How does the audio output work in amplifiers?....can someone explain to me? Pls - diyAudio
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Old 16th May 2010, 06:27 AM   #1
chipper is offline chipper  United States
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Default How does the audio output work in amplifiers?....can someone explain to me? Pls

Can someone explain how it works? Why do they use for instance two pairs of IRF540s and two IRF9540s? What's the purpose of that? Sorry for such noob questions just want to get a better understanding how it works? Thanks
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Old 16th May 2010, 06:32 AM   #2
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Quote:
Originally Posted by chipper View Post
Can someone explain how it works? Why do they use for instance two pairs of IRF540s and two IRF9540s? What's the purpose of that? Sorry for such noob questions just want to get a better understanding how it works? Thanks
With the greatest respect I think you need to start at first principles and do a lot of reading

Two pairs... in a stereo amp is one pair per channel, that is one N and one P type device in a push pull arrangement.

Two pairs in one channel... and they are paralled for greater power handling, so a more powerful amp can be realised.
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Old 16th May 2010, 06:37 AM   #3
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I don't know how much detail you want/need but the simplest explanation is that the transistors act as variable resistors to deliver varying amounts of rail voltage to the speaker terminals. One type of transistor (P-channel, N-channel) is used to pass positive rail voltage to the speaker terminals, the other type is used to pass negative rail voltage to the speaker terminals. They are driven on/off alternately to produce the audio waveform. This would be for non switching amplifiers (class D, T...). If you could be more specific in what you want to understand, post specific questions.
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Old 16th May 2010, 06:39 AM   #4
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Quote:
Originally Posted by Mooly View Post
With the greatest respect I think you need to start at first principles and do a lot of reading

Two pairs... in a stereo amp is one pair per channel, that is one N and one P type device in a push pull arrangement.

Two pairs in one channel... and they are paralled for greater power handling, so a more powerful amp can be realised.
So that's why they got those like that in there? And do they all share voltage right after the power supply (rail voltage 35 volts)?
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Old 16th May 2010, 06:42 AM   #5
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They share the current (in parallel) the voltage across each is the same (on 99.9% of designs)
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Old 16th May 2010, 06:47 AM   #6
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Like this,
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File Type: jpg Parallel.JPG (26.0 KB, 78 views)
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Old 16th May 2010, 03:01 PM   #7
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A crude explanation is one side of the output transistor set pushes the speaker out and the other side pushes it in. If you're playing a deep bass note (~10hz or so) you can actually see how it works, higher frequencies are quicker and less visible.
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Old 16th May 2010, 05:44 PM   #8
chipper is offline chipper  United States
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Quote:
Originally Posted by Perry Babin View Post
I don't know how much detail you want/need but the simplest explanation is that the transistors act as variable resistors to deliver varying amounts of rail voltage to the speaker terminals. One type of transistor (P-channel, N-channel) is used to pass positive rail voltage to the speaker terminals, the other type is used to pass negative rail voltage to the speaker terminals. They are driven on/off alternately to produce the audio waveform. This would be for non switching amplifiers (class D, T...). If you could be more specific in what you want to understand, post specific questions.
Very impressive!, how is the music able to be played? Where does the signal go for it to be amplified? Sorry for such nood questions I just look in an amplifier and think about how this process is done?? Once again thanks to all who gave great information. Cheers
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Old 16th May 2010, 05:57 PM   #9
Mooly is offline Mooly  United Kingdom
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You need to study basic theory ... do you understand basic concepts such as ohms law and current voltage and resistance. Basic semiconductor theory ?

There is loads of help on offer on this forum, but it's too large and complex a subject to give one line answers.
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Old 16th May 2010, 07:24 PM   #10
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The overall amplification of the signal is typically produced in several stages. Some of the gain is produced in the preamp section and the rest in the actual power amplifier section. The variable part of the gain is virtually always produced in the preamp circuit.

If you really want to understand the power amplifier section, you'll have to understand the 'differential amplifier'. It's at the input of most all commercially available car amplifiers.

A differential amp has two inputs. Typically (but not always), one input is used for the audio signal. The other input is used monitor the output of the amplifier (the signal going to the speaker terminals).

The differential amp is only satisfied when the signals on the inputs match. If they don't match, it compensates and corrects for the error. This is what eliminates much of the distortion that you'd otherwise have without this 'feedback' from the output of the amp.

To get gain from the power amplifier stage, they use a voltage divider to reduce the level of the (feedback) signal going back into the input of the differential amplifier that's monitoring the output. Since the level of the feedback signal is reduced, the differential amplifier thinks there's an error (the signal is too low) so it drives the power amplifier harder to produce more output voltage. When the feedback signal again matches the audio input signal level, the differential amp is again balanced (satisfied). All of this takes place instantaneously.

In THIS image, The base of Q101 would be the input. The orange line between the point labeled as 'input signal' and '0 volts' would be removed if this were an audio amp. As you can see, R110 and R109 form a voltage divider to reduce the level of the signal reaching the feedback side of the differential amp (base terminal of Q102).
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