This is a review and detailed measurements of the Topping D90 Balanced USB DAC with Bluetooth. It was kindly sent to me by the company. The D90 costs US $699 with free shipping from Amazon. The D90 is one a few DACs using the latest DAC chip from AKM (AK4499).Given some recent comments that manufactures may be sending us "golden samples," Topping has offered that I also purchase a retail DAC to compare to this one at their expense. Actually they have offered that I re-buy everything they have ever sent me at retail at their expense! Personally, I have no concern about Topping's ethics in this manner so I don't want to wast time and expense doing so. If you feel otherwise, comment in the thread and I will decide what to do based on that.The D90 comes in a premium packaging that despite its rather small size, is very heavy:I am guessing that it is milled from solid chunk of aluminum, much like very high-end audio products. While this doesn't do anything for sound, it does make the unit sit there solidly and not be tugged by cables.I controlled the D90 with one of my existing Topping remote controls (one comes with it as well). I had not noticed this before so may be a new feature but you can independently control whether the output shows up on RCA, XLR or both. Speaking of that, here is the back panel:It is all the features you expect for a premium DAC in this era including the increasingly standard Bluetooth input.Power supply is of course included inside the unit which I appreciated. Less clutter on the desk.For my testing, I focused on XLR outputs only. It sharply reduces the chances of ground loop which can occur more often due to connection to a PC and long chain that creates.As usual, we start with our 1 kHz tone dashboard:Not that it matters audibly but clock accuracy is excellent showing a precise 1 kHz frequency. Output is 4 volts which is what we like to see form XLR output.The star of the show of course is astonishingly small distortion. It showcases the performances of the AK4499 DAC chip which until now, would lose ever so slightly to offerings from ESS on distortion front. With SINAD of 120.5, the D90 barely misses taking the top spot in our SINAD graph:With best case dynamic range of hearing being 116 dB, you are assured that the D90 is provably transparent. What you hear, is what your source has in it. Not distortion and noise from the DAC.Using 32-tone test track to resemble "music," intermodulation distortion shows incredibly low unwanted distortions:Someone had asked how my Audio Precision rates in this test. Here it is:Note however that when I test analog products (e.g. amplifiers and headphone amps), I don't use the built-in DAC in Audio Precision. The companion analog generator actually has less distortion than above.Anyway, the D90 loses a hair to AP in lower frequencies but bests it in higher frequencies. Either way, the D90 is instrument grade digital to analog convert and can be used to test analog audio gear.Testing intermodulation again but this time against level we get:We see the improvement in both noise (sloping down part of the graph) and distortion (right side where the graph starts to climb up).Linearity (precision of level) is nailed as well:Dynamic range shows the noise level:Had this been a couple of dBs better, it would have improved the SINAD to take the first place. As it is though, it is exceptional. You can play at 120 dB SPL (live concert levels) and yet have no audible noise from the DAC!I ran jitter with USB as usual but also added S/PDIF since there has been some concern about its performance:There are some spikes, especially with S/PDIF so it not as perfect as the rest of the performance from measurement point of view. Audibly though, it is more than perfect with spikes way below threshold of hearing. Note that these are with full amplitude 12 kHz tone. You don't have such thing in music. Jitter is proportional to level of the signal so if you lower the 12 kHz tone, they would go down in level proportionally. So no matter which way we look at it, this is not an audible concern. But a slight visual discomfort.THD+N versus frequency shows good performance but not as good as I expected:This test uses 90 kHz bandwidth to capture harmonics of 20 kHz (the dashboard uses 22.4 kHz bandwidth). So the question is, are we seeing distortion products or other ultrasonic junk? For that, let's fun a spectrum analysis at 500 Hz where there is a hump above:Harmonic products are below 130 dB so that is definitely not a problem. Instead we see a pretty tall spike near the sample rate of the source. That is caused by aliasing due to reconstruction filter not having enough attenuation. Speaking of that, here are the responses for the filter:I was disappointed to not see a very sharp filter. I wonder if there is a firmware bug that is causing two of the settings to be the same? Or AKM doesn't provide it. Back to our previous issue, we see that the two sharpest filters only attenuate 95 dB or so. This means that aliasing components will exist below that level and that is what we saw in the THD+N vs frequency. Fortunately we don't hear 44 kHz and higher and levels are too small to cause issues for speakers/amplifiers. So not an audible issue.D90 performance did not change over the 10 minute test so I got bored and stopped it:The Topping D90 produces lowest noise and distortion than 220 DACs tested so far. It shows that AKM is ready for business to compete with ESS on top of the performance charts. It has excellent build quality and comes from a manufacturer that believes in verification of design with measurement. Its measured performance is nearly flawless. To get rid of last few niggles, would cost you a few hundred dollars more. You decide.I live for such discoveries where a company cares about giving us the maximum performance they possibly can. And at a cost point that is thousands of dollars if not tens of thousands of dollars than high-end DACs.------------As always, questions, comments, recommendations, etc. are welcome.The panthers want to take yoga classes. I keep telling them they don't have the body for it but they won't listen. I looked up the prices for private yoga lessons and they are high! So please