If you are using digital media, you’ll use a DAC. Depending on how you store your music, this will have a bearing on how you interface this digital data out. Every format has its pros and cons, so let’s have a look here.

For digital media, to my knowledge, you have 3 choices today. SPDIF, USB and Firewire.

SPDIF is the de facto standard digital output. It’s available on CD/DVD players as “Digital Output”. Many media players like the Squeezebox has this too, as well as many PC soundcards. SPDIF even has an optical version, Toslink. A sonic upgrade can be experienced instantly if you ditch the lousy RCA socket and opt for BNC. Why oh why does everyone still use RCA then? For convenience rather than sonic reasons!

A major problem with SPDIF is that the SPDIF receiver in your DAC got to retrieve the clock signal from the incoming SPDIF. And this is a major problem. The older but still very popular obsolete CS8414 has a typical 200ps while the modern DIR9001 manages much better at 50ps. Irrespective of what comes after this, the fact that the recovered clock isn’t optimum will have a huge bearing on sonics later.

USB DAC is really popular these days. The most popular implementation is Texas Instrument’s PCM27xx chips. These are pretty good “as is” but still a lot can be improved on. Again, there is the question of how is the clock recovered?

There are better implementations of USB which do not use TI’s generic PCM27xx chips but I haven’t tried these yet.

Firewire is said to be the best but far from readily available. And too expensive at this point.

Which interface to use also depends on what is your source. If you are using CDs, SPDIF is most logical solution. If you store your music on hard disk, then USB or I2S via a SD card player is viable. The above briefly describes the pros and cons while the convenience of which format is really up to you. If you don’t mind a little trouble, go for the best sound!

My current favourite, however, isn’t any of the above. It’s via I2S! Provided you have a very good I2S source!

I started dabbling with I2S when I tapped out this signal from my old Marantz CD63 way back in 2003. The CDM12 transport isn’t that great and though the sound was already a huge improvement over SPDIF, there is still something lacking there. But hey, if you could ditch SPDIF, try this!

Later I played around with USB-I2S as well as USB-I2S-EIAJ in USB Monica. As good as all these sound, it’s still not a pure I2S solution. The interface is still via USB. You could say the weak link is how the PCM27xx chips derive the I2S out. I hope to have the resources to tackle a better way of doing USB one day…

Anyway, my current favourite digital player (The Digital Turntable) has, in my mind, the most direct route to I2S. A DSP chip reads WAV file data from a non-moving media (the SD card), then outputs I2S signal which is fed to a CS8405 chip to generate SPDIF. Both the DSP chip and CS8405 is clocked by a low jitter clock.

Since a good quality I2S is available, feeding directly to an I2S DAC chip (or through Black Crow for an EIAJ DAC chip) is all we need! Replacing the clock with a lower jitter implementation (like Kwak clock below or the plug-n-play Tent XO module) and I assure you your jaw will drop listening to music through this combo!

Okay, okay, enough about all this. So these are what we have here.

Above pics show the 3 implementation, coupled to mojo. They’ll couple nicely to mojo2 as well. mojo/mojo2 PCB has 6 PCB holes which couple nicely to the I2S-EIAJ, USB-EIAJ and SPDIF-EIAJ modules.

4 are EIAJ signals while the right 2 are your power connections to power the modules.

So instead of forcing you to buy a USB Monica or a SPDIF Monica, you now have choices and since this is in module form, you could play around slowly.

Hey, if there’s sufficient interest, how about an EIAJ selector to select from multiple inputs?

The post Let’s pay some attention to our Digital Interface appeared first on diyparadise.

Hello DIYers.

You may have came across my USB Convertor. That was meant as a temporary solution while I crack my head over a proper USB DAC. The USB Convertor outputs SPDIF (your vanilla digital output) which you could then feed your DAC. Now if you are looking for a dual usage DAC (meaning for both computer and CD/DVD player type), then this will be a good, albeit compromised, option.

However, if sonic quality is your utmost concern, then there is simply no business converting from USB to SPDIF then to DAC format again.

Therein lies a problem. Almost all the USB receiver chips in the market I know only outputs I2S and not the EIAJ format required by Monica’s TDA1545 chip. Boy, this isn’t fun.

