NAD C658 measurements and teardown Q

[kukynas 789]

Hi guys,

 

are you interested in measurements and tear down of this unit? I would do it anyway it's just matter of documenting it all and providing my findings, just let me know...

 

Dan 

[davewantsmoore 6,501]

100%, please 

[Monkeyboi 702]

Yes, I think that would make an interesting topic.

 

Cheers,

Alan R.

[kukynas 789]

first of all I'd like to just remind people about measurements and findings from ASR web where measurements and discussion started and based on which I made my own so I take Amirm's figures as reference point.

I came across same issues as he did in terms of inability to measure the unit under standard conditions so I had to overcome them but about that bit later 

 

before we start here are original measurements and findings from Amirm, what is more interesting is that the same findings were captured independently on 2 devices, node 2i and C658, what is even more interesting is that both devices even if in different price category exhibit similar performance and problems so I would assume (both owned by NAD) they share many similarities in terms of design of internals

node 2i is bit cleaner but with higher noise floor (most probably masking otherwise visible spikes like in C658) and C658 bit noisier but with lower noise floor and bit lower harmonics but more distorted  

 

https://www.audiosciencereview.com/forum/index.php?threads/review-and-measurements-of-bluesound-node-2i-streamer.6631/

https://www.audiosciencereview.com/forum/index.php?threads/nad-c658-streaming-dac-review.12090/

 

 

 

 

acquisition HW and SW

- RME ADI 2 PRO FS - instrument grade ADC/DAC

- Siglent SDS2102X Plus - precision DSO with software package

- Siglent SDM3065X  - precision 6.5 digits benchtop multimeter

- Arta and RMA analyser software 

before I show you the measurements something about setup and numbers, ADI 2 was connected to my PC via USB and controlled via ASIO drivers, C658 was connected to ADI2 via coax cable and output of the DAC part connected via XLR cables to input of the ADI 2, ARTA and RMA levels were set based on multimeter to ~4V, unfortunately I wasn't able to reliably calibrate ARTA's signal generators level so the numbers (RMS/THD etc) are bit off nevertheless the spectrum and pattern should be showing correct levels

I can't use external signal generator with ARTA exclusive mode so 1khz frequency fluctuate a bit but shouldn't be an issue once the signal is settled and averaged 

I can't measure SNR/DNR with ARTA so unfortunately we have to believe NAD and their figures, fortunately they usually underestimate their figures so we could believe them, I also can't measure SINAD so we have to believe Amirm's figures

I can't adjust range of div. in Arta so first 1khz of frequency takes half of the screen

RMA was used just to demonstrate how would you normally measure such device (in this case unable to do properly due to problems with locking signal and distortion somewhere in the unit) and read the measured figures automatically generated by RMA analyser, they look terrible 🤦‍♂️ 

 

RMA analyser:

 

 

 

ARTA 1khz sine as is normally set, look at the pattern also shown in Amirm's first measurements 

 

 

adjusted setting to overcome the problem shown above, no averaging...

 

 

final THD+N after averaging for both channels (red and green) if you look at the pattern and compare it to Amirm's measurements they are close (in his picture numbers are bit squashed)

 

 

had to follow same setting as before so first lock the signal and than change it and let it run otherwise it wouldn't work, multitone again both channels

 

 

2 tone

 

 

 

jitter vs. ADI 2 (red c658) , ignore the even harmonics (generated by the signal in ARTA) again very close to Amirm's measurements

 

 

I wanted to see FFT from the scope unfortunately I found out that the termination at the DAC end isn't quite sufficient so will have to redo once the new cable arrive, for now just quick and dirty screenshot, nothing what's stands out with limits to 350khz

  

 

 

  

that's about it, any questions shoot....

 

next we'll have a look under the lid but before here's some white paper from NAD of what to expect https://nadelectronics.com/wp-content/uploads/2018/10/NAD-C-658-White-Paperwhite.pdf

 

some quotes from the white paper

Quote

advanced ESS9028PRO 32 bit Hyperstream™ codec as the foundation of the DAC section. 

