Starlink Head Unit Removal- Schematics

[stavi]

So this maybe a stupid question but has any one tried "splicing" into the two front speaker pair wires (that also carry volume control apparently), into a line out converter while still leaving those connected to the amp? My thought is the amp might talk back to the unit through the volume control, so if you "splice" into that wire you might still be able to send the signal to a line out converter before it gets all jacked up in the DSP.

 

Reason I'm saying this is becuase I just had a line out converter tapping the signals coming out of the HK amp, and its sounds terrible. I'm better off connecting my iPhone into an aux in RCA out cord and pluging it directly into the speaker.

[chithead]

Which wires did you tap? I've done some extensive testing with the outputs of the HK amp, and you would be surprised about the signals coming out of each speaker location.

 

So far, from what I can tell, these are the approximate frequency ranges each speakers are playing with the HK setup:

 

Center speaker - 615Hz up to about 7000Hz

Left/Right Dash speaker - 615Hz and up, tweeter is crossed over around 7000Hz with a simple capacitor

Front Door/Rear Shelf speakers - play up to about 400Hz

 

Notice the gap there, between 400Hz and 615Hz? That's because the rear speakers play those frequencies. They cover from about 80Hz all the way up. The, "bulk" of your sound comes from the rears. If you are looking to simply add a subwoofer, then tapping the front door or rear shelf speaker is the way to go. If you're wanting to swap out speakers, then a signal summing device is almost a necessity, or you can go the processor route as I am doing. You will have to grab the signal from either the rears and dash and have a signal summing device combine them, or just tap the rears to get a wider signal range.

[stavi]

I originally tap'd the ones leaving the amp and fed them into a memphis line level driver, however I'm sure the guys who did it left some of the wires out as they weren't sure http://www.memphiscaraudio.com/products/signal-processors/16ll6a/

 

What I did find though was plugin my iPhone directly into my aftermarket amp via a 3.5mm to RCA, gave me WAYYYY better sounds. Tone is fuller, seperation is better, sound is alive. Currently I have this [ame=http://www.amazon.com/SABRENT-Receiver-Portable-Speakers-WF-RADU/dp/B00L26YDA4]Amazon.com: SABRENT Wi-Fi Audio Receiver for Home Stereo, Portable Speakers (WF-RADU): Electronics[/ame] connected to 3.5 and use it as an airplay reciever, which is far superior to bluetooth. Theres another product like "air enabler" may be a bit more solid. Only problem with these is it takes around ~30 seconds to boot up if the USB power adaptor is connected to the car, but plug it into one of these recharable batteries and is should run for days. [ame=http://www.amazon.com/Jackery-Portable-Battery-Charger-External/dp/B00EA1P8OI/ref=pd_cp_107_1?ie=UTF8&refRID=1C2RJ14527XAXNNX77RZ]Amazon.com: Jackery Giant+ Dual USB Portable Battery Charger & External Battery Pack for iPhone, iPad, Galaxy, and Android Smart Devices - 12,000 mAh (Black): Cell Phones & Accessories[/ame] . depending on how much you drive, connect the battery to the USB of your car and it might always keep it charged.

The only thing that sucks though is I can only control my volume through the phones up down vol button or manually increasing gain on the amp.

 

Also Chithead, here is my question for you/Tornik.

 

Tornik said he was dissapointed with the way the HK amp processed sound a page or two back, saying it essentially degrads the way the sound is put back together. If thats the case when you send the signal from the HK amp to your JBL MS-8, I couldn't immagine it could then repair that signal and send it out, it will just process it even more, right?

 

So, I'm wondering if you would be better off trying to replace the HK Fujitsu 10 head unit, with the normal Fujitsu 10 unit then sending that signal to your JBL MS-8? I know replacing the head unit all together with something like a http://www.pioneerelectronics.com/PUSA/Car/DVD-Receivers/AVH-4100NEX would give you the best sound but I really do like the factory head unit.

,

Which wires did you tap? I've done some extensive testing with the outputs of the HK amp, and you would be surprised about the signals coming out of each speaker location.

 

So far, from what I can tell, these are the approximate frequency ranges each speakers are playing with the HK setup:

 

Center speaker - 615Hz up to about 7000Hz

Left/Right Dash speaker - 615Hz and up, tweeter is crossed over around 7000Hz with a simple capacitor

Front Door/Rear Shelf speakers - play up to about 400Hz

 

Notice the gap there, between 400Hz and 615Hz? That's because the rear speakers play those frequencies. They cover from about 80Hz all the way up. The, "bulk" of your sound comes from the rears. If you are looking to simply add a subwoofer, then tapping the front door or rear shelf speaker is the way to go. If you're wanting to swap out speakers, then a signal summing device is almost a necessity, or you can go the processor route as I am doing. You will have to grab the signal from either the rears and dash and have a signal summing device combine them, or just tap the rears to get a wider signal range.