I built a few circuits to convert I2S to EIAJ but wasn’t successful. More studies later… then I realized I need to climb up the highest mountain in this region, consult the guru there and sprinkle some pixie dust.

Nah, the guru wasn’t much help. In the end, after lots of diligent nights (and wee early morning hours) of pouring over datasheets and building prototypes, I finally got it done.

USB – I2S – EIAJ – Monica!!!

Let me be anal here and declare this as the first USB DAC using an EIAJ based DAC chip!

[You could make me fall flat on my face with big dollop of humble pie by pointing out to me which USB DAC in the market that uses an EIAJ based DAC chip.]

So what’s the big deal you may ask? Well, as always in audio, less is indeed more. Going through one less data conversion, the gain in sonic quality is…. va va voom! Like the real Monica!

If you are new to computer audio, I suggest you take a read of my computer audio pages.

So this PCB consists of a USB receiver chip, an I2S-to-EIAJ convertor and asynchronous reclocking scheme, TDA1545A circuitry and of course, Rudolf Broertjes’ SS I/V Gain Stage. All in one smoking PCB!

Simple enough eh? It looks simple from the top but underneath, there’s quite a lot of surface mounted components soldered on.

You could power her at 12VDC though 18VDC is said to sound better especially for the SS I/V stage. If you intend to go this high, I’d suggest heatsinks for the LM317 chip.

Better still, note that L3 is a diode instead of an inductor or ferrite bead. If you remove L3, you could power TDA1545 circuitry through J2 and power the SS I/V stage circuitry separately through J4. How about that? ; )

Wiring is very simple. Just hook up power supply (you provide of course), and output to RCA sockets of your choice. Input is simply USB from your PC. I’ll suggest a USB cable of type A jacks and off you’ll go!

No software to install, and no PC casing to dismantle.

Why heck, install both USB Monica and Charlize in one little case and you’ll have a smoking PC audio system!

Due to complexity of build, no kit is available yet. Assembled/tested USB Monica could be purchased from our e-Store. http://store.diyparadise.com

For once, let’s end it short and sweet.

And spend more time with Monica!

Update on 27 Nov 2007!!!

Plug and Play USB Monica in hard wood chassis like Monica 3 available now!

Enhanced PCB featuring some changes ala Monica 3. Note the Super E Black Gates… Yummy!

The post USBMonica appeared first on diyparadise.

diyparadise selling cables? Yeah, yeah, this is a first for us. Seriously, never saw much value in cables/wires. Sure there are differences here and there, but nothing night and day, nothing earth-shattering, nothing really knocked me off my chair.

And I have felt this way too with digital cables.

Until one day, Gabriel showed me this biggest thickest coaxial cable I have ever seen. Dang! Looks like a power cord to me. But can it sing?

Well, after putting it in… Can’t take it out! So far, the best 75 Ohm digital cable I have tried!

No kidding!

Hands down, the BEST 75 ohm digital coaxial cable I have ever tried.

Comes in nice unassuming white.

Biggest girth ever seen in a coaxial cable, so much so that very few RCA plugs could fit.

Makes up for it though with darkest background, sweetest highs and unheard of dynamics.

Breaking away from tradition here and not going to name it after some hot hoochie mama. It’s white and thick like an anaconda… so Whitesnake it is!

PS: If you are a rock music ignoramus, Whitesnake is a late 70s, early 80s hard rock band, with typical big hair, loud music and most memorable music videos featuring scantily clad girls. Boy, we sure could have more of this these days!

PSS: More on Whitesnake – the band, whitesnake.com.

PSSS: Buy Whitesnake! – the cable of course, through the e-store.

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My USB Convertor

Here’s a very simple USB convertor. Plug this to your USB port, and all your music signal will go through it. No programming needed, no soundcard necessary. Just plug and play.

The star here is PCM2706. It’s a pretty cool chip that could do three functions. It could be a USB headphone amp, it could output SPDIF data and also I2S data.

I played with it, and unfortunately the internal DAC’s output is already over-sampled and kind of… sucks. Okay, okay, that’s too strong a word but if you are bitten by the Non-Oversampling magic, conventional DAC (meaning those oversampled types) really turn you off. What’s the magic word again? As Monica said it herself, “makes me puke”! Ha ha!

So instead, i’ll offer her as USB Convertor instead. Takes in USB and outputs either SPDIF or I2S. Headphone amp circuitry components will not be offered.

