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Tam Lin
14-11-2008, 13:08
CS8412/14 Substitute

The CS8412 is used in DIY, budget, and high-end DACs. The chip is long out of production but DACs that use it are still being made. So, what can be used as a substitute or upgrade? A popular choice is the pin-compatible CS8414 mounted on a SOIC-to-DIP adapter but the CS8414 is also out of production and getting hard to find.

I made this widget that uses a CS8415A (mounted on the underside of the PCB) operating like a CS8412 in mode 6. It is plug-in replacement for a CS8412-CP and makes a nice upgrade for most Audio Note and similar DACs. Other CS8412 operation modes can also be provided with minor circuit changes.

http://internet.cybermesa.com/~jmlpartners/images/dir6a.jpg

The 24-bit, right-justified output of the CS8415A is shifted right six bits yielding 18-bit samples. The CS8415A is a definite improvement over the CS8412 and shifting one or two additional bits reduces the DAC’s settling time and that yields even greater clarity and dynamics. Like jitter, settling is a period of time when the DAC is outputting the wrong value during the transition to the next sample, except jitter is measured in picoseconds and settling time is measured in nanoseconds: a thousand times larger.

http://internet.cybermesa.com/~jmlpartners/images/dir6a.png

The oscillograph below shows the output of a Lite DAC-AH and the difference between settling time and jitter. The falling edge of WS (red) initiates the digital -to-analog conversion. The analog output changes on the next rising edge of SCLK (violet). The right and left channel analog output (green and yellow) begins changing after the rising edge of SCLK but it takes a long time for them to reach the final signal level for that sample period.

http://internet.cybermesa.com/~jmlpartners/images/dir6a_01.png

Near the left edge of the oscillograph are two orange, dashed, vertical lines. One marks the trigger point, which is the rising edge of SCLK, and the other marks 200 picoseconds after the trigger. (The two lines are superimposed because the time interval is less than the width of a pixel on the ’scope display.) 200 picoseconds is the maximum RMS clock jitter spec for the CS8412.

As seen below, while the DAC’s analog output is settling, the signal is unpredictable and may include under-shoot, over-shoot, and oscillation.

http://internet.cybermesa.com/~jmlpartners/images/dir6a_02.png

Settling time is a function of step size. Right-shifting the sample data one or two bits reduces the RMS step size by a factor of two or four, respectively. The two oscillographs below show the composite output of the same DAC. The orange cursor lines are at the trigger point (rising edge of SCLK) and when the output signal appears to have settled. The first oscillograph is of the unaltered test data. The second is the same data right shifted one bit and amplified to the same scale as the first.

http://internet.cybermesa.com/~jmlpartners/images/dir6a_07.png

http://internet.cybermesa.com/~jmlpartners/images/dir6a_08.png

DACs with marginal linearity also benefit from right-shifted samples. In the oscillograph below, the green trace shows a full-scale 20Hz sine wave; the yellow trace is the same signal shifted right one bit and amplified to the same scale. The distortion evident in the full-scale signal is absent from the shifted signal.

http://internet.cybermesa.com/~jmlpartners/images/dir6a_09.png

The settling behavior of different DACs varies widely and makes a significant contribution to their unique sound qualities. I believe the differences you hear between different DAC chips are mostly due to their settling characteristics.

Telstar
26-12-2008, 12:06
Hi Tam,

Have a look here:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=133884

StanleyB
26-12-2008, 13:05
A popular choice is the pin-compatible CS8414 mounted on a SOIC-to-DIP adapter but the CS8414 is also out of production and getting hard to find.
I have been told that I am currently the world's largest user of the CS8414. The chip is not strictly out of production. There is a later revision chip available to me with a tighter clock specification. It's the most expensive IC in my DAC at more than U$13 a piece for an order of 1K pcs:(.

Telstar
26-12-2008, 13:42
Did you guys try the Wolfson WM8804? I heard good things about it.

leo
26-12-2008, 15:27
Theres a DIR9001 in one of the dacs I'm playing about with, I'll have to see how it compares against the CS types, I've not tried the Wolfson offering yet

Telstar
27-12-2008, 13:53
I think the DIR9001 is roughly equivalent to the CS. If you do the comparison, pls update us.
The real jitter seems to be 40ps instead of 200ps as declared.

The wolfson seems to sound a bit better.