LM324 wave generator/vco schematic

[Michael Circuit]

I am trying to create a vco using the LM324. I have the schematic to the korg monotron, https://3.bp.blogspot.com/_rScBRKlTdoE/TNQraMhovzI/AAAAAAABsz8/PJkljExPMXE/s1600/monotron_sch.jpg
which uses the lm324 as the IC for the vco, but I am struggling to create a simple circuit in which the lm324 will produce an audible wave form when connected to a speaker. can anyone help? from what i have gathered this should produce a square wave correct?

 

[MikeMl]

An LM324, by itself, is not a VCO; you have to add the JFet to make a VCO. An LM324, by itself, cannot drive a speaker; you will need an audio power amplifier, like an LM386 to do that.

 

[Michael Circuit]

thank you MikeMI, but can anyone please provide me with a simple circuit to produce a waveform using the LM324?

 

[ronv]

Osc.

I'm not sure if this is what you want, but it will produce a square wave and triangle wave. Change the frequency by changing C1 or R4. AC couple it with a large capacitor to your audio amplifier.

 

[Michael Circuit]

perfect, thank you so much ronv

 

[Ubergeek63]

An LM324, by itself, is not a VCO; you have to add the JFet to make a VCO. An LM324, by itself, cannot drive a speaker; you will need an audio power amplifier, like an LM386 to do that.

not true. a crude VCO can be made by feeding the cap from the voltage source and putting a diode where the feedback resistor was.

 

[audioguru]

The datasheets for the LM324 quad opamp and LM358 dual opamp show a VCO circuit that goes from a very low frequency growl to a fairly high audio pitch.

An MC34074 quad opamp (or MC34072 dual opamp) can be used instead in this circuit for a much higher frequency.

 

[Michael Circuit]

Its what is used in that little Korg Monotron synthesizer, which is why i purchased the chips. I am trying to figure out how to create an oscillator with it without using a 386 audio amp if thats possible? I know it can be done with a 40106 but can it be done with the LM324? audioguru thanks for that link.

 

[audioguru]

There are hundreds of ways to make oscillators. They could have sine-wave, triangle-wave or square-wave outputs.
A CD40106 IC can make six square-wave oscillators with just one resistor and one capacitor for each oscillator. An opamp can make the same oscillator but with an added resistor.

A voltage -controlled oscillator needs many more parts as I showed.

If you want to drive a speaker then you need a power amplifier. An LM386 has a low output power of only 0.45W at clipping into 8 ohms when it has a 9V supply.

 

[Michael Circuit]

im breadboarding this right now, thank you everyone for your help, im teaching myself about circuit building and am a noob, thanks for answering my stupid questions.

 

[Michael Circuit]

Although I can generate a square wave with the lm324 and with a bit of luck a triangle wave as well, and adjust the rate in which the capacitor charges and discharges using a potentiomiter, this still isnt an oscillator is it? How do i bridge the gap between a waveform generator and an oscillator?

 

[ronv]

I think we need a little more info about what you want as an end result. For example:
What frequency range?
Turn a knob to change the frequency?
"HI FI" or just a square wave driving a speaker?
Loud or soft?
End use?
Stuff like that.

 

[Ubergeek63]

Although I can generate a square wave with the lm324 and with a bit of luck a triangle wave as well, and adjust the rate in which the capacitor charges and discharges using a potentiomiter, this still isnt an oscillator is it? How do i bridge the gap between a waveform generator and an oscillator?

either you misspoke or you are a bit confused. a waveform generator IS an oscillator that generates special waveforms.

 

[MrAl]

Hello,

You can create a simple VCO from a single section of LM324 or LM339 and a capacitor and a few resistors (see diagram).

Note if you use an LM339 you will also need an appropriate pull up resistor.
Also note if the power supply is other than 10v then the input ranges will be different than shown in the diagram.

You can play around with the values to change the frequency range and other characteristics.

Added note:
A more accurate value for the input voltage where we change from increasing frequency (with Vin) to decreasing frequency is 4.3 volts.
Thus, the frequency increases from 0v to 4.3v and decreases from 4.3v to 10v.

 

[Michael Circuit]

Ubergeek63 THANK YOU!

 

[Michael Circuit]

what does that symbol mean on the VCO below R/2? its a straight line with an arrow at the bottom connecting to ground?

 

[audioguru]

what does that symbol mean on the VCO below R/2? its a straight line with an arrow at the bottom connecting to ground?

In the VCO circuit I posted from the datasheet of the LM324 and LM358 the "thing" is called an NPN transistor. The arrow is its emitter. Use a 2N3904.

 

[Michael Circuit]

audioguru thanks again. still learning, slowly but surely

 

[Dean Savage]

So your thinking like a tremolo circuit? Something that will oscillate the signal input?

 

[audioguru]

The definition of "tremolo" is a variation of the amplitude of a musical note. The variation of frequency is called "vibrato".