DIYHiFi.org

If you're talking acoustical measurements where ultra-low distortion and noise are not that important, the Tascam US-122MkII and Tascam US-144MkII are popular now. They have built-in mic preamps with phantom power, so all you need is a mic and some cables to round things out. I use an M-Audio MobilePre for these measurements, but the drivers are buggy, and I'll probably replace it with a Tascam. The 122 has only analog outputs, but the 144 adds an S/PDIF output. I used an E-MU 0404 USB for a while, but it crapped out on me. It had an async USB interface, but used about 45 percent CPU on my old Dell laptop and was never very reliable.

If you're looking for ultra-low distortion or very low noise measurements of electronics and such, I don't know. Probably would cost serious bucks.

Thanks. I'll check them out.

I think Thorsten has mentioned that he has some solutions for making distortion and noise measurements that don't require an AP or SRS level mortgage. Probably others have, too.

Hi,



Well, I do happen to have an AP... ;-)

But it is bit cumbersome at times, so it get's less airtime than you would think.

My alternative is a pre Creative EMU 1616m purchased 2nd hard of E-Bay with a custom breakout box. It somewhat parallels the AP2 in needing an old-fashioned PCI slot for it's interface card, so I'm running two ancient Dell "pizzabox" machines with P4 CPU's in the Lab to keep both of these running. ;-) I think the whole setup including the 2nd hand computer with screen and all cost under 500 Pound at the time (quite a few years ago).

You do have to either add calibration to the software, which is not possible for RMAA. I use RMAA use as the easiest way to do a quick suite of measurements to leave running while I make a coffee. Or you need to modify the analogue output stages for flat frequency response or simply eyeball the difference (I use the old MK1 eyeball myself).

Other than that you get 120dB SNR and nearly 100KHz bandwidth as well as SPDIF in/out. For most things in Audio one would desire to measure I think this suffices well enough.

Ciao T

_________________
Theory is when you know everything but nothing works.
Practice is when everything works but you don't know why.
Guruhood is when you know everything and everything works accordingly.

Folks,

Earlier we were talking about the competence or lack thereof in design.

As I am working on a products with an SPDIF output and with some unusual trickery, I decided to get a cheap E-Bay dac of the "turnkey kind" with each of the major solutions (except those we use inside our own gear) and to try these. Following the various holiday delays in arribal and all I got back to the Lab yesterday.

The first one up was a DAC with the ES9023 and the CS8416. The kit is described as "Sabre COAXIAL and OPTICAL inputs DAC. ES9023 + CS8416 incl PSU". It's PCB without Case and sold for around 90 USD delivered, plus duties tax...

What an utter POC. Clearly the designer is totally incompetent.

I'll first have to fix the major design faults (including the fact that the DAC clips with full scale signals) before I can get back to measuring the impact of my trickery on the DAC's jitter.

Of course over at the Pub they love this DAC and crucify anyone who sells anything more expensive, clearly not one of these guys has ever measured one! And that with all that pro objectivist agenda going on over there. I may be sick...

Maybe I'll publish the neccesary mods to make this PRC POC work, then again, I can't see why I should...

Ciao T

_________________
Theory is when you know everything but nothing works.
Practice is when everything works but you don't know why.
Guruhood is when you know everything and everything works accordingly.

Hi,



Okay, fixing was easier than I thought. They simply left the mandatory resistor to set the output voltage off.

There is a space on the PCB for it, but it's empty.

Fit the required resistor and voila, output voltage is 2V and the distortion is way down.

Using the AP2 as source the jitter is pretty bad. In my normal jitter measurement setup the Window is -95dBFs to -140dBFs, well the jitter was "off scale".

Using my upcoming product Jitter is much better, but it seems the CS8416 has enough noise on the PLL clock to degrade the SNR from 112dB to 106dB, even if feeding the DAC a near zero jitter SPDIF signal.

So I was thinking...

Hey, ain't ESS making a big deal of their DAC's Jitter rejection, in Async Mode? Are they just making it up?

So I check, well there is a 24.576MHz clock on board, but it does not seem to have any real job. It is attached to the CS8416, which doesn't really need it to work, and not to the DAC which could probably use the clock and it's funky ASRC to clean up the jitter.

A quick look and unsolder a tiny SMD Resistor in the DAC's MCK line and feed it via 1/2" of wire the 24.576MHz clock. Voila, now the ES9023 meets it's specification and is indeed quite impervious to jitter and it nearly meets the datasheet spec.

Are we surprised that the resultant DAC sound a lot better? It still ain't a match for my async USB ES9023 DAC in measured and subjective performance, but I think with these two small changes it is worth at least the 90 Dollar plus duty one pays...

These modern "designers", maybe they should start the design by reading the datasheet?

Ciao T

_________________
Theory is when you know everything but nothing works.
Practice is when everything works but you don't know why.
Guruhood is when you know everything and everything works accordingly.

Gee...

All the "real engineers" out there are convinced that serious audio guys only care about expensive boutique fashion parts and ignore the basic stuff.

