This is a review and detailed measurements of the Teac HA-501 headphone amplifier. It is on kind loan from a member. The HA-501 in black costs $549 including Prime shipping from Amazon. Oddly, the silver color is much cheaper at $354! Black anodizing must have become very expensive. 
The black does look a lot nicer though so it would be tough to settle for silver.
The HA-501 is one of the most attractive desktop audio products. If you are a fan of the 1970s and 1980s hi-fi gear, the Teac is the best way that look could have been modernized yet hold its retro appeal:
The controls feel fantastic and the head of the class for sure.
Controls are not unusual other than addition of "damping factor" which simply adds a resistor in the path of the headphone output (measurements later).
The other odd thing is the auto-muting. When you unplug the headphone, the red audio mute LED comes on and will not go off until you turn the volume all the way down to infinity and then back up. This is to assure you never plug in a headphone and have it play at exceedingly high levels. I am not sure that is worth the effort it takes to reset it every time if someone has multiple headphones they use often.
The back panel shows the generous inputs and outputs:
If it were up to me, I would make balanced XLR inputs mandatory on every headphone amp. So useful in getting around ground loops.
Nice to see switch selectable pass through RCA outs.
Being a proper audio companies, regulatory certifications are there and can be relied upon to mean this is a safe device that doesn't spit out a bunch of RF.
Overall, a headphone amplifier doesn't get much nicer than this from look and feel point of view.
Headphone Audio Measurements
Let's start with our dashboard output, driving the HA-501 using XLR inputs (same input was used for all the tests):
I set the volume to pass through (4 volt in, 4 volt out). Even at this reduced volume level, the amount of distortion is quite high for a top of the line headphone amplifier. The distortion is from third harmonic which sets the SINAD by itself to 83 dB. As a way of comparison, the Massdrop THX AAA 789 clocks at 117 dB while producing 5.8 volts output! That is an incredible gap in performance.
Signal to noise ratio is spec-compliant:
The 50 millivolt output which measures how well an amp drivers ultrasensitive headphones is not so good though:
Measuring THD+N versus frequency at my standardized 5.8 output level shows how much more the distortion rises with volume:
Even at 2 volt output the HA-501 is not competitive.
Intermodulation distortion distortion versus output power shows the same:
But also indicates that the HA-501 has more power than THX 789's single-ended output. We can see this clearly in THD+N versus output power at 300 ohm:
Switching to 33 ohm for a more current limited load we get:
Here, the rise in distortion is more severe but we still have ample amount of power at 1.4 watts.
Channel imbalance is very good until the end:
Finally, output impedance is very good at high damping factor setting:
The amount of resistance at low damping factor is still modest at 6.2 ohm. I thought it would be higher than it is.
Headphone Listening Tests
As usual, I start my listening tests with the Sennheiser HD-650. As the measurements predict, there was more than sufficient amount of power to drive these to produce excellent bass (they sound anemic otherwise). The authority and clarity erased any memory of less than excellent measurement graphs.
The situation was nearly the same with Hifiman HE-400i. There was plenty of power although I thought maybe at the limit it got a tiny bit distorted. Never mind as I could not listen at that level for more than a couple of seconds.
Using the HE-400i, I played with the damping factor. It makes quite a bit of difference going from High to Low, causing both the level and bass response to suffer greatly in Low setting. Of course this is not the main use of it but thought it was a good tool to measure the effect of high output impedance subjective.
Conclusions
The Teac HA-501 nails a number of my review criterias from look, feel, safety, reliability and amount of power. Subjectively it also meets its target of producing ample power to drive just about every headphone you throw at it.
Objectively it is far from top of class given the game changing headphones amps: Massdrop THX AAA 789 and JDS Labs Atom. These two amps have basically left everything else in the dust. Where they lose to Teac though is in overall feel and look. Even the THX falls behind by good few points.
So you have a choice to make: go with heart that is pulled by the look and subjective sound quality or engineering excellence as represented by the competitors. I am not here to solve that equation for you. I want both and Teac HA-501 doesn't have both.
------------
As always, questions, comments, recommendations, etc. are welcome.
This year I like to get an early start on my Christmas shopping. Being too cheap to spend my own money, I thought I ask for yours. So please donate using:
Patreon: https://www.patreon.com/audiosciencereview), or
upgrading your membership here though Paypal (https://audiosciencereview.com/foru...eview-and-measurements.2164/page-3#post-59054).
