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Audio component chain question - Page 2

post #16 of 21
5/24/11 at 9:09am
Quote:
Originally Posted by b0ck3n View Post

What of output impedance then? Is it important for all stages in the chain, or just the last stage that the headphones are plugged into? Can you solve the problem of a 10 Ohm DAP with a 1 Ohm amp?


I don't know what a DAP is, but the only impedance you care about is the output. Anything that happens internally between stages was hopefully optimized by the circuit designer.

 

--Ethan

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post #17 of 21
5/24/11 at 9:25am
Quote:
Originally Posted by EthanWiner View Post


I don't know what a DAP is, but the only impedance you care about is the output. Anything that happens internally between stages was hopefully optimized by the circuit designer.

 

--Ethan


DAP: digital audio player, iPods for example.
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post #18 of 21
5/24/11 at 2:07pm
Quote:
Originally Posted by khaos974 View Post

Exactly what I'm talking about, you analog line out is unlikely to have much distortion, on the other hand 10% distortion for speakers, while quite a horrible figure, is fairly believably, especially for non hi-fi stuff.


I was actually refering to a real speaker system though, the Sony CMT-A70. Although I received them as hand me downs from my grandfather and don't really mind, it think its inexcusible for a company like Sony to put out a speaker system with an MSRP of $230 that has audible distortion so noticeable that it nulifies its own equalizer.

 

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post #19 of 21
5/24/11 at 3:58pm

I think most speakers have audiable disortion, not all speakers are 10% though it depends on the woofer design, a cheap long-throw paper cone will have the most thd paper cones break up easily, while a strong kevlar cone with miminal excursion could have less than 5%thd, like with tube amps more thd could be desired.

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post #20 of 21
5/24/11 at 7:48pm
Thread Starter 

Crystal clear, thanks. And thanks to everyone else who posted as well.

 

I think I read it somewhere again yesterday that the main purpose of an amp is to clean up the signal. It's good to know that in truth in adds its own distortion to what's already there, even if it's too low to be audible.

 

Quote:
Originally Posted by xnor View Post

b0ck3n,

THD adds up like this:

 

0.01% THD => 20*log10(0.01 / 100) = -80 dB

0.001% THD = -100 dB

 

sum = 10*log10(10^(-80/10) + 10^(-100/10)) = -79.957 dB => 10^(-79.957/20)*100 = 0.0100496% THD

 

or sum = 10*log10((0.01/100)^2 + (0.001/100)^2) = -79.957 dB

 

 

For driving your headphones only the output impedance of the amp is crucial.

DACs can have outputs with several hundred ohms and expect a 'load' of several kiloohms, because they are supposed to output the signal (voltage) only and not power.

Of course, if you load any component down (i.e. drive a low-ohmic load) it will cause a lot of distortion which will propagate through the rest of the chain (see calculation above).

 

But, as others have noted, the transducers will most likely dictate THD (around 0.01% with high-end headphones) in your chain.



 

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post #21 of 21
5/25/11 at 4:37am

The main purpose of an audio amplifier is to amplify the input signal as linearly as possible.

 

The voltage gain is the ratio of output/input voltage, for example with a voltage gain of 10 a 0.1V input will be output as 1V.

To drive the transducers properly, the amp also has to amplify (i.e. provide enough) current for the given load.

 

Imagine an ideal amp, it would always output exactly the input voltage times gain instantaneously without introducing any noise. And if you short the output it would theoretically provide indefinite current.

But it doesn't clean up anything.


Edited by xnor - 5/25/11 at 4:46am
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