Originally Posted by dallan
The problem is that the distortion is compounded without an amp because the laptops output has to work harder to drive the 650s thus distorting. In addition, the hd650s are feed at a lower impedance than they want and being very hard HPs to drive are underdriven as well.
You mean higher impedance ? The lower the impedance, the easier is the driving. A power amplifier for speaker has an impedance nearly equal to zero, and it has more than the ability to drive headphones through its speaker output.
If the output impedance of the laptop is too high, the frequency response will be affected. Data for the HD650 have been removed from the headphone.com database. But if we assume that it is similar to the HD600, the impedance of the headphones is 300 ohms with a peak of 550 ohms at 100 Hz.
If the output has a 300 ohms impedance, which is very high, the problem will be a 1 dB boost at 100 Hz.
The power ability of the output is another problem. Not enough current, and the signal gets clipped. We must take into account the impedance of the laptop, the impedance of the headphones, and the sensitivity of the headphones.
Grado SR60 are 32 ohms at all frequencies. HD650 has a nominal impedance of 300 ohms, like the HD650.
The sensitivity of the headphones are strange. Sennheiser says 103 dB for 1 Volt, and Grado says 98 dB for 1 mV... which would mean 158 dB for 1 Volt !
The impedance is ten times lower, which means that the power is ten times higher, but all the same, the numbers given in the technical specifications seem wrong.
Anyway, we don't know the impedance of the laptop, nor its maximum power output, and not even its maximum voltage output.
Originally Posted by spc100
I'm not against getting an external DAC/AMP in future, But............this is the science section, and I'm failing to see a scientific explanation, of why I need an amp, other than to increase the volume?
Outputs produce a distorded sound if the volume is too high. With an amp, you'll get a clean sound even at high volume.
If you don't get any distortion at maximum volume with the laptop and the HD650, then you don't need an amp.
Problem : hiss and poor frequency response (and maybe a bit of distortion in the DAC if the internal resampling is poor).
Solution : USB DAC.
Problem : an USB DAC has no headphone output.
Solution : USB soundcard with headphone outpout.
Problem : will the headphone output of the soundcard be powerful enough for the HD650 ?
But keep in mind that differences between headphones are way, way bigger than differences between DACs.
I don't know the Grado SR60 (according the Headphone.com measurments, they should sound close to the HD600, that themselves sound close to the HD650).
Compare the difference between HD600 and SR60 on this graph. Pay attention to the vertical scale in dB : Products - HeadRoom - Right Between Your Ears
And look at the RMAA results that you posted above about your audio chipset.
Differences between Grado and Senn are 5 dB. Differences between the chipset and a good DAC are 0.5 dB.
The major problem are output power and noise. Inherent distortion (except distortion caused by the volume) is a minor problem.