NOS ADC discussion

[anthonybisset]

I haven't seen much discussion of NOS ADC's on diyAudio or really anywhere other than Altmann's site, so I'm curious if any forum members have built their own or have interest in doing this?

I understand the maximum practical NOS R-2R bit depth is around 18, although I've only been able to find 16 bits from Analog Devices (I believe they have/had an 18 bit r2r?).

Some chip offerings are capacitive ladders while others are resistive, should I care? Does one settle faster than the other?

Any recommendations for the simplest part count to get S/PDIF from the A/D and into toslink optical?

My ultimate goal being to build a very low part count NOS A/D-D/A with toslink for use with a MacBook... At this point I'm thinking outboard PSU or batteries makes the most sense as it is a portable.

Music studio's don't have access to this type of technology as there is no commercial NOS converter offering and while DSD sounds good, nearly all post production utilizes 16-24bit PCM (EQ/Filter/Dynamics/Etc). It's very likely most SACD's have been through a second DSD conversion after PCM edits occurred. Why does this matter? Well, you can hear it.

My conclusion is that sampling 192 Khz at true 16-19bits will give the best digital capture, post processing won't need decimation and finally something like Weiss Saracon could be used to convert to DSD.

Any help and discussion relating to simple NOS ADC and DAC designs will be both enjoyed and appreciated.

Btw, this inquiry is purely for building my own recording system and there are no commercial motives (outside of making good recordings).


Thanks,
Anthony Bisset
http://www.dspaudio.com

[rfbrw]

Unless you know of a non sigma delta audio dac, then any device you are likely to encounter may well need some form of format conversion.

[whatsup]

Originally posted by anthonybisset
My ultimate goal being to build a very low part count NOS A/D-D/A with toslink for use with a MacBook.

Btw, this inquiry is purely for building my own recording system and there are no commercial motives (outside of making good recordings).

I think your two goals are mutually exclusive. For the lowest parts count, get a CODEC that has ADC, DAC, S/PDIF, and USB all in one chip. There are many to choose from; but that gives you delta-sigma coming and going. For best sound with 18-bits and at least 98 KHz you should make your own R2R ADC & DAC with discrete components.

[QSerraTico_Tico]

Perhaps Audionote is working on it.

[rfbrw]

Originally posted by QSerraTico_Tico
Perhaps Audionote is working on it.

To be released around the same time as Duke Nukem Forever.

[anthonybisset]

Post #2 -
There are many NOS DAC's designs around and some have very low part counts like the DDDAC and similar TDA1543 layouts. For the first try (and many will cringe, I'm gonna clock both the DAC and ADC controllers from the incoming SPDIF signal. If the MacBook's SPDIF is too jittery then I'll go with an inline reclocker of some sort until I've developed brain circuits which can understand the nuances of PLL reclocking.

Regarding Post #3 -
Low part count, not lowest

With Napolean's hat tipped to the right (http://www.dhm.de/gifs/sammlungen/militaria/eh181.jpg)

I continue:

So far I'm thinking version 1 NOS_ADDA:

D/A:
- CS8412
- TORX79
- TDA1543 tower (no gain stage necessary, I like this simplicity for V1 anyway)

A/D
- CS8404a-CS
- TOTX79
- AD7690 (x2)

Regarding the AD7690 -
(http://www.analog.com/en/prod/0,,AD7690,00.html)
(http://www.analog.com/en/prodDesc/0,...90%5F0,00.html)

Pinout shows: SDI, SCK, SDO, CNV || will these talk to the CS8404a directly?
And more importantly, how can we use two A/D's for stereo.. Do we need to MUX the two chips data lines. I'm lost on this angle. Maybe I'll build the first version as mono.. Most of my recordings focus on frequency and dynamics rather than stereo separation anyway.

References:

http://en.wikipedia.org/wiki/Success...roximation_ADC

Further questions:

If we feed an 18 bit signal to a CS84xx series chip, does it pad the last 6 bits with 0's, or must we again do some formatting to make sure the computer sees a 24bit word?

Anyone with an Altmann creation ADC know what chips are being used? I'd just buy one outright but don't have the money and was bothered it's only 16 bit's.

-anthony

[whatsup]

Originally posted by anthonybisset
D/A:
- CS8412
- TORX79
- TDA1543 tower (no gain stage necessary, I like this simplicity for V1 anyway)

Didn’t you say you wanted 18-bit R2R performance? The TDA1543 performs like a 14-bit DAC: Read the datasheet. There are plenty of 18-, 20-, & 24-bit R2R DACs that will outperform a tower of 1543s with a lower total parts count and much less power consumption.

[gaetan8888]

Hello

I plan to built a non-os dac this year.

I did suggest to a friend to listen some non-os dacs, he just send me an email and say that;

''I have heard few non-oversampling DACs, yes. Most of them lose quality and resolution when the music gets really busy.''

Anyone know about any resolutions loss of that kind with non-os dacs ?

Thank

Gaetan

[anthonybisset]

Whatsup

Could you point out some non-sigma delta DACs that feature 20+ bits?
I've looked through all the Analog Devices DAC datasheets and the closest I can find is the
dual channel AD1865 with 18 bits precision and decent specs and it's being phased out, the recommended replacement is a sigma-delta design.

anthony

[rfbrw]

AD1862
PCM63
PCM1702
PCM1704