Author Topic: QA660 usage with PCM1704 DAC  (Read 5778 times)

45Triode

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QA660 usage with PCM1704 DAC
« on: May 13, 2013, 04:18:11 PM »
Is is possible to do a software update so the I2S output can drive a TI/ Burr Brown PCM1704 DAC?

This would reduce external circuit complexity and may lower jitter.  One must keep the rest of the system
as pure and clean as you have done in the QA660.



aliu

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45Triode

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Re: QA660 usage with PCM1704 DAC
« Reply #2 on: May 14, 2013, 09:09:12 AM »
Thanks Aliu

I all ready have a working shift register board to drive the worlds best ladder DAC (PCM1704). My board uses 7 SMD IC's
and lots of discrete parts. It would be great to get rid of all this extra hardware.

I'm looking for someone that can tweek the code to make the QA660 I2S output the correct
format for this DAC.

aliu

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Re: QA660 usage with PCM1704 DAC
« Reply #3 on: May 14, 2013, 01:55:49 PM »
If you check the PCB of QA660, the microprocessor based functional unit is the SD card board, that says the firmware is mainly for this board. I might be wrong, but I think the I2S signal process should count on non-programmable chips completely, so the firmware is not able to do anything with the I2S output.

45Triode

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Re: QA660 usage with PCM1704 DAC
« Reply #4 on: May 14, 2013, 05:27:40 PM »
The I2S output comes from a quad buffer U3 (74VHC125).
U3's input comes from a ATMEL  32UC3A3256 uP.
The processor is responsible for format/ timing of the DATA.

Anyone out there who can reprogram this processor, I will make it worth your while!
I'm a hardware guy as you can tell.

aliu

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Re: QA660 usage with PCM1704 DAC
« Reply #5 on: May 14, 2013, 07:46:40 PM »
There is one concern about the output format programming, the Optical and Coaxial are count on the I2S, if the processor output is programmed as "PCM" interface, that would cut the Optical and Coaxial off.

Since the signal conversion has to be implemented inside the  ATMEL processor, I think only QLS-HiFi has the ability to do that.

45Triode

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Re: QA660 usage with PCM1704 DAC
« Reply #6 on: May 14, 2013, 11:41:58 PM »
No reason that it should stop the other outputs.
I'm not using those outputs because they are compromised outputs and are lower quality compared to I2S.
It does not get any better than I2S the input format DAC's use.
There are many, many other less expensive players out there to buy if you want SPDIF or TOSLINK.

aliu

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Re: QA660 usage with PCM1704 DAC
« Reply #7 on: May 15, 2013, 07:25:26 AM »
Did some research last night, it seems that PCM1704 has to work with an outside filter chip such as DF1704, and DF1704 can be fed by I2S directly, what's the filter chip does your DAC use?

45Triode

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Re: QA660 usage with PCM1704 DAC
« Reply #8 on: May 15, 2013, 08:30:12 AM »
For now-  JUST SAY NO TO DIGITAL FILTERS.
I use a simple analog RC filter and a tube amplifier output stage for filtering.
Sound is better than the best JFETS, or OP AMPS.

Digital filters only look good on paper they do not improve jitter only make it worse.

The plan is to give this system analog like vinal quality sound. I have spent $$$ auditioning
digital playback devices and they all sound different and none as good as a good CD player.
Why is that? Even QLS says this is only equal to a few $$ CD player. Theory says a pure
digital devices like the 660 should sound better than all the processing that takes place in a CD player.

Look at all the power supply work QLS did in the QA660. That rigor needs to be applied
to the D/A processor also.

Remember all digital signals are really analog in nature. They can have overshoot, ringing, noise, etc.

aliu

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Re: QA660 usage with PCM1704 DAC
« Reply #9 on: May 15, 2013, 09:23:57 AM »
DF1704 is a digital filter for the signal sending into the PCM1704 chip, I am not talking about the output stage. Normally a digital filter needed for I2S or "PCM" signal before sending into the DAC process.

By the way, have you tried the new pure Wav firmware for QA660? I saw a lot of good feedback in the Chinese HiFi communities.

45Triode

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Re: QA660 usage with PCM1704 DAC
« Reply #10 on: May 15, 2013, 12:52:23 PM »
Normally people would use a digital filter to make the waveforms look good on test gear.
How do they affect the sound is what you should ask yourself? There is no free lunch in life
as you know there is always trade offs.

All amplifiers are low pass or bandpass filters like it or not. Mine is a bandpass where the
upper pole is low enough to add additional filtering of the unwanted high frequency products.
In listening tests these out of the audio band filters still have some effects in the audio band
that you hear.

Yes I'm running the WAV only firmware ver. WAV-1.0.0   date  2013.04.10.
Seems to work good.

There are 20 to 30 file formats out there and once again I'm using the best (UNCOMPRESSED) possible.

Only way to get the best sound is to very very carefully choose each part/ circuit of the player as it all has to
work as a system to bring out the emotion in the music.


aliu

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Re: QA660 usage with PCM1704 DAC
« Reply #11 on: May 15, 2013, 05:39:53 PM »
That's a good point. I guess your 1704 is on the NOS way, something like the attached diagram. No matter using hardware or software to convert I2S to "PCM", there is an additional conversion element on the loop. So the best way would be modifying the firmware of QA660, packing the data directly to "PCM" other than I2S, I do not know if there is a big enough market can catch QLS-HiFi's attention to this direction.

My DAC is 1794 NOS with I2S input directly, the whole design is very simple so just hook the I2S of QA660 to the I2S of 1794 DAC and it works. Now I am trying a very simple transformer as the I/V stage. I have to say this kind of hobby burns a lot of holes on my pocket.
« Last Edit: May 15, 2013, 08:01:48 PM by cowboy »

clark

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Re: QA660 usage with PCM1704 DAC
« Reply #12 on: May 15, 2013, 08:37:07 PM »
QA660 use CS8406 in I2S  Master Mode, And MCU AVR32 is work in I2S Slave Mode, and it is can't through firmware change I2S output.



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