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| What audio amp gain setting does? |
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| fonograph:
I mean what happens inside the amplifier,I am not asking what gain setting does to output signal,that would be like asking what color does blue have.For example Violectric headphone amp can set gain to 5 different levels that are spaced 6db apart. When I flick the gain switch,what changes inside the amp? Can class D/switch mode amplifiers have gain settings too or only class A/AB/linear amplifiers have it? |
| spec:
+ fonograph An audio power amplifier of any type, class A, A/B, D, in essence converts a low level voltage signal into a higher voltage signal that has sufficient current capability to drive a speaker or headphones (see attached image below). So, for example, say you had an MP3 player. The digital to analog converter (DAC) will convert the digital MP3 files to a 1V RMS analog signal. But that signal would not be able to supply any current worth mentioning. If you take an 8 Ohm speaker running at 2 watts, it will need a signal of 4V @ 0.5A. This means that you will require an audio power amplifier between the DAC output and the speaker. The audio power amp will need a voltage gain of 2 and be able to supply at least 0.5A (power in watts = I*V or I squared * R). To change the audio volume from the speaker you need to change the speaker power and you do this by changing the voltage of the signal driving the speaker. And this is done by a restive potentiometer, which can be continuously variable or stepped as in your case. The potentiometer, or volume control as it is called, connects across the output from the DAC, so that the voltage of the signal being fed to the input of the audio power amp can be varied. If you are wondering about dBs, they are based on a logarithmic power scale to match the way that humans hear sound. Just look up decibels on the internet if you need more information. Or if you want another lecture, just ask. :D |
| BrianHG:
Use the table at the bottom right to find the Voltage or Current Ratio/dB from this site: http://www.learnabout-electronics.org/Amplifiers/amplifiers13.php Example, a gain of 6db means the input voltage p-p will come out of the amplifier at 2x the voltage p-p a gain of 20db means the voltage coming out is 10x Vp-p compared to the input voltage. As for what the gain does, most of the time it can be 1 of 2 things: A) At the audio input, there is a trim-pot or resistor divider to lower the signal going into the amplifying electronics which may have a 1 designed huge gain. Altering the input level, usually called a pre-amp attenuator, changes to overall signal gain from input to speaker output. B) Within the core of the amplifier electronics, the gain of the amplifier may be changed by altering the feedback circuit. Today, typically, an amplifier has what's called a negative feedback design. This means a portion of the output signal being fed to your speakers is sent back to the beginning of the amplifier's input circuitry to control how much voltage should be sent out to the speaker compared to the source audio coming from the audio input source. Shrinking this fed back portion of the speaker's output will increase the overall gain of the amplifier since the amp purpose is to match this signal level with the source signal level. This is known as a negative feedback portion of the amp. To learn more about this, look up on op-amp theory. |
| boB:
--- Quote from: fonograph on November 11, 2018, 05:29:30 am ---I mean what happens inside the amplifier, When I flick the gain switch,what changes inside the amp? Can class D/switch mode amplifiers have gain settings too or only class A/AB/linear amplifiers have it? --- End quote --- Probably changes a resistor value. Most likely the amount of negative feedback from output to input in a voltage divider. Even a Class D amplifier will have an analog feedback network since it's analog in and analog out. boB |
| Dave:
--- Quote from: boB on November 11, 2018, 07:02:17 am ---Most likely the amount of negative feedback from output to input in a voltage divider. --- End quote --- No, it would be a bad idea to do that, as it would also change the frequency response of the amplifier and potentially make it unstable. It's usually done as spec's image above shows - the attenuation of the input signal is varied, while the gain of the amplifier remains fixed. |
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