Topping A90 Headphone Amplifier Review
Subjective Product Test from the Famous Audio Science Review Founder-Amir Majidimehr
This is a review and detailed measurements the Topping A90 Balanced and Unbalanced Headphone Amplifier. It was kindly sent to me by the company. The A90 is available for ordering and I am told ships by end of this month. It costs US $499.
The A90 is one of the best executions of the Topping series of products:
It is elegant without going overboard. The switches on the left have long handles and throws that give them much better feel than tiny ones we usually see.
The volume control feels good despite requiring light amount of effort to turn. The latter is good in that it is rather shallow even for my narrow fingers to comfortably grab and rotate around. But because it requires little effort to turn, you can using the chamfer on the knob and rotate it that way.
Three gain settings are provided with the lowest one being under one which should come in handy with very sensitive IEMs. Using this, you can operate the volume control in its higher and more accurate range.
The back panel is self-explanatory:
Power supply is built-in of course giving the unit heft so that even the heavies headphone cable won't make it skate around your desk.
It is just hard to find any reason to complain about look and feel of the Topping A90.
Headphone Amplifier Audio Measurements
With a million headphone amplifiers out there, measurements is the only way to find the good from bad. So let's start with our usual dashboard of unity gain (same voltage output as input). Connection is XLR input and unbalanced 1/4 headphone out unless said otherwise:
Wow! SINAD which represents the worst case/sum of noise and distortion is at 121 dB. Distortion output is less than -140 dB. I put the analyzer in loopback mode measuring itself and distortion only went down a to -150 dB. So we are not far from my state of the art, nearly $30,000 analyzer utilizing dual analog to digital converters to achieve this! Just look at the number of zeros in the THD+N percentage.
As I have mentioned a number of times before, our best case hearing dynamic range is -115 dB. So at the distortion and noise levels we are seeing here, you are seeing absolute transparency to the source.
Here is the ranking in our headphone amplifier table:
It is a tie for top spot of every headphone amplifier tested so far.
If distortion and noise are inaudible, let's see if there are any frequency response variations:
There is none well beyond our hearing range. This proves yet again that you have superb transparency here.
Just to dig into the noise factor by itself, we get this:
This is basically the noise limit of my analyzer which thankfully per above, is more than adequate to determine transparency for human hearing and then some.
Dropping the output down to just 50 millivolts to determine what dynamic range we have for very sensitive headphones the A90 takes the top spot:
This says that despite operating at such low level of output, you have almost 16 bits of dynamic range! The lowest level is 50 millivolts/65536 volts!
Let's go the other extreme and see how much power we have on hand given the popularity of power hungry headphones, starting with 300 ohm load:
Notice the much lower noise level compared to the drop THX AAA 789 which started this trend toward state of the art headphone amplifiers. We have a bit more power and seemingly equal distortion at at the limit. Alas, this test is run in single ADC mode of my analyzer which has a higher distortion floor than what I use in the dashboard. So anything better than that shows the same performance. I can fix this easily but then messes up with the historical data so I have left it alone.
Anyway, my threshold of adequate power in this test is 100 milliwatts and we have double that. So headphone users like Sennheiser HD650 should be very happy as should people with even higher output impedances.
Switching to the other extreme with 33 ohm load we get:
Same story repeats with us having 2 watts of power.
Switching to balanced output with a load of 50 ohm we have even more power:
This is nearly 5 watts of output power at superbly low SINAD of 113 dB.
Channel balance was very good although as I note on the slides, there may be units that are worse or better than this:
Output impedance is a very low 1.3 ohm which is about the limit of what I get with my current test jig:
Headphone Listening Tests
I started my testing with driving my very inefficient and low impedance (25 ohm) Ether CX headphones. These headphones bring most headphone amplifiers to their knees with either distortion, lack of power, muting, or sum of the above. None was in play here. The A90 drove them with authority using its balanced XLR output to ear bleeding levels! It was the best I have heard them sound. Detail, bass impact, loudness, you name it, it was there.
Switching to the Sennheiser HD-650 repeated the same experience even though I opted to use the 1/4 unbalanced out. I was sitting there with smile playing track after track.
The combination of power with transparency in noise and distortion leaves nothing to be desired. In a nutshell, this is what the hobby is all about.
The Topping A90 comes later to the party of leading edge headphone amplifiers. It comes there though with guns blazing producing exceptionally low noise and distortion while providing ample power to drive just about any headphone. It has an elegant enclosure which is of course a match for their excellent D90 DAC. The combination should be beautiful to look at, as much as listen to.
I am happy to give one of my strongest recommendations to Topping A90.
Click here to buy TOPPING A90
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