Micro DIR9001 + PCM1794A DAC

I don't solder under a magnifier, but I do check the pins under one after I'm done just to make sure there isn't anything between them.

The solder braid is to suck up any extra solder that ends up bridging the pins. It's bound to happen when soldering packages like SSOP with a regular tip.

It's not really that difficult, but the tip has to be in brand new condition when doing the IC's. I "sharpen" my tip and then do the IC's first before it starts to wear out. The tip doesn't last long this way as the copper is exposed to the air, but it's what works best for me.

Pics of before and after "sharpening"...

I wired up a switch to change between 96kHz and 192kHz. So far my impression is that at 192kHz the low end seems kind of thin compared to 96kHz. I need to make the wires longer or use a remote switch so I can sit at my listening position to get a better impression.

I beleive I have read some people say they thought the SRC4192 lacked low end, maye they were listening at 192kHz as well.
100R resistors

theAnonymous1 wrote:
"In the ezDAC schematic there are 100R resistors in series with the data lines between the CS8416 and the SCR4192 and also a 47k from the SDOUT pin to ground. Are these needed with the DIR9001?"

that depends on the transmitter and receiver chips
and the interconnects.
The resistors are supposed to dampen any ringing
due to inductances and capacitances on the lines
and chips. I tried some on my cdplayer long time
ago, it did not help me, or at least not that
I could hear of.

btw, many thanks for sharing your design.
The TI eval board uses 33R resistors on the data lines so that is what I used. I learned the 47k from SDOUT to ground is specific to the CS8416, so it wasn't needed.

It works perfectly and I can't wait to finish the IV stage.

Just to be clear, this is by no means my design; I simply used my excellent cut and paste skills to throw this together. All credit goes to Evan and his ezDAC, TwistedPear's COD/IVY, and of course good ol' Texas Instruments.
I have perhaps a silly question.

Suppose I want to use an external oscillator with the DIR9001. The datasheet says I have to use 24.576MHz. That means fs is either 48kHz or 96kHz.

Can it still receive 44.1kHz SPDIF input from a redbook CD ?
How does it actually deal with the difference in sampling frequency ?

Thanks in advance,


2007-11-25 11:52 pm
IIRC the external osc doesn't have anything to do with the receiving portion of the chip. Reception is always handled by the PLL. The oscillator is for providing a clock when nothing in coming in on the input, and also for doing the input frequency calculation. (Which is pretty limited: the input frequency calculator only works for 32, 44.1, and 48 kHz.)

The datasheet says:
The DIR9001 does not require an external clock or resonator for decode operation if the internal actual-sampling-frequency calculator is not used. Therefore, it is possible to reduce the cost of a system.
Finally, I finished an output board for this DAC. :smash:

I didn't go with the active I/V stage I planned on before; instead I opted for passive I/V and an active balanced to SE converter.

For the balanced to SE conversion I chose to use TI's DRV603. The DRV603 is capable of a 3Vrms output with only a single 5V supply and has differential inputs.

Right now the board only has a 1Vrms output. I'm using 357R resistors for I/V conversion and no gain with the DRV603. I plan to add some gain to get a 2Vrms output.

The circuit is DC coupled and has about 15mV/19mV output offset with the DAC attached. Without the DAC attached the offset is only 2mV/3mV. I'm not sure if it's the input bias of the 603 or the passive I/V that's making it that high, but it's easy enough to add a cap on the output if needed.

The DRV603 circuit was so small I was able to add a low noise regulator circuit based on the LME49600 buffer. The entire DAC only needs a single power supply of >7VDC. Later I'm going to make a new board that replaces the LME49600 regulator with a DC-DC boost converter so it can run everything from a single Li-Ion battery.

Considering how much effort this took, I don't think I will ever get around to an active I/V board. I'm happy with how this one is performing though, so I don't think it would even be worth the effort for me.