So before you proceed, just know that this is less “a review of the Topping A90” and more “rambling about why the Topping A90 is going to be used for future headphone reviews on IEF”.
Topping is a brand that has taken the headphone-source-market by storm, with the ever-growing ubiquity of measurements and the rise of Audio Science Review, arguably the authoritative stronghold for such discussions. For those seeking sources with the highest SINADs and dynamic ranges, Topping is usually the first thing to dominate the conversation and so has been gaining traction within these circles as a “default recommendation”.
But if you’re familiar with me and/or my work, you would know that I’m basically a non-believer when it comes to all these things. So now the question is: where does the flagship A90 fit in exactly within IEF?
This A90 was kindly provided by HiFiGo.
Outputs & Inputs
- XLR balanced
- RCA single-ended (beware noise issues!)
- Headphone output
- Single-ended (1/4″)
- XLR balanced
- RCA single-ended
The Ground Loop Issue
Unfortunately, I’m a victim of the infamous ground loop issue that had plagued other Topping owners in the past. On the DAC side I use either the iFi iDSD Micro Black Label or the Motu M2, both of which are USB bus-powered when plugged in. Though do note that while the ground loop hum was basically inaudible with open-backed headphones, it was basically unusuable on IEMs (especially when said IEMs were plugged into the 4.4mm balanced outputs).
While both of the M2 and the Black Label were perfectly fine when used by themselves with their own headphone-outs, the problem kicks in when the A90 is connected to them via single-ended RCA. Basically:
- PC > USB > M2 = Clean
- PC > USB > Micro BL = Clean
- PC > USB > M2 > RCA > A90 = Ground loop hum
- PC > USB > Micro BL > RCA > A90 = Ground loop hum
- iPhone > USB > Micro BL (battery) > RCA > A90 = Clean
Fortunately, switching to 1/4″ TRS balanced-out to XLR balanced-in fixes the ground loop. But it’s still a little disappointing that I’m locked out of SE inputs on a $500 amplifier due to noise issues.
The A90 acts as both a headphone amplifier as well as a preamp, which helps my audio chain a ton ever since I got my newly-acquired Neumann KH120s. Not much else I can say, pre-outs aren’t exactly a fresh new thing on headphone amps (hell, modern $100 amps like the Fulla and the Atom have those) but at the very least having it available in balanced XLR is a nice thing to have, especially if your speakers run longer cables.
Power is not an issue, though my own listening volume requirements are not high in the least. With my DAC (Motu M2) almost-permanently at 50%, I hardly ever go above 50% on the A90 itself. This is with the Sennheiser HD800 and the Hifiman HE1000, both on low gain too.
The output impedance of the A90 is plenty low enough to not cause any trouble with “problematic” IEMs (I’ll defer to ASR for actual non-manufacturer measurements), with single-ended being the most optimal for IEMs.
Sound-wise, the A90 is as you would expect: a clean, basically uncoloured source that probably wouldn’t be a good fit for many headphones (signature-wise), unless you got yourself a really warm, really blunted headphone (*cough* Nighthawks). There is a bit of sharpness going on in the overall presentation of the sound, though nothing I would call offensive or a dealbreaker. Then again all this doesn’t really mean much for me, something I’ll get into next.
The IEF Stance on Sources
So at this point I’m sure that most people would already know my stance on sources (which includes DACs, amplifiers, and everything in-between): I don’t really care too much for them.
Which would seem like social suicide especially as a recognised portable audio reviewer, but I’ve held strong to this stance for the last 10 years and I won’t be changing anytime soon. To be clear, if I were to budget an audio chain from scratch I would personally go for a 80/15/5 split for the transducer, amplifier and DAC respectively (80/20 if the source was a DAC/amplifier combo). So… you wouldn’t be seeing me spending a lot of cash on sources, especially since my personal budget ceiling for IEMs are at US$1,500.
(“Transducer” in this case meaning the device that generates the physical sound, an umbrella term that can refer to headphones, IEMs, earbuds and/or speakers.)
This is just one way to play the audio game of course, not necessarily the most legitimate (nothing is in this inherently-subjective hobby) but it is my way. I follow the philosophy of min-maxing, that is to focus on the component in the audio chain with (IMO) the most significance, “maximising” said component and putting “minimal” attention to the others. And so it is because of this that I’d prefer to do “transducer rolling”, that is I prefer to match the transducer to a consistent source, rather than rolling a bunch of sources against one or two transducers.
But even as a “transducer specialist” reviewer, an important question still needs to be asked: what will be the consistent source(s) that will used as a reference for all future reviews on In-Ear Fidelity? Currently there are three:
- The Digitial Audio Player reference: the iBasso DX160
one true GodAcceptable Minimum: the Apple dongle (at least for IEMs)
- The Emergency Transportable Powerhouse: iFi iDSD Micro Black Label
Which only leaves one big missing usecase: the Desktop Setup, which is what the A90 will be fulfilling. Then again, out of all the desktop amplifiers out there… why the A90?
