AVR headphone output impedance guessing game :D

[Aerith Gainsborough]

Good evening, ladies and gentlemen.

I recently noticed, that the bass of my clear sounded a wee bit muddy and overbearing when listening through my AVR headphone out.
I never noticed this before, since I only use it to watch movies that have insane LFE effects anyway.

So I decided to measure my 3 devices using @solderdude's "poke the UMIK-1 through a CD" trick.

This was the result.

I was flabbergasted since it was so hilarious that I just had to share. Yes I did double check: all post processing was disabled. It was the raw output of REW, routed through SPDIF into the AVR.

Sorry if I stepped on any toes by creating a topic that isn't very scientific.

 

[solderdude]

Yes, this is a classic case of very high output resistance. Power amps often have a single high resistance resistor on the output of the power amp.
The output resistance of your AVR headphone out calculates to 270 Ohm.
I reckon 35 Ohm is about the max.output R you could use it with.
I would recommend not using amps over 10 Ohm.

Of course you can 'fix' the output R just enough so it will be more usable when it comes to tonal balance.
You can lower the output resistance to 25 Ohm by paralleling a 27 Ohm resistor to the Clear.
Requires a 6.3 TRS plug, a 6.3TRS socket and 2 small resistors of about 0.3W or so and some wire.
The penalty is 10dB less maximum output level.
You would need to build this (except use 27 Ohm where it shows 3.3 Ohm)

 

[Aerith Gainsborough]

What an interesting idea!
The -10dB would not be a problem, since the amp has more than enough headroom.

 

[bobbooo]

What an interesting idea!
The -10dB would not be a problem, since the amp has more than enough headroom.

Or just get the iFi Ear Buddy (reviewed on ASR here), which iFi state will give an output impedance of ~3 ohms. They say it attenuates by -16 dB though, so it would need more headroom. A 25-ohm output impedance would still cause a 2-3 dB bass boost on the Focal Clear.