[chithead]

I actually decided to go away from the MS-8, because the factory HK setup stages and images better than 95% of the competition audio cars I've ever heard. The biggest problem for me, is the speakers and lacking amplification. They still need some upgrading. But to pop in a stand up bass, and hear it up above the glove box, and not down near the floor as in most cars, that's something special. Going with a Rockford Fosgate 360.3 now just because of the monster EQ capability, higher output voltage to the amplifiers, the remote knob that comes with it, and it can retain that amazing stage that HK engineers obviously worked very hard to accomplish.

 

The AVH-4100NEX really is a very nice head unit, but the aftermarket dash kits are what kill the deal for me. Plus I just don't see getting the sound image that the factory setup already has by swapping to any other head units. Just needs a little bit more improvement is all.

[stavi]

Okay I think I get what your saying a little bit better now, but I can't say I agree with the imagining they did is good. I can only imagine your gonna run active then? I honestly think one of the biggest issues with the sound quality is simply the speaker location of the dash speakers, I totally disconnect the center when I was running the stock HK, and found it was a little improvement, but I think having the mids/tweeters firing into the window shield causes an almost harsher sound. Even with my JL audio C5 tweeters sitting in that dash location firing strait up seem to be a bit over powering in the same way the stock ones were.

[chithead]

Yes, totally. Windshield reflections are a common topic of debate in the audio community, but the best advice I ever read, don't fight them. You'll always have to overcome them in one way or another, so might as well just get it over with. Moving the speakers around can change the sound a bit. Also the angling can change things too. A friend of mine with a BRZ has his 4" mids in the dash, angled towards the rear view mirror. Sounds crazy, but it is easily one of the top five cars I've ever listened to, and that includes all the 2015 MECA and IASCA winners. Will be experimenting with that myself once a midrange selection is chosen.

 

I too tried disconnecting the center channel as it is not a common thing to have in any competition cars, but Harman has snuck a lot of audio information into that speaker, even if it has reduced volume compared to the left/right speakers, and doesn't play a full range. There was a wide gap in the stage for me. Fading all the way forward is how I discovered the midrange being played by the rear speakers. If you can picture a boat hull, that's how the image appeared when fading from center, to all the way forward. The stage raised higher, but also was much narrower. My plan is to remove the rear speakers, and use that signal for the left/right dash 4" midranges. Then use the left/right dash speaker signals for a pair of tweeters, all running active just as you suggested. Will be swapping out the front door speakers for 8" drivers, and using a pair of 3" dome midranges in the center channel location.

[stavi]

Just watched this video on using a DD-1 to find at what level distortion starts to become an issue

.

 

Has any one used one of these and found what volume the harmon kardon units output begin to distort at?

 

Also chithead are you going to be redoing the doors yourself to to get the 8in drivers in?

 

Just read a pretty good article on the center channel stuff as well. Here is the link, http://www.diymobileaudio.com/forum/technical-advanced-car-audio-discussion/85018-ms-8-center-channel-speaker.html but this was the take away in my opinion..

 

"The benefit of the "wideband" 2" tweeter is that it can be crossed low enough to match the woofer at a frequency where the woofer's dispersion is wide (low directivity). However, dispersion fro the 2" is bound by the same law as all other speakers (no matter the cone material or the marketing spin), so the same thing I've illustrated here with the 8" holds for the 2", but at much higher frequencies. There isn't a lot going on at 15k, so it probably doesn't matter.

 

The simplest and best sounding system is a 3-way (with a 3" mid) mounted in the door and a center channel pointed at the windshield"

[chithead]

DD-1 is a pretty neat device. I haven't tried one due to my personal opinion of the person that it is associated with, but still a cool tool to use.

 

Eight inch woofers shouldn't be too much of a hassle, hoping a simple baffle/adapter will mount them relatively easily.

 

Here is a little diagram of the plans:

 

http://www.caraudiojunkies.com/attachment.php?attachmentid=4626&d=1452650458

[stavi]

Ahh, didn't even know 6x9" to 8" adaptors existed. Are you planing on cutting out the door paneling to make an 8" hole, then refinish it with mesh or maybe Frogzskin? To fit my 4" and 6.5" speakers into the 6x9" cut away, the 6.5" is some what recessed behind the non-perforated plastic. I've found once I get enough bass coming out of them I get a reasonable amount of door rattling, especially with certain songs/frequencies.