The codec is followed by a filter stage based around an instrument grade OPAmp with a 15MHz bandwidth offering an extremely high slew rate (13V/uS) and super low noise and distortion

 

we should be excited right? 

 

I know what's there already but let's wait for tomorrow 😂😉

 

 

[davewantsmoore 6,501]

"super low noise and distortion"

 

 

 

The marketing department can pretty much say whatever they like, eh.... 🤣

That being said.... it seems passable.

[davewantsmoore 6,501]

The RME is very good

[kukynas 789]

6 hours ago, davewantsmoore said:

The RME is very good

Oh yes, for that kind of money hard to beat, it’s discontinued for some reason so harder to find 

[kukynas 789]

 

10 hours ago, davewantsmoore said:

The marketing department can pretty much say whatever they like, eh.... 🤣

That being said.... it seems passable.

 

yeah, and same applies in this case...

 

generic picture of the inside

 

 

dinosaur regulators supplying +/- 12V to op.amps  🙄 oh well, could have been worse, thought can't expect miracles with their 360uV noise  

 

 

now becomes the funny part and where marketing starts to play their role, 9028PRO? nope...

 

 

well, it's not that bad, Q2M is just stereo version of PRO and share similar characteristic in stereo mode, next super low noise opamps...

 

 

again nope, these are decades old opamps currently used in mid-fi electronics, their performance these days is at best mediocre  https://www.eetimes.com/op-amps-in-small-signal-audio-design-part-2-distortion-in-bipolar-and-jfet-input-op-amps/

 

now most interesting part...

 

 

high freq. switching buck converters in hi-fi DAC/Preamp, really? NAD really? these are supplying 5V into converters and main board, 20mV ripple and noise 🤦‍♂️🤦‍♂️🤦‍♂️ (500x higher noise and ripple than standard low noise regulator such as LT1963, LT1764 etc), not even talking about potential nasty HF stuff injected back to the traces and spread to the surroundings

I understand they are efficient and do not produce excessive heat even if supplied directly from 14V SMPS but these are meant for TV's or general consumer electronics not high performance ultra low noise circuit

 

not sure where to go from here, 2 options spring to mind, pack it all to its original box and ship it back to shop I bought it from...or, strip it further, check all surrounding electronics and start following traces how it's all connected, start writing down all the components which need to be changed and look for alternatives (no direct replacement in case of buck converters) , overcome some problems with DIY effort and pray it'll work 🤔😂 not even taking into consideration lost warranty 

 

[davewantsmoore 6,501]

15 minutes ago, kukynas said:

now most interesting part...

Hmm...

 

Not so concerned by the opamps or regs.  Can be good enough if used right.

 

.... but, that's pretty grim.

[kukynas 789]

Unfortunately measurements shows they aren’t good enough, es9028 has THD+N of -120db, we are nearly 30db below that and these are not lab figures, look at other DACs using this DA chip from Octo, SMLS or others, but all of them taking care of their circuit with uln regs, uln opamps and overall design of their boards

[kukynas 789]

don't get me wrong, it's lovely pcs of equipment full of features I was hoping for but lack of sound quality doesn't really match its potential so I hoped I would be able to fix it in case of need...but I didn't expect I would find such a low cost completely misunderstanadble solution and nowhere near standards you would expect in this price category  

[kukynas 789]

never mind, I pulled the trigger, in worst case scenario I'll end up with expensive brick to look at 😂

 

first I need to check if the PSU is sensed from the board, second check if the buck converters are sensed from the board, if in both cases answer is no I might be lucky and be able to improve its output quality (unless there's something else sinking performance I didn't found yet) , noise floor in measurements indicates sufficient shielding and grounding of the board which is good starting point...

[davewantsmoore 6,501]

13 hours ago, kukynas said:

don't get me wrong, it's lovely pcs of equipment full of features I was hoping for but lack of sound quality doesn't really match its potential so I hoped I would be able to fix it in case of need...but I didn't expect I would find such a low cost completely misunderstanadble solution and nowhere near standards you would expect in this price category  

Agreed.

I think you can get much better than this performance even with caveman opamps and regs..... but if you go pollute it all with noise, then you sink back down to these "just passable" results.

