Question about DAC Design

gene

Member
2001-10-28 6:06 pm
Hi everyone!

I plan to build a dac with upsampling, use cs8420 + cs43122 or cs8414 + ad1896 + ad1853, I'm looking for some suggestion.

On cs43122 Eval board, there's no LPF follow the dac, but cs4397 Eval board has a LPF, why? for cs43122 has second generation DEM while cs4397 has not? should I add a LPF after cs43122?

Another question is how to design a differential input LPF? how to transfer a single input LPF design to differential ? Can I just add a balance impedance the same as input+ to OP's input- and wire it to the output- of dac?

I can't browse http://www.diyaudio.de, can anyone mail DAC 4's data to me? Thanks.

[email protected]
 

gene

Member
2001-10-28 6:06 pm
micke,
Now I am searching the parts, I will not start drawing pcb until I know the footprint of the part which I can get. I also plan to order special frequency TCXO from the local factory, to get a 1 ppm clock. for me it cost less than Lcclock XO2.
 

gene

Member
2001-10-28 6:06 pm
Dave,
I can't browse any web base on geocities, what a pity.
please send it to [email protected], thank you .

TCXO are normally between 10M to 20M, you can buy 12.8M/14.4M/16.5M TCXO anywhere for just several $, but special TCXO such as 24.576M /33.8688M for dac is not available from retail market. Maybe too expensive for consumer products. My company use 70M and 81.264M (1 ppm) from a local factory, they can make any value as you specified, so I decide to order some 49.152M from them. It can be divided to 24.576/12.288M.

Use an ad9850 to build a DDS clock source maybe a good solution, you can get any frequency with the same circuit, but I don't know how to do it.

[Edited by gene on 11-09-2001 at 12:46 AM]
 
I am going to order some TCXO for DAC and CDP use. If someone want to order can leave the message here or e-mail to me for the detail!

The TCXO are from Japan and Raltron(USA). The price is about USD$45 (not include shipping cost)

I've got some of the 33.8688MHz on hand(Japan)

Hope can help you all!!

Thanks!
 

gene

Member
2001-10-28 6:06 pm
Andy,
you may look at Dave's website.
In jeff chan's review "Listening Comparison Of Digital Audio Filters"
http://www.jeffchan.com/audio/filter-comparison.html
PMD200>PMD100>DF1704, another friend told me DF1700>SM5843 in sound quality.

It seems that sigma-delta converters are the main trend in 24/96,192 generation, and they have built-in digital filter,I prefer sigma-delta converters for the future compatibility, such as dvd-a or sacd.
 
Gene - Its funny you should mention the AD9850 as I have just started working with one. I am using it for a FIFO based jitter reduction system in out board DACs. Its pretty simple to setup with a micro controller and its output frequency can change in very small steps, about 0.029Hz.

The AK4114 ( http://www.asahi-kasei.co.jp/akm/english/ ) is an interesting chip, I imagine crystal and Burr-Brown will follow. Is there now a 192 kHz interface for consumer use (its about time)? Does anyone know of any DVD-Audio Players with a 192 kHz output?
What about an DSD interface?

I have heard before that there is a big difference in sound between oversampling filters but I have not had an opportunity to compare them. I am cuurently using a DF1704 in my DAC. I will have the opportunity to try an SM5847 which had better be good, its 4.5 times the price of the DF1704.
 
I can vouch for problems with the CS8420 chip; we recently designed it into a board here and now we're designing it out ;)

The chip behaves wonderfully during regular operation, but if the AES/EBU input becomes loose or gets unplugged multiple times, the chip can enter an "undefined state" where it puts out garbage until you reset the chip (and sometimes reset it more than once!)

This is OK for a homebrew DAC, but if you want a "bulletproof" design then you might want to include a PIC12C508, ATtiny or some other microcontroller to handle resetting the 8420.