The black does look a lot nicer though so it would be tough to settle for silver.The HA-501 is one of the most attractive desktop audio products. If you are a fan of the 1970s and 1980s hi-fi gear, the Teac is the best way that look could have been modernized yet hold its retro appeal:
The controls feel fantastic and the head of the class for sure.
Controls are not unusual other than addition of "damping factor" which simply adds a resistor in the path of the headphone output (measurements later).
The other odd thing is the auto-muting. When you unplug the headphone, the red audio mute LED comes on and will not go off until you turn the volume all the way down to infinity and then back up. This is to assure you never plug in a headphone and have it play at exceedingly high levels. I am not sure that is worth the effort it takes to reset it every time if someone has multiple headphones they use often.
The back panel shows the generous inputs and outputs:
If it were up to me, I would make balanced XLR inputs mandatory on every headphone amp.
So useful in getting around ground loops.Nice to see switch selectable pass through RCA outs.
Being a proper audio companies, regulatory certifications are there and can be relied upon to mean this is a safe device that doesn't spit out a bunch of RF.
Overall, a headphone amplifier doesn't get much nicer than this from look and feel point of view.
Headphone Audio Measurements
Let's start with our dashboard output, driving the HA-501 using XLR inputs (same input was used for all the tests):
I set the volume to pass through (4 volt in, 4 volt out). Even at this reduced volume level, the amount of distortion is quite high for a top of the line headphone amplifier. The distortion is from third harmonic which sets the SINAD by itself to 83 dB. As a way of comparison, the Massdrop THX AAA 789 clocks at 117 dB while producing 5.8 volts output! That is an incredible gap in performance.
Signal to noise ratio is spec-compliant:
The 50 millivolt output which measures how well an amp drivers ultrasensitive headphones is not so good though:
Measuring THD+N versus frequency at my standardized 5.8 output level shows how much more the distortion rises with volume:
Even at 2 volt output the HA-501 is not competitive.
Intermodulation distortion distortion versus output power shows the same:
But also indicates that the HA-501 has more power than THX 789's single-ended output. We can see this clearly in THD+N versus output power at 300 ohm:
Switching to 33 ohm for a more current limited load we get:
Here, the rise in distortion is more severe but we still have ample amount of power at 1.4 watts.
Channel imbalance is very good until the end:
Finally, output impedance is very good at high damping factor setting:
The amount of resistance at low damping factor is still modest at 6.2 ohm. I thought it would be higher than it is.
Headphone Listening Tests
As usual, I start my listening tests with the Sennheiser HD-650. As the measurements predict, there was more than sufficient amount of power to drive these to produce excellent bass (they sound anemic otherwise). The authority and clarity erased any memory of less than excellent measurement graphs.
The situation was nearly the same with Hifiman HE-400i. There was plenty of power although I thought maybe at the limit it got a tiny bit distorted. Never mind as I could not listen at that level for more than a couple of seconds.
Using the HE-400i, I played with the damping factor. It makes quite a bit of difference going from High to Low, causing both the level and bass response to suffer greatly in Low setting. Of course this is not the main use of it but thought it was a good tool to measure the effect of high output impedance subjective.
Conclusions
The Teac HA-501 nails a number of my review criterias from look, feel, safety, reliability and amount of power. Subjectively it also meets its target of producing ample power to drive just about every headphone you throw at it.
Objectively it is far from top of class given the game changing headphones amps: Massdrop THX AAA 789 and JDS Labs Atom. These two amps have basically left everything else in the dust. Where they lose to Teac though is in overall feel and look. Even the THX falls behind by good few points.
So you have a choice to make: go with heart that is pulled by the look and subjective sound quality or engineering excellence as represented by the competitors. I am not here to solve that equation for you.
I want both and Teac HA-501 doesn't have both. ------------
As always, questions, comments, recommendations, etc. are welcome.
This year I like to get an early start on my Christmas shopping. Being too cheap to spend my own money, I thought I ask for yours. So please donate using:
Patreon: https://www.patreon.com/audiosciencereview), or
upgrading your membership here though Paypal (https://audiosciencereview.com/foru...eview-and-measurements.2164/page-3#post-59054).
