Driving 600 ohm headphones - AVS Forum
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post #1 of 8 Old 08-20-2010, 12:06 PM - Thread Starter
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I just acquired the Beyerdynamic DT770 headphones, 600 ohm edition, to use in my office with a 3G Ipod Touch. Based on everything I had read, I fully expected to need a dedicated headphone amplifier (solid statehave no interest whatsoever in tubes). Although Beyerdynamic does not specify sensitivity, I imagined the 600 ohm impedance would result in only minimal volume out of the Ipod's headphone jack. Totally wrong. I'm listening right now with the volume bar at the halfway point, and the music is as loud as I like it. I also tried them last night with the headphone jack on an older Cambridge Audio 6.1 channel receiver. Again, my ears will bleed before I run out of power.

My question is, should I be surprised? Is it just that these headphones are very sensitive? This isn't based on a measurement, but I feel like I am getting more volume with the Beyers at the same volume position as a pair of AKG k601s I have, rated at 120 ohms and 101dB sensitivity.

My next question is, am I hearing the full potential of these headphones? If I am getting the volume I want without noticeable distortion, what scientific justification would there be to using a dedicated solid state headphone amplifier? According to HeadRoom, the 600-Ohm impedance DT770 model is expressly engineered for audiophile listeners using powerful high-quality headphone amps in their arsenal. The extra high impedance makes this model tough to drive directly from most audio sources but, once properly powered via a good head-amp, the stiff impedance will also help to present an extremely quiet background noise floor . . . . Really? I spent some time comparing short passages with the Ipod and my receiver's headphone outputs, and am sure I could not identify them in a level matched blind test. While I don't know the output specs of either headphone amp, I think it's safe to presume the receiver's is at least equal to the Ipod's, if not higher. So, I feel confident that even more voltage from a dedicated headphone amp is not going to have some magical effect.
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post #2 of 8 Old 08-20-2010, 12:35 PM
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Realize that the drivers are RIGHT next to your ears. That means very little power is needed.

I have experienced bad headphone outputs. Such as on laptops. I don't know what the problem is. Perhaps they have high distortion regardless of volume.

I have also known some headphone outputs where the bass seemed to hit harder.

My feeling is that if you don't experience listener fatigue, and bass seems ok, then don't worry about it.

"But this one goes up to 11"
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post #3 of 8 Old 08-20-2010, 01:46 PM - Thread Starter
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Quote:
Originally Posted by MichaelJHuman View Post

I have also known some headphone outputs where the bass seemed to hit harder.

I am glad you said this, which is exactly what I was getting at. Do you have any idea why bass would be different (relative to other frequencies) between headphone outputs, and presumably, different output impedances and voltages?
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post #4 of 8 Old 08-20-2010, 01:56 PM
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Quote:
Originally Posted by amicusterrae View Post

I am glad you said this, which is exactly what I was getting at. Do you have any idea why bass would be different (relative to other frequencies) between headphone outputs, and presumably, different output impedances and voltages?

It's a mystery to me why that would be. I would doubt myself, except I was not listening for it specifically. I just noticed, after one of my discmen died, and I replaced it, that I was dissapointed in the new one.

Damping factor? Clipping on strong transients? Don't know. I have never heard a standard stereo or multi-channel amp limit bass like that. Just a headphone output.

"But this one goes up to 11"
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post #5 of 8 Old 08-21-2010, 08:44 AM - Thread Starter
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anyone else care to weigh in?
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post #6 of 8 Old 08-21-2010, 09:06 AM
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I believe its about matching impendance between amp output and headphones. Some amps seem to go out of comfort area when headphones have very low or very high impendance. Obviously 600 ohms belongs to the other extreme and I have witnessed some amps running out of juice with my 600 ohm AKG 240M headphones. I like using 32ohm headphones with portable devices for this reason as it is relatively safe rating.

In addition, for example, some headphone outs of receivers have substandard implementation, as my old receiver was the only one of several headphone connnections I found sounding bad when comparing with A/B headphone switch I built.

I happen to think that my Musical Fidelity headphone amp is good match to my Sennheiser HD600 headphones, but I am not quite sure that there is clear difference comparing with well implemented headphone outputs.
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post #7 of 8 Old 08-21-2010, 07:48 PM
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Quote:
Originally Posted by karrih View Post

I believe its about matching impendance between amp output and headphones. Some amps seem to go out of comfort area when headphones have very low or very high impendance. Obviously 600 ohms belongs to the other extreme and I have witnessed some amps running out of juice with my 600 ohm AKG 240M headphones. I like using 32ohm headphones with portable devices for this reason as it is relatively safe rating.

In addition, for example, some headphone outs of receivers have substandard implementation, as my old receiver was the only one of several headphone connnections I found sounding bad when comparing with A/B headphone switch I built.

I happen to think that my Musical Fidelity headphone amp is good match to my Sennheiser HD600 headphones, but I am not quite sure that there is clear difference comparing with well implemented headphone outputs.

Seems most power amps have very low impedance. Not sure about headphone amps, or headphone outputs on various devices though. With low impedance, they should have minimal speaker interaction.

I thought it was mainly tube amps which benefited from impedance matching due to the use of an output transformer. Solid state amps just couple the output to the output transistors.

"But this one goes up to 11"
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post #8 of 8 Old 08-23-2010, 08:36 AM - Thread Starter
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Quote:
Originally Posted by MichaelJHuman View Post

Seems most power amps have very low impedance. Not sure about headphone amps, or headphone outputs on various devices though. With low impedance, they should have minimal speaker interaction.

I thought it was mainly tube amps which benefited from impedance matching due to the use of an output transformer. Solid state amps just couple the output to the output transistors.

I think you're right.
FWIW, Musical Fidelity specs the V-Cans output at 5 ohms. Others are less forthcoming.
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