Originally Posted by nikongod
The 10 ohm resistor is there to protect the AMP when you plug in headphones with the volume way up high.
A 10ohm resistor will not protect the headphones from much of a fault in the amp.
You could PROBABLY use a smaller resistor, but why? Lots of headphones sound great with a bit of source impedance and compared to what a high voltage tube operated at low voltage and current does to the signal a 10ohm resistor is nothing.
Keep a bit of safety factor, leave it in.
Safety is definitely important, don't want to ruin your equipment or, worse, hearing!
I have read that impedance matching headphones to 1/8 the output ohms is one more thing to help drive headphones to their full dynamic potential... I think that many people who see the 10 Ohm output and then may immediately write the amp off without even hearing it. A lot of the most affordable headphones are rated at 32 Ohms. But then, this is the Internet, full of conflicting reports and misinformation. Some people actively seek out things to raise impedance between the amp and headphone, like the Etymotic adapter to "convert" the ER-4p into the ER-4s. They say that it helps to dampen the background noise, which obviously would be great for tube amps (and vinyl LP record albums). Now you, Nikongod (reference to the camera brand? Love Nikons, almost got one instead of my Olympus), are saying that tubes for headphone amps (low voltage & current) add so much of their own distortion, that the output ohms doesn't even make a noticeable difference in comparison.
So, is there a grain of truth in all three perspectives, or what? How are we defining the effect of this distortion, anyway? When I would use the word "distortion" to describe a sound, I would say something like "The overdriven bass in that bad Kanye West song called 'Gold Digger' usually produces really bad distortion in low-fidelity headphones." Am I actually thinking of "clipping" instead of "distortion?"
Thanks very much for the information so far - I think I would have to take classes to learn all this for myself.
Also, my curiosity about possibly lower output ohms is purely selfish... I have a pair of 62Ohm AKG Q701 headphones, if the output was within that target of 1/8 the ohms of the headphone, I would have both the benefits of lower distortion AND amp protection. As they say, "have your cake, and eat it too."