This is a review and detailed measurements of the PS Audio PerfectWave DirectStream DAC. It is on kind loan from a member. The unit that I have has the network "bridge" streaming option and costs US $6,899. Without that option it costs US $5,999.The DS DAC is quite heft with a textured matt finish:Other than a power button, you have the touchscreen to use for all other functions. I found the display graphics to be lackluster for a product at this price. It is hard to touch buttons even though I don't have large fingers (no jokes about the size of my mouth please). It actually looks better in the picture above because I used photoshop to increase its contrast. Otherwise it has a blue background which seems to suffer from lack of backlight uniformity. On the plus side, the normal display shows the details of the format which I appreciate. And changes in volume using the remote results in a large numerical values of the current level. So it works but misses an opportunity to impress aesthetically.Back panel shows all the usual suspects plus dual I^2S ports:For my testing, I mostly focused on USB input and XLR outs unless stated otherwise.I call the PerfectWave DirectStream a boutique DAC meaning it implements the DAC functionality on its own rather than using an off-the-shelf DAC. In this case, it takes PCM and converts it to high-rate, 1-bit "DSD" and then uses a transformer for low pass filter and balanced output. The former is typical approach but the latter, was a head scratcher for me. We use transformers in audio when we have to, not because we choose to. More on this later.Ted Smith is the designer behind this DAC (a software guy who used to work at Microsoft the same time I was, turned hardware designer) and has that great professorial look. Stories he and rest of the gang at PS Audio tell of the superiority of DSD format and simplicity of implementing it in hardware. Here though, an FPGA is used with all of its ancillary logic which throws out any arguments for simplicity. Certainly the cost shoots way high.A rather clever scheme is used to extract the sample rate of the incoming stream and ignore its clock. For USB this doesn't matter anyway but for other ports, the claim is made that incoming jitter doesn't matter and hence all the inputs sound the same. I investigated this and report below.Someone asked me about version and firmware numbers. I could not make sense of PS Audio support page as to what software package went with what. Guessing, I downloaded one and it seemed to be lower version number than the one I tested. So I did not mess with it.Edit: here is the version info:I am told 3.0.6 is the latest version.: right after this review was completed, the new "Windom" update was made available. It made no difference in performance. See here: https://www.audiosciencereview.com/...perfectwave-directstream-dac.9100/post-239292 And oh, as you see the cling plastic is still on top of the unit. The unit was just purchased and the owner expressed dissatisfaction with its sound relative to current DAC. He offered to unit to me to test to see if we can find any clues regarding that.For testing, I downloaded PS Audio driver package which had an ASIO interface which I used for my testing. Before that, I used the stock windows driver and it worked the same.PS Audio provides the following specs:We see that we are right on the money with output voltage. Unfortunately that is much lower than nominal 4 volt that should come out of the XLR output. For such a beefy product, it is strange to see such a shortfall. Same issue exists on RCA outputs as they note with 1.4 volt output instead of 2 volts (I did not verify this).Our measured THD+N of 0.016% is much better than 0.03% they spec. But before celebrating, we need to consider that this awful performance. When converted to SINAD, we get only 75.5 dB which firmly places the PerfectWave DirectStream DAC at the bottom of the rankings of all DACs tested so far:From my rough count, there are 171 DACs in the above graph and DirectStream DAC ranks #10 from the bottom.High-end dacs always advertise ability to present detail so let's see how it does on dynamic range:Gosh, we can't even clear 16 bits of audio hear let alone have lower noise floor than other DACs.Poor low level linearity (caused by noise) confirms the same assessment:Here is the spectrum of said noise:Despite my use of balanced XLR output, we have mains leakage. And on top of that, power supply related spurious tones. And some odd tones at 80 Hz and such. Perhaps coming from the microprocessor controlling the front panel?Filter is analog and created out of the combination of a capacitor and inductor on the primary side of the output transformer:I am fine with this as it nicely cuts right off at 22.05 kHz but sure goes against the trends of "high-end audio dac" these days with gentle slopes and such. Same is confirmed in square wave output:You get your "pre-ringing" so audiophiles hating that should run away. Not!Here is the jitter and noise spectrum at 48 kHz sampling:We have the low frequency spikes that we saw in the noise floor analysis. Outside of that, the spectrum is very clean and just compromises of noise. That noise floor is high due to poor dynamic range of the unit. I worried that it was hiding something. I increased FFT depth and averaging but nothing came out of that.Next, I hooked up Toslink from my APx555 analyzer. It too