Chris's NosDAC

This evening Chris1968 brought his nosdac over so that we could see if we could figure out what was wrong with it.

Connected up, and the first thing to do was bring out the Maroon 5 that had upset it before and see if it was still happening.

Answer was a very definite yes.

So, we ran through a few other discs to see if we could provoke it with anything, and failed. However, we knew it had been provoked by other discs.

After attempting a few other things with the behringer as spectrum analyser and some test tones, there was still nothing to go on.

Time for the oscilloscope.

With most test tones the output was fine, but then we hit on the problem that we'd heard at the bake-off:



The top trace is the analogue output of my Toshiba SD330e. The bottom trace is the nosDAC. Signal is 1kHz, 0dB FS. The bottom half of the sine-wave is clearly clipping, and this was resulting in the rather unusual effect heard at the bake-off and subsequently. Knowing now that it is an amplitude issue, a quick run of Massive Attack's Angel prompted misbehaviour in a low-frequency signal (which we hadn't heard before). This is the fault with the unit.

The other thing that you'll notice about the output of the nosdac is that the trace is not smooth like the DVD player output. This is inherent to the nosdac design. Using a 15kHz -14dB FS signal shows up the difference much more clearly:



Again, top trace is the DVD player, bottom trace is the nosDAC. This is not a fault condition, but simply what happens if you don't filter or oversample. This could well be characterised in listening as "harsh" or "grainy" or "coarse".

 

excellent work isaac
i do have a question tho
a guy over at hifichoice bought the cd i had a problem with (katie melua)
and did not hear distortion/harshness.

also, why is it that i don't hear it on all cd's?

cheers kane

 

Now I wonder where at that presence comes from

 

kane - It is hard to say... I don't have enough information about what you're hearing (ie I'd have to hear it myself), nor about the systems involved. Or ideally get it on the scope.

Different systems will behave different ways, as will different people's ears.

 

Which is interesting since AFAIK no one has ever complained of a (working) NOS DAC having any of those qualities...quite the opposite in fact

Here are some more pictures of a NOS DAC output (a 47 Labs Shigaraki):


47 Laboratory 4715, waveform of 1kHz sinewave at 0dBFS.


47 Laboratory 4715, waveform of 20kHz sinewave at 0dBFS.


47 Laboratory 4715, waveform of undithered 1kHz sinewave at -90.31dBFS, 16-bit data.

...if you think the last one looks bad, remember it's at -90dBFS which is an extremely small signal level. Stereophile always do these -90dBFS traces as if they actually told you anything about how a bit of kit sounds, which they don't. They're quite irrelevant but it shows the levels to which they have to go to find measureable differences between digital sources

Michael.

 

Note the similarity of the first stereophile plot to the trace I have of a 1kHz 0dB FS (other than the clipping fault).

 

isaac what effect does the clipping have on the sound?

fwiw my problem only happens on vocals and even then not on all my cd's

kane

 

Hi,

Any of the "direct output" DAC's (like 47 Labs) need careful tuning of the Load resistor, Supply Voltage (Value) and Reference Resistor (TDA1543) or Reference Volatage (TDA1545).

You first need to get it right for a "bogey Chip" and the literally adjust the reference for each specific chip with a Scope and 0dbfs test Signal, unless you design with less output voltage and added active stage. Both TDA1543 & 1545 have a significant range of tolerance in the Chip, something like +/-20% or so.

The staircase nature and "crappy" treble waveform, that is what is on the CD unless you use a filter that rings like a bell to smooth it out. It is choose your poison time, both are wrong.... ;-)

Ciao T

 

I think this is an individual problem TBH, the description is nothing like mine at all and its been used with a wide range of transports (ranging from a basic dvd up to a top-end meridian) in a wide range of set-ups and its never failed to impress. Everything from classical to dub is imprived with my nos DAC. The only critism Ive got is that the input socket for the DC is quite poor and needs some attention when Ive got the time.

 

In the light of 3dsonic's comments regarding the chip variation and reference, I think it most likely that kane's dac is suffering the same thing that chris's is, although perhaps not to the same magnitude.

 

If I remember rightly did you not have to wait for yours (and chris) coz he'd run out of parts?? If so I wonder if he got a bad batch. I got mine about a week or so after Michael and we both report nothing but improvement. I think its over too Derek.

 

Interesting analysis Isaac - always nice to be able to see the effect you are hearing.

Kane and Chris - when did you receive your DACs? FWIW I've had mine for near 4 weeks now and am very happy with what I'm hearing. My Rega CDP has been turned off and most of my CDs have now been transferred to the server. Derek has his new PS ready for the DAC and I'll be looking into this option over the weekend.

 

I've pointed this thread out to Derek so let's see what he says

Michael.

 

thanks again Isaac - good to see you diagnose it without even having to take the lid off!
also interesting to see the room eq device in action - not a thorough listen but there was a differnce for sure

so folks - there you have it, as i understand (what me with being an electronics genius in the making! )flux capacitors are ok but the dilithium crystal needs looking at

looks like derek has been made aware of the thread but he has the details on an e-mail from me as well, we'll see what comes back (hopefuly a repaired dac, i'll also be investigating his new PSU )

as for the other comments my unit is about 6 weeks old, delivery was delayed, dereks e-mail at the time says it was due to his waiting delivery of more black-gate caps. looking forward to having a fully operational unit for the next bake off.
t-bone - thanks again for the offer looks like Isaac has sussed the job now. have to ask - the chorley connection has me thinking you could be someone here under new name, seeking sanctuary from madness elsewhere?

 

Chris, yes its me

 

t-bone-that wasn't me,i bought my dac secondhand from a guy over at hifichoice.

i have had the dac since 25th of feb-don't know how long the previous owner
had it.

also i might be the third owner.....

kane

 

3dsonics, was that your kit recently reviewd in HFC?, if so well done, nice review, I like the look of the speakers, very nice indeed.

 

The power supplies are being "made to order" with a build time of 1-2 weeks.

I ordered mine a few days ago.

Harryo

 

Folks - Dereks reply to my e-mail

Hi Chris,

No problem! as I mentioned to you, I will fix the problem for you.

The reason I asked you to shot some photo on the PCB, as I can find out the resistor values from the photo. As I remember, in fine-tuning the sound, I have tuned a DAC to marginal settings, so that it can deliver higher output voltage and sounds more dynamic. Before I send the DAC out, l had tested it with my CD transport and sacrificed with the results.

I suspected your case should be this one, and the clipping problem is only happened to some CDs which was record at a higher sound level.

Anyway, sorry for the inconvenience caused! The problem can be easily fixed, pls kindly send it back to me, and I will fix it.

Thanks!
Cheers
Derek

 

Chris - If you want, we can replace the resistor ourselves if derek tells us which and what to change it to (or toward). Saves on shipping and time.