ratt359

My understanding is that the Bose amp only takes the MOST input.

Is this correct? Surely the HU can only provide a small amount of amplification. In a non-Bose set-up, quadlock outputs will go the car amp. I would have thought an in-line amp would still be needed. If so, the using the (retrofitted) RCA outs would be preferable to using the quadlock outs.

andy2111

Well on my non Bose it's definitely sending out an amplified signal, so if its not designed to power speakers then I don't know why it's not simply a line level output?

I guess we need someone with Bose to try a few experiments to reduce the guesswork and give us something a bit more concrete to work with

jadski

I thought Z mentioned that they HU is capable of driving the rear speakers without an additional amp

obviously, I would have to disconnect the rear speakers from the Bose amp and connect the tapped wires from the quad lock directly to the rear speakers with an attenuator to control volume

ratt359

As ​​​@andy2111 suggests, it's got to be worth a go. Perhaps a safer/less disruptive test would be to a connect a spare/cheap pair of 8 ohm loudspeakers to those quadlock outputs?

boxdriver

I think we are making this harder than it is.
If you have a Bose amp that is running your system, you should be able to disconnect the rear speaker wires from it. Then connect the rear speaker wires directly to the rear outs from the HU (see jadski's schematic above). As Zed and Andy pointed out, these should be powered, so they will power the rear speakers just fine. If you do this, then there is no reason to add anything to control the volume because they are hooked up to the rear speaker outs, the fader should work to control the volume of the rears if they ae coming directly from the HU and not running thru an amp.
I believe the non-Bose systems are still utilizing and amp in their system, that is why there can be an issue with unwanted noise from tapping into powered speaker wires coming from the HU. So, this method should work for them as well.

Based on what everyone is saying about not having fade control in their systems no matter what setup they have (Bose/Fiber optic or non-Bose/wired), I believe that the PCM is sending a different signal to all speakers for their "surround sound", but the fading is actually controlled by the amp and not the HU. The HU just sends a signal to the amp on what the fade setting are, and the amp controls the volumes to each speaker. The Android HU controls the fade at the speaker outputs and doesn't send a signal to the amp. This would explain why nobody has fade control, no matter their setup. But this should also allow control of the rear speakers if they are connected directly to the HU and bypass the amp as I stated in my first couple paragraphs. At this point, this is a theory, but one that I am fairly confident in. Ratt359's suggestion about using a spare set of speakers to test this would be the easiest.

drawz

I think anyone that’s not getting rear speaker audio should figure out why before jumping to crazy work around solutions, especially without fully understanding how the system is designed to function. Trying to mix speaker level output to the rear with Bose via MOST for the front probably isn’t going to work well. Those Bose speakers are designed to be driven by a real amp, not the little chip amp built into the headunit. The wiring could be entirely different and the Bose amp may be handling the crossover duties.

Roman ACS

Your incorrect. all PCM systems are fiber systems. base, bose and burmeister. only CDR units do not use fiber.

andy2111

I don't think that is correct. I have the base audio system and there are no fibre connectors at all in my car, and you can see that from the picture of my quadlock a few posts above. My original unit is a PCM eg with navigation

Roman ACS

Is not in the harness but it is in your pcm. I modify the fiber harness for this specific reason.
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bigkraig

so, has anyone replaced a PCM4 with one of these? the PCM4 screen is OK but it looks pretty dated when coming back from the Taycan. Faster touch response would also be pretty welcomed. Considering people have coded PCM4s to replace PCM3.1s, I think it should work and may try it out.

andy2111

You need to find one that specifically mentions PCM 4 otherwise it won't work as the canbus adapter is different

If you search aliexpress for 'pcm 4 android' you will find some options. They might not be Chstek branded, but if it looks the same it'll be the same underlying unit
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https://a.aliexpress.com/_EwRN1X3

Per the installation guide we recommend the 7862 CPU with 8GB memory. Looks like they offer the UIS7870 CPU now on this unit which is newer and should install and setup in a very similar way, but you'd be the first to try it (and the author of the 7870 section of the guide!!)