 

Skeptical you can improve it lots with just "component replacement".... but it can be fun excercise.

 

13 hours ago, kukynas said:

noise floor in measurements indicates sufficient shielding and grounding of the board which is good starting point...

.... and like you say.   You never know..... but for me that would be even more surprising (and make no sense.... why nad?  why?)

[Mikahakk1 14]

Any idea how it compares with the pre section of the M33?

[kukynas 789]

20 hours ago, kukynas said:

first I need to check if the PSU is sensed from the board

confirmed, not sensed so I can hook up my lab PSU and see if there's any potential

 

6 hours ago, davewantsmoore said:

Skeptical you can improve it lots with just "component replacement".... but it can be fun excercise.

you can possibly eliminate a lot of PSU background noise by changing opamps with better PSRR/CMRR, look at the OPA1612 datasheet and compare it with NE5532, same for regs, that's what I wanted to do but now not sure when I just found this in the middle of the output board 🤦‍♂️

 

 

why would anyone like to decrease performance of the DAC circuit just to implement tone control??? why adding another IC to the output stage and complicate things if all of this can be done in FPGA in digital domain prior to DAC chip? I can't follow the traces due to different layers of the board so can't confirm how and by how much it affects the performance but looking at the control mechanism of the menu and adjustable levels these have direct link with the IC capability 

 

link to entire gallery of the output stage below

https://postimg.cc/gallery/NcvVJm3

 

6 hours ago, davewantsmoore said:

.... and like you say.   You never know..... but for me that would be even more surprising (and make no sense.... why nad?  why?)

as stated above it's possible that something else is sinking it's distortion performance but the noise floor stay pretty much untouched

 

going to test the PSU and see how it all acts, anyway wanted to check the current draw of the board to find out what to expect from those 3A regs...

[kukynas 789]

6 hours ago, Mikahakk1 said:

Any idea how it compares with the pre section of the M33?

https://www.stereophile.com/content/nad-masters-series-m33-streaming-integrated-amplifier-measurements not much said about preamp/DAC stage so we'll have to wait for Amirm's measurements once someone send him one unit

[davewantsmoore 6,501]

46 minutes ago, kukynas said:

why would anyone like to decrease performance of the DAC circuit just to implement tone control???

I suspect volume... not tone.

[Primare Knob 351]

On 10/10/2020 at 6:44 AM, kukynas said:

Hi guys,

 

are you interested in measurements and tear down of this unit? I would do it anyway it's just matter of documenting it all and providing my findings, just let me know...

 

Dan 

I am glad that you are willing to take the time to perform a second set of measurement. At least that can put some science into audioSCIENCEreview  as something can hardly be accepted (scientifically)  by a single set of measurements.  It is good to see these type of measurements as it can temper my emotions by facing reality ;)

[kukynas 789]

Just now, davewantsmoore said:

I suspect volume... not tone.

sure but that's secondary function, if you look at the IC you clearly see the treble/bass control functionality, if they wanted to control just volume they could pick much better performing NJW1195A with much better figures but lacking tone control or they could just use more precise digital volume control in the DAC chip, you can control treble/bass directly from the front panel buttons

[kukynas 789]

fast forward, below measurements with Siglent SPD1305X lab linear PSU, original SMPS has about 150mV ripple and noise, Siglent about 350uV so ~400x lower noise

 

much cleaner signal (especially below 1khz) and tighter 1khz signal amplitude

 

 

I just realised all my measurements were made with tone control switched on dooooooh  🤦‍♂️😂 not much difference but anyway, now with control switched off on lab PSU

 

 

multitone

 

 

2 tone

 

 

jitter

 

 

 

I got even lower noise linear PSU but not sure if it can further affect the output performance, I would expect noise and distortion from onboard ICs and regs would dominate and mask the PSU benefit

 

[kukynas 789]

it takes about 10w in normal operation, under full load up to 12w, so again no idea why using 3A switching buck converters instead of 500mA ultra low noise regs if entire preamp/DAC needs less than 1A 🤔🙄

 

[davewantsmoore 6,501]

13 hours ago, kukynas said:

sure but that's secondary function, if you look at the IC you clearly see the treble/bass control functionality, if they wanted to control just volume they could pick much better performing NJW1195A with much better figures but lacking tone control or they could just use more precise digital volume control in the DAC chip, you can control treble/bass directly from the front panel buttons

Hmmm... Perhaps you are right.

