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?

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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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Non-Oversampling DAC project

What is the easiest, cheapest way of trying out non-oversampling?

If you can trace the I2S signal in your CD player, tap it, fit in a TDA1541 (and attendent signal gain circuitry), then you have it!

You save a chassis, an interconnect cable and have the shortest signal path. What more can you ask for? Furthermore, it saves you lots of unnecessary circuitry in between. Imagine, I2S gets converted to SPDIF, then converted back to I2S… Why go through all this trouble? Why not just tap the I2S straight off? You save an expensive CS8412, you save a lot of unneccessary headache.

With the Marantz CD63 service manual, I think I have found the I2S signal.

If I’m not mistaken, signals WCLK, SCLK and DATA constitute the I2S format.

Wiring to a TDA1541 is easy and it’s only these 3 signals. However, due to the sin(x)/x filter, many builders of the non-oversamping DAC hear a marked loss of high frequency energy. Reason being, the DAC starts to roll off at 10kHz and at 20kHz, it’s already down 3dB. Hardly great stuffs huh? It’s even worse on my Hammer Dynamics as the treble is already laidback, putting down another 3dB isn’t pretty…

To get back the 3dB lost at 20kHz, a simple LC resonant filter will do. Thorsten Loesch has pointed the way in using the TDA1543. With YH’s help, I have adapted one for the 1541.

The circuit on the left is Thorsten’s for TDA1543. The right is my adaptation for TDA1541. The simulation has 2 traces. The top trace is the frequency response. Note that it gradually rises and reaches a peak of about 3dB at ~20kHz. Phase shift is about 10 degrees at 20kHz.

This is even better! (Thanks YH!) A notch filter is added to filter out the 44.1kHz CD sampling frequency. The wild swing on the phase plot is expected, courtesy of the notch filter. The 2 inductors in the circuit can be hand wound, then adjusted (add/reduce windings/ferrite) until “right”.

Do realize that the above is all just circuit simulation. When you build this circuit with real world components, all hell breaks loose. Stray inductance and stray capacitance will make their prescence felt. Imperfect components (is there any perfect component?) will make matters worse. Oh well, live with it…

Anyhow, you need to add a gain stage to amplify this signal. The output is only ~20mV at the node between the 100uF capacitor and 100kohm resistor, so a gain of 100x is needed to reach full output of 2V. Fill in your choice of gain stage, op amp or tubes. You can, of course, add another stage of RC filtering after your gain stage to reduce any output after 20kHz. The choice is yours.

That’s all to it! Again, there’s nothing new here. Stole some ideas here and there, and got the above. Thanks to buddy YH for his ideas.

Simulation was performed using Linear Technology’s excellent SwitcherCAD.

Are you ready to build one? I just did the above with a TDA1543. A non-oversampling DAC for < RM20.

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