Topping A90 Discrete Preamplifier/Headphone Amp Reviewed

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The Topping A90 Discrete ($599 buy at Amazon), while marketed principally as a headphone amplifier, ranks as one of the most ideal analog preamplifiers I’ve used. A couple of months back, I reviewed Topping’s Pre90 analog preamp. The A90 Discrete is better. It delivers more features with equally good sound for a similar price. The Topping A90 Discrete also has a remote control that works successfully when more than three feet away, which was the Topping Pre90’s fatal flaw.

Topping A90 Preamp and Headphone Amp reviewed by Steven Stone
Here’s a pair of Topping A90 preamps in both black and silver – stacked

What Makes the Topping A90 Discrete Preamp Headphone Amp Special?

  • Instead of a volume potentiometer. the Topping A90 Discrete uses a stepped resistor array to control levels. This is a far more precise volume control and also includes a numerical front panel volume display so you can repeatably set accurate listening levels. 
  • The Topping A90 Discrete has both balanced inputs and outputs for both its stereo preamplifier and audiophile headphone sections. Whether your input is single-ended or balanced, both balanced and single-ended outputs are active. You can also add Topping’s EXT 90 extension box to add additional inputs. With the EXT90, you have four Balanced XLR and two unbalanced RCA inputs available.
  • The Topping A90 Discrete uses discrete components to assemble their nested feedback composite amplifier (NFCA). Four modules, each with 39 transistors, form the fully balanced circuit topology.
  • The Topping A90 Discrete’s front panel has connections for 4-pin balanced XLR, 4.4mm balanced, and 6.35mm single-ended headphone connections. It also has two gain settings for balanced and single-ended headphones. 
  • To ensure the lowest noise floor possible in any setup, the Topping A90 Discrete included a ground lift switch on the back. In some situations, this can reduce or eliminate any issues with ground loop hum. The Topping A90 Discrete also can be used in any country in the world without modification due to its ability to accept anything from 100 to 240 volts and 50 or 60 Hz.
  • The Topping A90 Discrete remote control has excellent range. In my system, with direct line of sight, the remote’s range was 17 feet. At 18 feet the remote stopped working reliably. This range should allow for consistent operation in most installations.
  • The remote control has two custom memory buttons that can be used to recall specific custom settings. I use then to go quickly from preamp output to headphone output. You can also set the headphone amp gain and adjust display brightness via the remote.

Why Should You Care About the Topping A90 Discrete Preamp/Headphone Amp?

While I have reviewed lots of excellent headphone amplifiers and preamplifiers throughout my years, preamplifiers that also include headphone amplifiers and support both single-ended and balanced analog sources are not as common. Finding one that performs as well as the Topping A90 Discrete as both a headphone amplifier and preamplifier and at such a low price is even more rare. The A90 Discrete offers an extremely high level of performance, ergonomics, functionality, and build quality at an extremely attractive price.

Topping A90 Preamp and Headphone Amp reviewed by Steven Stone
The Topping A90 is a perfect match with a good pair of Ultimate Ears IEM (in-ear monitors)…

Some Things You Might Not Like About the Topping A90 Discrete Preamp 

  • If you plan to use the Topping A90 Discrete in a system that has more than one balanced and one single-ended input, you will need to acquire the EXT90 extension box to add more input options
  • While the Topping A90 Discrete has an all-aluminum chassis, it is not especially heavy at only six ounces. You may need to add some weight to the top to keep it from being pulled around by your headphone cables. 
  • On the first firmware version, output gain adjustment on the Topping A90 Discrete was only available via the remote. The latest firmware version corrects this and adds the option of adjusting the high/low gain by pushing in the volume control and turning it counterclockwise to employ low gain and clockwise to switch to high gain. 
  • When you use the Topping EXT90 for additional inputs, there are no indicators on the A90 Discrete or EXT90 to designate which input on the EXT is active.
  • If you use a beefy power cord, it may make it difficult to fit in the 12-volt trigger input cable. The two connections are too close together. 

Listening to the Topping A90 Discrete Preamp/Headphone Amp…

I used a wide variety of headphones with the Topping A90 Discrete. The most sensitive in-ear monitors I have, the Empire Audio Zeus (119 dB), were absolutely silent even when the volume control was turned up to 99 (the maximum level) and the gain was set to high. With my least-sensitive full-sized headphones, the Dan Clark Stealth (buy at Amazon for $3,995), using the balanced output, the Topping A90 Discrete could deliver loud levels at the 55 level, which was just over half the maximum level. Listening to Nickle Creek’s latest release Celebrants the Topping A90 Discrete/Dan Clark Stealth combination did a superb job of retaining even the subtlest low-level details on the title cut. 

