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-   -   Dac output stage ?? (http://www.diyaudio.com/forums/digital-source/11384-dac-output-stage.html)

Chris 20th February 2003 01:09 PM

Dac output stage ??
 
Hi all

I`m currently in the process of planning som tweaks for my cdp.

And I wondered if some of you have an idea or know any ways to build a general dac output stage using opamps.
My old marantz 63mkII uses a npc sm 5872 dac and it does not have any analouge filtering like many other dacs.

Any ideas and advice will be fine and recived with gratitude ;)

ashok 20th February 2003 01:33 PM

CD 63 issues
 
Hi Chris,
Please do a search for Marantz cd63 on the forum. We covered a lot of issues earlier and a service manual was also available in pdf form. These should give you lots of information. You will then be able to put up some more questions in detail.
I have modified my CD67 output. But have a look at the threads. TNT audio also has a very detailed upgrade proceedure for these machines. I can't remember the URL. You can get it by typing in Marantz cd63 upgrades and look for the tnt URL in GOOGLE.
have fun,
Cheers.

Chris 20th February 2003 01:48 PM

I have done searches on the forum but havent found quite what I`m looking for. I have read the TNT audio articles. And I have downloaded the service manual.

SvErD 20th February 2003 02:00 PM

Quote:

Originally posted by Chris
I have done searches on the forum but havent found quite what I`m looking for. I have read the TNT audio articles. And I have downloaded the service manual.

I guess you're aware of the LC-audio stuff aswell, if not take a look here:
http://www.lcaudio.dk/zapfilter.htm
http://www.lcaudio.dk/ad825.htm

Pedja 20th February 2003 02:27 PM

Chris,

See:

http://www.diyaudio.com/forums/showt...&threadid=2770
http://www.diyaudio.com/forums/showt...=&threadid=985

Pedja

Pedja 20th February 2003 03:51 PM

Bessel type analog filter for CD63
 
Quote:

Originally posted by Chris
And I wondered if some of you have an idea or know any ways to build a general dac output stage using opamps.
My old marantz 63mkII uses a npc sm 5872 dac and it does not have any analouge filtering like many other dacs.

CD63 already has an output stage, actually analog filters made with opamps. Strictly talking its output stage (HDAM) is made with bjts, but I donít see any point in swapping them with the opamps.

First, it is really worthwhile to change opamps to something better as LM6172.

Second, I can suggest you one thing that was mentioned earlier, but concrete solution, as I know, was nowhere explained. It is about changing filter type to Bessel instead of the original Chebychev. There is a 2nd order filter around the second opamp. It has peak at treble to compensate treble roll-off (0.7dB at 20kHz) which is the consequence of the RC filter around the first opamp. This filter has ringing of some 10%. I swapped this to Bessel type changing C605 and C606 to 390pF. This also forces changing of the L601 and L602 to (ideally) 520uH to preserve frequency of the notch filter at ~352kHz. Unfortunately, all this means further treble roll-off of 0.5dB (1.2dB total). You can also model this filter to move roll-off further above the audible range, but effectiveness of such filter will be dubious.

Pedja

Chris 20th February 2003 08:30 PM

2 Attachment(s)
would this work? (schematic of the cd63mkII dac outputstage with possible changes in red)
Sorry for the bad quality :(

The npc sm 5872 dac need some filtering at its output to work.
Please have a look at this website:

http://thunderstoneaudio.nav.to/

and look up the following project:

Thermionic Valve Analogue Stages for Digital Audio

Pedja 20th February 2003 10:36 PM

What\'s the goal exactly?

Schematic you drawn doesn\'t have anything with thermionic valves.

Pedja

Chris 20th February 2003 10:54 PM

Quote:

Originally posted by Pedja
What\'s the goal exactly?

Schematic you drawn doesn\'t have anything with thermionic valves.

Pedja

Thats true.
My initial goal with this thread was to ask if anybody had any idea on how to make a new/better outputstage for the particular dac that marantz cdp 63 use.
The point with the link was to give you some information about the npc sm5872 dac.

Having done some searches on the web and reading a few datasheets I see things a bit more clearly now.

Henrik 21st February 2003 02:10 PM

Hi Chris!
I started this thread some time ago: http://www.diyaudio.com/forums/showt...5&pagenumber=1
My Onkyo uses SM5861AP which is very close to your SM5872.
I am working on my last suggestion, though it will be a little different.

Why do you think SM5872 needs filtering?

My Onkyo sound much better when I take the output just after the first opamps.


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