Also, will be offering as a kit here. Don’t worry, I’ll make it simple for you. I’ll solder in the 2 chips instead, so you just have to solder in those little surface mounted resistors/capacitors.

Afraid of SMD? Don’t worry! I’ll show you in a video how to solder SMD. Sorry, the clips aren’t very clear as I’m really an amateur here. I’m really better in front of the camera. Also, I kept my mouth shut so as not to distract you from viewing how to solder SMD. You know I’m quite a chatterbox…

smd-tutorial

Components

R8, R9 22ohm. SMD resistor “220”

R7, R14 1.6kohm. SMD resistor “162”

R15 1Mohm. SMD resistor “105”

R10 360ohm. SMD resistor “361”

R11 100ohm. SMD resistor “1000”

C5, C6, C8, C9, C10 1uF. SMD capacitor

C13, C14 10pF. SMD capacitor

C7, C12 47uF “Low ESR” electroltic capacitor

C11 100nF metallized polypropylene

L1 Ferrite bead.

Y1 12MHz crystal

And of course, the USB jack. Note the placement in photos above.

This is all you need! Solder SMD components FIRST, then only the Thru-Hole components.

To configure for SPDIF output, short R12. To configure for I2Ss output, short R16.

I built one in 15 minutes, then brought to a friend’s place to test. We copied a track from a disc to lossless WAV format. Then played through his notebook and compared to his DVD player. The same system was used except the source where we are comparing DVD player to notebook+USBconvertor combo. Boy, the latter is definitely more organic!

For a limited time only (feel free to question my sanity), 10 such USB convertor kits will be offered at USD25 only.

Order from http://store.diyparadise.com.

Your assembled USB Convertor should look like this. Note orientation ofo USB jack. Note that I shorted R12 for SPDIF output. If you desire I2S output, short R16.

If you desire a slim profile, you could lay down the 47uF caps like this.

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Computer Audio is Soooooo Much Fun!

Boy, I have been having so much fun with computer audio, or do you prefer the term “PC Audio”? Playing music through a PC is addictive. We’ll look at the hardware side first before going to the software end.

I admit I have been late to this “PC audio party” but as they say “better late than never”! And I’m glad I joined the party! The sonics has so much potential compared to conventional CD playback and most folks believe this is mainly due to much reduced jitter when playing through PC. You see, with conventional CD playback, we almost can’t escape from using digital output (SPDIF) format. The Achilles’ heel of SPDIF has to be the way the critical Bit Clock is recovered from it.

This is the work of the digital receiver (like CS8412, CS8414 etc) and we are limited by how well it recovers this clock signal. CS8412 for example has jitter specifications of Bit Clock of 200ps. Not very impressive! Monica’s asynchronous reclocking (as shown the light by Kunosoki san more than 20 years ago) ameliorates this but it’s no way a solution either.

With computer audio, let’s say this together. “To hell with SPDIF!” Ha ha!

Back to hardware, the Squeezebox is a little computer gadget that appeals to geeks like you and me. It streams (wired or wirelessly) audio files stored on your PC to your hifi system. Of course, if you do it wirelessly, you could have your noisy PC in one room and your hifi set in another. Wonderful!

To be honest with you, I know nuts about playing music through a computer but ever since I got a Squeezebox, have to start a crash course on it!

Fancy having a dig at DIYing your own Squeezebox? Well Ole Schüsseler here shows you how to do it with his Linux based Audio Appliance.

So what if you don’t want a player like the Squeezebox and prefer to play from your PC? Sure, no problem! Back then you’ll need at least, a good quality soundcard, but nowadays, there are USB DACs to consider. Yup, takes USB data and converts to analog signals.

The Wonderful World of USB DACs
You see, operating systems (at least for Windows and Macs) are smart enough to know that when they detect a USB DAC, all audio signal will be routed through there. Of course, you could control not to do this as well, but unless your soundcard has better sonics, it’s good to consider USB DACs.

