Hello again,
Not sure if everyone's aware of the main lowlight of E1 amplifier: the output impedance of about
11 ohms (I actually measured 10.9 ohms on mine with 1kHz sine signal and 30-ohms resistive load). I usually don't complain about this because it sounds very good with most of my cans, but I got into troubles recently with the newly purchased 16-ohms IEM's because of bass roll-off and the sub-bass was impaired when A/B compared against a discrete amplifier I have it on my desk. Also, my Fostex T50RP MK3 planars were having a bit of issues in the sub-bass department too when paired with E1's amplifier, instead with my Matrix HPA-3B or Burson Play bass was just fine. With other cans I found no such issues!
Here's the
2 x 10-ohms resistors in the signal path, just between the LME49600 and the 6.3mm jack plug:
I could probably just short-circuit both resistors, because they're unnecessary based on TI's specs of
LME49600, but I find it safe & easy to parallel 2 more 10-ohms resistors on top of existing ones to lower the output resistance and impedance as well.
Sorry for how it looks like, but these were the only resistors I had at home for the moment. However, I was able to measure about 2.9 Ohms output impedance with 30-ohms resistive load after doing the above mod. This is all I needed so I can be able to have a proper listening experience out of my planars and low-impedance IEM headphones and I'm quite happy with this easy mod.
Why are those 10-ohms resistors in there in the first place if TI is not recommend them? Well...most likely to protect the output stage LME49600 chips when we plug/unplug the headphones while music is still playing (there's a short-circuit creating inside the jack when we do that). So a common sense would be to lower the volume or simply stop the music from playing when plugging or unplugging the headphones and no issues will occur.
Some links regarding the initial concern/lowlight/con:
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https://www.stereophile.com/content...-processor150headphone-amplifier-measurements
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https://headmania.org/2014/05/16/asus-xonar-essence-one-review/
L.E.: Second pic got re-edited later for a better close-up view.