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Topic: Amplifier for a 17Hz sine wave from a 555 timer (Read 1 time) previous topic - next topic

boylesg

Can anyone recommend a simple complementary pair amplifier schematic for this application.

Hopefully using BD139/BD140 which I have to hand.

And sound quality is not a particular issue - it doesn't matter if there is a little distortion going on.

Simplicity of schematic is more important than sound quality.

DVDdoug

I assume you want an amplifier to drive a speaker?

Any idea how much power (Watts) you need?

It's easier to use an integrated circuit than to build an amplifier with discrete transistors and a linear power amplifier usually requires more than 1 or 2 transistors.

Or, you can buy an amplifier or you can use regular "powered" computer speakers.

wvmarle

A 555 produces a block wave, not a sine wave.
Quality of answers is related to the quality of questions. Good questions will get good answers. Useless answers are a sign of a poor question.

boylesg

A 555 produces a block wave, not a sine wave.


With this on pin 3 I will get a sine wave.

Wawa

So wvmarle was right. The 555 produces a square wave.
You forgot to mention the LC filter.

An NE555 (not the Cmos variety) should be able to drive a speaker directly.
Increase supply voltage to 12volt, use an inductor that can handle some current (1Amp?), and add a 470uF cap in series with the speaker (between inductor and speaker+).
Leo..

wvmarle

Interesting circuit - no timing cap.

Indeed that will give you (kind of) a sine wave. But what do you plan to do with a 17 Hz sound? That's infrasound, people can't hear this frequency.
Quality of answers is related to the quality of questions. Good questions will get good answers. Useless answers are a sign of a poor question.

boylesg

Interesting circuit - no timing cap.

Indeed that will give you (kind of) a sine wave. But what do you plan to do with a 17 Hz sound? That's infrasound, people can't hear this frequency.
Let's call it an amusing experiment :-)

slipstick

And let's say again that without knowing what output power you need it's basically impossible to recommend an amplifier circuit.

Steve

MarkT

Can anyone recommend a simple complementary pair amplifier schematic for this application.

Hopefully using BD139/BD140 which I have to hand.

And sound quality is not a particular issue - it doesn't matter if there is a little distortion going on.

Simplicity of schematic is more important than sound quality.
The 555 output is beefy and doesn't usually need amplification to drive a small speaker.  You will need
beefy decoupling on the 555's power rails though, 1000uF or more would be wise.

If you need lots of watts, by far the simplest approach is an IC amp, so many to choose from, analog
or class-D.  You'll need to ac-couple the 555 output, and probably attenuate it.

However if you stick with the two transistors, just use the standard class-B circuit, no need to bias for a
square-wave, so its pretty simple, but you'll need a large output capacitor.
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MarkT

#9
Jul 20, 2018, 12:58 pm Last Edit: Jul 20, 2018, 01:00 pm by MarkT
With this on pin 3 I will get a sine wave.
Of unknown amplitude, perhaps _much_ higher than the supply voltage if bang-on resonance,
but an LC tank for 17Hz is very impractical (huge values for C and L).  A Sallen-Key bandpass
filter using opamp is a better approach, or for such a low frequency its not difficult to generate from
a PWM output using an RC filter - you'd need to code the sinusoidal PWM updates of course.

Perhaps if you explained what you are trying to do, not how you think it can be done, we'll have
some better approaches to suggest.  I sense xyproblem territory here.
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ChrisTenone

The 'x' part of the problem is the "an amusing experiment". My guess is that you will need to drive big speakers with a lot of watts.

Wikipedia says "that infrasound may cause feelings of awe or fear in humans." Ghost sightings are enhanced by infrasound. This was employed in Disneyland's "Haunted House" ride. It makes people feel creeped out.

Put the output from your 555 through an opamp into a big amplifier and big speakers. You will be rattling bones.
What, I need to say something else too?

DVDdoug

Quote
Let's call it an amusing experiment :-)
If it helps, Audacity can generate tones down to 1Hz that you can play through whatever speakers/headphones you have connected to your computer (and you can optionally make a WAV or MP3 file).

...But as Chris says, it takes big woofers/subwoofers and big amplifiers to reproduce those frequencies.     


MarkT

These days there's another approach for generating sine waves that's got a lot cheaper than it
used to be:
https://www.ebay.co.uk/itm/Program-Microprocessors-Sine-Square-Wave-AD9833-DDS-Signal-Generator-Module-UK/152364443598?hash=item2379a0e7ce%3Ag%3AnNwAAOSwFb5aRhAo&_sacat=0&_nkw=ad9833&_from=R40&rt=nc

I think that module goes down to DC, no transformer or coupling cap obvious on the board, and the
resulution is 0.1Hz, so 17Hz should be doable.  Just need an output capacitor to remove its
dc offset.
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MikeLittle

If you are trying to get an acoustical output with this, you are going to need a serious speaker and power amp to drive it. No chip level amp will stand a chance.

if you are looking for the creep factor, take a look at this:
https://www.instructables.com/id/The-Psychoacoustic-Bucket-from-Hell/

I've dealt with Servo Drives a long time ago. Quite impressive.

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