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Old 26th August 2004, 10:20 AM   #1
Fabian is offline Fabian  Switzerland
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Cool Non Oversampling with PCM1704

Hi everybody,

After building a DDDAC1543 and modding a Philips CD650, I wanted to build a non oversampling DAC (CD player) with other chips than TDA1543/TDA1541. I soon found out that it's not that simple as with these Philips chips. It would require some glue logic to connect a PCM1704 to a Philips decoder.

As I had no idea how to shift those I2S signals and how to design a working shifting circuit, a lot of reading datasheets and searching through forums was on my task list.

There are some circuit's available, but non of them fitted my needs. And a circuit without functional description is hard to understand (at least for me, as I'm not an EE). With some further reading, I got a more clear picture and I felt like being able to design a circuit that would do the job.

And it worked! First object was a Denon DCD 3000 (PCM1702). Then I married my Philips CD650 with a Teac VRDS 25X DAC board (AD1862) and lastly an Elektor Audio DAC 2000 (PCM1704) built into a Marantz CD72.

I'm so happy with the results, that I've made a little guide on how to design a shifting circuit that fits your needs: http://www.geocities.com/nonospcm1704/

I hope you'll find some usefull information and that maybe some of you are encouraged to try some other chips than TDAs for their nonos projects.

Is there anybody having done or building something similar and what is your experience?

Fabian
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Old 26th August 2004, 02:46 PM   #2
Charles is offline Charles  Germany
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Default Yes,,

Hi Fabian,,

I did a similar glue logic for the PCM1704 a couple of years ago.

I was curious how a high-precision DAC would behave in a non-oversampling configuration.

It worked out well, but not filterless:

I used a transformer to smooth (or should I say resonate) out the edges -> see pic. Without that transformer the sound was very harsh.

Surprisingly enough, with the TDA1543 a filterless design can sound decent.


Thanks for your cool site.

Charles
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Old 26th August 2004, 06:24 PM   #3
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Default Re: Non Oversampling with PCM1704

Quote:
Originally posted by Fabian

<snip>
Is there anybody having done or building something similar and what is your experience?
<snip>
Fabian
Tried it. PCM 63 and PCM 1702. Stopped clock and shift-register. Not keen on either method.
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Old 31st August 2004, 10:12 AM   #4
Fabian is offline Fabian  Switzerland
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Charles,
I've always used filterless opamp IV/buffer at the output. Every time I compared I liked it better without any filter at all. I've no experience with transformer "smoothing", maybe I'll try some day.
Right now I can't dedect any harshness in the sound, for my ears it's very smooth and revealing at the same time.

rfbrw,
You say you're not keen on either method. I guess you must have compared this to something other that you liked more. What do you prefer then? I also wonder what IC (decoder/inputreciever) you had in front of the DACs, if you can remember...



I've listened all DAC IC I've mentioned in the first post in different setups:

AD1862 I first combined with SM5843 (I prefer slow roll), then with CS8420 and then I used the shift register.

PCM1702 I first combined with SM5845 (Denon Alpha Processing) and then as well with shift register.

PCM1704 I interfaced with DF1704 (I prefer slow roll of again), then with SM5813 and again with the shift register.

With every DAC IC I clearly prefer the non oversampling shift register setup. The best sounding digital fitler of these is imho the Denon Alpha Processor. I could have almost be able to live with that. Althought there were differences I felt that the others are more or less destroying muscial flow, smearing the higher frequencies and reducing the perceptible dynamic range.

Fabian
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Old 31st August 2004, 11:01 AM   #5
Charles is offline Charles  Germany
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Quote:
Originally posted by Fabian
Charles,
I've always used filterless opamp IV/buffer at the output. Every time I compared I liked it better without any filter at all. I've no experience with transformer "smoothing", maybe I'll try some day.
Right now I can't dedect any harshness in the sound, for my ears it's very smooth and revealing at the same time.
Fabian
Hi Fabian,,

I don't know why it did not work out for me with 'just' the OPamp I/V.

I feel, its always a combination of many things (sometimes too many) that make something work out or not...

As I remember I added a "bad" transformer between the OPamp I/V and the output OPamps, and then it worked quite nice. I still have that DAC in my private stock and it sounds very good. I also have the same DAC with DF1704 (without the tranny) and there I totally agree with you that the slow rolloff setting sounds invariably better.

Its funny I had this argument in the mastering forum, and the experts coming down on me, that slow rolloff is totally wrong and should not be included in DACs and digital filters anymore. And I just said: "Hey, yes it may be wrong for your understanding of it, but it sounds right"

For me R2R (or multibit) is the only valid conversion method, and the PCM1704 is the most precise machine and still made today. On the other hand I find it totally astonishing how damn far you can get with a 1543.

But as I said, its always a combination of things...

Charles
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Old 31st August 2004, 05:50 PM   #6
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Quote:
Originally posted by Fabian

rfbrw,
You say you're not keen on either method. I guess you must have compared this to something other that you liked more. What do you prefer then? I also wonder what IC (decoder/inputreciever) you had in front of the DACs, if you can remember...
Should have been clearer. I do not like the sound of the PCM63 or 1702 without the OS filter irrespective of how the filter is bypassed.
CS8412 and YM3623.
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Old 16th June 2011, 03:04 PM   #7
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Are there now more current information?

I want to create a DAC with the PCM1704 with follow modes:
1) Non (zero) oversampling (NOS)
2) normal oversampling
3) normal oversampling include upsampling

All modes in a reclocking mode.

Additional I want to use various digital filter units like the DF1704 and the PMD100 so as the PMD200

The question is for me, whether there is therefore any justification.

Because the CD system (PCM) is far less perfectly than the SACD system (DSD) some guys recommend the use of various modes by a DA concerter to match the requirements for balancing the various unwanted error effects, which are already created by produce of the CD recordings itself.

Non oversampling 2xPCM1702 feed by I2S experiment results
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Last edited by tiefbassuebertr; 16th June 2011 at 03:13 PM.
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Old 10th August 2011, 07:37 PM   #8
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No experiences?

here additional URLs:
Jundac Two, High-End NOS DAC Kit with PCM1704 up to 24bit/192KHz
Creating a DIY non oversampling DAC with PCM1704
Cs8412 - Pcm63 Non-oversampling
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Old 11th August 2011, 12:17 AM   #9
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Sounds to me like you're wanting a 'soft' system - why not choose a microcontroller/DSP based approach? Then you can implement any digital filter that takes your fancy and not go hunting around for those hard-to-find PMD100/200. In point of fact, the PMD200 is based on a Freescale DSP and nowadays there are better solutions than that as technology has progressed. I'd be inclined to look at an LPC17XX based solution (but then I'm obviously biassed...).

As regards experience, I've programmed a 4X OS filter using LPC1113 and it works jolly well into my TDA1541. I needed a little glue logic - 8 * 74HC595 - to convert I2S into something the LPC can read.
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