This is a review and detailed measurements of the FLUX FA-12 balanced headphone amplifier. It was kindly sent in for testing by a member and costs US $749 from the company direct.
I must say, this is a luxurious and substantial enclosure for a headphone amp:
Size wise, it is like an enclosure for a 50 watt linear amplifier. Speaking of which, this is a (discrete?) class A amplifier.
Operationally I found having the low gain in the middle a bit odd. Like to see Low, Med, High in sequence. Another oddity is that to use unbalanced 1/4 headphone jack, you have to use unbalanced input. Balanced input only routes to balanced output:
Volume control is implemented using R2R relay so channel matching should be perfect for those of you using sensitive IEMs.
I could not find any safety/regulatory marks on the unit itself. When mains power supply is included in an audio device, I like to see third-party certification for safety.
FLux FA-12 Measurements (balanced)
As usual, I start with balanced input and out with such amps, setting the input to 4 volts and adjusting the volume for unity gain (4 volts out):
I must say, I did not expect such excellent performance! Distortion is vanishingly low at nearly -140 dB. It is noise that limits SINAD to 117 dB and change:
Noise is the limiting factor:
It is paradoxical that there is good volume control for sensitive IEMs but noise floor is rather high for such devices.
Company advertises bandwidth up to 1 Mhz. I don't test that high but the unit has very wide bandwidth:
Let's test all important power versus THD+N at 300 ohm:
Performance is excellent in low gain but drops below the leaders in medium and high gain, producing less power at slightly elevated noise.
There is a bit more struggle with 50 ohm load requiring more current:
We can see the load sensitivity better when we go through full suite of loads:
Flux FA-12 Unbalanced HP Measurements
Switching both input and output to unbalanced we get:
Power naturally drops:
Channel balance is as perfect as it gets:
Flux FA-12 Listening Tests
As usual, I start with my Ether CX 25 ohm headphone using balanced in/out. At first this sounded quite distorted. Then I realized I was playing with the volume control. Doing so causing stepping between levels which results in fair bit of distortion and some static. This happens more or less the same in all R2R implementations but I thought it was maybe a bit more extreme here. Leaving the volume control alone produced superb performance. I could cause the amp to clip but it would be quite loud by then.
Performance with the Sennheiser HD-650 using unbalanced in/out was just as good. Tons of detail, dynamics, etc. I could get the amp to limit out though earlier than others I test with lots of distortion. As with Ether CX though, this occurred at a level you would not use but which you may need with a higher impedance headphone.
As a practical matter, subjective performance was excellent.
Conclusions
By deviating from the current formula of "composite op-amps" I automatically assumed performance would not be good. Flux FA-12 proved me wrong, delivering extremely low distortion and noise. Not enough to land at the top of the class but far better typical boutique amps. You get slightly less performance than state-of-the-art but then you gain R2R volume control for perfect channel matching. Subjective performance is superb if you don't mess with the volume control while listening. Price is high but for that you get a nice package.
I am happy to recommend the Flux FA-12 balanced headphone amplifier. Good to see doing it your way can still result in performant products.
------------
As always, questions, comments, recommendations, etc. are welcome.
Appreciate any donations using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
I must say, this is a luxurious and substantial enclosure for a headphone amp:
Size wise, it is like an enclosure for a 50 watt linear amplifier. Speaking of which, this is a (discrete?) class A amplifier.
Operationally I found having the low gain in the middle a bit odd. Like to see Low, Med, High in sequence. Another oddity is that to use unbalanced 1/4 headphone jack, you have to use unbalanced input. Balanced input only routes to balanced output:
Volume control is implemented using R2R relay so channel matching should be perfect for those of you using sensitive IEMs.
I could not find any safety/regulatory marks on the unit itself. When mains power supply is included in an audio device, I like to see third-party certification for safety.
FLux FA-12 Measurements (balanced)
As usual, I start with balanced input and out with such amps, setting the input to 4 volts and adjusting the volume for unity gain (4 volts out):
I must say, I did not expect such excellent performance! Distortion is vanishingly low at nearly -140 dB. It is noise that limits SINAD to 117 dB and change:
Noise is the limiting factor:
It is paradoxical that there is good volume control for sensitive IEMs but noise floor is rather high for such devices.
Company advertises bandwidth up to 1 Mhz. I don't test that high but the unit has very wide bandwidth:
Let's test all important power versus THD+N at 300 ohm:
Performance is excellent in low gain but drops below the leaders in medium and high gain, producing less power at slightly elevated noise.
There is a bit more struggle with 50 ohm load requiring more current:
We can see the load sensitivity better when we go through full suite of loads:
Flux FA-12 Unbalanced HP Measurements
Switching both input and output to unbalanced we get:
Power naturally drops:
Channel balance is as perfect as it gets:
Flux FA-12 Listening Tests
As usual, I start with my Ether CX 25 ohm headphone using balanced in/out. At first this sounded quite distorted. Then I realized I was playing with the volume control. Doing so causing stepping between levels which results in fair bit of distortion and some static. This happens more or less the same in all R2R implementations but I thought it was maybe a bit more extreme here. Leaving the volume control alone produced superb performance. I could cause the amp to clip but it would be quite loud by then.
Performance with the Sennheiser HD-650 using unbalanced in/out was just as good. Tons of detail, dynamics, etc. I could get the amp to limit out though earlier than others I test with lots of distortion. As with Ether CX though, this occurred at a level you would not use but which you may need with a higher impedance headphone.
As a practical matter, subjective performance was excellent.
Conclusions
By deviating from the current formula of "composite op-amps" I automatically assumed performance would not be good. Flux FA-12 proved me wrong, delivering extremely low distortion and noise. Not enough to land at the top of the class but far better typical boutique amps. You get slightly less performance than state-of-the-art but then you gain R2R volume control for perfect channel matching. Subjective performance is superb if you don't mess with the volume control while listening. Price is high but for that you get a nice package.
I am happy to recommend the Flux FA-12 balanced headphone amplifier. Good to see doing it your way can still result in performant products.
------------
As always, questions, comments, recommendations, etc. are welcome.
Appreciate any donations using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/