New DAC with measurements!

[ojg]

I have been lurking around here for a while, commenting on other peoples designs. Well, it's time to put my own head on the block...

This is a DAC based on PCM1704 with a AD1896. It also has five Jung/Didden regulators. I have taken some measurements of this DAC and a TDA1541 with some interesting results. Instead of posting everything here, I made a website for it.

Let the flames begin!

[AD1865]

If you bypass DF1706 and set AD1896 to 192KHz
output formart, what would happen? And If you use DIR1703 direct to PCM1704UK,what would happen?

[ojg]

Thank you!

These are both good questions that I unfortunately will not be able to answer.

1. I don't have a 49.152MHz clock required to run the AD1896 at 192kHz.
2. The output data format of a DIR1703 is not compatible with the PCM1704 without using some glue-logic.

[tschrama]

Hi,

I looked at you website yesterday night.. late.. and I'm very impressed ! Good work!!.. I am very curious about that TDA1541 in oversampleing mode idea... anybody tried that?

Regards,
Thijs


PS
What hardware did you use for your measurement, could elaborate about the measurement methods?

[rfbrw]

Originally posted by tschrama
Hi,
I am very curious about that TDA1541 in oversampleing mode idea... anybody tried that?

If you want to try connecting the DF1704 to the TDA1541 there was a thread a while ago about using the TDA1541 in simultaneous mode.

[ojg]

Originally posted by tschrama
What hardware did you use for your measurement, could elaborate about the measurement methods?

I made some test signals in Cooledit and burned them to a CD. The output of the CD-player and my DAC was hooked up to my M-Audio Audiophile 2496 through a simple 10kohm 0.5 voltage divider. I used the Spectralab software.

The jitter-test signal is the same that Stereophile uses for their tests.

I also tried sending the 1kHz signal through a notch filter to eliminate distortion in the soundcard ADC, but this did not change the results (the harmonics did not change), so I dropped that idea.

All in all, the Audiophile 2496 is a pretty decent card for doing measurements.

[AD1865]

Originally posted by ojg
Thank you!

These are both good questions that I unfortunately will not be able to answer.

1. I don't have a 49.152MHz clock required to run the AD1896 at 192kHz.
2. The output data format of a DIR1703 is not compatible with the PCM1704 without using some glue-logic.

You can set DIR1703 to 24bit right-justified output formart, then it can compatible with PCM1704. The max frequency of AD1896 is 30Mhz, when use it for 192khz, you need to set it to slave mode(see AD1896 Datasheet). If you use SRC4192 instead of AD1896, the result must be much better and it supports 192KHz without set it to slave mode.

[ojg]

Yes, the DIR1703 would have to be set for right-justified, but that would only work for the left channel. What about the right channel? The data would need to delayed by 32 BCLK's to be in sync with the left channel, no?

You are correct about the AD1896 not needing the 49.152MHz though if you run it in slave mode (which I don't), but you would still have the same interface problem as for the DIR1703 above.

[AD1865]

You can use 4 74HC164 for delay DATA by 32 BCLK's or use 74HC04 to invert L/RCLK for RCLK.

[JonPike]

Very interesting.. and I will be awaiting some of your other tests!

The 1704 is a DAC chip I am thinking of building something around, and a friend of mine has an old Cambridge CD2 (?) that we've slowly been modding up.. and it uses TDA1541's, actually 4 of them all summed together..

Only done a few things so far, and it's improved nicely.. Especially interested in the new digital filter being used with it.. as well as trying the AD797's!! (got a few samples to try but haven't got to it yet)

I'd like to know a little more about how you're generating that jitter test tone in CE.. looks like a possible easy way to test modding results!