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Old 13th March 2004, 09:19 PM   #1
Lugoman is offline Lugoman  Kyrgyzstan
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Default Laymen explanations of sensitivity and bandwidth?

I have been reading the lm3886 datasheet before I dive into making an amp and was wondering if someone could help me with a few terms.

What do they mean by bandwidth in the amp world? Is this a variable or set by the chip?

What is meant by sensitivity? What is a desired range for it? From the equation (8) in the data sheet as the gain goes up the sensitivity goes down. Is there a rule of thumb for balancing the gain and sensitivity or is sensitivity not important?

Thanks. This is the most times I have ever typed the word sensitivity!
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Old 14th March 2004, 08:15 AM   #2
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Well from laymen to another. To me bandwidth, is like a speaker, how far it can go before it runs into trouble.

I guess 100Khz is the big one for audio stuff. I see alot of gear thats measured as flat out to 100Khz. This may mean that we will only be pushing it to 20% of its usage, that it can produce things that we can't "hear", but we can unconsciensly (I'm not endorsing this idea, just saying that some poeple feel this way). Or that it may be a harmonics thing, if its good till 100Khz, then maybe stuff pops up at 50Khz, but is still out of the audio band.

Then there are RF stuff thats good for like Mhz applications, but no good here.

Like a tweeter is great for highs, but not so much for base.

Or an Indy car can hit 13,000 RPM's but driving around town would be a pain due to no low end torque, simply because its optimized for a particular bandwidth, or volumetric efficiency in a cars case.

Or it may just be a crazy marketing scheme, I mean if your amp has a 48db low pass at 50Khz, are you really gonna notice?


Sensitivity? You got me.
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Old 14th March 2004, 06:02 PM   #3
GregGC is offline GregGC  Canada
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Default Re: Laymen explanations of sensitivity and bandwidth?

Quote:
Originally posted by Lugoman
I have been reading the lm3886 datasheet before I dive into making an amp and was wondering if someone could help me with a few terms.

What do they mean by bandwidth in the amp world? Is this a variable or set by the chip?

What is meant by sensitivity? What is a desired range for it? From the equation (8) in the data sheet as the gain goes up the sensitivity goes down. Is there a rule of thumb for balancing the gain and sensitivity or is sensitivity not important?

Thanks. This is the most times I have ever typed the word sensitivity!

Bandwidth is determined by the difference between Fmax and Fmin @ -3dB or whatever other level (0.5dB for example) you specify. So the wider the better (depending on the application, off course).

Sensitivity s the Input voltage that you need to apply to get the specified output power of the amp. So it depends on the gain of the amp.
I you specify 20W over 8 Ohms speakers, the output voltage has to be 12.6V. For a gain of the amp of 10, the sensitivity of the amp is 1.26V. If the gain is 20, the sensitivity is 0.63V.

/Greg
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Old 14th March 2004, 06:30 PM   #4
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So as to avoid confusion -

As the gain goes up the sensitivity NUMBER goes down but the amp becomes more sensitive to the input.
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