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Gain vs. Impedance

post #1 of 6
Thread Starter 

Hi everyone.

 

I am new to the forum, new to headphone amps, and new to tube amps sooooo...I'm hoping I can get away with what I'm sure is a dumb newbie question:

 

I have a pair of Sennheiser HD580's and a Little Dot Mk. III amp. With a little research here I have found out the 580's hve a 300 ohm impedance. When I look at the gain settings on my Little Dot, my options are to set the amp for low, medium or high impedance.

 

Um, is 300 ohms low, medium or high?

 

Sir G

post #2 of 6

It has nothing to do with the headphones. The gain in the amp sets how much the input signal is amplified. It might be as low as 0 dB (1x) or as high as +20 dB (10x). The little dot has 3, 4, 5 and 10x afaik.

 

Generally, you want to use the lowest gain that still gives you enough volume with your headphones. Too high gain and you might hear the noise floor and decrease the usable range of the volume control.


Edited by xnor - 2/1/13 at 9:11am
post #3 of 6

Ohms don't really have much to do with how easy/hard to drive the phones are. It's the SPL/sensitivity rated in dB (i.e 108dB which can be driven easily from an idevice).

 

Gain is the amplification of the signal. The less efficient your phones are (say 90dB), the higher gain you'll want to make it louder. However, at lower gains, you'll be able to use more of the volume pot (as xnor has said), which is better since you won't be experiencing channel imbalance and all that stuff with the lower part of the knob.

post #4 of 6

Use whichever setting sounds best. I think the impedance of the headphones is actually related to the gain you'll need from the amp. Low impedance headphones need less power to drive. So with low imepdance headphones you could use the lower gain setting. I believe 300 ohms is relatively high, so you might try the medium or high setting. I think. I'm sure someone will correct me if I got it backwards.

 

I use the medium setting on my headroom amp for my Sennheisers. Now that I'm thinking of it, I need to try the other settings out of curiosity.

post #5 of 6
Quote:
Originally Posted by Nightspore68 View Post

Use whichever setting sounds best. I think the impedance of the headphones is actually related to the gain you'll need from the amp. Low impedance headphones need less power to drive. So with low imepdance headphones you could use the lower gain setting. I believe 300 ohms is relatively high, so you might try the medium or high setting. I think. I'm sure someone will correct me if I got it backwards.

 

I use the medium setting on my headroom amp for my Sennheisers. Now that I'm thinking of it, I need to try the other settings out of curiosity.

 

Nah, power required doesn't really relate to headphone impedance, but you're right about impedance relating to gain.  Headphone amps are more or less like voltage sources, though with some non-negligible output impedance in series for some models, so by P = V^2 / R — power equals voltage squared divided by resistance  — if the headphones have higher impedance then they will require higher voltage to receive the same amount of power.  i.e. for higher R and equivalent P, you need higher V.  Headphone resistance is the real part of impedance, can pretty much just be considered the impedance for many models and at least for simple ballpark estimates.  Thus you may need higher gain and volume knob setting to achieve higher voltage, for higher-impedance headphones, to get equivalent power delivered and thus output sound pressure levels.  That's assuming equal dB SPL output per mW input (sensitivity), which of course in practice can be very different between different headphones.  The gain and volume knobs are pretty much just multiplicative factors on output voltage.

 

 

Practically, as mentioned above, just use the lowest gain setting that gets you to your desired volume and adjust from there.  You can try the other settings if you want, but usually they shouldn't be much different in terms of performance; mostly higher gains will be noisier, if anything, with maybe a little higher distortion.

post #6 of 6
Thread Starter 

Thanks for the feedback, folks. I had got the impression these were related from the Little Dot`s reference guide, where they show the various gain settings and then indicate which settings they believe are for "low, medium, or high impedance/ sensitivity" headphones. They do also state, however, that these are just guidelines and to try what works best, as most of you have indicated also.

I just hoped that since my cans and amp combo is fairly common, someone had direct experience.

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