NAD C658 BluOS Streaming DAC with DIRAC and MQA

The NAD C658 is about anything you need, save a power amp and speakers. It’s a pre-amp, MQA DAC, streamer and even room correction. Digital techniques have changed the looks and functions of stereos over the years. Tuners are replaced by internet radio streaming, cd’s are replaced by file based audio and streaming services like Spotify, Tidal and Qobuz, Bluetooth is used to send music from your smartphone to the stereo or music from you stereo to you headphones and TV sound is connected to the stereo over SPDIF or HDMI. O, and we still like to play the odd vinyl too.

00:50 - The C658 does all this and more for it is also an MQA decoder and renderer and offers DIRAC room correction. In true NAD tradition the front of the C658 looks sober but it hides a lot of functionality. Being a source it has to be connected to the analog inputs of an amp, that in turn will drive a set of speakers. Since it also offers input switching and volume control, a power amp might be a simpler choice. Then the connection to your router over either network cable or wifi has to be made to facilitate internet radio, streaming services and software updates.

01:34 - To play music stored on your computer or NAS, these have to be connected to the same network. Alternatively you could also connect a USB drive containing music directly to the C658 or do both. The C658 can be controlled using the infrared remote but far more versatile and needed for the BluOS functions is the free app on smartphone or tablet. Both iOS and Android versions are available. And although you can play all the music in the world this way, you can still connect a cd-player digitally or analog, a tuner - analog only of course, other analog or digital sources and even a turntable, provided it has a moving magnet cartridge.

02:18 - If on digital sources MQA encoded music is played, it will be reproduced fully decoded and rendered. And the DIRAC room correction system will work with all sources. The analog inputs need to be converted to digital to have DIRAC work with them. It’s up to the user to have it converted or left in the analog domain. The bottom and rear of the cabinet are of pressed metal, the front is made of plastic and the top and sides are of rather thick metal.

02:52 - I suppose to fight vibrations which can be disastrous for digital gear since the clock crystals are sensitive to it. The C658 measures 435 by 405 by 100 mm and weighs 10.1 kg. On the front left the standby button with integrated bi-color status LED. The navigator lets you move up, down, left and right through the menus with in its center the OK or select button. Then the 6.3 mm headphone jack, the display with integrated infrared sensor, two buttons to select the input and the volume control.

03:32 - On the rear right the power switch, the IEC mains connector with integrated fuse, 12 volt triggers in and out, infrared links in and out, two subwoofer outputs - sending identical signals by the way - the left and right RCA outputs and the left and right XLR outputs. Then two sets of analog inputs on RCA, the phono input on RCA with above it the ground screw, two SPDIF inputs, two TOSLink inputs, the network connector, a USB A connector for storage media, a mini USB and button for service purpose only, two expansion slots and two Wifi and Bluetooth antenna sockets. The matching antennas come with the unit. After opening the device on test we see a mains filter, the switch mode power supply and the main voltage regulation - there are also local voltage regulators on the circuit boards. This circuit board contains the streamer and the DSP that does the digital filtering for DIRAC and the reconstruction filtering. On top of it the Wifi and Bluetooth radios, connected to the antenna sockets of HF leads.

04:50 - The large circuit board below it contains all audio electronics, including the Burr Brown PCM5121 DAC chips and loads of N5532 op-amps. On the left the cage for the expansion boards. The system does all popular PCM music files up to 24 bit 192 kHz. DSD files can be played back using the PC app that will convert DSD to PCM 24 bit 192 kHz on the fly. It is surprising how simple the C658 is in use, considering the enormous versatility. Using the infrared remote you can easily select inputs, set volume, enter the menu’s and so on. But it really gets convenient when you use a smartphone or - even better - a tablet. Selecting inputs or the streaming services, selecting music on your computer or NAS, making playlists, setting volume, it all can be done in the Bluesound app. You can name inputs to match the sources connected. I changed names to match the following external sources: CD-player, FM tuner, PlayStation, Settopbox and TV and selected pictograms accordingly.

06:09 - Switch over to another BluOS player and the list of inputs changes to the inputs of that device. The same goes for if you add the optional 4K HDMI input module. The output of the module is connected to the TV - also providing the audio return channel - while three HDMI sources, like a blue-ray player and game console, are connected to the inputs. Since the C658 does not do surround, you do need to set the ARC feed on the TV to stereo. You will see four new inputs in the setup menu in the app, three sources and the audio return channel, which you can name accordingly and give appropriate logos.

06:54 - Listening to streaming services you might be subscribed to can’t go wrong either. Look at this list of services. And, yes, there are even some more. Not all of these will be available in every country but if they are available, they are supported. And, as mentioned, you can also hook up a turntable with MD cartridge. The C658 supports full decoding and rendering of MQA files and my experience is that the non-MQA files benefit from the MQA technology due to a very good reconstruction filter. Whether you like MQA or not, it’s your choice.

07:29 - I find MQA clearly but subtly improving transients. Even a bigger influence to the sound quality under most conditions is DIRAC. It lets you measure the acoustics of your listening room and correct it. It might even correct flaws in your speaker system. I have reported on DIRAC in the review of the NAD M10 and on the C658 it works the same so I will insert the DIRAC part of the M10 review here. Just think C658 in stead of M10.