 

I will repeat..... why nad?  wwwwhhhhyyy?!    

[kukynas 789]

12 hours ago, davewantsmoore said:

Hmmm... Perhaps you are right.

so far just bunch of assumptions but in my POV pretty logical 🙂

 

The aim right now is to suppress the background noise by few notches, I find the harmonics content in this unit pretty pleasant so I don't care about THD much

 

sensing of the regs is sorted so plan is:

 

need to check b.converter traces for DAC chip, audio ICs and oscillator, so far assumption is that only one TPS54335A is supplying all of these, remaining of converters supplying processing board and input/preamp board  

 

replace old regs as follows:

 

LM317 -> TPS7A4701 

LM337 -> TPS7A3301 

TPS54335A -> TPS7A4701

 

Need to source new heatsinks with bigger surface area from Farnell but need to measure old first so that's plan for this week

[kukynas 789]

most of the regs and heatsinks arrived but still waiting for +/-12V version, also it seems I have to strip it further to find out how's the USB port supplied, if from the same reg or different as this is potential bottleneck when changing lower current reg otherwise I won't be able to use external HDD in case of need...

been able to trace the oscillator reg and below picture speak to its self 🤦‍♂️ , for .... sake why... oscillator needs as clean power as possible so reg as close to it as possible to minimise noise and interferences, not on the other side of the board 🙄

 

 

so far confirmed that the middle buck converter supplying DAC, preamp and part of the processing board, left supplying remaining part of processing board and right one supplying external add-on modules and front panel 

[kukynas 789]

so, all the parts ordered for final rebuild, this thing will get the most advanced PSU I've ever built, 2x XP power low r&n SMPS with linear voltage reference regulators, 110w, 14V/4A + 5V/8A, PSRR 132db, r&n ~5uV/1khz, ~85% efficiency on 120x100x35mm footprint 👍

left and middle buck converters will be kicked out and replaced with detachable pin header connected by 2.54mm coax cable directly to the 5V regs, like this I'm not limited by surrounding parts and space around it 

[kukynas 789]

don't wanna derail the owners thread but... 

 

I think NAD intentionally crippling this category to not jeopardize their master series where more profit's happening, I believe they are going to release master series version of this streamer as they are refreshing entire line of master series so it would be logical

we already know they can build highly capable DAC section as the specs and measurements of the M33 are out on several sites already so it's real shame as Dave pointed out they didn't utilized same potential of the DAC inside of the C658

 

don't get me wrong, this streamer sounds great but could have sounded better (in this respect cleaner compared to other DACs I own) especially as there is no alternative on the market 

they could have raised the price a bit if they felt they couldn't produced better sounding/measuring unit for said amount and people would still buy it, and maybe even more, I'm sure I would knowing I would get 10db extra noise floor and 30db extra distortion free and clean spectrum

 

at the end of the day no matter how I look at it there's no streamer/dac/preamp/dsp all in one box on the market in this or anywhere near price category so if anyone is looking for one which does all of this in one box I think C658 is no brainer 

 

[Satanica 1,541]

11 hours ago, kukynas said:

at the end of the day no matter how I look at it there's no streamer/dac/preamp/dsp all in one box on the market in this or anywhere near price category so if anyone is looking for one which does all of this in one box I think C658 is no brainer

 

miniDSP SHD?

 

https://www.audiosciencereview.com/forum/index.php?threads/review-and-measurements-of-minidsp-shd-dac-dsp-and-streamer.4286/

[kukynas 789]

I’m aware of SHD but if you ever worked with volumio you wouldn’t consider it as a streamer, in best case renderer or end point so no competion in my pov

different case if we would add node 2i into the package than you might get better combo but with 2 boxes

[gillmaverick 711]

Hi Daniel ,

That's a massive effort Mate. How does it sound after your upgrade and how much did it all cost If you don't mind me asking ?. I  am happy with the NAD but If can improve it further like what you have done that would be awesome. I have zero skills and knowledge though.