[Saltdet]

Which wires did you tap? I've done some extensive testing with the outputs of the HK amp, and you would be surprised about the signals coming out of each speaker location.

 

So far, from what I can tell, these are the approximate frequency ranges each speakers are playing with the HK setup:

 

Center speaker - 615Hz up to about 7000Hz

Left/Right Dash speaker - 615Hz and up, tweeter is crossed over around 7000Hz with a simple capacitor

Front Door/Rear Shelf speakers - play up to about 400Hz

 

Notice the gap there, between 400Hz and 615Hz? That's because the rear speakers play those frequencies. They cover from about 80Hz all the way up. The, "bulk" of your sound comes from the rears. If you are looking to simply add a subwoofer, then tapping the front door or rear shelf speaker is the way to go. If you're wanting to swap out speakers, then a signal summing device is almost a necessity, or you can go the processor route as I am doing. You will have to grab the signal from either the rears and dash and have a signal summing device combine them, or just tap the rears to get a wider signal range.

 

My rear door speakers are the worst sounding speakers in the car. Plus very low volume?

[SVXdc]

...

I'm 99% sure this is it:

Metra 71-1761

...

(I used that and a Metra 70-1761 to create an extension that I will splice into for my speaker level inputs to my amp. Unfortunately the 70-1761 is missing a wire so I had to order two and steal a wire to make one complete...)

 

Thanks a lot mate! This combination of male and female connector for extension is exactly what I was looking for.

 

The plastic plugs on the Metra 71-1761 also require a slight modification to fit into the sockets on the back of the OEM HU. The HUs have "keys" that are taller than (reach deeper into) the corresponding slots on the Metra's plugs. You'll need to saw or otherwise nibble out a "dam" at the front of those slots in Metra's plugs.

 

The equivalent reverse harnesses from Scosche and American International don't have those dams. I'm guessing that eventually Metra will exhaust their older plugs and start using the same ones as those other companies.

 

However, all of them omit a wire on the 6-pin portion, and many of them omit the 2nd dimmer lead on the 6-pin. While most have wires in every slot on the 10-pin, one is a short loop that is pinned back into another pin. If you sever the loop so it's a separate wire, it is much shorter than the rest.

 

You might find this one better.

[Lithoss]

The plastic plugs on the Metra 71-1761 also require a slight modification to fit into the sockets on the back of the OEM HU. The HUs have "keys" that are taller than (reach deeper into) the corresponding slots on the Metra's plugs. You'll need to saw or otherwise nibble out a "dam" at the front of those slots in Metra's plugs.

 

The equivalent reverse harnesses from Scosche and American International don't have those dams. I'm guessing that eventually Metra will exhaust their older plugs and start using the same ones as those other companies.

 

However, all of them omit a wire on the 6-pin portion, and many of them omit the 2nd dimmer lead on the 6-pin. While most have wires in every slot on the 10-pin, one is a short loop that is pinned back into another pin. If you sever the loop so it's a separate wire, it is much shorter than the rest.

 

You might find this one better.

I didn't have the keying issue.

 

Metra just doesn't seem to have good consistency. I ordered two of the 70-1761. They both had the exact same part number and packaging, but one had the orange wire and one didn't. wtf

[SVXdc]

I didn't have the keying issue.

 

Metra just doesn't seem to have good consistency. I ordered two of the 70-1761. They both had the exact same part number and packaging, but one had the orange wire and one didn't. wtf

 

Often Metra will switch the factory they contract to make one of their harnesses. Since they have so many warehouses, they'll continue shipping both older and newer runs of a harness (sometimes even in the same shipment) before they finally exhaust the older ones.

 

Also, in some cases they'll start out making harnesses with more slots pinned, but then a newer factory will make a cheaper version that omits things like a 2nd illumination/dimmer lead, or loops the amp trigger pin back onto the power antenna pin.

 

The initial 71-1761 harnesses provided the latter as separate, full-length, blue and blue/white wires. But now, everyone's seem to have the loop. That's wrong! If a HU actually has separate outputs on those pins (which some Subaru models do), tying two outputs together is bad.

 

Of course, occasionally you might get one that's simply defective (where the pennies-per-hour worker failed to include a wire). Complain to the vendor and they'll likely just mail you a replacement (without asking for you to send the bad one back).

