Putting an external DAC inside a dvd/cd player - diyAudio
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Old 8th July 2003, 11:25 AM   #1
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Join Date: Apr 2003
Location: Boston Area
Default Putting an external DAC inside a dvd/cd player

Hi,

I am modding the crap out of a Denon 2800 dvd/cd player.
I would like to hook up my external dac INSIDE my player.
Here is some info:

There is a chip on the main pcb of the Denon that outputs a SPDIF signal. Actually, it is a 3.7Vpp signal, not true 0.5Vpp SPDIF at this point. The signal then passes through a 47 ohm resistor, and then gets sent to the audio pcb where it goes through some inverters, resistors, a pulse transformer, emi filter, etc and then ends up at the RCA digital out at the back of the unit (0.5Vpp, 75 ohm impedance).

I noticed using a scope that the digital data looks cleaner (less overshoot, less noise) BEFORE it is sent through all the components in the audio pcb that I mentioned above. And, it is 3.7Vpp vs. 0.5Vpp.

I would like to hook up the output of that chip on the main pcb directly into my external dac that has a Cirrus Logic CS8414 digital receiver.
This way, I will use a very short cable and no connectors, and hopefully will introduce less jitter and noise onto the input of the dac.

Now, my question is since I would take the signal right off of the chip on the denon, should I be concerned with putting a resistor in series with the chip output and the dac input? Should I also remove the 75ohm resistor on the input of the dac since I am not dealing with a true SPDIF impedance matched case anymore? I don't want to load down the denon chip with 75 ohm to ground because I wouldn't be using any of the buffers. I'm just curious what is the best way to do this to obtain the cleanest signal to the dac, minimizing noise, backreflections, jitter, etc.

I hope what I am explaining is clear and not too confusing. Let me know if I need to elaborate further, and thanks for all your input.

Sincerely,

Vinnie Rossi
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Old 13th July 2003, 10:21 PM   #2
A 8 is offline A 8  Sweden
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Join Date: Mar 2003
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Seems like the long way home, why use the spdif when you are already inside?
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Old 14th July 2003, 01:20 PM   #3
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Join Date: Apr 2003
Location: Boston Area
Quote:
Originally posted by A 8
Seems like the long way home, why use the spdif when you are already inside?
Well, the SPDIF is so easy to access off the MAIN PCB. Note, it isn't true SPDIF off this board, as it is 3.7 Vpp and isn't set up with the 75 ohm impedance. It become true SPDIF after it passes thru the AUDIO PCB and out to the RCA coax jack. The digital signal looks cleaner off the dvd decoder chip than it does at the rca digital out.

If this is the long way home, what is easier?

Thanks,

Vinnie
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Old 14th July 2003, 04:31 PM   #4
 is offline  Russian Federation
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Join Date: Jul 2003
Location: Russia
Hi
Quote:
If this is the long way home, what is easier?
Use directly I2S, and it is not required CS8414.
SPDIF spoils a signal by jitter only.
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sorry my wrong English
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