Dsd without D/A stage....

[kyrochan]

Hallo, recently I've read a Ken Ishiwata interwiew (suono 3/05) above the DSD format and his own system.
In wich the signal coming from the SACD drive going directly trought a simple low-pass filter, without it go trought a D/A converter. I'm a little bit puzzled from this opportunity...isn't a DSD signal a digital bit sequence that need to be converted in a analogue stream? Some one can help me and suggest me some litterature on this format? Or explain how should work a system like the Ishiwata one?
Many Thanks
Domenico

[seoman]

With a simple R/C network the Cap will becharged with every '1' and discharged with a '0'
As you can see from the picture above al lot of '1's wil give you a higher Voltage on the Cap and vice versa.

You would need a decoupling Cap to remove the DC offset (½Vdd)
Don't ask me about the values

Greetz Simon

[Duck-Twacy]

There is a old post of Remco Stoutjesdijk somewhere on the web, that also mentions this filter

http://131.109.59.51/techstuff/digit...mat_primer.htm

Als I understood the Vacuumstate mod uses this principle?
http://www.vacuumstate.com/son-kits.htm

[kevinkr]

Its just a simple low pass filter that integrates the dsd pulse train. I am actually planning to do this to my sacd player in my next round of modifications. (See my thread for progress so far.)

A simple first order filter designed to roll off above 50kHz will do it, but the amount of RF present on the output would be substantial. I believe a third order filter would provide enough attenuation for most applications.

I am thinking of buffering the digital outputs of my dsd decoder ic and feeding that signal to a passive RLC filter designed to do the job - possibly if I can keep the impedances low enough I will not even need active buffering at the output of the filter. Using level translation would actually allow me to have voltage gain in the digital domain where in theory there is no added distortion.

The 0 baseline is at half rail and therefore the output must be ac coupled or the baseline offset nulled out. (easily done, but requires a good op-amp or two.)

Kevin

[kyrochan]

Grrrreat replies, expecially the kevin one!
Please would you like to explain approfonditly your project? I'm really intersted. Some english words are not so clear to me and I cant' find a good technique translation.
Also little drawing are wellcome!
Thank you!

[stolbovoy]

Didn’t anybody think about making high current DSD "DAC" to feed loudspeaker directly, controlling volume by altering rail voltage. Pretty interesting and simple at first glance…

[kyrochan]

How could it be possible?
I think that a DAC should be a bit puzzled to have a so complex element (like a speaker) at its output, and should not be able to bring to its output something like 4-5 ampére at 23V
Please explain your tought

[stolbovoy]

Originally posted by kyrochan
How could it be possible?
I think that a DAC should be a bit puzzled to have a so complex element (like a speaker) at its output, and should not be able to bring to its output something like 4-5 ampére at 23V
Please explain your tought

"In wich the signal coming from the SACD drive going directly trought a simple low-pass filter, without it go trought a D/A converter. "
I suppose by doing the same with high power push-pull output driven by DSD and may be without low-pass filter.

[kevinkr]

In effect you are talking about a power dac, and yes it can be done by varying the raw dc voltage to the power amplifier - note that you still need a post filter to reconstruct the signal after the digital amplifier. I think in this case an air core inductor of a couple of mH and a capacitor such that your cut off frequency is around 50kHz would work well.. The digital amplifier would need to consist of a couple of high speed complementary mosfets and some level translation to provide gate drive. The power supply would be the most complex part of the equation and would need very good regulation and stability. If you desire to avoid using a large output capacitor either a bridge configuration could be used or tightly tracking bipolar supplies.

In my system I am planning to do something similar at line level, except that the supply will be a low noise fixed 5V.

Designing a good power dac as you describe is not trivial, and one of the biggest issues you will probably face is linearity in the output inductors and caps - you do not want to rely on the speaker inductance to integrate the pwm at the voice coil, not to mention the idea of 2.8224MHz RF running around speaker cables at high amplitudes may cause emi problems with other components in your hifi.

[kevinkr]

When I actually get going on this I will post details of my design here, but that may be some weeks or months away due to busy work schedule.. LOL

For other SACD mods check out my old xb770 thread..

Kevin