08:06 - Dirac is a patented program to correct for acoustic problems in your room. It lets you measure the room response in a number of places and then calculates a correction in both amplitude and time. Here is how it works You first have to download the NAD version of Dirac and install it on your computer, smartphone or tablet. There are versions for Windows, MacOS, Android and iOS - currently renamed to iPad OS. Then plug in the supplied microphone into the USB socket on the rear of the M10, using an also supplied 3.5mm jack to USB adaptor.

08:49 - When the program is started, it will detect the NAD device - or devices - on the network. We select the M10 and select the M10 connected microphone. Normally you need to select the calibration file, which I did when testing but while recording this video, it was already erased again. Then you set the loudness of the measurement signal so that it is in the lower region of the green section. Next you have to decide whether you want a very tight listening area or a somewhat wider area. I chose sofa with a wide imaging.

09:29 - This gives mild, average processing and suites my room and listening preferences. Choosing the chair gives a more correct room correction but only for that one spot. The next step is to do the first measurement for which the microphone has to be in the center of the listening position, as shown in the illustration. The microphone has to point upwards and if you can avoid it, do not place it on a larger solid object. I mounted the mike on a mike boom with duct tape - it has a thread that fits a camera tripod.

10:03 - After clicking Measure selected position, the measurement starts. After three sweeps the result is stored and you can pick the next position to measure, place the mike accordingly and start measuring again. This then should be repeated until all 17 positions are measured. The measured positions are ticked so you can see which ones remain to be measured. Then you proceed to Filter Design. The green line shown here is the proposed target line and as you can see it has a 5 dB slope between 25 Hz and 20 kHz.

11:02 - For although we would like to see a flat frequency response in our equipment, when measuring room acoustics this curve has been accepted as a good target. The correction, calculated by Dirac, will result in the the curve behind the target curve. And although it doesn’t look like an ideal curve, it is a lot better than without correction. Do realise that timing information is of great importance to our ears, more important than the frequency response. And Dirac also does time corrections. You can see the impulse response too, but I forgot to record that.

11:37 - For the next step you proceed to Filter Export. You see that I already made to filter curves, named 1 normal and 2 bass boost. I now overwrite 1 Normal but you could give it any name. If you like you could return to the Filter Design page and alter the target curve. Let say I want a lot more bass. I start at 500 Hz increasing the curve like this. I could then store that under 2 bass boost and still have three filter settings left. This is ideal for trying out several target curves or even do another set of measurements, for instance one optimised for your listening position only and one with microphone placement all over the room. It does take some time to do it all and you shouldn’t do it at 2 AM for the measurement signals are played at a loud level, but in most cases the outcome will improve the sound quality since room problems are dealt with to a large degree. Dirac Live that comes with the M10 is restricted to 500 Hz downwards. If you want to influence frequencies above 500 Hz, you need to buy a $ 99 upgrade.

12:52 - In many cases the standard version will be sufficient since acoustic problems like room modes are in the lows. Above that I expect mainly speaker problems to be corrected. That might be interesting too, if you like to experiment. But then you do need to buy the update. I was quite surprised by the sound quality. A box so full of features usually is more focussed on the features than on sound quality. Not in this case.

13:25 - Here the refinement, the resolution and the stereo image are clearly above the quality of my setup 2, say lower end of my setup 1. See the link below for a description of both of my reference setups. Of course the combination of the SOtM sMS-200 Ultra Neo and the Mytek Brooklyn Bridge with Syntaxx power supply is of another level, let alone the Auralic Aries G2 in stead of the SOtM. But only a few years ago I would have been very pleased with the C658 in my set-up 1 for it does nothing wrong. It’s not harsh, it’s rather good on transients and has a rather wide, deep and well focussed stereo image for its class.

14:01 - Add to that the DIRAC room correction that does far more than MQA to reduce time smearing - this time acoustical time smearing - and you get a sound quality that will be hard to beat by other streaming DAC for this money. I am quite impressed by the C658. At € 1,700 it offers not only an extremely versatile BluOS streaming DAC and pre-amp but also high quality room correction. Most of all the sound quality is above what I expected. You can use your existing amplifier and if it has separate inputs for the power amp part, use these. Or get yourself a new power amp or active speakers.

14:48 - And get yourself an iPad, for controlling the C658 is made for control per app. BluOS is one of the best streaming systems around, offering a variety of playback systems. For me it’s only trumped by Roon, which is of a completely different price category. And, by the way, if you do want to use Roon, the C658 can also function as Roon Endpoint. I try to find products to review that will be attractive for you to buy and I normally succeed quite well.

15:23 - Very rarely I come across a product that appears to be less attractive than I thought. I then don’t review it. There is no point in spending production time and money just to tell you what you shouldn’t buy. Just as rarely I come across products that are better than I expected, like this time. They are a joy to work on - bad products are a pain - and they are fun to inform you about. Let’s see what next week will bring. There will be a new video, as always at Fridays at 5 PM central European time.

15:58 - If you don’t want to miss that, subscribe to this channel or follow me on the social media so you’ll be informed when new videos are out. If you liked this video, give it a thumbs up. Many thanks to those viewers that support this channel financially, it keeps me independent and thus trustworthy. If that makes you feel like supporting my work too, the links are in the comments below this video on Youtube. I am Hans Beekhuyzen, thank you for watching and see you in the next show or on theHBproject.com. And whatever you do, as always, enjoy the music. .