SX4 OEM HU: By pass surgery for Amp section

[omishra]

Having SX4 for myself giving lots of driving pleasure. The missing thing was good quality of ICE. Always listening to OEM ICE and giving consolation to myself this is only thing you can get in lieu of steering volume control and in dash look.

But for a keen listener, I could not suppress my desire to get rid of this crap sounding piece. Wait! still can I look inside why it is so crap?
Because -
1. You have AM/FM tuner which is same in all HU.
2. You have CD drive same everywhere.
3. DAC and volume controls are one and the same.
4. The difference starts from pre-Amp stage where you start this delicate piece of information called audio signal.

SIGH!

Look at inside and probably replace the AMP section (+ speakers later).

AMP Requirement -
1. 4 channels
2. Don't want to loose any interface including steering volume control.
3. Sound with SQ and somewhat moderate SPL.
4 Can fit inside current HU (if possible).

Started looking at AMP sections and found this -> AMP9-BASIC

• Four channels of Tripath sound quality, based on Tripath TAA4100A
• Output 4x50W at low distortion, 4x100W peak
• Suitable for low impedance loads, 4 x 2 ohms 12V typical
• Up to 27V supplies make them suitable for 12 or 24V systems.
• Outputs can be paralelled for even higher outputs into very low impedance loads
• Mostly hole mounted components. Relatively low component count.

http://www.41hz.com/main.aspx?pageID=130

Before opening SX4 HU I started building AMP9-BASIC.

Still problem is there- its switching AMP kind of PWM based. Means it will trouble the AM/TM tuner's reception of HU. Means I need to run it class A/B mode while playing radio section.

Building control section for AMP - Mute + Analog/PWM mode changes.

[omishra]

Now amplifier kit on the table.




More about this guy later

[greenhorn]

building any non linear device ( smps, class D/T amps etc) are not a trivial job, there are a lot of, er , electronics black art involved.The output of your project will be digital - it will either work or not at all.since it will be hard to troubleshoot

Why not continue it at http://www.team-bhp.com/forum/ask-gu...-thread-4.html (SX4 ZXi - Integrated HU Audio Thread!!) where you were discussing this

EDIT: seems you've started already. I think instead of taking it apart, use the signal from the pre out to drive the amp you're gonna make

[omishra]

This is homemade PCB for the purpose. This will control AMP MUTE and take input from HU MUTE logic (active high). Same time when CD is started this will make AMP to PWM switched mode which will save power and have very wide sound stage.




AMP is also nearing completion.





Under testing ->

Only Amp



And with Mute and other controls



OK, back to our topic, SX4 OEM HU ->



Verifying that it works on my desk w/o flaw. means I haven't screwed anything upto this point.



Now operation will start to identify what is crap there?
Why people don't get power from this?
Why it does not sound better after putting Amp from preouts.
Will I get good sound from this?

Please wait for next episode.

[gopinathann]

excellent work omishra, so any doubt with SX4 audio think we can ask you.

[omishra]

Built quality is good for metal work. PCB quality is pathetic as it could have been better than single sided phenolic. I was expecting Epoxy king of thing . At least double sided was required.

This is rear, now let picture explain this



OEM chip removed from HU ->



TA8263BHQ_en_datasheet_060428.pdf









Now it is clear that TOSHIBA TA8263BHQ delivers 5W/channel for sane user. and with 13.2V supply you get per channel 12W Max with acceptable sound and per channel 24W with 10% THD.

So you HF LF is gone and remaining mid range is deprived by THD. Now remaining is eaten up by crap OEM speakers.

Now its clear what happened to sound quality and output power.

Wait! Story doesn't end here. THere is something called preout and Aux In.

More about it later.

[omishra]

My new AMP works either switching digital AMP (Class-T, PWM - Pulse Width Modulated) or class A/B (Analog Mode). I wanted it to change in Analog or Swtched mode by selection of CD /Radio source. So I searched logic high input for CD which will pull my AMP to digital mode. Yellow wire in next snap



Also the MUTE Function, logic high input to mute AMP which will switch off output MOSFET's of main chip. Green wire in next snap.



All wires are taken out. I avoided to take input from preout because first I tested my Amp by feeding it from preout. There are some RC passive components and transistors in line. They take out sound details from preout. If you put AMP at preout still you will find the details and sound dynamics are missing. So many people complained that HU itself sounds very poor. It is found true. That's why I avoided preout and trapped the audio singal at the source, just at the output of DAC(+Volume control). Four wires at the center of PCB, circled red. Faint blue rectangle shows OEM chip removed. Output from my new AMP is again back to OEM socket as I already mentioned "NO INTERFACE CHANGE"



Testing once again with all in one place.



