DF1704 replacing PMD100 in Adcom GDA-700

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#3
Why did you replace the PMD100, was it defective? The PMD100 has an excellent reputation for performance, both objective and subjective, so it you're not likely to significantly improve upon it with the DF1704.

If you're comitted to replacing the PDM100, the trouble signs you report may be due to an incorrect audio port (input or output) mode setting. Verify the required mode settings via the relevant datasheets, and then ensure that those setting are correctly applied to the DF1704 module.
 
#4
I also have a GDA-600, which I reworked, and frankly it smokes the GDA-700. After some research, I see the PMD100 seems to be a much unliked DF in audiophile world and I suspect it is responsible for the crappy 16 bit/44.1Khz performance of the GDA-700.

Well, the original PMD100 appeared to be set at Left justified input mode with 20 bit output.

The DF1704 has selectable input modes. I tried them all. Anything right justified just produces white noise. 24 bit left justified input works best, but with static and distortion. I2S input modes also work, but with more static and distortion.

I'm a bit stuck at the moment. The PMD100 has a PLC to the left of it inbetween it and the digital receiver and and it is not entirely clear to me what this is doing.

I also cannot find inpout receiver Ultra Analog AES 21 AESC003 datasheet. Anyone have one?

Also, the PMD100 had a dither input connected to the PLC output. The DF1704 has no dither input, so this is now not considered by the DF1704.

Any ideas?
 
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#6
Well, we will see. Fact is, the DF1704 is in and needs to be configured now, so I'd appreciate any help I can get.

You think that PLC is upsampling the the output of the DF? The receiver chip sends its data straight to the DF, which outputs 20 bit data that loops through the PLC and then goes to the PCM1702s. Yet, the BCKO0 and WCK0 outputs of the DF go straight to the PCM1702s. 😕
 
#7
Sorry, I didn't look too much into the schematics. You're right. The function of U301 is unclear (Sample rate indicator?). What I heard is that PMD100 has a unique way of data timing. It's sending the data to DAC in a faster way, then stop all the channel until latch triggered. You may need a logic analyzer to see if the DF17XX will fit into the position. BTW, the special feature of PMD100 is no longer useful for PCM170X.
 
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#9
As long as the AES21 hasn't gone bad, which they are known to do, then bypassing PLC is the logical next step. There is no conceivable reason to have it in the path with the DF1704.
And I concur that the PMD100 is a TERRIBLE digital filter chip. The only df chip that does plainly audible damage to the sound. I've done some seriously fair a/b tests of PMD100 against other df chips, and the PMD consistently makes things sound 2-dimensional & artificial. It's simply awful.
That said, once you get the 700 working with the DF1704(a superb DF), the GDA600 will still sound better, due to advantage of PCM63's. In order to make the 700 "catch up" and sound as good, you'll need to put at least three PCM1702's in parallel to rival the 63's dynamic & richness advantage. Happily, the 1702's can be directly "piggybacked", all pins soldered to next chip's pins, with only change needed the adjustment of i/v resistor value to compensate for added output level.
 
#11
Well, I connected the 1704 DOL and DOR directly to the PCM1702 chips. Output connection between DF and D/A is now direct and doesn't concern anything else.

I still have exactly the same problem. Static and distortion in music. I have tried all input modes of the DF1704 and 24 bit left justified is the one that works best.

AES21 worked fine until I tried the DF swap. But I'm still flying blind not knowing what it outputs and not having a datasheet.
 
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