Amplify 17Hz sine wave from a 555

[boylesg]

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

Sound quality is not an issue, i.e. it doesn't matter if there is a little distortion happening.

 

[barry]

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

Sound quality is not an issue, i.e. it doesn't matter if there is a little distortion happening.

1) You're not going to get a sine wave out of a 555
2) Could you be just a LITTLE more specific about what you want?

What do you want, 100Watts? Why complementary pair? What are you driving?
You say "this particular application" and then present zero particulars.

 

[boylesg]

1) You're not going to get a sine wave out of a 555
2) Could you be just a LITTLE more specific about what you want?

What do you want, 100Watts? Why complementary pair? What are you driving?
You say "this particular application" and then present zero particulars.

With the following on pin 3 I will get a sine wave from the 555:


http://www.learningaboutelectronics.com/images/Sine-wave-generator-circuit-with-a-555-timer.png

Putting the 17Hz sine wave through a low frequency 8R speaker, so perhaps 5-10W at 12V.

 

[FvM]

"Small" error regarding order of magnitude: Circuit frequency is 17 kHz, not 17 Hz.

The circuit purpose isn't clear, but I would consider to "amplify" the square wave before the low pass filter.

 

[boylesg]

"Small" error regarding order of magnitude: Circuit frequency is 17 kHz, not 17 Hz.

The circuit purpose isn't clear, but I would consider to "amplify" the square wave before the low pass filter.

Well I was going to power the 555 with 12V and I wanted to boost the current through the low frequency speaker. Hence the class B amplifier.

 

[KlausST]

Hi,

The NE55 output contains a DC offset. If you amplify this, it will soon kill your speaker.
Even the 2nd order low pass filter will give not a perfect sine.
If my mind calcualtion is correct then the theoretical limit is about 3.5% distortion. The fundamental will be attenuated, too.


***
My recommendation:
* use an additional high pass filter to get rid of DC.
* use a ready to buy audio amplifier IC with BTL output to get about 8W of audio from DC 12V.

Klaus

 

[FvM]

I wanted to boost the current through the low frequency speaker

Did you read my previous post? The circuit output is 17 kHz, no low frequency. A LC filter for 17 Hz would be very bulky, no good idea.

It's probably better if you tell the intended purpose of your design so that people can make alternative suggestions.

 

[boylesg]

Did you read my previous post? The circuit output is 17 kHz, no low frequency. A LC filter for 17 Hz would be very bulky, no good idea.

It's probably better if you tell the intended purpose of your design so that people can make alternative suggestions.

That is the type of circuit I am using not the exact circuit - I just pulled it off the internet.

My 555 will be generating a 17Hz square wave and I have calculated my LC filter for a resonance of around 17Hz.

 

[KlausST]

Hi,

I have calculated my LC filter for a resonance of around 17Hz.

This means unpredictable output voltage and very, very low 17Hz impedance.
--> difficult to drive.

Use a simulation tool like LTspice to check if the results meet your expectations.

Klaus

 

[FvM]

My 555 will be generating a 17Hz square wave and I have calculated my LC filter for a resonance of around 17Hz.

How should we know?

The idea doesn't make much sense either. To generate a 17 Hz sinewave of some quality, you'll use a different generator concept, or a more effective filter.

Due to human ears sensitivity curve, the harmonics will be perceived much louder than the fundamental. You really need good filters and a low distortion amplifier (in case there's no filter after the amplifier) to suppress the harmonics.

 

[boylesg]

How should we know?

The idea doesn't make much sense either. To generate a 17 Hz sinewave of some quality, you'll use a different generator concept, or a more effective filter.

Due to human ears sensitivity curve, the harmonics will be perceived much louder than the fundamental. You really need good filters and a low distortion amplifier (in case there's no filter after the amplifier) to suppress the harmonics.

I apologize - should have mentioned it.

Can you explain what generator concept you are thinking of?

Harmonics? I have read that a square wave consists of multiple harmonic sine waves so I think I 'get' the general idea.

Sorry I am rather 'weak' on audio stuff but trying to learn.

- - - Updated - - -

Oh I get the harmonics thing - in the simulator there is a second sine wave superimposed on the expected sine wave. In the real circuit I assume there would be many superimposed sine waves.