[kukynas 789]

4 hours ago, gillmaverick said:

Hi Daniel ,

That's a massive effort Mate. How does it sound after your upgrade and how much did it all cost If you don't mind me asking ?. I  am happy with the NAD but If can improve it further like what you have done that would be awesome. I have zero skills and knowledge though.

 

Hi, 

no upgrade as yet, still collecting parts, custom made regs from Korea supposed to arrive end of this or early next week so than I can start working on it but still no guarantee we'll see any improvement/benefit. I'm afraid that the volume control chip at the back of the output stage will be limiting factor for any improvements but hope is there and unless I try it we won't find out, I plan to do it in steps and measure it after each upgrade stage so we should see if and what and after all this we can calculate what's the cost of each (potential) improvement

Anyone can do it as parts are available on the web, it's mainly about soldering skills and appropriate gear (soldering and rework station) 

 

most of the parts arrived and how it will look like compared to original PSU

 

 

[sleach 198]

On 26/11/2020 at 1:38 AM, kukynas said:

at the end of the day no matter how I look at it there's no streamer/dac/preamp/dsp all in one box on the market in this or anywhere near price category so if anyone is looking for one which does all of this in one box I think C658 is no brainer 

 

That's how I think of it too: excited to see how your experiment goes and maybe try and replicate some of it if you have success. But....

 

13 hours ago, gillmaverick said:

If can improve it further like what you have done that would be awesome. I have zero skills and knowledge though.

That is me as well!

[kukynas 789]

regs arrived so started to work on PSU...

 

 

rework rig...

 

 

all mounted on the board, tested with main supply and all works as it should...tomorrow soldering traces, output connectors, cables and desoldering old buck converters

 

   

[kukynas 789]

it's aliveeeee!!! lol

 

[kukynas 789]

good news, it works...bad news it does nothing to the distortion, I spent good half day to think about it and I'm bit afraid that unless I completely eliminate those buck converters I won't be able to move on and fix that psu distortion...

 

below captured with no signal playing, basically 100hz psu distortion with its harmonics, at this point there is no reason to continue with digital part PSU tweak, so I will move onto step #2 which is power rails for analog section and will hope to get better result, if not than there is very little to do unless as said I would completely replace the power rails circuit with my own which is impossible as it's all sensed by m-processor for stand by and time out function

Another set of regs is on the way so hopefully in week or 2 I'll be able to continue...  

 

 

    

[martinhdk 2]

Just curious... (Please bare with my lack of technical insight)

I am considering the C 658 purely as a streamer with Room Correction. So: fixed volume/tone control and no "external" analog/digital input.

Would "bypassing" preamp and not using external inputs improve noise and distortion in any way?
Or are the issues present throughout the entire signal path?

 

(I see that you have done a test with Tone Control disabled - so I'm guessing it's a lost case)

Best regards
Martin

[kukynas 789]

Hi Martin,

unfortunately you can't bypass preamp section or I didn't found the way how to do it but you can set fixed volume output for each input channel including network streaming, I would stay above -2.5db on the dial as that's the point where the distortion starts to rise proportionally

 

distortion + noise (no signal) is well below -130db so shouldn't be a concern to anyone, it's slightly worse with signal playing as distortion gets into audible range, on the other hand still in low levels.

The main difference I can hear compare to my Adi RME 2 PRO is in fine details, i.e. cymbals are better articulated and more delicate but one have to be really focused to pick it up, if I never heard Adi I most probably won't notice it, NAD has on the other hand more pronounced dynamics most probably caused by higher harmonics which ads slight warmish character to it...  

 

Dan

 

[martinhdk 2]

1 hour ago, kukynas said:

Hi Martin,

unfortunately you can't bypass preamp section or I didn't found the way how to do it but you can set fixed volume output for each input channel including network streaming, I would stay above -2.5db on the dial as that's the point where the distortion starts to rise proportionally

 

distortion + noise (no signal) is well below -130db so shouldn't be a concern to anyone, it's slightly worse with signal playing as distortion gets into audible range, on the other hand still in low levels.

