larrysb

This is what's inside the "smooth cast" Bose amp used in 997.2 and other models of Porsche with PCM 3.0.

Some highlights:

There are 5x Class-D power amp chips, which provide up to 10 channels of speaker level outputs.
The MOST section is a Tyco-style MOST-25 optical block and Oasis systems (now owned by SMSC/Microchip) NIC chip.
The amplifier controller is an ST-Microelectronics type, 32-bit which provides control functions and network stack software services for the MOST25 network.
DSP functions are provided by an Analog Devices SHARC, which feeds two Cirrus Logic DAC's which directly feed the ST Micro class D amps in differential mode.
The class D amps are supplied with +/- 20 power by the voltage booster.

I haven't traced out whether any of the class-D are running bridged.

DSP is providing crossover functions. Sub-woofer has its own power amp and gets line-level sub-woofer via the DSP/DAC section and power through the power/speaker block connector.

DSP appears to be providing HPF/LPF crossover services for rear, front mid + dash tweeters, door mid-woofers. The front tweeters have a simple high-pass capacitor from the door mids.

A couple of curious functions - I think the "surround" effect is done in the DSP as well as whatever EQ curve is standard vs. "linear". The most interesting DSP function is the road noise function, which unlike most cars isn't based on speedometer data, but is actually fed by a sampling microphone in the car.

Just incase you were wondering what's in there and what it does.

Bruce In Philly

Very interesting ..... a five channel amp the size of a pack of cigarettes... and about as good for you too.

I was unaware of any road noise cancellation system in our units (only speed volume)..... Hmm.... I gotta go back and read the manual.... just don;t remember any switches for that one.

So here is the challenge.... the head unit is sending, at times, a DVDA 5.1 signal. So how does a MOST/HUR device intercept the signal and peel out and L/R signal? Given what you or others have posted, these are brand new devices and I never heard of anyone using them. I would love to now how it works and what the results are in sound quality.

So..... maybe you can solder some leads to those bridge connectors and get the L/R outputs there... after the processing.... hmmm.......

Peace
Bruce in Philly

gasongasoff

I believe that the DSP also incorporates a NHNL filter.

larrysb

LMAO!!! No Highs, No Lows, must be Bose!

I was frequency sweeping the system and it has lows, but the highs really suck for sure. Had to make sure the tweeters were still working, or perhaps functioning would be a be a better description. It does have lows, with a real big bump at 50hz and audible response down to 40hz.

Well, that's an interesting question. The MOST25 link can handle as many as 15 channels of CD quality audio. It isn't possible to tell from the hardware what it might be doing, as the MOST25 components are just network interfaces. The protocol is all software driven on top of the physical and transport layers. That's done in the ST Micro CPU on this board. In addition to audio data, the fiber link can transfer data and control packets.

I don't know if the Bose system as implemented is actually transferring encoded 5.1 audio across the fiber link, or if it is doing something else, like just transporting stereo + center, 4 channel + center, etc. Decoding most 5.1 audio formats like Dolby or DTS requires a license and usually, requires badging with the symbols as well. Digital transport usually requires some kind of content protections, but maybe not.

The aftermarket MOST links are also simple devices. I bought one to pull apart and play with. It too, consists of a stereo A/D chip, a small ST Micro CPU and an Oasis OS8401 chip and optical link. Since they are stereo devices, it would appear they are simply injecting 2-channel audio onto the optical bus. I haven't received the MOST optical link that I need to do some more experimenting yet. But my guess is that the aftermarket MOST boxes are functioning like an "aux in" stereo device. They depend on the DSP in the Bose amp to add the rear channels and to feed the subwoofer summed-and-filtered LFE channel signal. There was a reference design for the "aux in" type device by the chip maker and it appears to me that the little aftermarket boxes are based pretty much on the reference design - perhaps entirely.

Since the aftermarket optical interfaces just have stereo inputs, they cannot "fade" with the head unit controls, there's simply no input for it on the converter. Most likely, the Bose amp holds whatever fader setting was last set by the original head unit to get the rears to work.

The "audio pilot" function is the noise-sensitive sound feature on the Porsche Bose system. There is a second microphone in the steering column adjacent to the hands-free phone microphone. There's an input on the Bose amp for this mic. Supposedly, this adjusts volume and EQ for ambient driving noise conditions. In my car, I don't think it does a damn thing. It either it isn't implemented well, or perhaps, is not working for some reason. Most cars just use speed data for similar functions.

Class-D digital amps like this are pretty common. I would estimate this system as being capable of something around 25 watts per channel. A modern version of these 5 amplifier chips would be the ST Microelectronics TDA7492, although the pin outs seem to be flipped. I can't read the numbers on these.

The people at Bose know what they are doing - but they are doing what they are contracted to do by the vehicle manufacturer. Other than the little bitty Bose badges on the doors, Porsche's designers rule what happens with the grilles and final placement of speakers. I've had cars with factory Bose systems that sounded pretty good. This one sounds particularly poor. The Mercedes SL400 I just turned in had an excellent Harman Kardon system in it. Mercedes integrated the subwoofer compartment into the firewall and passenger footwell and the speaker placement was quite good.

At this point, I'd venture that most of the sonic shortcomings are due to the physical placement of speakers and the construction of grills which create a lot of mechanical comb filtering effects.

kellyG

. Hi question, I was hoping to intercept the balanced inputs to the chipamplifiers in my Audi, which is supposedly full range stereo, flat. and thenfeed the balanced lupus into DSP prior to returning to chip amps. That way I could utilize six or eight channels of amplification, not set codes for amp while powering mids an tweets, and just add a couple larger amps for mid bass and of course something in the trunk. any ideas if this is a good idea or not it seems fine to me, but I’ve never tried.