USB DACs like Texas Instrument’s PCM2706 (used in My USB Convertor) not only functions as a USB DAC but also as a headphone amp, USB-SPDIF convertor as well as USB-I2S convertor. The last function is the most interesting as once converted to I2S, we could hook up many DAC chips directly. DAC chips like TDA1543, TDA1541… etc. Like this:

If you want to try this yourself with my USB Convertor,

Pinout of I2S on my USB Convertor pin 1 is GND pin 2 is Word Select leave pin 3 blank pin 4 i Bit Clock pin 5 is Data

I guess you know which pins to connect to which pins right? Told you it’s very easy! Power your DAC chip separately though. Don’t be cheap and use the USB’s 5V supply. If you do so, don’t complain if it doesn’t sound good ok?

If you are ooo-laa-laa over sonics of Monica, then this isn’t so simple. Monica’s TDA1545 chip uses EIAJ format instead of I2S. The main difference between both signal formats is the where upon the DATA signal is sent. I2S sends the DATA signal at the beginning of the Word Select signal but EIAJ sends at the end.

No, please don’t ask me why can’t those folks sit down and agree on one format. I have no idea. But look at SPDIF. The very few instances where all folks concerned agreed on a format but it turned out to be a lousy format. Oh well…

Anyway, I tested and built a pure USB Monica, taking in USB signal to I2S then converted to EIAJ then fed to TDA1545. Give us a few more weeks and you can jive with her soon! [USB Monica is ready!]

Squeezing more juice out of the Squeezebox
Back to the Squeezebox. I’m sure many will be wondering how does the Squeezebox compare to audiophile CD players? Well, stock player is nothing to shout about however never ever under-estimate the power of DIY! I’ll share with you 2 mods I tried here.

The very first upgrade every Squeezebox owner should do is to replace the stock power supply adaptor with a beefier unit. One capable of at least 1A (2A is better). Some folks prefer linear supplies while some prefer switching. My preference is switching power supplies but don’t let me influence you. Go try yourself. Just make sure it outputs 5V REGULATED and you’ll be fine. Oh yeah, pay attention to polarity too since we are dealing with DC voltages here.

For the adventurous diyers, the first mod is considered too easy, no fun at all. The second mod, you need to pull out your Torx T10 screwdriver and dismantle the Squeezebox unit.

This is a relatively easy tweak. Easy to understand and easy to implement if you are good with soldering surface mount components. If your soldering skills isn’t up to par, then forget it. Find someone to do this for you. Remember as with all mods, you can kiss your warranty goodbye so if you are not up to it, don’t try to be cheap here. It ain’t worth it brudder.

What we want to do here is modify the SPDIF circuitry. If you trace the digital output RCA socket, you’ll find it ends at pin 6 of chip U15. This is just a 7404 invertor chip. What we have here is that the invertor output goes through a coupling cap then 2 resistors to ground. The resistors form a voltage divider to scale down the output of the invertor from TTL logic level to SPDIF level. If you find all this Greek, don’t worry.

By right, there isn’t a lot of problems with this circuit but due to the very noisy environment of the Squeezebox (what more with a wireless card nearby), we don’t want all the noise to be carried all the way through the digital output (via SPDIF format) to your DAC and the rest of your audio chain. And the easiest way to accomplish this is to use a digital pulse transformer.

The digital pulse transformer accomplishes 4 things.
First it breaks the ground. The SPDIF signal ground is no longer the Squeezebox unit’s ground. This is possible due to usage of transformers.
Secondly, I believe the trans has better driving capability then just a the invertor and voltage divider circuitry.
Third, with a trans, we could benefit from its common mode rejection capability. Meaning, it rejects noise common to both signal and ground. Like in a noisy environment inside the Squeezebox.
Lastly, we could better match the impedance output impedance with the usage of suitable trans.

So first remove L8 and L9. Then desolder the R67 107ohm resistor. One end of R67 goes to ground while the other end is tied to R66. There’s a mistake in above diagram though. Primary (red dot, pin 1-4) has ratio of 1 while secondary (pin 5-8) has ratio of 2. So you should wire pins 5-8 facing the 7404 invertor chip and the other end (pin 1-4) facing output RCA socket. To anchor the trans, I soldered one leg (pin 8) to junction between 107 and 245ohm resistor. Thus pin 5 goes to ground. Pin 1 (red wire) goes to SPDIF output. Pin 4 – SPDIF ground. (If you are fussy, replace 245ohm resistor with 300ohm for even more accurate 75ohm output impedance.)

Now you know why I’m enjoying computer audio?

Moving on to the Software side

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