Keep us updated and good luck!

ZedZed

You are correct in a pedantic sense. I think (hope) it was clear from the context of my post that I was comparing Bose with non-Bose systems. You asserted that the sound had to be superior with your add-on board solution because it used the OEM fiber (digital) signal path. I countered by saying that not everyone has fiber (ie all the non-Bose systems). Obviously if they had Burmester they would have fiber.

But the bottom line is this: an add-on solution using the OEM fiber brings zero benefits to cars that do not have fiber. That is what I (clumsily) was saying. I think most would have understood that, but I apologise is my post was not sufficiently clear.

ZedZed

Yes, he is wrong about it. My wife's Cayman has PCM 3.1 and no Bose and no fiber, just like your car. All PCM 3.1s may well have an optical output buried inside them (it is not at all uncommon for amplifiers to feature both analog and digital outputs - most TVs these days do for example). This 'hidden' optical output goes to the additional plug/orange fiber lines in Bose-equipped cars and then on to the digital input in the amp of cars so equipped.

But Roman's point is moot. In your car, and my wife's Cayman, the optical output is unused. It is connected to nothing. The orange fiber lines do not exist. So no matter what Roman's add-on board does, it will make zero difference to the SQ in your, or my wife's, car. Roman seems to be trying to claim that his solution offers superior SQ to ALL cars because he taps into the optical output. But with nowhere for that digital output to go, there can be no advantage. In Bose/Burmester setups, Roman does have the advantage of maintaining an unbroken digital signal path. Whether an additional DA conversion makes an audible difference to SQ is a much debated issue, and some people beleive it makes an audible difference, and some don't. AFAIK, there have been no blind ABX tests to objectively verify it, so it remains a subjective difference, if at all.

ZedZed

But the point remains the same. In non-Bose (or Burmester) cars, there is no optical output that is actually connected to anything. And therefore no benefit from your add-on board solution in these cars.*

I am intrigued by how your add-on board solution uses the optical/fiber connection inside the PCM. In non-Bose/Burmester cars, like my wife's Cayman and Andy's 911, the amplifier has no means of using an optical signal. So your solution would not provide any benefits in SQ for those cars*. Now, in Bose-equipped cars, you would have an advantage (if eliminating an additional analog-digital conversion really is an (audible) advantage) since the Android HU's use the MOST box conversion route and thus utilise an analog signal to a digitally-equipped amp, which is, technically at least, inferior.

* Which is what we were originally discussing prior to your intervention.
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ZedZed

We seem (or I seem, to be more accurate) to be complicating things here. If we take a more familiar example, it may clarify things. Many TVs these days feature both digital and optical outputs. Many soundbars feature digital and optical inputs, Users can choose one or the other (but not both at the same time) depending on their needs. I, for example, have an LG television and a Sonos soundbar that feature both types of connection.

Now if I choose to connect with analog (RCA) leads and have no actual fiber connection at all between the two optical connectors, then clearly I do not gain any advantage at all from my optical connections. The optical connection does not physically exist. No matter what I do inside the TV to utilise or improve its optical circuitry will make any difference whatsoever to the SQ - it cannot because I have no actual optical connection. This is the parallel with Bose (and Burmester) systems and non-Bose systems in our cars. If you are not using the optical connection (by physically not connecting it to the amplifier) then no amount of tinkering inside the TV is going to impact the optical connector's sound quality (SQ). Of course, if I then disconnect my RCA analog connectors and instead used the optical connection on my TV and soundbar, I will benefit from any improvements made to the optical output of my TV.

So if I used an add-on board in my car which tapped directly into the PCM's optical output, then this could be better than using a MOST box. That is a legitimate claim which Roman can make. It is NOT a legitimate claim to say that it will improve ALL cars, meaning non-Bose/Burmester as they do not have that physical optical connection I am talking abut here.

Having said all this, we (me included of course) perhaps need to remember that this thread is dedicated to Android head units, and there is a perfectly good alternative thread dedicated to add-on boards.