A90 as a "Reference"
With the plethora of desktop amplifiers out there of varying qualities and uh… signatures, what exactly makes the A90 a proper reference from a reviewing point of view?
First, we’d have to define what exactly makes a source (in this case, the amplifier) a “reference”. Is it ubiquity? In which case the Apple dongle would be the best reference, given that it’s available in both lightning and USB-C outputs and is the most accessible dongle that covers 99% of the audiophile userbase.
But that’s for efficient portable audio, and as I’ve said the Apple dongle is the Acceptable Minimum, though still falling short of the power requirements of the ultra-inefficient headphones that are getting more common by the day. In the realm of desktop amplification, Schiit have cemented itself as one of the most popular brands with the $100 Magni, now on the “3+” revision with a new “Heresy” edition catered specifically to the measurement-obsessed crowd. Beyond that, there’s also the Drop + THX AAA 789 retailing triple the price of a Magni, though at 8,000 units sold it’s hard not to acknowledge its popularity.
However, ubiquity is no indication of performance as the infamous Audio Technica ATH-M50X can attest to. In that case, the question inevitably comes to what exactly “performance” entails, and which source(s) balance ubiquity and said performance to at least be relatable to the reader. After all, having the “best” source in the world means nothing if it’s some obscure, limited-run and/or ultra-expensive model that nobody has ever heard of (or will ever hear).
So in order to determine what “performance” is in the realm of amplifiers and DACs, there are two factions that have been at war since the dawn of sound:
- The Subjectivist Camp, that rely on personal listening experiences to determine performance. They embody the “what I hear is what I hear” philosophy and usually do not pay much heed to measurements as they see no correlation between good measurements and good sound.
- The extremists in this camp (I highlight again, extremists) believe that subjective listening experiences cannot be quantified, and so all measurements are useless and cannot be trusted.
- The Objectivist Camp, that typically focus on hard, quantifiable data to inform themselves on purchase decisions. They embody the “what can be heard can be measured” philosophy, and so purchasing something that measures poorly makes no logical sense to them.
- The extremists in this camp believe that measurements are the be-all end-all, and that anyone with opinions that contradict currently-available measurements are delusional.
So which camp am I on? On the source side… I’m agnostic. I’m a filthy fence-sitter by virtue of the aforementioned min-max philosophy that I’ve adopted. So on this end, I’ve decided to poll people on both camps and see if they can suggest me a long-term, reference amplifier that I can use for future reviews as well as being acessible enough to not cause confusion within my readerbase.
As expected, the objectivist camp converges to the usual suggestions of Topping (mostly pointing to the A/D90 stack for “futureproofing”), THX (789 of course) and JDS Labs Atom (with the occasional RME ADI-2 recommendation as well), all well-measuring amplifiers at a reasonably-accessible prices. After all, in this camp numbers are the name of the game so the popular choices are easily predictable.
However, do I believe that a well-measuring source would sound better than a worse-measuring source? Well kind of… to a certain extent. If you’re asking me if a 120dB SINAD amplifier would sound better than another with 110dB SINAD, I would say that at that point you’d be obsessing over minutiae that don’t matter, especially given that most transducers tend to have THD+N typically around 0.01% in the best case scenarios. After all, I literally use an Apple dongle for daily listening, so at the very least you can’t call me a hypocrite.
On the other side of the pond, the suggestions from the subjectivist side are a little… inconsistent, to say the least. Here is a snapshot of just a few of the suggestions that I’ve received:
- Schiit Magni 3+/Magnius/Mjolnir/Asgard 3
- Massdrop x Cavalli Tube Hybrid
- iFi Zen
- Soekris 1541
- Bryston BHA-1
- HeadAmp GS-X Mk2
- Chord Hugo 2
And since I need to take ubiquity and accessibility into consideration, that strikes off the bottom half of the list.
Taking on a more “subjectivist” perspective, exactly what kind of signature/sound makes an amplifier suitable as a reference source? Arguably, a “neutral” or so-called “uncoloured” signature would be the most appropriate given that it would be unrealistic to review headphones with “source synergy” factored in, given that not everyone has the same sources and I don’t have the time, energy nor resources to match one headphone with every amplifier ever built.
In that case, a neutral/colourless amplifier is essential so as to better separate “the signature of the source” from “the signature of the headphone”, so that’s the tube amps struck off as well. Certain combinations may not have the most optimal sound or synergy, but again what I’m reviewing is not the combo but rather the transducer. If you’re looking for someone with impressions for specific combinations, you’re better off going to a different site.
Taking all of these into account, the A90 falls short on the ubiquity factor (given its recency and somewhat-high price of $500 in a sea of sub-$200 amplifiers), but its status as “the best measuring amplifier ever made” (up till Topping’s own L30, though the A90 still out-powers the L30 by a significant margin if you’re stickler for power) is a massive consideration. Again, not that I care about that at all, but at the very least it’ll keep some source-diehards off my back when I start doing headphone reviews.