This is a review and detailed measurements of the Okto Research DAC8 8-channel DAC and headphone amplifier. I was sent a prototype unit for measurements. From my understanding, the company has been producing the internal DAC module for a while for the DIY market. But now are building complete systems. So what makes this an early production unit is not the DAC module but the integrated version with input and other features. The version I have has the Okto DAC8 module plus an off-the-shelf UBS Input. My understanding is that the final units in production in April will also have their own USB input implementation plus 4xAES/EBU. It will cost 989 EUR in this configuration (about $1,120 as of this writing). This version will be known as DAC8 Pro. I will just be calling it DAC8 from here on.
There will be two other versions, one with DSP and the other in stereo configuration where four channels are folded into one to get better performance. See:
https://www.oktoresearch.com/index.htm
Due to large number of outputs, the unit comes in "rack mount" 1U size (at least I think it complies with that spec). But through out any impression of dull, industrial look out of the window. The DAC8 employs two beautiful and highly legible OLED displays flanking its rotary control, giving it an exquisite look:
From what I have read, they have done the mechanical design (and production?) themselves too. The metallic part of the front panel looks a bit cold to me so if there is an option in black would be nice. Any misgivings on that part goes away the moment you interact with the unit. Display changes are instantaneous, giving you a very solid feel that you are making changes. I love all the key information nicely visible including the sample rate, input, volume, etc. Love it!
I had no trouble navigating the unit with the rotary control. The DAC8 though is able to learn the remote control of your choice or you can get it with an Apple Remote.
One minor thing is the top: it has screws on each side but none in the middle. This allows the top or flex a bit. I suggest putting a single additional screw in the back middle to remedy this.
The back panel on my unit is not fully populated per intro:
I am too lazy to usually show you all the menus but I thought I make an exception here.
Pushing the rotary control changes the left side to:
View attachment 23762
A second click changes the right side to this for volume. The menu will scroll down to let you lower the levels in all 8 channels:
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I turned on the 18 dB boost and it produced severe clipping at anything above -19 dB. I am not sure of its use other than for digital input that is at very low level. I hope
@Okto Research can explain what they think this is useful for.
System menu is such:
View attachment 23764
Display shows the usual stuff:
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And finally the ESS Sabre DAC settings which I left alone:
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Okto Research advertises superlative specs for this product -- numbers which we have not seen in our reviews. Is it the usual marketing games or real? Let's find out.
DAC Measurements
As usual, we start with our dashboard view:
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Wow! What a way to impress. Distortion+noise of just 0.000127%? And with such excellent channel matching? This places the SINAD at 118 which is a new record:
View attachment 23785
Yes, a new SINAD king has been crowned!
In honesty though, there is an unfair advantage here. Can you spot it? The output voltage is 3.3 volt, not the usual 4 volt we like to see. Okto says they can program this to any level one wants. Usually distortion sets in when levels are increased so I expect some performance will be lost if this were boosted to 4 volts. Fortunately in use you are not going to need more voltage since you have a volume control in DAC8 so will be driving an amp below these levels anyway.
As if to deliver a one-two punch, the DAC8 delivers exemplary stable and noise-free linearity results sailing to -120 dB (20 bits of resolution):
View attachment 23769
Dynamic range pushes the limits of my analyzer so likely the actual DNR is better than reported:
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With threshold of hearing being -116 dB, this is one silent DAC!
Jitter shows tiniest imperfection made more visible by very low noise floor:
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I had to remove audiosciencereview.com sticker at the bottom of the graph since the noise floor slid under it!
DAC8 is using ESS DAC chip so for sure we will see our famous "ESS THD IMD," yes?
View attachment 23772
There is a tiniest hint of that -- maybe -- around -32 dB or so. Or then again it could just be the variations we see throughout the graph. Whatever, it bests my reference DX3 Pro DAC I use for this test.
Distortion and noise relative to frequency shows flat response which indicates plenty of bandwidth/gain:
View attachment 23773
With some 30 dB lower distortion at 20 kHz, you do get something for paying more than $99 for your DAC (read: Khadas Tone Board).
For multi-tone test, I switched to a new method as the one I was using was too finicky and would generate garbage results if the delay through the DAC was not what it was expecting. So don't quite compare this to previous measurements:
View attachment 23774
The accumulation of distortion products stops around -150 dB. Our tones are around -20 dB meaning there is almost 130 dB of distance between the peak and distortion products!
Folks, we have to stop here. I can't find any holes in this design. Surely we find a fertile in the headphone amp though. It has to be a throw-away feature made to fill the spec sheet....
Headphone Amplifier Measurements
Let's jump right into our power versus distortion+noise:
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From distortion and noise point of view, the DAC8 easy bests my DX3 Pro reference even in its low-gain mode. Alas, power is highly limited due to maximum of 1.6 volt output. So we don't even make it to 10 milliwatts. Those of you who have the DX3 Pro and operate it in low gain mode would have almost the same amount of power here.
Switching to 33 Ohm load gives us more power as expected but still not as much as we like:
View attachment 23776
Again, power output is near what DX3 Pro produces in low gain mode.
No, the 18 dB boost doesn't help here. Again, it just makes the clipping point -18 dB on the volume control.
Output impedance is excellent at 1 ohm which is close to limit of how low I can measure with my fixture:
View attachment 23777
Headphone Listening Tests
I plugged in my HD-650 into DAC8 and was greeted by what you see in the measurements: there is no hint of distortion to max 0 dB volume level. Due to limited power, there is no sensation of "subwoofer in your ear" as I like to see.
What was there though is likely sufficient for many though. I was able to listen at levels between -9 to 0 dB.
The situation was a bit better with Hifiman HE-400i. A very pleasant experience but no chance of rattling off the screws on the drivers.
If you are interested in this product for headphone listening, I would start with what is there and see if it is enough. If not, then a pairing with Massdrop THX AAA 789 would be in order.
Conclusions
Let me confess that I had a few down moments prior to testing the Okto DAC8. There is such a large backlog of gear to review and it seems I am jumping from one measurement to another. Nothing cured that better though than putting the Okto Research's DAC8 on the bench. The DAC8 Pro is superbly engineered and delivers on objective measurements like there is no tomorrow. Heck, I got tired of putting exclamation marks in my review above.
Could we have predicted this? To some extent yes: despite being a small company, they used the major competitor to my Audio Precision analyzer from Rohde and Schwarz. Time and time again we have seen that companies that measure their designs, product superb products. You have to verify what you build folks.
And this is not just some 2-channel DAC. You have 8 channels of output that should satisfy anyone who needs that many channels now or in the future. It is remarkable that Okto achieved such excellent results without combining four or 8 channels together as other companies do.
Then we have highly responsive, well design and clear displays. And excellent connectivity in the final version with more inputs to let you tailor this with your favorite DSP upstream.
The only miss is lack of infinite amount of power in its headphone stage for anyone wanting to use it that way. But what is there is high performance and distortion and noise-free.
As you call summize,
the Okto Research DAC8 is an incredibly well designed and featured product. It is my absolute pleasure to recommend the DAC8.
I am also so happy to find a device designed and manufactured in Europe (Prague). I always feel bad giving high marks to US built devices that wind up being very expensive to import into EU.
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