Clarion HX-D1 Car Head Unit To Home Audio CD Player (Part 1) Comparison With Clarion DRX-9255

On previous post, I have talked a lot about the Nakamichi DAC-101 for home audio. My interest to explore the multibit DAC is still continue. The PCM1704 is believe to be the last multibit DAC before all DAC replaced by delta sigma. This DAC can be found on Clarion HX-D1 which is the HDCD CD player using dual PCM1704U. This is the successor of the previous generation the Clarion DRX-9255. I really don't think the difference on them is just the DAC IC only.

So in this post, I will exploring the components inside while modify it to become a home CD player.

This Clarion HX-D1 is a better looking unit compare the Clarion DRX-9255. The chassis is all made from thick copper. Then the face plate design looks modern and the color match to the copper body. Again for the sound performance wise, it using the latest Burr Brown R2R 24 bit DAC, PCM1704 HDCD compatible.

When this post is published, this unit is probably already sold to one of my friend.

His beloved CD player somehow having a reading disc problem and need to get service. It will takes some time for the player return to him. So, rather he neglected all CD's he have right now, he prefer to bought this Clarion HX-D1 for temporary replacement. 

My friend is a demanding customer. This is what he want from this unit.

First, the unit should look as simple as possible, especially no pig tail cables on the back of the unit like common car audio head unit does.

Then I also explained this Clarion HX-D1 is intended for car audio and for home audio application, then it is require a external power supply unit.

He doesn't need the radio and don't want hear any radio buzz sound coming from this unit when the CD is not insert.

The last request is the line level output should be fixed. He is using pre-amplifier and he want all control from his pre-amplifier instead.

So with those requirement, let's begin this Clarion HX-D1 modification stories.

I haven't clean this unit since I got it few months ago. The overall condition is also not perfect. Lots of scratch and cracked especially at the front face plate. Cleaning and polishing this unit will sure help to make this unit looks better.

I start it by opening the top copper cover then continue by prying the lower cover.

Then start to remove the aluminum volume knob, fader knob, and tone knob. Then I continue by opening the front face by pull the sides tab.

I continue by opening the front face and clean it first. I carefully remove the display board and buttons, then clean them all one by one with soft rag.

As I mentioned earlier, when it is all cleaned, it looks fresh now.

I also clean the copper plate as much as I can.

Then I continue to analysis the components inside this unit.

Many said this Clarion  HX-D1 is the same unit as DRX-9255 EXL and the only slightly different are for the DAC and DSP receiver IC. But what I found is more than that. The PCB quality is improved on the Clarion HX-D1 compare to the Clarion DRX-9255.

Then for the analog components section is also have some minor different especially for the type of components and the PCB layout.

The digital receiver CS8412 has a resistor on the negative input side before going to the ground. That statement is actually tolerable since by looking them side by side, they are looks the same. There is also no service manual available for HX-D1 that makes this unit quite hard to mod.

The very similar on both circuit is only at the radio tuner and the voltage regulator. This photo bellow is the HX-D1 compares to the DRX-9255 EXL next to it. They are having the same schematic but different layout.

I start to highlighting the analog stage after the DAC. This section is laying on the main board after the DAC IC's. This stage is consist of I/V and LPF stages before the selector relay. The photo bellow is taken from Clarion DRX-9255 EXL service manual which shared same function as the HX-D1.

On the photo bellow is the I/V and LPF stage inside HX-D1. The I/V using dual op-amp OPA2134 and the LPF using 5532D. This approach in my opinion quite right for cost cutting since for LPF stages, you don't need high performance op-amps.

HX-D1 I/V & LPF stages

Next photo is the analog stages on DRX-9255 EXL. Same function like photo above but it has different layout compares to the HX-D1. There is 2 op-amps OPA2604 as per data sheet. This high performance op-amps are handle the I/V stages and the LPF stages each per channel. This approach is better for sound quality since both channel analog stages are using high performance op-amps, but also more costly compares to HX-D1.

DRX-9255 EXL I/V & LPF stages

If you notice, in my DRX-9255 EXL, actually those photo above is not OPA2604, I have replaced them with LM4562 which in my opinion has better sound performance especially for wider sound stage.

DRX-9255 EXL Op-amps

After the I/V & LPF stages, there is a relay for input selector then going to the second board which control the volume and balance. This schematic diagram bellow are also taken from DRX-9255 EXL data sheet. It can be a reference although the implementation for HX-D1 is slightly different.

The difference on the HX-D1, the signal are pass through balance potentiometer and then goes to volume potentiometer. So there are 2 stages of potentiometer, then the signal go to the pre-amp / gain op-amps. Because all op-amps in this unit are all in dual op-amps package, so it only need 1 op-amp for both channel.

HX-D1 second board

Unlike in DRX-9255 EXL, the volume and balance implementation is like this: first the signal pass though the volume potentiometer then goes to the first stage pre-amp / gain op-amp. After that, the signal go to the balance potentiometer, then pass to second stage pre-amp / gain op-amps. So there is total 2 stage of pre-amps section for each channel that have function to back up the signal again after pass through those potentiometer. And it easily reflect to the number of op-amps in the second board of DRX-9255 EXL are 1 pieces more than in HX-D1.

Then, I will highlights the op-amps on the tone control stages. It is on the third board attach to the second board. The HX-D1 shared the same schematic as DRX-9255 EXL and they are also using the same op-amps, they are UPC4570. A low cost general purpose audio op-amps. Nothing fancy here so I continue to the last section.

HX-D1 Tone Control

The last section on the analog stages is the buffer stages. It split the channel into 4 channel, front and rear by using op-amps. Surprisingly on HX-D1, I cannot read the label on the op-amps. They are intended to be unknown. But I am not expecting any fancy op-amps here.

HX-D1 buffer stages

On the photo bellow, the buffer stage on DRX-9255 EXL using OP275 as a high performance op-amps. This op-amps also produce by reputable audio company: Analog Device. This is clearly why the DRX-9255 EXL has so much different in audio performance compares to the HX-D1.

DRX-9255 EXL Buffer stages

Those details can only seen by tracing the PCB and drawing the schematic on paper. Then I compares them one-by-one. The op-amps selection and analog layout that makes both unit sound completely different. As I mentioned before, I like the sound of DRX9255 EXL more over the HX-D1. It is liquid smooth and very engaging. And after this examination, clearly this is how the good sound come from.

I almost forgot that HX-D1 using red shiny capacitor for all signal audio. I also find those capacitor near the op-amps for the power supply ripple rejection. They are Elna capacitor probably the Cerafine type. Additional information about this Elna Cerafine is a high grade capacitor and well known for an audio capacitor. But in contrast, the OEM capacitor for DRX-9255 EXL are only general purpose Elna capacitor for both signal and power supply section. But mine is upgraded to Elna Silmic and the result are remarkable.

Continue to the next post about upgrading components in HX-D1 here.

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