My belief system is now shattered!

On further review...

After spending a few minutes this morning wandering through some of the more popular audio fan forums, I've reached a somewhat different conclusion.

Audio, like most things these days it seems, is really a consumer transaction hobby. In other words, "Why kind of deal did you get?" That's the biggest part of the hobby. That is what drives people. Not how it sounds or how much enjoyment you derive from listening to the assemblage of gear playing music you like. It's all about the way you "beat the system" and came out ahead of the great unwashed.

I think that's why you get various rationalizations why a $2000 amplifier can not possibly be better than a well designed $200 amplifier. (It might not be, but you'd think that with a better budget, you have a better chance of getting better results.) You get guys on DIY forums - largely not this one - who suffer angst over using $.30 capacitors instead of $.05 seeming equivalents. And so on.

So, a $90 DAC is just fine. Especially if you can get a discount on that. Even if you can show how adding a resistor in one place, while removing one from another (no net cost change) makes a significant change in measured performance - never mind that nasty old "how does it sound to you?" idea - you won't get any traction in that discussion.

No, let me 'splain......................

Those are intentional errors. They copied my practice of supply PCBs, with mistakes, that will not render the unit inoperative, but hinder performance. They do this so PRC copy cats will spend money making PCBs that are wrong.

Where they screwed up is............................

I wait, a few months, and tell everyone I have discovered a lay-out error, or two. I tell them they must respond, and I will tell them how to correct the mistakes. What happens is none of the PRC buyers respond, and we know why!!!!!!!!!!!

See, they can't even copy that part of my routine, without screwing things up.

So, there is an easy explanation.


Now, as to why no one who bought this could hear those problems, and did not point any of that out......................well, just goes to show what is wrong with hobbyists. They complain the "golden ears" only pee themselves over something that comes in a fancy box, yet sounds worse than a '4558. Yet, they will only pee themselves over something that is cheap, and has all the right cheap parts, that are supposed to measure well. But doesn't, because of implementation.

And some folks wonder where the inspiration for my signature comes from. Now you know!!!

_________________
"Because, I hate you guys. I hate you guys so very, very much.

Yours,
General Cartman Lee"

Jocko,



Actually, the "company" selling this is from china. As their name is not embedded in the PCB, but attached via a sticker on the PCB it seems they buy the stuff in, from PRC Kopy Kat's...

And as said, the space for the resistor is there, but they send assembled PCB's and the resistor is not there.

Result, serious clipping at 0dBFS...

The clock thing is by design. Some applications use a clock on the 8416 so it can tell you what clock rate is used. BUT, this DAC does not indicate clock rate!

So just mindless copying...

Ciao T

PS, this 2013 - nowadays you cannot have layout errors unless your schematic is wrong or you still do things like last millenium. Modern CAD tools do not LET YOU make layout errors....

_________________
Theory is when you know everything but nothing works.
Practice is when everything works but you don't know why.
Guruhood is when you know everything and everything works accordingly.

Well, I don't use "modern CAD tools". Unless you consider something that runs on DOS as modern.

My mistakes are usually intentional. If all you do is copy it, you have no idea the error even exists.

Of course, the practice of direct lifting a layout is not confined to PRC. A certain mod, over at The Pub got burned, by a buddy of mine. I won't tell you his technique. But, the practice he uses is not unlike what is done in the semi industry. They do little things, on the die, to catch copiers. I knew a guy who writes the code, for the scribing machines, over at TI. He says they occasionally do catch copiers, that way.

Having said all of that...............since I do not use "modern" techniques, I have been known to make honest mistakes, on PCBs. Of course, I could do the dishonest thing, and say it was intentional, for the above reasons. I'll let everyone decide for themselves.

_________________
"Because, I hate you guys. I hate you guys so very, very much.

Yours,
General Cartman Lee"

Y'know, you just can't win with this stuff.

While working at Company A back in the 90's, another guy and I came up with a simple solution to a problem. We applied for and received a patent - part of the job.

Fast forward to the, ahh, teen's. Now working at Company B, I looked at a product made by another group in the new company. Lo and behold - I see a copy of the little widget we came up with 10 plus years ago. Actually, there was a half dozen. Per unit.

So, I take a stroll through the on-line patent office filings and find at least three other copies of the original patent! The new patent holders just reworded the original. A little. With no additional anything. Entirely ignored the first patent.

Some friggin system.

They probably heard the clipping as "bloom" or just listen to "chicks with guitars".
Some people seem to like the sound of "some" jitter ...

I was going to link this to the other place but now I'm not going to.

Just so everyone knows what we're talking about:

Really? Sure could have fooled me.

Brian,



Not un-routed or mis-routed connections etc. Of course, you can still arrange things wrong...

But you really should not be able to get "stupid mistakes"...

Ciao T

_________________
Theory is when you know everything but nothing works.
Practice is when everything works but you don't know why.
Guruhood is when you know everything and everything works accordingly.

Always thoroughly review the Gerber files!