Basic audio circuit
 

Hello,
I would like to make a very simple circuit. I have a small speaker and
I'd like to learn how to make the simplest circuit to output sound at a
specific frequency and a specific volume through the speaker.

I don't want to use integrated circuit chips, I want to build it from
the basic components: capacitors, inductors, transistors, resistors,
diodes, etc. and that's about it.

I'm wondering if you guys can first tell me whether what I'm planning
to learn are right to complete my project, and then, point me out to
resources to learn about that?

I think I would have to learn how to:
1) Make a circuit with a current oscillating at a specific frequency
(which could be done with capacitors/inductors/resistors, as far as I
know.)
2) Amplify the current in order to generate audible sound in the
speaker
3) Combine the speaker with the circuit and still be able to calculate
the oscillation frequency

Is my assumption that a simple oscillating circuit going through a
speaker in serie is enough to generate a sound? i.e. a circuit
oscillating at 440hz connected to a speaker will output what
corresponds to a middle C in music.

I have some experience doing electronics, but mostly digital and am a
beginner with anything touching audio and oscillating circuits.
Pointers toward good sources of information would be really welcome!

Thanks a lot.

Basic audio circuit
 

On 18 Sep 2006 22:49:40 -0700, "Hedos" wrote:

Hello,
I would like to make a very simple circuit. I have a small speaker and
I'd like to learn how to make the simplest circuit to output sound at a
specific frequency and a specific volume through the speaker.

I don't want to use integrated circuit chips, I want to build it from
the basic components: capacitors, inductors, transistors, resistors,
diodes, etc. and that's about it.

I'm wondering if you guys can first tell me whether what I'm planning
to learn are right to complete my project, and then, point me out to
resources to learn about that?

I think I would have to learn how to:
1) Make a circuit with a current oscillating at a specific frequency
(which could be done with capacitors/inductors/resistors, as far as I
know.)
2) Amplify the current in order to generate audible sound in the
speaker
3) Combine the speaker with the circuit and still be able to calculate
the oscillation frequency

Is my assumption that a simple oscillating circuit going through a
speaker in serie is enough to generate a sound? i.e. a circuit
oscillating at 440hz connected to a speaker will output what
corresponds to a middle C in music.

I have some experience doing electronics, but mostly digital and am a
beginner with anything touching audio and oscillating circuits.
Pointers toward good sources of information would be really welcome!

Thanks a lot.

An inductor capacitor and resistor won't oscillate it needs an active
component (transistor)

You want a circuit called a "Twin Tee" oscillator - about the
simplest audio frequency oscillator built from discrete parts. Uses
resistors and capacitors to phase shift the output of a transistors
collector back to its base and is tuned to one frequency.

These days a lot of sites have the TT oscillator in an op amp
configuration (the dreaded integrated circuit), but I remember
building and using them with a single transistor to drive a loud
speaker.

http://www.njqrp.org/quickies/osc_1.jpg

http://geofex.com/FX_images/q+dosc.gif

Since you mention you want A-440 you'd have to tweak the values a bit
to tune the thing to the frequency you want. Use the 500 cycle values
to start on the first site - the normal tolerance accuracy of the caps
will give you something close to 440.

Output has to be taken from the collector and isolated with an
electrolytic cap of ~100 ufd to drive a speaker directly - that load
will affect the feedback so start with something smaller like a 1 ufd
and work up - load it too much and it may stop oscillating. Typically
you'd use a buffer amplifier to prevent interaction between the
speaker and oscillator.

Vary the components and it is possible to get it to emulate a bell or
tom-tom or bass drum with just less than enough feedback to keep it
oscillating - but that requires another source of pulses to drive it.
And isn't what you want - a million years ago I built such a circuit
for an uncle who wanted a metronome that sounded like a bass drum.

Middle C? Middle A is 440 cycles per second

Goggle for the twin tee- there might be some better schematic out
there. Back in the day, the electronics mags had nomographs to make
selecting caps easier.

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Basic audio circuit
 

On 18 Sep 2006 22:49:40 -0700, "Hedos" wrote:


http://www.kkn.net/archives/html/QRP.../msg00431.html

Some more twin tee stuff - says to vary one resistor to set frequency



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Basic audio circuit
 

Hedos wrote:

Is my assumption that a simple oscillating circuit going through a
speaker in serie is enough to generate a sound? i.e. a circuit
oscillating at 440hz connected to a speaker will output what
corresponds to a middle C in music.

440Hz is A above middle C

Basic audio circuit
 

On 2006-09-19, Hedos wrote:
Hello,

1) Make a circuit with a current oscillating at a specific frequency
(which could be done with capacitors/inductors/resistors, as far as I
know.)

google for "Wein-bridge oscilator" if you want a pure tone with few harmonics.
there are transistor designs for this device as well as ones that use ICs.

but if you're wantiong it to repeatably produce the exact same frequency (like a
tuning fork) it gets tricky. I'd cheat and use a crystal oscilator driving
a tone generator chip...

2) Amplify the current in order to generate audible sound in the
speaker


There are many transistor based amplifier circuits out there, picking a good
one is hard.

3) Combine the speaker with the circuit and still be able to calculate
the oscillation frequency

As long as the amplifier has a relatively high input impedance
that will work.

Is my assumption that a simple oscillating circuit going through a
speaker in serie is enough to generate a sound? i.e. a circuit
oscillating at 440hz connected to a speaker will output what
corresponds to a middle C in music.

correct.


--

Bye.
Jasen

Basic audio circuit
 

Get a Radio Shack or similar electronics 101 Project Kit. You will learn how
to build circuits, how they work. Then you can build circuits to do anything
you want. Have Fun!

Scott
"Hedos" wrote in message
ups.com...
Hello,
I would like to make a very simple circuit. I have a small speaker and
I'd like to learn how to make the simplest circuit to output sound at a
specific frequency and a specific volume through the speaker.

I don't want to use integrated circuit chips, I want to build it from
the basic components: capacitors, inductors, transistors, resistors,
diodes, etc. and that's about it.

I'm wondering if you guys can first tell me whether what I'm planning
to learn are right to complete my project, and then, point me out to
resources to learn about that?

I think I would have to learn how to:
1) Make a circuit with a current oscillating at a specific frequency
(which could be done with capacitors/inductors/resistors, as far as I
know.)
2) Amplify the current in order to generate audible sound in the
speaker
3) Combine the speaker with the circuit and still be able to calculate
the oscillation frequency

Is my assumption that a simple oscillating circuit going through a
speaker in serie is enough to generate a sound? i.e. a circuit
oscillating at 440hz connected to a speaker will output what
corresponds to a middle C in music.

I have some experience doing electronics, but mostly digital and am a
beginner with anything touching audio and oscillating circuits.
Pointers toward good sources of information would be really welcome!

Thanks a lot.