400 Ohms Headphone Output - Good or Bad?


Active Member
May 13, 2015
Hi all,

Im using my HPs with the headphone out from marantz PM5005 (pure analog amp, no digital ins or outs). Compared to portable options (Nx4, Q1Mk2), the sound output is quite good. Just out of curiosity, contacted marantz customer to check specs. Got a reply stating the output impedance for headphone out on the unit is 400 Ohms. No reply given on power output specs (wonder why?).

Now, going by the rule of 1/8th & factoring HP impedance of 37 Ohms (planars) and 300 ohms (senn), the headamp output impedance is not at all favourable. However, my use case doesn't seem to throw any issues and contrarily, the SQ is actually quite good. Since the amp uses speaker taps, assuming there is sufficient volume/gain to peak out the planar HPs before reaching distortion.
Some of the questions that come to mind:

  1. Would the high output impedance be damaging for the HPs, especially the planar HPs due to impedance differences (despite outputting sufficient current)?
  2. What difference would dedicated headamp with typical 0.1 ohms output impedance bring?
  3. Does the high current feedback typology in the marantz amp make it better than dedicated headamp?
  4. Does the high output impedance impact traits like noise floor, distortion, etc.?
Looking forward to FMs informed views!
  1. Not at all
  2. Night and day, better frequency response and improved damping factor to count a few.
  3. Once an engineer puts a resistor to limit power to headphones, all SQ factors are thrown out of window. 99.99% of headphone out socket on power amps fall in this category. Putting a 1c resistor is the laziest way to give headphone output capability
  4. Any resistor will introduce Johnson noise, higher the resistor , more the noise
One doesn't needs to spend big $$$s on h/p amp, I use Objective2 headphone or a DIY CMOY amp for the same reason

for further reading-
IS THERE A STANDARD FOR OUTPUT IMPEDANCE? The only standard I’m aware of is IEC 61938 from 1996. It specifies an output impedance of 120 ohms. There are numerous reasons why this is standard is way out of data and a really bad idea. In a Stereophile article about headphones, they said of the 120 ohm standard:
“Whoever wrote that must live in a fantasy world.”

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