Clarion HX-D1 Car Head Unit To Home Audio CD Player (Part 2) Tone Control & Pre-amplifier Bypass

So today post is about doing some modification for the input output in this Clarion HX-D1.

As you might remember, I had the demanding customer who bought this unit and request it to make this unit more simple to use in the home audio. This modification process is quite easy because the only input would be the power DC replaced to the socket input from home power supply.

Then the output could be a line out via 3.5 mm socket. It is no other method simpler than this when modify the car audio source for home audio.

What I am doing first is remove this source selector relay. This relay function is to switch between signal source such as radio, AUX or CD controlled by the front panel of this head unit. Although this relay can be stay there, but the customer request this head unit is only for playing CD, not else.

There is a price should be paid when removing this relay.

Since the relay is attached firmly to the double side PCB, then the removing process made the PCB trace broken.

As you can see I also remove the four DC blocking capacitors near the op-amp 5532. This lead to the second step which is upgrading the capacitors.

While I try to figure the schematic of this analog section, I found something wrong with the original layout of this unit.

The white dot mark on the capacitors holes are for the negative polarity of the each capacitor.

I did tracing all components to get the schematic then I can make sure that Clarion engineering installed the capacitor reversed.

Here is the schematic.

This schematic is taken from the DAC IC output goes to I/V stages then the LPF stages. There are 2 red circle that I mentioned are in wrong polarity. The schematic above is the original polarity of the capacitors. As you can see the output from LPF op-amp 5532 is should be goes to positive side of the capacitor, but the original circuit goes to the negative side.

The second capacitor are goes from inverted op-amp input to the ground with several passive circuit. For the common application they should be goes to the ground and the capacitor negative polarity should be facing to the ground as well. This quite confused me a bit because there is another additional circuit that consist of few transistors and resistors. This circuit connect to other channel as well and triggered to something else. I still don't know the purpose of this circuit yet, perhaps this is related to de-emphasis circuit for HDCD mode when active.

So I install the new capacitors with all polarity reversed from the original PCB marking. This new capacitor is Elna Silmic which having the same value as the original.

The third step is put the 3.5 mm socket for the audio signal output.

Finding a good quality 3.5 mm socket is quite difficult. Especially when it require the small socket to fit inside this tight car head unit. Previously I had dismantled an Apple Docking but I actually made a mistake by pulled out the 3.5 mm socket from the main board. This makes the Apple dock cannot functioning at all but I can use the 3.5 mm socket for this project instead.

I attach the cables on it and glued it besides the optical socket. This location is fit perfectly with this 3.5 mm socket.

I attach the end of the cables directly to the capacitor out at the bottom of the board.

I also put the impedance resistor, each 47k ohm resistor per channel from the signal to the ground. This resistor also become the signal output point that goes to the 3,5mm mini jack.

And it is all finished.

I can put every components back to this unit and test this new line output sound quality from my home audio system.

So with the same system but now this unit is modify to become the fixed line output, then I should rely on my amplifier volume to control the loudness instead with the Clarion HX-D1 volume control.

First impression with this unit, the sound is flat. Not as energic as before the modification. This is because I bypassing all pre-amplifier and tone control after the DAC. The overall sound from DAC PCM1704 characteristic is still there but not as bright and analytical as before. The music timing that makes the music beat alive are still there but somehow less engaging now.

The sound-stage are a little bit narrow with the vocal presentation is now more forward. This Clarion HX-D1 sound right now is less bright and I can say it become similar to TDA1541 characteristic on the Sony CDP-75 here. Strange huh?!

This modification is take the signal output directly after the analog stage of the DAC. The sound are actually raw, unpolished and natural from the DAC itself.

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