Audio science review Topping A90 Discrete balanced pre/ head amplifier
This is a review and detailed measurements of the new Topping A90 Discrete balanced preamplifier and headphone amplifier.
Announcement was supposed to be a few hours from now but one of the distributor already released it so here we go. As you can tell, there is a new design in the form of those pin-hole LEDs which I find quite elegant. Inside there is stepped relay for volume control. Of course as the name indicates, this design uses discrete transistors rather than op-amps. 39 transistors are used to accomplish that task in each module. Will performance be as good as op-amps? And is there an advantage? We will find out in the measurement section. Here is the back panel:
I was pleasantly surprised to see the same extension connector to connect to Topping EXT90 to provide more inputs. In addition there is 12 volt trigger which many have been asking for. And even a ground lift switch.
In use, I found minor ticks during quiet parts of the music when changing the volume quickly. This is quite common in stepped relay implementations.
Topping A90 Discrete Measurements
In order to save time, all measurements are with balanced XLR input and balanced 4 pin XLR headphone output. Unbalanced has quarter of the power. Here is our dashboard:
While SINAD of 119 dB is superb and assures transparency in all conditions, it is a hair worse than A90:
This is incredible performance as every other discrete headphone amplifier I have tested has given a lot of performance (in the form of noise and distortion) to get there. Dynamic range is a bit lower which is responsible for that:
We see that penalty in the 50 mv test:
Multitone test shows how low the distortion products are:
Frequency response is of course extended and flat:
THD vs frequency shows a slight rise at the top end:
I measured power at three impedances: 300, 50 and 32:
The advantage of discrete implementation seems to be in current delivery into low impedances:
Usually I see a pull back at 32 ohm but here, that load doesn’t impact the amp at all. It is not until we get to 20 ohm that the output voltage starts to drop a bit. This is a first since I started to make this measurement.
When pushed into protection with loads < 32 ohm, the unit shut off. Powering on everything was fine so it passed this stress test.
The beauty of stepped relay volume control is perfect channel matching which we see here:
I am amazed how well this works. Some stepped relay implementations lose their grip at low volumes but there we go past our limits of hearing before the mismatch even registers!
Topping A90 Discrete Listening Tests
I have been using my everyday Dan Clark Stealth headphone as a “it won’t drive it but let’s see what it does” test for headphone amps. This is the first time I have seen an amplifier have such an upper hand over these headphones. The sound is incredibly dynamic and beautiful. “Loud” listening is at volume level 80 in high gain. I cranked it up to 95 before I got scared for my hearing without any hint of distortion. I had not heard these headphones come to life so well.
Needless to say, driving Sennheiser HD650 and Drop Ether CX was in a walk in the park. I am talking incredible bass, detail and fidelity with volume indicator in 60s.
What a joy….
Conclusions
I must confess that I got a bit worried when Topping told me about the A90 Discrete. I worried that they were making a discrete version just to appease audiophiles but with much loss in noise and distortion metrics. Happily Topping approaches everything with extreme focus on performance and they managed to get the A90 discrete within a split hair of the op-amp version. But then innovated with stepped ladder volume control, trigger support and major step up in class/look of the unit. I happily take these as a trade off for that 1 dB of SINAD.
From design point of view, this is another watershed audio/engineering event brought to us by Topping. Who would have thought that this company would keep breaking new ground instead of all the major/usual names we know in hi-fi.
It is my pleasure to add Topping A90 Discrete headphone amplifier/pre-amplifier to my recommended list. My challenge is to figure out if it goes in my main system or desktop!
