Clarion DRX9255EXL (Part 3) DIY SPDIF Digital Audio Input

So here I am today doing another modification to this Clarion DRX9255EXL. The main goal is making this unit accept SPDIF digital audio input from the external source such as PC or any media player that support the digital audio output via coaxial cable. In short, this unit will become a stand alone DAC + preamplifier unit.

A brief explanation for this modification is like this. The Clarion DRX9255EXL has the ability to set the input mode from the optical input at the back of the unit. This can be done by a simple jumper or a switch from the BUS connection. But as I intended this unit to become a DAC in my home audio system, so no switch option for this unit.

Further more, with this SPDIF input available, your option for any kind source input can be widely available. This is including using USB input by making the converter to SPDIF. For the example by using PCM2706 or any others converter available in the market that will do the same. But in this post, I will not make the USB converter. I will focusing on how to make this unit to accept the SPDIF input.

So the first step to make this Clarion DRX9255EXL accept the digital input is by shortening the 2 pin at the DIN connection. This is the simple method shown on the photo bellow.

If everything is correct, than the unit will switch to the ACCS mode. This mode means that the unit will take the input from the BUS connector.

On my previous post here, I had remove the DIN cable for cleaner look at the back panel of the unit. So right now I will show the pin that need to be short directly in the main board. It is on pin number 4 & 5 if you count it from the top.

You can also do in different way by adding a pair of cable extension and connect to a switch outside this unit. This will be the option for this unit to become a stand-alone DAC or as a normal head unit like I mentioned earlier.

The optical input for this ACCS mode is the Clarion proprietary optical connection that not available widely. This connection is also not suitable to the Toslink cable. That is why I should make a digital BUS converter to accept 75 ohm from the coaxial SPDIF digital input.

The circuit is so simple. It is basically CMOS to TTL converter consist of several capacitor and a resistor connect to IC SN75176. I got the schematic somewhere in Russian forum, which I forget what is the forum name right now. Maybe if someone know it, please share the link on the comment section so I can put the link in this post.

Looking to the schematic above, the input is coaxial digital cable connect to your source that has SPDIF digital output. The VCC, OUT, and GND is connect to the Clarion optical circuit. This simple schematic can be built by using small universal board.

At the bottom of the Clarion optical terminal, there is 3 pin which are INPUT, +5V and GND. You can make sure each pin configuration by measure by volt meter while the unit is power on then connect them to the above circuit accordingly.

Then I using standard RCA plug for SPDIF digital input and I install it at the back of the unit. It is look so clean.

This modification is now finish and I just need to put the top cover back on.

I am not put back the CD mechanism inside this unit anymore. This Clarion DRX9255EXL is now a stand-alone DAC unit.

My initial test with this unit is works flawlessly. I am using the LG DVD player, playing a CD audio and the output is SPDIF digital output. This output connect to the digital input Clarion DRX9255EXL that I've made before.

I also test this digital input from my PC, the output using the coaxial digital out connect to this unit without any issue. The 24 bit to 16 bit music files can be play in Clarion DRX9255EXL. I am not sure if there is any down sampling from the unit since the DAC inside Clarion DRX9255EXL is a pair PCM1702 which only 20 bit.

The sound quality, as expected, wonderful without any sound degradation at all compares when using the internal CD drive.

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