The main difference I can hear compare to my Adi RME 2 PRO is in fine details, i.e. cymbals are better articulated and more delicate but one have to be really focused to pick it up, if I never heard Adi I most probably won't notice it, NAD has on the other hand more pronounced dynamics most probably caused by higher harmonics which ads slight warmish character to it...  

 

Dan

 

Hi Dan,
Thank you for the elaboration.
Sounds like the C 658 will have more than sufficient resolution for my gear & ear. 🙂

I'm probably more likely to hear (and hopefully appreciate) the overall sonic signature than the lack of dynamic range.
 

Best regards
Martin

Edited December 7, 2020 by martinhdk

[Lars V 7]

@kukynas thanks for all the work. I am currently also looking at the NAD C658. However, this thread and others, plus the fact that I just sent back the NAD C298 cause it turned off by itself every time after 4 hours running, is making me cautious of NAD products. 

My current setup is Quad Z2 speakers, Musical Fidelity M5si, Bluesound Node 2i, Topping E30 DAC (temporary), REL T/7i, IFI Power Station, Silent Angel Bonn N8 and all good cables (power, ethernet, RCA). I have an XTZ Edge laying around and had it connected to the Schiit Saga+ before, which sounded nice. The M5si is a step up. I do like the all in one box idea of the C658 as I really like to combine DIRAC, Bluesound Node 2i (Tidal Hifi MQA) and the bass control and definition of the XTZ or C298 all together. Of course I can add MiniDSP Studio or SHD, but then I start to get a lot of "boxes". Such a shame that NAD just didn't get their quality level up one notch more.... I mean for the money. The fact that the C298 (which sound very neutral, detailed with great bass control) just turns off while the music is playing is just unacceptable, no matter the price. Guess I am hoping for too much (Dirac, MQA, BluOS, Purifi, etc) for the moment. I am sure in the next few months other brands will come with similar all in one boxes. One thing I forgot to mention (the reason I didn't get the NAD M10) is that I am looking for a HT IN option, cause I am connecting the power amp to the Pre amp of my HT receiver. The M10 doesn't have that option, the M5si has, and on the C298 you can switch between XLR and RCA in puts. Well, long story, and not yet a satisfying solution 😉

[Snoopy8 3,344]

8 hours ago, Lars V said:

@kukynas thanks for all the work. I am currently also looking at the NAD C658. However, this thread and others, plus the fact that I just sent back the NAD C298 cause it turned off by itself every time after 4 hours running, is making me cautious of NAD products. 

My current setup is Quad Z2 speakers, Musical Fidelity M5si, Bluesound Node 2i, Topping E30 DAC (temporary), REL T/7i, IFI Power Station, Silent Angel Bonn N8 and all good cables (power, ethernet, RCA). I have an XTZ Edge laying around and had it connected to the Schiit Saga+ before, which sounded nice. The M5si is a step up. I do like the all in one box idea of the C658 as I really like to combine DIRAC, Bluesound Node 2i (Tidal Hifi MQA) and the bass control and definition of the XTZ or C298 all together. Of course I can add MiniDSP Studio or SHD, but then I start to get a lot of "boxes". Such a shame that NAD just didn't get their quality level up one notch more.... I mean for the money. The fact that the C298 (which sound very neutral, detailed with great bass control) just turns off while the music is playing is just unacceptable, no matter the price. Guess I am hoping for too much (Dirac, MQA, BluOS, Purifi, etc) for the moment. I am sure in the next few months other brands will come with similar all in one boxes. One thing I forgot to mention (the reason I didn't get the NAD M10) is that I am looking for a HT IN option, cause I am connecting the power amp to the Pre amp of my HT receiver. The M10 doesn't have that option, the M5si has, and on the C298 you can switch between XLR and RCA in puts. Well, long story, and not yet a satisfying solution 😉

NAD is no different to other brands in reliability but sorry to hear about the C298.  Curious why you did not swap with another unit and try it.

 

You already know about the advantages of C658 and there is an owners thread here

The C658 does have HT bypass..  You can fix the volume of an input (page 13 of manual).

