DIYHiFi.org

BTW this is the USB DAC I'm working on (AW-D3 kit from Audioworkshop.hk.com) sitting on top of 12V SLA battery powering a modded t-amp (off picture)

Good kit - so far I like the sound of the PCM2706 internal DAC but having problems getting I2S working - does anybody know how to test I2S output without an oscilliscope?

John

By proper PSU I mean that DAC chip is isolated from noisy PC using separate PSUs (3 transformers) and ADUM1400. There is 3 groundplanes:
One for PCM2706 and two for AD1852 (analog and digital). The AD1852 groundplanes are connected together using ferrite bead. PCM2706 and AD1852 groundplanes are not connected!

Connect USB +5V to voltage regulator enable pin for detecting is it connected to USB port or not.

Look my schematics http://www.diyhifi.org/forums/viewtopic.php?p=8465#8465

pupsik46,

Didn't know about REG102's with enable pin - good work. Did you use ADUM1400CRW - is digital isolation worth the effort?

bryman79,
Have you experimented with clean Host & Ground yet?

Not on a PCM2706, but I did find that ground must be hard connected on another TAS1020A unit in order for XP to recognize the device. From this I gather that D+/D- are referenced to USB ground... why is this? Does the PCM2706 require this as well?

Also, I've been wondering about replacing the 12MHz crystal with a powered oscillator... they have lower jitter, but would this really help with the whole SPACT circuitry?

Thanks,
Bryan

I did use ADUM2400CRW, also ADUM1400CRW should be suitable.

If you have read this thread from the start you know I have been working away on this USB interface to a TDA1543 DAC chip. Peter Daniel style. I am finally ready to show it.


It has been a labour of love and I wanted to make it available to others because it sounds so darn good, fun and easy to build.

You can find more details here.

Any questions?

Hi brentw,
If your post is meant to sell more kits you are on the wrong board.

Really, what's with the two power cords? I would think the extra ground loops would cause more harm than good. Dual-mono supplies when the channels are common in the USB chip? What exactly are you trying to separate?

jh

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Jim Hagerman

Hi Elso and others. No, I am not showing it to sell more kits.

I would think anyone interested in the original thread would be very interested in my results and the resources at my site.

Like I said a "Labour of Love". It doen't get any more diy that that. Or am I missing something?

Hi Jim,

Why two cords... There are two circuits that can be separated. The board snaps into 4 pieces. More options this way for diy. Or jumper them to use one cord if need be. It is not doing anything to harm the sound.

I know not everyone will like the idea of two cords.

It looks like there is only one USB connector and onde DAC chip. What part of the circuit can be separated?

jh

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Jim Hagerman

Hi Jim,

Sorry I should have described my DAC in more detail.

The schematic may be helpful.

The two circuits are 1) USB NOS TDA1534 DAC and 2) OPA627 unity gain buffer with volume control. Each circuit has its own power supply and power cord. The circuits have a score line between them so that the two circuits/boards can be separated. The transformer boards also snap off. All 4 snapped off boards are the same size so they can be stacked, swapped around or used in some creative way.

I use the full board as one unit and mount it on a 6"x8.25" wooden board. It sounds best open than boxed up. It takes a month for it to break-in. Probably a year for a full break-in. There was a ton of tweaking to make the DAC sound the way it does. No secret the basis of this DAC is Peter Daniel's DAC. By the way... I do have permission from him to use his design as I have done. I have also spent countless hours testing different caps, transformers, resistors for the best sound quality to get to this point.

My findings are that a standard NOS TDA1543 DAC with passive I/V section is pretty lifeless without a good buffer. This OPA627 buffer brings this DAC to life. With the built in volume control the outputs go straight to the power amp or headphones. Simple signal path. Only one coupling cap in the signal path.



This DAC's functionality is like an iPod in that it plays audio files and has a volume controlled output. When I compare it to the sound quality of an iPod on a scale of 1 to 10 the iPod is a 7 and this DAC is a 10. Nice upgrade for iPod users :)

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Brent Welke

Why do you copy something that is flawed by nature?
You would have much better (sonic) results with sin(x/x) compensation, mandatory for any NOS dac implementation, and the TDA1543 is no different.



That's right, but the way I do it is using much lower value resistors for I/V and a gainstage.
Shame that you already made the PCB, because sin(x/x) compensation on the gainstage is as simple as using an inverting op-amp with a cap across the input resistor, and a small cap across feedback for a 1st order filter.
It's curious that I've done things like this years ago and what amazes me is that apparently it's not common, the net is full of passive unbuffered I/V stages and uncompensated NOS dacs... and they say it sounds good but I don't like it, I've been there, done that.

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Carlos Filipe

"Any intelligent fool can make things bigger, more complex, and more violent. It takes a touch of genius - and a lot of courage - to move in the opposite direction." Albert Einstein

Sorry, but it functions nothing like an iPod. It doesn't really "play" audio files, it isn't portable, isn't all in one, has no headphone output, is mains powered, etc.

Carlos thanks for your input. I will look into sin(x/x) compensation and listen to it when I have time. If you come across an implementation of it please consider sending it to me or post it here. If I find it an improvement I would add it to the next version and give you credit for your input. I am more of an integrator then a designer :)

A few years ago I visited a local HIFI shop and was told that if I wanted quality sound from my computer my only option was to burn my audio files back to CDs and use a high quality CD player. I couldn't leave it alone, I started Googling and found DIY audio. Bought a TDA1543 prototype DAC from Peter Daniel and managed to get SPDIF out from my computer to the DAC. A year later this thread shows up, I remove the SPDIF interface on the DAC and replace it with a USB interface. All the while I am also building gainclones and noticed how good it sounds with a OPA627 buffer between the DAC and gain clones. Plus having the volume control before the buffer and not harming the sound quality was the icing on the cake.

The simplicity, musicality and good feeling of having built a device that brings high quality music to computers makes me want to share it. So here I am trying to share it.

So far everyone who has heard it really likes it (I like to watch the expression on their face when they first hear it :). I hope to get some comparisons to some brand name CD players and DACs on my site soon.


Hi Chris. I only recently heard an iPod. My neighbour left me with it overnight a few weeks back. Very nice device. All that functionality in such a small device and the sound quality was better then I expected.

The functionality that I find similar between an iPod and my DAC is the fact that CDs are not part of it, huge play lists, everything at your finger tips, and musical. A huge differences is that my DAC is not portable. Sure you can use a old $300 laptop as the user interface (all it needs is a USB port) but this DAC uses mains for power. If you take a close look at the DAC you will notice it is 90% power supply with most of the tweaking in this area. I believe this is a big reason why it sounds so heavenly. From experience I know that changing one of the power supply caps with a different value, brand, polarity(type N BlackGate) or one that isn't broken-in makes a sonic difference. My favorite version of this DAC is with two 130VA transformers, try putting that in your shirt pocket.

Use the iPod when you are out and about, but when at home you can take the sound quality up a few notches by using a high quality USB DAC without leaving your iPod lifestyle. I almost never go out, but if did I would own a iPod to continue with my music lifestyle when out and about.

Enjoy the music.

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Brent Welke