How good is the headphone amp in Axe III..? (A question from an interesting discovery)

M

Mark Al

Inspired
I spent some time comparing HX Stomp XL and my Axe III, and I noticed something VERY interesting:

1. I am using headphone plugged into to HX Stomp XL going into Fractal Axe III, and I have an empty signal/patch in Axe III, so all tones are from HX, it's dry clean Twin Reverb patch, no effect.
2. Then I switch my headphone between plugging in either HX or Axe III (same volume) and amazingly, there is a noticeable difference in the dynamic response, aka FEEL, especially when hitting the string hard on the clean tone patch!

The exactly same (dry Twin Reverb) patch in HX, when monitored via HX's headphone and hitting string hard, it'd compress at the end of notes quite a bit earlier/more than when monitored via Axe III's headphone.

It looks like Axe III's headphone amp has more dynamic range than that of the HX Stomp, and hence perform a bit better! Note this is not a volume thing, as both headphone amps can drive the volume up to crazy levels.

It seems headphone amp DOES make a noticeable difference to the resulted feel. And it's pretty clear to me that Axe's headphone amp is better than that of HX stomp, to my ear/finger.

So I am wondering:
1. How good is the headphone amp in Axe III?
2. Will one get better dynamic response via a standalone high quality & high-power after market headphone amps?
3. How would the playing experience/feel change if one uses a high quality tube driven headphone amp?
 
Mark Al said:
1. How good is the headphone amp in Axe III?
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Mine sounds pretty darn good driving custom-mold FutureSonics IEMs. Haven’t thrown it on an analyzer, but sounds clean to me.

2. Will one get better dynamic response via a standalone high quality & high-power after market headphone amps?

Maybe. Depends on several interacting factors, with power (assuming both have enough power to achieve desired volume level) being only one.

Mark Al said:
3. How would the playing experience/feel change if one uses a high quality tube driven headphone amp?
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Hard to say. I’d prefer the most accurate and uncolored amp possible (which tube amplifiers are generally not — more even-order harmonic distortion, i.e. that “tube sound” we love) so I can hear what the AFX3 is/isn’t doing.
 
The headphone amplifier is the Ultra-low Noise, Ultra-low Distortion Analog Devices ADA4075-2. I don't think you can get much better than that using a external amplifier.

The chip at the upper right
input_phones-jpg.72892
 
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Cannot offer you any measurements or diagnostics, just pure user experience:

Started out with an AX8 many years ago and therefore had to use an external headphone amp.
First with a entry level Fiio, which instantly sounded better than anything built-in at that time.
Upgraded to the next bigger Fiio (HiRes Audio) and heard a noticeable difference.
Moved to the FM3 as soon as the headphone out version was available and always felt the urge to go back to my external headphone amp.
Got an AxeFX III Mk2 recently and never looked back :)
 
juka said:
Cannot offer you any measurements or diagnostics, just pure user experience:

Started out with an AX8 many years ago and therefore had to use an external headphone amp.
First with a entry level Fiio, which instantly sounded better than anything built-in at that time.
Upgraded to the next bigger Fiio (HiRes Audio) and heard a noticeable difference.
Moved to the FM3 as soon as the headphone out version was available and always felt the urge to go back to my external headphone amp.
Got an AxeFX III Mk2 recently and never looked back :)
Click to expand...
Interesting story, thanks for sharing 👍

Your experience seems to indicate Axe III has a better headphone amp than FM3... :p
 
The headphone amp on my FM3 is excellent. It can drive even my 300 ohm Sennheiser HD6XX to very loud volumes. My Helix Floor on the other hand can't go as high but it can get loud enough. HX Stomp, being a cheaper and smaller unit might make bigger compromises. I haven't tried one.

Personally I cannot tell any real tone difference when I have the volume roughly matched. The real differences will be in how the software processes the sound.
 
Mark Al said:
So I am wondering:
1. How good is the headphone amp in Axe III?
2. Will one get better dynamic response via a standalone high quality & high-power after market headphone amps?
3. How would the playing experience/feel change if one uses a high quality tube driven headphone amp?
Click to expand...
The Axe-Fx III headphone amp is excellent. There are likely dedicated headphone amps that are better but I would have to see the schematic to form an opinion. Many OTS headphone amps are nothing more than a cheap op-amp in a box.

IMO the best way to make a headphone amp is to use an op-amp and then add a current booster inside the feedback loop. You can use a complementary pair of transistors to do this.
 
Yes, the Axe-Fx III headphone amp is excellent. With good headphones it is my reference sound. The level of detail and dynamics is awesome.
 
If you have moderate to high impedance headphones then the Axe-FX headphone amp is great. It has loads of clean headroom and drives all of my full sized headphones well.

However, if you have low impedance cans like my IEMs have (6 Ohms), then you will run into damping issues because the output impedance of the internal amplifier is 35 Ohms if my memory serves me correctly.

I am running my IEMs off of the Schiit Audio Magnius and it makes a world of difference with its 0.1 Ohm output impedance. The bass frequencies running the IEMs off of the Axe's internal amp are farty and compressed whereas the same patch through the Schiit is punchy and clear. If I didn't need the super low output impedance then I wouldn't bother with an external headphone amplifier.
 
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OrganicZed said:
If you have moderate to high impedance headphones then the Axe-FX headphone amp is great. It has loads of clean headroom and drives all of my full sized headphones well.

However, if you have low impedance cans like my IEMs have (6 Ohms), then you will run into damping issues because the output impedance of the internal amplifier is 38 Ohms if my memory serves me correctly.

I am running my IEMs off of the Schiit Audio Magnius and it makes a world of difference with its 0.1 Ohm output impedance. The bass frequencies running the IEMs off of the Axe's internal amp are farty and compressed whereas the same patch through the Schiit is punchy and clear. If I didn't need the super low output impedance then I wouldn't bother with an external headphone amplifier.
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My trusty headphones are two pairs of Etymotic ER4SR, while I also have HD560s currently and used HD650 in the past.

The Etymotic has 45 ohm impedance, which sounds good through Axe III, but I sometimes wish the headphone amp can provide MORE voltage swing to give me more dynamic, you know, like the surreal dynamic swing experience we get from tube amps…
 
Could we know more data in reference to the headphone out?
It has been asked many times, but never been answered.
I have read everything related to the headphone out in the manual, in the fractal wiki and in the forum but I have not been able to find any more information than the impedance out being 35 ohms.
I think that to have the best experience with headphones it would be necessary to know the output amplification power.
I recently bought some 300 ohm headphones (Sennheiser hd600) some users have said that the headphone out has enough power to drive them, but I feel that they are not driven at 100 percent.
The dedicated amplifier sold by Sennheiser has a max output power with a 600 ohm load of 480mW and I believe that the hd 600 supports a maximum load of 500mW.

What is the rage of mW we have on the fractal products?

@FractalAudio

Thank you so much
 
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