Edited December 18, 2020 by Snoopy8
Typo

[stereo coffee 362]

On 11/10/2020 at 8:42 AM, kukynas said:

first of all I'd like to just remind people about measurements and findings from ASR web where measurements and discussion started and based on which I made my own so I take Amirm's figures as reference point.

I came across same issues as he did in terms of inability to measure the unit under standard conditions so I had to overcome them but about that bit later 

 

before we start here are original measurements and findings from Amirm, what is more interesting is that the same findings were captured independently on 2 devices, node 2i and C658, what is even more interesting is that both devices even if in different price category exhibit similar performance and problems so I would assume (both owned by NAD) they share many similarities in terms of design of internals

node 2i is bit cleaner but with higher noise floor (most probably masking otherwise visible spikes like in C658) and C658 bit noisier but with lower noise floor and bit lower harmonics but more distorted  

 

https://www.audiosciencereview.com/forum/index.php?threads/review-and-measurements-of-bluesound-node-2i-streamer.6631/

https://www.audiosciencereview.com/forum/index.php?threads/nad-c658-streaming-dac-review.12090/

 

 

 

 

acquisition HW and SW

- RME ADI 2 PRO FS - instrument grade ADC/DAC

- Siglent SDS2102X Plus - precision DSO with software package

- Siglent SDM3065X  - precision 6.5 digits benchtop multimeter

- Arta and RMA analyser software 

before I show you the measurements something about setup and numbers, ADI 2 was connected to my PC via USB and controlled via ASIO drivers, C658 was connected to ADI2 via coax cable and output of the DAC part connected via XLR cables to input of the ADI 2, ARTA and RMA levels were set based on multimeter to ~4V, unfortunately I wasn't able to reliably calibrate ARTA's signal generators level so the numbers (RMS/THD etc) are bit off nevertheless the spectrum and pattern should be showing correct levels

I can't use external signal generator with ARTA exclusive mode so 1khz frequency fluctuate a bit but shouldn't be an issue once the signal is settled and averaged 

I can't measure SNR/DNR with ARTA so unfortunately we have to believe NAD and their figures, fortunately they usually underestimate their figures so we could believe them, I also can't measure SINAD so we have to believe Amirm's figures

I can't adjust range of div. in Arta so first 1khz of frequency takes half of the screen

RMA was used just to demonstrate how would you normally measure such device (in this case unable to do properly due to problems with locking signal and distortion somewhere in the unit) and read the measured figures automatically generated by RMA analyser, they look terrible 🤦‍♂️ 

 

RMA analyser:

 

 

 

ARTA 1khz sine as is normally set, look at the pattern also shown in Amirm's first measurements 

 

 

adjusted setting to overcome the problem shown above, no averaging...

 

 

final THD+N after averaging for both channels (red and green) if you look at the pattern and compare it to Amirm's measurements they are close (in his picture numbers are bit squashed)

 

 

had to follow same setting as before so first lock the signal and than change it and let it run otherwise it wouldn't work, multitone again both channels

 

 

2 tone

 

 

 

jitter vs. ADI 2 (red c658) , ignore the even harmonics (generated by the signal in ARTA) again very close to Amirm's measurements

 

 

I wanted to see FFT from the scope unfortunately I found out that the termination at the DAC end isn't quite sufficient so will have to redo once the new cable arrive, for now just quick and dirty screenshot, nothing what's stands out with limits to 350khz

  

 

 

  

that's about it, any questions shoot....

 

next we'll have a look under the lid but before here's some white paper from NAD of what to expect https://nadelectronics.com/wp-content/uploads/2018/10/NAD-C-658-White-Paperwhite.pdf

 

some quotes from the white paper

 

we should be excited right? 

 

I know what's there already but let's wait for tomorrow 😂😉

 

 

ASR has perpetual habit of using levels much higher than any commercial CD or stream contains. Why they do this is a topic all of its own.  

 

I would suggest to measure a commercial CD - lets say Swiss band Sonar's Tranceportation CD , you should get figures as shown. You should then use the much lower figure that appears as +/- 350mv RMS ( shown in light blue ) , that is then realistic in terms of actual level - and not  artificial as ASR insists on using,   to assess your NAD .