Switching over to the more mainstream and approachable Sennheiser HD600 headphones, I was impressed by the A90 Discrete’s ability to deliver superior dynamics and good tonal balance throughout the entire frequency range. While not as involving as the Dan Clark Stealth, the HD600 delivered excellent image specificity and placement, even if it didn’t have the same level of low-level detail. Listening to the Band of Heathens’ latest album, Simple Things, I was impressed by the HD600/A90 Discrete’s ability to easily illuminate all the instruments in the mix. 

Used as a preamplifier, I was impressed by the Topping A90 Discrete’s ability to sonically disappear. I usually employ a passive preamplifier such as the Tortuga LDR 300 in my nearfield reference system, but I found after doing several A/B tests and even a bypass test (where I inserted and removed the Topping A90 Discrete from the signal chain) that I could not reliably tell any sonic differences when the A90 was present in terms of added noise or distortion. Even with my own live concert recordings of the Boulder Philharmonic, which were made at a much lower volume than most commercial recordings, I could not discern any noticeable sonic differences between the two preamplifiers. When I compared the Topping A90 Discrete with the Schiit Freya S in passive mode, once more I could not identify major sonic differences between the two preamplifiers. Both produced virtually transparent sonic results. 

Does the Topping A90 Discrete Preamp and Headphone Amp Have Any Resale Value?

Yes, sir. The standard rule of thumb for resale value is one half the original retail, which in the Topping A90 Discrete’s case would be approximately $300. Of course, this raises the question: “Why would you ever want to sell the Topping A90 Discrete?” I seriously doubt you will find its specifications bettered in a meaningful way that would require its replacement based on performance. You might want or need a more fully featured preamplifier in terms of tone controls or DSP functions, but if your system is optimized for a minimalist approach, then the A90 Discrete should deliver exactly what you need and remain in your system for many years. 

Topping A90 Preamp and Headphone Amp reviewed by Steven Stone
Here is the Topping A90 as a part of a Topping stack at Steven Stone’s listening room

Who Is the Competition for Topping A90 Discrete Preamp/Headphone Amp?

The Schiit Freya+, which I reviewed recently, is an excellent US-made preamplifier that has three single-ended and two balanced inputs. This offers one more single-ended input but two fewer balanced inputs than the Topping A90 Discrete (when you have the EXT90 attached). The Schiit remote has slightly more range, and while both use a stepped relay volume control, the Topping A90 Discrete has a volume level display, which the Freya+ lacks. Sonically, you would be hard-pressed to tell the difference between the Freya+ in passive mode and the A90 Discrete. When switched to tube mode, though, the Freya+ will produce more tube coloration and a higher noise floor, but for some music you may prefer this.

The Topping Pre90 has the same input options as the Topping A90 Discrete, but it lacks the volume display and a remote control with decent range. In terms of sonics, I seriously doubt you will hear a difference. Both have an exceeding low noise floor and are as quiet as some of the passive preamplifiers I’ve used.

The S.M.S.L. HO200 ($399) has most of the more important features of the Topping A90 Discrete in an even more compact package. With both balanced and single ended outputs, the HO200 can serve as both a headphone amplifier and preamplifier. While it lacks a remote, since it was intended primarily for desktop or nearfield use, it has all the important controls on its front panel. The three-level gain control makes it so the HO200 can handle any headphone sensitivity. 

Final Thoughts on the Topping A90 Discrete Preamp/Headphone Amp

If you have any analog sources or need to adjust the volume of a DAC with a fixed output, you will need an analog preamplifier. I have, during my many years as a reviewer, had many preamplifiers in my various systems. None, at anywhere near the Topping A90 Discrete’s price, have the same combination of excellent features and superb performance. Besides delivering a virtually silent output for powered speakers or power amplifiers, the Topping A90 Discrete also includes an excellent headphone amplifier capable of successfully mating with any headphone, whether high- or low-sensitivity. In, short, when I need a reference-level analog preamplifier in the near future, I will be reaching for the Topping A90 Discrete.

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