of amplitude and frequency modulation), that would be extremely helpful.

So far I know I'm going to need high frequency oscillators as carrier signals... 555 timer chips? Could I use transistors instead? Also, do I need to create a circuit before the amplitude and frequency modulation circuits to prepare my voice signal to be modulated? And, should I be creating filters as well to block unnecessary frequencies that may cause distortion? How about what kind of resistors/capacitors should I be working with?

Sorry for the loads of general and basic questions... I'm just trying to understand this all and it's very difficult with limited knowledge.

Any ideas/help/explanation of the theory would be greatly appreciated.

Thanks!

 

[dr pepper]

Amplitude modulation is similar to the tremolo effect used by musicians and isnt too hard to do.
Heres a circuit, you could mod this into a simpler mono version:

**broken link removed**

Freq mod is much more involved and would probably require digital techniques, not the kind of thing for a noob, maybe a flanger would do the trick.

 

[audioguru]

The circuit from free Info Society uses a very old light + LDR that might not be available anymore. Instead, a Jfet can be used as a voltage-controlled variable resistor (used in automatic volume control circuits) which will be part of a variable attenuator.

FM modulation of a voice can be done using a Single-Sideband Circuit where the carrier frequency is varied. I made a simple one from a pair of MC1496 balanced modulator/demodulator ICs. Digikey still has them in stock but they are surface-mount, not through hole.

 

[BobW]

"Then the modulated signal will be fed through a 8-ohm output speaker."

Did we miss a step somewhere? If your carrier signal is a high frequency, I don't think you're going to hear very much when you feed it into a speaker. On the other hand, if you're using an audio frequency carrier with the intention of generating interesting audio sound effects, then FM is very easy. All you need is a VCO (voltage controlled oscillator). You could use the oscillator section of any commonly available phase locked loop chip, eg., CD4046

 

[audioguru]

All you need is a VCO (voltage controlled oscillator).

It is the voice frequency that needs changing with Frequency Modulation, not just a tone.
A VCO can be the carrier of the demodulation of a single-sideband transmission.
Of course the demodulator feeds an audio power amplifier that drives the speaker.

When I made a voice scrambler with MC1496 balanced modulator/demodulator ICs I used crystal controlled carriers so that the demodulated sound was exactly the same as the original. The carrier in the transmitter was suppressed so that an ordinary receiver heard the sound frequencies in reverse so that low frequencies sounded high and high frequencies sounded low. Then voices were completely unintelligible. If the demodulator carrier is a VCO and the correct sideband is detected then the pitch of a voice (or music) can be changed.

 

[BobW]

It is the voice frequency that needs changing with Frequency Modulation, not just a tone.
A VCO can be the carrier of the demodulation of a single-sideband transmission.
Of course the demodulator feeds an audio power amplifier that drives the speaker.

My understanding is that the OP wants to use voice to frequency modulate a carrier of some unspecified frequency, not the other way around. But more details would be very useful.

 

[audioguru]

That is a good point. Which modulates what??

 

[alec_t]

Guys, did you note that the OP "can't use Integrated circuits or anything... I have to create my own circuits to show that I know what's actually going on in terms of amplitude and frequency modulation" ?

 

[JMAntonucci]

I want my voice to be modulated in amplitude and frequency... I want to be able to use the carrier to do this... Can't use IC's... I'm just looking for two circuits (AM) and (FM) that can be connected with a HF carrier signal to produce results that can be changed with potentiometers (one for amp and one for frequency)... Then I would like the output to come out of a speaker.... Is this possible? I'm sorry, again bare with me.. I am just a beginner and this is all very confusing to me haha!!

 

[audioguru]

Guys, did you note that the OP "can't use Integrated circuits or anything... I have to create my own circuits to show that I know what's actually going on in terms of amplitude and frequency modulation" ?

Back to the dark ages.
Is anybody here old enough to remember making projects using only discrete parts? I am pretty old but I used mostly ICs for almost everything.
About 45 years ago I was using Schmitt Trigger ICs and RTL logic ICs.
A long time ago guitar effects circuits and synthesizers also used ICs.

 

[alec_t]

Google 'ring modulator' to see how AM can be done without ICs. FM would be a lot trickier.