Packing back. The shielded wire is input signal from DAC going to AMP. I used kitchen aluminium foil and gounded it internally. put cello tape all around it to protect any short circuit.







Baby is ready for final place.



Back to home, swet home



Playing happily.



More things to do (Suggestions please)

1. Replace aluminium shielded wire by good quality signal wire

2. Now someone please listen to this and tell me if I have to replce OEM speakers too. I think they are lacking punch.

Things I messed -
Only one, Left and right are interchanged now,

Aux-In was just passed to Vol Control, but I did neither trace it nor tested it. I will update later on this.

Final cost ->
1. AMP9-BASIC-> Rs 4087 with shipping
2. Control Ckt -> Rs 200 approx
3. Wires -> Rs 25
4. Plastic box inhouse, metal box from Scrap market (Juna Bazar) Rs 30.
5. My 4 week ends in design and execution.

That's all! Now enjoying the traffic jam so that I can listen good music @ 60W/ch. Waiting to blow OEM speakers.

[hydrashok]

Whoa! Most of it just went over my head, but I think you're doing a great DIY job. RESPECT!!!

Do let us know how the sound has improved -- since you're still running the OE speakers with just your DIY job being the change it will be easy to make out how things have improved. Once you succeed in blowing the OE speakers do update us with the improvements after the change to aftermarket speakers.

About changing the speakers, maybe you can find a friendly ICE shop and try out a couple of makes right in the car to feel the difference.

I have just one suggestion to make (you may have already done this). DO wrap the the plastic box inside the HU assy with some foam to prevent rattles. If you can pack the insides with some foam, that would be good too (if it doesn't screw-up the parts inside the box).

[greenhorn]

congrats

Thats by far the best DIY I've seen yet. *respect* from an ex electronics geek

PS: I don't think your amp can do 60WPC from a 14.4V supply. The datasheet mentions 22W @ 14.4W and 1% THD

But still a huge improvement from the stock ICE !

Time to change your speakers!

[im_srini]

Great DIY !

Kudos * insert standing ovation here * !

This has got to be the most interesting ICE post I've read (I'm not really into ICE) here

[Ajaybiz]

Mishra jee you are real electronic guru you remind me my days of 90's when i was purely into hardware and use to repair motherboards, SMPS etc.
Very nice effort and clean job executed by you.

[omishra]

Originally Posted by hydrashok

Whoa! Most of it just went over my head, but I think you're doing a great DIY job. RESPECT!!!

Thanks!

Originally Posted by hydrashok

Do let us know how the sound has improved -- since you're still running the OE speakers with just your DIY job being the change it will be easy to make out how things have improved. Once you succeed in blowing the OE speakers do update us with the improvements after the change to aftermarket speakers.

About changing the speakers, maybe you can find a friendly ICE shop and try out a couple of makes right in the car to feel the difference.

Now there are details + bass. Clarity and channel separation are distinguished. On high power I think speakers are not able to handle it properly. Anyway those were operating on 5W range. What is expected at 20W RMS?

But one thing I figured out that there is some noise floor at all time which does not increase with volume but that is constantly coming from HU. I verified this by hooking another input source and it disappears. So something more needs to be done in HU. May be that's why they set big resistor inline audio signal, so that everything gets suppressed. To get audio you have to make volume levels up (10+ level).

Originally Posted by hydrashok

I have just one suggestion to make (you may have already done this). DO wrap the the plastic box inside the HU assy with some foam to prevent rattles. If you can pack the insides with some foam, that would be good too (if it doesn't screw-up the parts inside the box).

Yes all new blocks are bolted to chassis of OEM assembly (including PCBs). That plastic box + PCB inside it are bolted to outer metal plate.

[omishra]

Originally Posted by greenhorn

congrats
PS: I don't think your amp can do 60WPC from a 14.4V supply. The datasheet mentions 22W @ 14.4W and 1% THD

Time to change your speakers!

Thanks for correction. You are right. I got overrun by enthusiasm.
It could be 22W @ 14.4W and 1% THD for 4 ohm speaker. But I can get double of that if I can hook 2 ohm load.

[ph03n!x]

Most of it was like Concordes taking off right over my head.



Looks like this is one of the best dissections over here!!

[greenhorn]

PS: another suggestion. Have your thought aboug upgrading the stuff currently in the signal path ( op amps, capacitors etc ) ?