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Headphones Voltage/Current requirements

post #1 of 6
7/27/11 at 2:59am
Thread Starter 

I am aiming at DT990, but my questions are general:

 

1) offset voltage: What is the range of acceptable DC offset voltage at the amp's output

2) offset voltage: What is the expected offset voltage at the input (assuming a mobile source such as an ipod/smartphone)

3) Signal voltage: Whats is the expected input voltage?

4) Signal voltage: What is the needed output voltage (probably very headphone specific)

5) Output resistance: I have read somewhere that the output resistance should be close to 0. Is putting a 50ohm resistor at the output acceptable (so i wont harm my 18 ohm IEMs if i plug them in instead of a 250/600ohm DT990)

 

If you can point me to some tutorial on the subject - that would be great.

At the Cmoy site he addresses some of those issues. But it is scattered around the site and seems to be a bit Cmoy specific.

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post #2 of 6
7/27/11 at 6:15am

1 - 100mV ABSOLUTE max, 20mV or less prefferable. 

 

2 - measure it and see. 

 

3 - depends on source. 

 

4 - again... depends. I will add this - as much as people like to go fap-crazy over dynamic amps that swing 30vrms very few people actually know how much voltage swing they use. Its not always as much as you think. What many people mean when they say "drives the headphones properly" is not "has more than ample power" which would be the literal translation. it is better thought of as "does not sound like garbage". 

 

5 - Output impedance is a tricky question. There is only one way to run beyer headphones (IMO, 250 or 600 ohm models.) which is from an amp with a "very" non-zero-ohm output impedance. 120 ohms, and often higher is preferable. Multi-driver IEMs on the other hand are a different and more difficult story. Due to the crossovers in multi-driver IEMs they are EXTREMELY sensitive to output impedance, and the only right value is 0ohms. Id build separate amps for each headphone. 

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post #3 of 6
7/27/11 at 11:49am
Thread Starter 

Thanks for the answer

Can you explain why 120ohm would be better than 0?

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post #4 of 6
7/27/11 at 12:46pm

120 ohms is part of the (optional) IEC standard for driving headphones. 

 

Its better because that seems to be how they were designed to be used. 

 

Soundwise, everything just comes into focus better (DT880-250 & T1) with a 120ohm output impedance. Most importantly (to me anyways) the "beyer treble spike" gets knocked down a bit, and after that's out of the picture everything else just falls into place. 

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post #5 of 6
7/27/11 at 1:32pm
Quote:
Originally Posted by nikongod View Post

... Id build separate amps for each headphone. 



If all else were the same, wouldn't making an impedance plug be cheaper option?  Or even using a transformer for impedance matching?  Or is there something I'm missing here?

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post #6 of 6
7/27/11 at 3:42pm

the difference in sensitivity and impedance make no hiss in iem and sufficient headroom with 600 Ohm headphones pretty incompatible

 

a output R divider that keeps the output Z low enough for multiarmature iem can be done but is too heavy a load on many amps - the idea of xfmr step down as a solution for iem seems to meet with extreme psychological resistance here

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