showed identical output to above. I then turned on jitter on Toslink and no matter what I did with sine wave jitter, nothing would disturb the DAC's output. Or its ability to lock on it. So this claim regarding input independence and ignoring input jitter is correct. Nicely done.High noise floor and general distortion of course hurts in intermodulation test versus level:On top of that, we have output saturation starting at around -8 dB.Multitone test starts to reveal new issues of interest:This is something we have not seen before. Intermodulation distortion between the tones is much higher at low frequencies than high. That pushes the distortion floor to just 60 dB. That gives the stunningly low distortion-free dynamic range of just 10 bits! Yes, this is bad. Really bad. Let's keep going with THD+N versus frequency:Let's ignore for now that the entire curve is way, way up there (i.e. is bad). We have the same rise in low frequency distortions we saw in multitone test. What explains that? Use of output transformer! Ted Smith said he built his prototype using Jensen transformers. Jensen is the king of high-quality audio transformers. But high-quality does not mean high performance in vocabulary of audio DACs.Bill Whitlock is the foremost expert in transformers (and grounding) at Jensen so let's go to his bible on transformers here: https://jensen-transformers.com/wp-content/uploads/2014/09/Audio-Transformers-Chapter.pdf And focus on this distortion versus frequency:Distortion starts to rise from 200 to 300 Hz as we go lower in frequencies -- precisely what we see in our measurements.I investigated the high frequency distortions and they are clearly harmonic distortions, not some ultrasonic junk:For this test (and with THD+N vs Frequency) sampling rate is set to 192 kHz so we don't have to deal with aliasing components. As you see in red, with a 10 kHz tone, the distortion products are much taller than at 1 kHz (in blue). They line up almost perfectly on multiples of 10 kHz.In that sense then, our dashboard test at 1 kHz was very beneficial to DirectStream DAC. It provides its best performance there. Above and below, SINAD drops to 60 would would firmly put it in the category of worst DACs we have ever tested.Frequency response was flat:For subjective testing, I chose to use the recently reviewed and superb Monoprice Monolith THX 887 Balance Headphone Amplifier . This Monolity has vanishingly low distortion and hence is completely transparent to DACs being tested. For the alternative DAC, I used my everyday Topping DX3 Pro 's line out RCA to Monolith. I then used the XLR input to connected the DirectStream DAC. Once there, I played a 1 kHz tone and used my Audio Precision analyzer to match levels using PS Audio's volume control. PS Audio claims perfection there ("bit perfect") so I figured they can't complain about that.The final matching was 0.3 dB difference between the two.For headphone I used DROP + MRSPEAKERS ETHER CX with its XLR connection to THX 887 amp.I started the testing with my audiophile, audio-show, test tracks. You know, the very well recorded track with lucious detail and "black backgrounds." I immediately noticed lack of detail in PerfectWave DS DAC. It was as if someone just put a barrier between you and the source. Mind you, it was subtle but it was there. I repeated this a few times and while it was not always there with all music, I could spot it on some tracks.Next I played some of my bass heaving tracks i use for headphone testing. Here, it was easy to notice that bass impact was softented. But also, highs were exaggerated due to higher distortion. Despite loss of high frequency hearing, I found that accentuation unpleasant. WIth tracks that had lisping issues with female vocals for example, the DS DAC made that a lot worse.Many of you would have guessed that PerfectWave DirectStream DAC would not do well on the bench. That is of course true. The real issue in my opinion though is not the internal design of the DAC functionality. After all, there are other companies that use the same approach and achieve superb measured results. The problem here is simple: the output transformer. Transformers are just not linear to the levels we expect to have in a DAC (as opposed to say, in a tube amp).The sonic effects are there in my semi-formal tests. Perhaps the older audiophiles including the designer Ted Smith, have lost so much high frequency hearing that the harmonic distortion this DAC adds makes up for some of that and they think they are hearing more. If that is the case, just buy a Jensen transformer and put it on the output of your DAC and you would get the same effect!The fidelity loss here is apparent in both objective and subjective testing. There is nothing to hang your hat on hence the decapitated Pink Panther which leaves no room for such attire.Needless to say, IThese companies need to hire trained listeners and perform a simple level matched test before spending so much money on engineering and producing subpar products. Our hobby deserves better. Much better.------------As always, questions, comments, recommendations, etc. are welcome.Our weather is getting colder but I think I am going to jump in the bay and see if that can uplift my spirits after this test. To enable the uplifting, some more money in my bank account would surely help. So please considerusing: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/