NEWBIE: Designing a Simple Audio Amp
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Posted by Ricky Romaya on January 1, 2005, 8:04 pm
Please log in for more thread options 8ohms speakers from (onboard) pc soundcard. I figure I'm using op-amps. I'm a newbie and all I know about op-amps are basic, mostly from text book. Basically, I'm a little confused. Usually I see that the type of amplifiers to drive speakers are called 'power amplifiers'. From the basic building blocks of op-amps, I could only find circuits for voltage and/or current amplifiers. Do those 'power amps' are really 'voltage amps', cos I figure the main drive factor for speakers are voltage variations (voltage are converted into air preassure by the speakers, and hence creating audible sound)? Further more, I figure that the input stage of the amps I want to build will simulate that of LINE-IN/AUX/CD-IN lines found on commercial sound systems. Anybody knows whether there are standards to the input voltage and input impendance of those lines (LINE-IN/AUX/CD-IN), and if there are, what are the values? And how about output impendance standards for driving 8ohms speakers? Also, anybody knows how the input parameters (voltage, current, power) to the speaker relate to the SPL (Sound Preassure Level) generated by it? This indirectly means I'm asking the relationship of the amplifier gain to the loudness of the sound generated by the speaker. Last, but not least, what are the recommended op-amp series for audio processing (I only know the multi-purpose u741 series)? Well, that's a long list of questions, and there are more. Any help is appreciated. TIA | |||||||||||||||||||||||||||||||||||||||||||||||||
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Posted by John Popelish on January 1, 2005, 3:58 pm
Please log in for more thread options Yes, speakers are usually designed to be driven by voltage sources. A voltage source is one that regulates the voltage applied to a load (the speaker, in this case) while supplying whatever current is required to apply that voltage across the load. If the speaker was a resistive 8 ohms, that would mean that for every 8 volts the amplifier applied across the load, it would have to deliver 1 ampere through it. So just because it is a voltage source, does not mean that you can neglect the current side of the equation, it just means that voltage is what the amplifier regulates most precisely. One of the big differences between a typical opamp and a power amp is that the opamp has a maximum current capability somewhere between 10 and 30 milliamps while a power amplifier that operates from the same supply voltage may have large enough output transistors to pass more than an ampere. > Further more, I figure that the input stage of the amps I want to build
> will simulate that of LINE-IN/AUX/CD-IN lines found on commercial sound > systems. Anybody knows whether there are standards to the input voltage > and input impendance of those lines (LINE-IN/AUX/CD-IN), and if there > are, what are the values? And how about output impendance standards for > driving 8ohms speakers? > > Also, anybody knows how the input parameters (voltage, current, power) to > the speaker relate to the SPL (Sound Preassure Level) generated by it? > This indirectly means I'm asking the relationship of the amplifier gain > to the loudness of the sound generated by the speaker. > > Last, but not least, what are the recommended op-amp series for audio > processing (I only know the multi-purpose u741 series)? > > Well, that's a long list of questions, and there are more. Any help is > appreciated. There are integrated power amplifiers (essentially high output current capability opamps with some internal bias and gain setting resistors) that are available for very little cash. I think you might start with one of these for your experiments. The data sheets show the typical speaker amplifier circuit diagram and additional parts needed. Some examples: http://www.national.com/ds/LM/LM380.pdf (one of the most common) http://www.national.com/ds/LM/LM386.pdf (low voltage version of the LM380) http://rocky.digikey.com/WebLib/ST%20Micro/Web%20Data/TDA1905.pdf http://rocky.digikey.com/WebLib/Panasonic/Web%20data/AN7513.pdf http://rocky.digikey.com/WebLib/Panasonic/Web%20data/AN7511.pdf -- John Popelish | |||||||||||||||||||||||||||||||||||||||||||||||||
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Posted by John Popelish on January 1, 2005, 4:04 pm
Please log in for more thread options Forgot this one (I just bought 10 of these so I should have remembered
it) http://rocky.digikey.com/WebLib/ST%20Micro/Web%20Data/TBA820M.pdf -- John Popelish | |||||||||||||||||||||||||||||||||||||||||||||||||
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Posted by Graham Knott on January 1, 2005, 9:38 pm
Please log in for more thread options John Popelish wrote:
> Forgot this one (I just bought 10 of these so I should have remembered
> it) > http://rocky.digikey.com/WebLib/ST%20Micro/Web%20Data/TBA820M.pdf -- Have a look at http://homepage.ntlworld.com/g.knott/elect24.htm | |||||||||||||||||||||||||||||||||||||||||||||||||
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Posted by Anthony Fremont on January 1, 2005, 10:21 pm
Please log in for more thread options
"Graham Knott" wrote: > John Popelish wrote:
> > Forgot this one (I just bought 10 of these so I should have
remembered
> > it)
> > http://rocky.digikey.com/WebLib/ST%20Micro/Web%20Data/TBA820M.pdf > Have a look at
> http://homepage.ntlworld.com/g.knott/elect24.htm I have a question about your circuit. R2 and C3; what is their function? | |||||||||||||||||||||||||||||||||||||||||||||||||
> I want to design and build a very simple audio amplifier to drive my
> 8ohms speakers from (onboard) pc soundcard. I figure I'm using op-amps.
> I'm a newbie and all I know about op-amps are basic, mostly from text
> book.
>
> Basically, I'm a little confused. Usually I see that the type of
> amplifiers to drive speakers are called 'power amplifiers'. From the
> basic building blocks of op-amps, I could only find circuits for voltage
> and/or current amplifiers. Do those 'power amps' are really 'voltage
> amps', cos I figure the main drive factor for speakers are voltage
> variations (voltage are converted into air preassure by the speakers, and
> hence creating audible sound)?