 

[barry]

You could use a Wein-bridge oscillator to generate a sine wave. Or an FPGA or microprocessor DDS. Or use a triangle rather than square wave and filter that. (Triangle has lower amplitude harmonics). But you still haven't told us what you're driving. 17 Hz is below the nominal audio range. And you're going to need a large speaker.

 

[boylesg]

You could use a Wein-bridge oscillator to generate a sine wave. Or an FPGA or microprocessor DDS. Or use a triangle rather than square wave and filter that. (Triangle has lower amplitude harmonics). But you still haven't told us what you're driving. 17 Hz is below the nominal audio range. And you're going to need a large speaker.

**broken link removed**

Was going to try one of these - 75mm inside a PVC pipe.

Also have an XR8038 function generator that can handle frequencies down to 1 Hz according to the data sheet.

Is that likely to generate a better quality 17Hz sine wave than a 555?

 

[barry]

Again, a 555 produces a SQUARE WAVE. The XR 8038 produces a 1% distortion sine wave. Which do YOU think would produce a better sinewave? You can certainly play around with a square wave and a filter, but why bother? Your original post said you didn't care too much about distortion.

 

[boylesg]

Again, a 555 produces a SQUARE WAVE. The XR 8038 produces a 1% distortion sine wave. Which do YOU think would produce a better sinewave? You can certainly play around with a square wave and a filter, but why bother? Your original post said you didn't care too much about distortion.

Re not caring too much about distortion......except that it defeats my purpose if the 'victims' can hear the additional harmonics on top of the 17Hz infrasound.

 

[Easy peasy]

You can modulate a 555 to produce a low (or high) freq PWM waveform which, when filtered will give a near sine wave, a simple C -R blocking ckt will then remove the DC to give a 0v reference for driving an amplifier. If you modulate with a triangle wave (17 Hz) and then filter you will get good enough.

From a 12V supply a simple darlington emitter follower could be used to buffer the filtered 555 output (with DC average level in place) and then feed to the speaker - with a blocking cap ( 220uF 63V) to prevent DC from entering the speaker.

This would suffice for the stated app.

 

[betwixt]

I wouldn't worry too much about the distortion, or amplitude , or even the frequency if you are going to use one of the mentioned loudspeakers.

It's a diaphragm plate, it has no voice coil! They are designed to act as ABR (Auxilliary Bass Radiator) units in large loudspeaker enclosures to make use of existing low frequency sound pressure. A kind of second bass speaker but using existing air pressure rather than producing any by itself. They work very effectively as ABRs but are of zero use as a sound source.

Brian.

 

[FvM]

Re not caring too much about distortion......except that it defeats my purpose if the 'victims' can hear the additional harmonics on top of the 17Hz infrasound.

I wouldn't worry too much about the distortion, or amplitude , or even the frequency if you are going to use one of the mentioned loudspeakers.

It's a diaphragm plate, it has no voice coil! They are designed to act as ABR (Auxilliary Bass Radiator) units in large loudspeaker enclosures to make use of existing low frequency sound pressure.

Fortunately a minimum of acoustic and electronic knowledge is required to make an effective infrasound source. No need to worry about your neighbor's health...

 

[boylesg]

Fortunately a minimum of acoustic and electronic knowledge is required to make an effective infrasound source. No need to worry about your neighbor's health...

Well my jail trash neighbor will make an ideal subject to practice the art on until I get it right! ;-)

The 'c' deserves it because has about several security cameras directly monitoring our property rather than his own!

So I feel entitled to have some electronics amusement at his health expense if I can pull it off!

- - - Updated - - -

I wouldn't worry too much about the distortion, or amplitude , or even the frequency if you are going to use one of the mentioned loudspeakers.

It's a diaphragm plate, it has no voice coil! They are designed to act as ABR (Auxilliary Bass Radiator) units in large loudspeaker enclosures to make use of existing low frequency sound pressure. A kind of second bass speaker but using existing air pressure rather than producing any by itself. They work very effectively as ABRs but are of zero use as a sound source.

Brian.

DAMN! I thought they were similar to regular speakers. What sort of speakers are you meant to use for this sort of thing then.

 

[hexreader]

Mythbusters already proved that a "brown frequency" is a myth. They used far bigger speakers than yours to show that low frequency audio has no significant effect on the human body.

Myth Busted.....