 

The picture of the 71-1761 currently on Metra's site shows the older-style plastic shells with the dams:

 

You got one with the newer shell (as Scosche's have had from the start)...

 

BTW, you can't trust the pictures you see on vendors' sites (including Sonic Electronix, Crutchfield, eBay, Amazon, etc.). Each vendor typically takes a picture of the harness as it existed when they first began selling that item, and usually won't bother to update the picture (unless they become aware of a major change). Bottom line: You won't know how many wires you'll get unless you can see the actual harness they'll be giving you.

[SVXdc]

... has any one tried "splicing" into the two front speaker pair wires (that also carry volume control apparently), into a line out converter while still leaving those connected to the amp? My thought is the amp might talk back to the unit through the volume control, so if you "splice" into that wire you might still be able to send the signal to a line out converter before it gets all jacked up in the DSP.

 

Reason I'm saying this is because I just had a line out converter tapping the signals coming out of the HK amp, and its sounds terrible.

 

The h/k amp doesn't work that way -- the HU's front speaker outputs don't convey volume control information, and the amp doesn't "talk back" to the HU (at least, not in any way that you can use).

 

Look back at my post #27 (earlier in this thread) and Subaru's wiring diagrams that tornik posted. The HU sends the audio at a fixed volume (on the pins non-h/k models use for the front left & right channels), and uses other pins to send data signals to control the h/k amp.

 

Bottom line: If you remove the h/k amp, you'll need to either:

 

A) Add aftermarket amplifier(s) and some kind of processor box that provides you with external controls to adjust EQ, fader, and possibly also balance. All of those controls/settings on the HU will be useless.

 

B) Replace the HU with something different -- either a non-h/k OEM HU, or an aftermarket HU.

 

You could use my 10- & 6-pin combined "breakout" harness to help with "A", but you would still have to add those other components.

[SVXdc]

Has anyone checked whether the h/k HU still controls the left/right balance on its fixed-volume outputs? In other words, if you set the balance all the way left, does the HU's output on the right channel (10-pin socket pins 1 and 5) go completely silent?

[SVXdc]

BTW, here are pictures of the inner parts of HK amp (can make more if someone needs). I was trying to reverse engineer it's schematics, and am very disappointed with usage of diode bridges on each stereo channel being amplified (see U1620RG and U1620RG in the center). Apart of the fact that they don't amplify with "High Currents" the analog sound, - they amplify digital signal, which is TDM formatted (see ADC converter on the left - CirrusLogic 5364-DQZ) !!

 

All of the large components in the center of the board (including those large diode bridges you pointed out, as well as the transformers and toroid coil) comprise a switching power supply circuit. Nothing more.

 

The box is not "amplifying digital signals".

 

The box does take as its input the analog left/right audio pair from the HU and feeds those into an ADC to convert to digital signals.

 

It then sends that into a DSP, where all of harman/kardon's "magic" happens -- deriving 8 separate channels to feed to the various speakers and subwoofer, adjusting the EQs, and perhaps even doing some time alignment.

 

Finally, the outputs from the DSP are converted back to analog signals and fed to the amplifier ICs -- those two 22-pin Cirrus chips at the far right edge of your first picture (which had heat sinks pressed onto them with thermal grease before you disassembled the box). Those control the relative volumes (including front/rear fade).

 

Briefly looking over the specs of the CS5364 ADC, it looks like the box may operate the amps as class H, which is likely part of the reason for the large switching power supply.

 

Similar to the h/k amps in previous-year Subaru models, you'll find that the outputs of those amp ICs are wired straight to the output pins on the 30-pin connector, which then connects to all of the car's speakers. Each output pin has a tiny capacitor to ground, to filter high-frequency noise from coming in or going out.

 

If you can take and post some higher-resolution pictures of the PC board, we can investigate some of the other IC part numbers to look up their specifications.

[stavi]

I think I figured out Tornik's question, and why there are only two audio in lines feeding into the amp..

 

HK Subaru claims their amps put out "576 equivalent watts", this term "equivalent watts" I could only assume is a marketing ploy they use with the Green Edge Amplifier.

 

This article say the green edge technology uses:

http://www.technologytell.com/in-car-tech/7577/harman-kardon-greenedge-in-the-2015-subaru-legacy/

 

"Class-H amplification technology adopted to monitor input signals & predict output voltages to significantly reduce power losses (compared to Class-AB amplification)"

 

So by the amp actually controlling the voltage of the signal coming in it is able to substantially reduce the amount of energy used, so that they can get the same "loudness" as a typical 576 watts, hence they say "576 equivalent watts"...

