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Topic: "Up to 24db gain, which is pretty loud. Hurts your ears." (Read 896 times) previous topic - next topic

scswift

So I saw LadyAda released a new amplifier:
http://www.adafruit.com/products/1552

But her comments in the video confused me.  I have a 3W amplifier on my boards.  And I would in no way refer to it as "loud".  More like "any quieter than this and I might as well not bother, so why the hell is almost every speaker 8 ohms?"

In a quiet room, 3W is okay... but not awesome.  And definitely nowhere near earsplitting volume.  Hell, even 15W isn't earsplitting.  Standing close to a 20W?  Okay now you can say that hurts your ears.

So what's she on about here?  Specifically, what's this about gain?

My understanding of how amplifiers work is this...  Assuming I have the input set up properly, if I input +2.5V then the amp outputs 5V.  Into a 4 ohm speaker that gives me 2-3W.  I'm not sure of the exact amount.  Furthermore, my DAC will output 2.5v if the sample I input to it is at the maximum value. 

Given this....  assuming I am inputting audio data where the volume has already been maxed out...  By maximizing the peaks, and possibly applying some compression...  What would a 24DB do for me except to create horrible clipping on my output?  I'm not even sure what  24B boost means in terms of how much the voltage is increased, but since the amp would be limited to a 5V output, a boost to the input when the input is already telling it to go to 5V is not desirable.  Cause then when you're telling it to go to 2.5v it's going to boost that as high as it can go as well and that's where your clipping comes from.

So am I missing something here?   Am I right that this boost is only useful if the input voltage is low, due to how the dac  or input to the amp is configured or due to the sound file itself?  Cause if so I don't see how that translates to a measly 3W amp hurting your ears.  Unless maybe she's talking about if you're wearing headphones?

CrossRoads

24dB gain would be to boost low level signals up to 0 to 5V levels (2.5V +/-2.5V)
Putting in a larger signal and using higher gain would just boost you to clipped levels.
10% distortion - I don't know how bad that sounds.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

retrolefty

The gain setting of a given amp stage is designed and established knowing the maximum audio input voltage and knowing the load impedance of the speaker. Vcc does set a limit of how much audio power can be supplied to a given speaker impedance. Of course also the speaker's power rating (wattage) should to be able to handle the designed maximum gain/power of the amp.

Lefty

Grumpy_Mike

Maybe it is all the distortion of overdriving the amp and speaker that is causing the pain in the ears not the absoloute volume.

CrossRoads

Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

D4p0up

It's class D, meaning it's very likely there is a H bridge on the output : the full output span is theoritically +/- 5V not +/- 2.5V
P = R x I²  and I =Ueff/R ==> P = 1.56W @ 8Ohms. Seems fair.

That's coming out with 10% THD, so it's intended for portable systems with maximum efficency and minimum space count. The deal here is to amplify current to drive a low impedance load, cause basic arduino stuff can deliver 5V voltage with poor current capability.

So use it as an amplifier, not to "empower" en existing design output.

Hope that helps.

Arduino sound Reseach - http://bit.ly/fullmaj [fr][en] | Homemade Free VST - http://zomg.zxq.net [en]

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