The question is how low were the impedance(s) on the headphone(s) you tried?   ER-4PT is 27 Ohm, ER-4S and ER4SR are 100 ohm. The hum is louder with ER-4PT and as I wrote earlier, I shorted all inputs on M9 and the hum noise is constant regardless volume level ( = even level 00).   And I...

Already did.    Already did. Either someone else will confirm this trying M9 + Etymotic ER-4*, or my M9 is not functioning correctly.   Knowing the impedances of the in-ear and headphones you've tried, would help me to suspect it's my M9 is wrong. I see several of starved solder joints...

  HE-350 gets much hotter. You can keep your hand on M9 indefinitely. With HE-350 you cannot. The temperature gets above 60 C / 140 F in my configuration (room temperature of 25-27 C / 77-80.6 F).   I turn it on few hours before I start to listen then turns it off during night. My gear sounds...

I got an answer back from Kingwa. I quote:   "Audio-gd headamp product models had high power output and high gain, they are not suited in ear headphones. Kingwa"   A disappointing answer. During the years, I have tried around 10-15 different high-end headphone amplifiers. None of them had...

It could be assembly/wiring issue with my M9. As the hum exists even when only M9 is switched on, all analog inputs are shorted and volume set to zero. Maybe I should inspect how wiring goes from XLR jacks to 1/4" jack and how chassis- and signal ground are connected. But first I will wait...

Yes, I tried that too. HE-350 also have a ground lift switch, which also didn't make any difference.   Is it time to contact Audio-gd?

Hi and thanks for your suggestions, I have tried it and some more:   Neither HD650 nor HD800 causes noise even with volume maxed out on M9. With Etymotics however, the noise is present and constant regardless of volume level and also when all the analog inputs are shorted. So I'd say it is a...

High-end digital room correction system/loudspeakers would probably come close if you don't already have a very well-damped listening room.   Lyngdorf RoomPerfect, Genelec or Meridian. 

I believe the clamp that is holding the cable for ER4SR shirt clip is too weak. It detaches too easily from the cable. I fear I will loose it some day.    The clamp for ER-4PT and ER-4S is much sturdier and NEVER detached from the cable during 10 years I have been using them. Sadly the shirt...

Hi,   I wonder if someone has tried connecting Etymotic ER-4PT, ER-4S or ER4SR to M9?    I hear low humming noise when I connect these. The noise is louder with ER-4P than with ER4SR.    I don't hear any noise when I connect HD650 or HD800 single end.   Could it be due to the lower...

Hi,   Has anybody tried Quad PA-ONE paired with HD800?

There is a noticeable improvement of sound changing the stock cable of HD600 to Cardas Clear cable. That improvement sustains in both HD600 and HD650. Even comparing between HD600 with Cardas and HD650 with stock cable, HD650 still sounded less unveiled and engaging to me.

  I bought the second HD600 2-3 years later than the very first HD600 and found the sound of the latter to be more close to the characteristics of HD650. The older HD600 sounded slightly more veiled and less controlled in the bass area. I sensed HD650 has better control in the bass and more...

I have had two HD600 and still owns HD650 as in my comparison, HD650 is the better headphone.