 

If you scroll down to the bottom of the this link you will see what I am talking about.

http://www.harmankardon.com/content?ContentID=automotive-technologies

or

http://www.automotive.harmankardon.com/en/innovations/greenedge.aspx

 

Now, maybe Tornik or SVXdc could confirm this but, but this is the conclusion I came up with. While, they are running the sound through a DSP and I'm sure the R&D cost quite a bit to rig the system up initially, the overall manufacturing cost is less for HK and the car companies that employ these systems. I could be completely wrong about all this, but I would immagine the components are much cheaper to produces the amp seen (class H), than producing a class A/B which amplifies the analog sound. On top of that, by the unit demanding less energy, I would think car manufactures do not need as large batteries, thicker wiring, fuses, etc.

 

 

While I don't have info about power outputs of each channel and frequencies, I can share this:

was measuring voltages of HK outputs to speakers on medium sound levels (~16-20 points on Starlink screen) - it was floating around 150mV - 350mV

Was not sure how this could drive up to 50 watt per channel when listening on bigger volumes.

 

BTW, here are pictures of the inner parts of HK amp (can make more if someone needs). I was trying to reverse engineer it's schematics, and am very disappointed with usage of diode bridges on each stereo channel being amplified (see U1620RG and U1620RG in the center). Apart of the fact that they don't amplify with "High Currents" the analog sound, - they amplify digital signal, which is TDM formatted (see ADC converter on the left - CirrusLogic 5364-DQZ) !!

TDM means Time Division Multiplexing - that analog wave from each channel is cut into little pieces aka "packets" and they are put in sequence into one line\wire. And on another side of the line they catch these sequences of packets and glue them back into several analog lines (see two CirrusLogic DAC chips 4234-ENZ on the right ).

Amplifying TDM signal means you hit transient processes - edges of the packets are "smudged" and after gluing back into one analog signal you don't get smooth wave. That adds "digital noize" that was irritating me a lot in the factory sound system, and irritating in most modern DSPs.

[Saltdet]

Hey Stavi. Bottom line is we as 3.6 Limited owners were sold an inferior system and overpaid for it. Take a look at the new Infiniti Kappa K5 amp and see if it would work for us.

 

Hk mentioned it to me yesterday.

[tornik]

So Tornic do you think we got what we paid for? Based on your testing looks

Like we overpaid. I found similar results.

Saltdet, I guess we overpaid. I spent at least 2k more for that car trim to get HK, while my aftermarket amp Audison5.1 was $400 + aome installation spendings.

[Saltdet]

Saltdet, I guess we overpaid. I spent at least 2k more for that car trim to get HK, while my aftermarket amp Audison5.1 was $400 + aome installation spendings.

 

How does one he Audison sound? What else did you do?

[AirBorne1Cav]

Anyone know what the port on the bottom right is for? (Image pictured is for the 7" NAV)

 

 

Edit - Found what it's for (GPS Antenna) I'm going to try and switch out the 7" Radio for the 7" nav next week, bought a used Nav on Ebay and just ordered the GPS Antenna from the dealer. Looks like everything else should be plug and play (fingers crossed)

 

https://farm2.staticflickr.com/1536/24207974889_d2246de4dc_c.jpg' alt='24207974889_d2246de4dc_c.jpg'>s-l1600 by AustinB747, on Flickr[/img]

[tornik]

biggest issues with the sound quality is simply the speaker location of the dash speakers, I totally disconnect the center when I was running the stock HK, and found it was a little improvement, but I think having the mids/tweeters firing into the window shield causes an almost harsher sound. Even with my JL audio C5 tweeters sitting in that dash location firing strait up seem to be a bit over powering in the same way the stock ones were.

 

I in opposite liked the way center speaker sounded, it was reproducing "thicker" the frequencies of "guitar body" that I want to hear.

And when i tried to suppress harsh sound of the corner tweeters by just adding resistors in sequence, then when it did not help much - just put center speaker on one of the corners, and now i'm searching for another center speaker on salvage car yard websites to put it in another corner tweeter place. Salvage just because I don't want to pay $110 for the brand new on official subaru parts website.

What concerns speakers - harsh sound is due to resonance happening between tweeter and part of the glass, where windshield reflects sound back towards the speaker. I don't want to fix it because I already spend lots of time fixing resonance on frequencies of 224 hz between back door speakers and 59hz from the rear speaker (sort of subwoofer, but it's actually same speaker as in front doors). Because my aftermarket amp is purely analog, no DSP, I got suspicion that stock HK amp and another DSPs that people are installing already have built in suppression of the resonance frequencies with digital algorithms. As I don't want any digital - i had to build my own narrow band passive filters to do so.

[tornik]

How does one he Audison sound? What else did you do?

 

Sounds pretty well! I like the smoothness of purely analog amp, no digital distortion\fractureness. BUT! It's only when I listen input from non-digital source (i soldered in separate input directly to the amp, bypassing aux input of stock head unit). Currently it's temporarily old cassete player, which is bad, because CD gives much clearer sound comparing to cassette. So when I listen to CD player of HU, or Sirius xm - I love channel 69th Escape, - Is'm hearing that built in amp in HU also gives digital distorion. I don't know how to fix it now yet.

Answering to some questions about volume controlling that were risen up the thread - I did not find the way to control sound right at the amplifier, because stock HU sends control signals VOL+ and VOL- via 2 wires going to stock HK amp. Unfortunately it does not change volume of audio signal coming out of stock HU. So I had to temporarily install Clarion EQS755 - the preamp+equalizer. This guy also gives digital fractureness to the sound, and i have to be patient on it until I figure out what to do with HU. I don't lose hope, because when I listened to HU of one of my friend's 10y.o. BMW - it sounded quite "analog style", though it does not have satellite radio .

Also had to do some hand-made passive narrow band filters to suppress 214Hz and 59Hz because of resonance bw back doors, and from back "subwoofer". In order to cope with only 224 hz and not cope with other modes of standing wave between back doors I had to also twist for 3-4 degrees (space did not allow more) direction of the back door speakers, so that they don't face towards each other now, - they face a little bit up and forward. Here I regretted that I don't have DSP, because i spent lots of time on it and suspicion grew strong that DSPs automatically suppress the resonance frequencies (figures are pretty much the same in the cars with similar dimensions).

Also doubled capacitance of the capacitors that protect tweeters built in in back door speakers + added 4 ohms non-inductive resistors. Thus the tweeters still are protected while peak of frequency response shifted from 2KHz closer to 1KHz, and made peak wider, so the sound a little bit "sweeter\warmer".

Also found some double-layered 1" thick foam&fiber, and glued it to most of the metal door surface from inside of the doors. This helped to decrease 2.6Khz resonance in the door for ~20% based on measurements i did. Disassembling of the doors originally seemed too scary, but appeared to be very simple in the end. So that after all I also cut 2 big cones out of foam, made them having vertical cuts from center to edges, and glued them behind the back speakers inside of the doors. Was lazy after that to re-measure 2.6kKhz resonance degradation.

That's all i did, Saltdet

To sum-up - HU is not good too. DSP owners are happy because installation is simpler.

[tornik]

All of the large components in the center of the board (including those large diode bridges you pointed out, as well as the transformers and toroid coil) comprise a switching power supply circuit. Nothing more.

 

The box is not "amplifying digital signals".

I'm prone to trust you here. At the moment I was tracing the circuits on the board - I discovered that left and righ channel digital outputs from CS5364-DOZ (which is ADC converter) on the left are connected via simple filter with 2.2Ohms resistor + pair of 9uf capacitors to the mosfet transistors source pin in the middle of the board. then I discovered that drain is connected to input of one of the coils. And the last big coil on the right was giving it's output that was split to 4 channels right on the board, no magic digital chip here, that were fed through series of medium complexity filters to inputs of 2 DAC chips on the right. As I'm not an expert in microelectronics and can't read boards easliy - I had to manually trace circuits with multimeter.

But again I may have mistaken with my conclusions, and I lost interest to stock HK amp for now. Now I'm curious what to do with my stock head unit.

[tornik]

I think I figured out Tornik's question, and why there are only two audio in lines feeding into the amp....

 

So by the amp actually controlling the voltage of the signal coming in it is able to substantially reduce the amount of energy used, so that they can get the same "loudness" as a typical 576 watts, hence they say "576 equivalent watts"...

....

 

Now, maybe Tornik or SVXdc could confirm this but, but this is the conclusion I came up with. While, they are running the sound through a DSP and I'm ....

thicker wiring, fuses, etc.

 

I guess you're right that it's the way to save power. Stock HK amp with DSP had ~500 watts announced, and aftermarket analog Audison amp also has similar power. But power cable is much thicker.