Ignition/alternator noise and a added-on amplifier. The "final solution" - it works.

I have no idea how many people followed the rather long thread of the winding paths I followed attempting to get rid of what's probably alternator noise on my '09 Boxster - noise that showed up when I added an additional amplifier to power some additional speakers I'd installed in the storage-bin behind the seats/roll-bars. The speakers were a kit from Suncoast I believe (it's been a LONG while since I received these as a Christmas present). I just looked, and can't find them on-line at the moment, but I didn't do extensive research. The kit replicated an option that was available for the ASK equipped Boxster 987 cars. It converted the storage unit that was behind the seat headrests into a speaker housing. The kit consisted of 4 speakers (2 per side) - about 3.5" cone, 4 Ohms each. It also had metal brackets for each side that replaced the end storage cubbies, and grilles to go inside the openings. Plus various wiring harness components to run the speakers to the ASK headunit. The ASK headunit had 2 unused speaker level output circuits, that were intended for the rear speakers in a Cayman , but were unused in a Boxster . The original kit from Porsche made use of the outputs. Meanwhile, I had replaced the aftermarket system that had been installed in the car with the AliExpress one (there is a LONG thread on that journey), which besides having speaker outputs for all the factory installed ASK speakers, had 2 additional RCA jack outputs for left/right. I decided to make use of these RCA outputs, using them to feed an amplifier and have the amp drive the speakers in the rear cubby. Great plan - except for electronic noise. The layout of the Boxster , with the engine in the middle, and the battery in the front results in needing a long heavy wire to connect the engine to the battery (starter and alternator .) This heavy wire runs alongside the center tunnel under the carpeting. Since the alternator can produce RF noise due to diode rectification - the wire works like a broadcast antenna and the electrical noise radiates out from it. After a lot of trials, I finally got the alternator whine down to an almost unnoticeable level - not perfect - but useable. The amp I originally installed was a Blaupunkt - good German name, made in China of course. For some reason the amp was quite inexpensive from Amazon , so I bought it, and installed it in the open compartment in front of the battery in the Frunk, where if you had a CD changer - the changer would live. The location seemed perfect.. but the electronic noise was driving me crazy. I finally got the noise down to a tolerable level by adding a filter capacitor across the alternator output - at the alternator , before the big wire that connected it to the battery. That quieted things down a lot, and I was able to use the rear speakers to fill in the sound, particularly useful when driving top down (is there any other way?) since the speakers were basically inches away from my ears. SO - this all seemed OK, but not perfect. I started doing some thinking about how to eliminate the final remnants of alternator whine. I remembered that Porsche , BMW , Mercedes used a unidirectional fiber optical loop communications system/protocol call "MOST" for all their more involved entertainment systems. If you have a Bose system in your Boxster , you have that loop network. It's the orange fibers. Why would they do this? An optical fiber is inherently immune from radio frequency electronic noise. Since the receivers are designed for a light signal, they never see an RF signal, and the fiber, being glass, won't pickup any RF noise. Plus the signal was converted to digital format (0's and 1's) and coded and decoded. Random radio frequency noise doesn't consist of 0's and 1's. So I wondered if Amazon had such a things as an aftermarket offering. Turns out they do: an RCA-to-fiber transmitter and a fiber-to-RCA receiver. But it was sorta pricey, and there was no obvious source of the fiber needed to connect the two. When Amazon showed me this system, it also showed me another option. A digital radio link system - using Bluetooth. Amazon has a kit with an RCA-to-Bluetooth transmitter and a Bluetooth-to-RCA receiver. It was rather inexpensive and available quickly. So I ordered it just to see what it was and decide if it was worth keeping. The system was originally designed to be used for home-theater, where you wanted to take the output from your TV set and pipe the sound through a receiver of some sorta perhaps across the room. I believe they claim a range of 100 feet for it. Two boxes, about 2x2x3/4", with a USB power input, and two RCA connectors and an in-line mini-stereo audio jack, with a cable that converted that jack into two RCA plugs. Perfect setup. I also bought two very inexpensive 12V-USB power supplies. Has a 12V input and USB output. I hooked all this up with my old amplifier, and the noise was gone. Not a sign of it. YEA! At least for a while. For some time, I have been getting periodic freakouts of the amplifier; I think caused by the noisy input signal and the 2 Ohm impedance of the add-on speakers. The manual for the amp specifically warned against 2 Ohms, claiming it might cause issues and damage. I believe I found why the amp was so inexpensive. The freakouts were becoming more persistent. So it was time for a new amp. Again - Amazon to the rescue - MBQuartz has a line of amps, "Crunch" - which aren't huge, and one that claims a billion-Watts* (real RMS, 0.1% harmonic - probably ~120 W/channel at 2 Ohms.. more than adequate since the speakers are for fill in, they aren't primary sound sources.) It is actually rated at a very reasonable 2x125W (I assume each channel), and it seemed perfect for the use. The original amp - was considerably larger than the Crunch amp. Large enough that I built a platform for inside the cubby in front of the battery, home to the vapor recovery system, and room for a CD changer. The amp was on top of the vapor recovery system and extended 6" to the side of it, mounted on the platform I built. The CD changer area is about 4" below the top level of the vapor recovery system. With the new amp, I'd hoped to mount it where Porsche originally put the ASK amp - on the 987.1 cars - in front of the fuel tank in the compartment your compressor and can of goo live in. So I asked here for photos of an amp in that location It turns out, that even the smaller size of the Crunch amp wasn't small enough to fit there. So it was back to the CD changer cubby. Some pictures below.. you'll get an idea of how it fits in. Rather nicely actually, and mounted on a steel surface let me screw it into the mount for the CD changer, giving a solid chassis ground. (I had learned that to do things in this area, I was able to do them much easier if I spent the 5 minutes to remove the interior liner of the FRUNK. This image is with that liner removed.) So - put back together, with the Bluetooth receiver double-sticky-mounted to the plastic trim panel: You might notice the copper braid on the left side of the compartment. This is the old audio cable, a double-shielded RCA cable, then put into copper braid for an additional level of RF suppression. It didn't make a huge amount of difference and was really a PITA to route from the CD changer spot into the headunit space. I'm debating removing it. That'll involve some additional disassembly, or simply taking a pair of tin-snips to it, cutting it in chunks and just pulling it out. Right now - it looks like it might get the tin-snips treatment. It's a waste of a rather expensive cable - that I have no use for if I remove it intact. So, no real loss in destroying it to get it out. I ended up using the audio-jack to RCA cable that came with the receiver end on the final assembly; it fit better and made for a neat installation. Didn't introduce any noise. The new amp has a high-filter, low-filter control. I used this to cutoff the low-frequency response at about 150Hz, which is perfect since the 3.5" speakers can't reproduce frequencies below that - without buzzing. Limiting them to mid-range/high frequencies seems to work great. The door speakers handle the low frequencies just fine.

Sources (All Amazon Links): Amazon.com: Crunch 2125W 2 Channel Subwoofer Car Audio Amplifier with Adjustable Crossovers, Bass Knob & Remote, LED VU-Meter, QTD Cooling and PWM Power Supply : Industrial & Scientific - $70. Amazon.com: YMOO 2.4GHz Wireless Audio Transmitter Receiver Set (1 TX+1 RX) for TV | 25ms Low Latency 200ft Long Range with AUX RCA in/Out, Wireless Audio Adapter for TV PC Powered Speakers Soundbar Amplifier : Electronics - $60 2x Amazon.com: USB Female DC Converter 12V 24V to 5V 5A 25W DC Buck Converter Adapter Buck Module : Electronics - @9/each. There'ya go..

Wow that’s quite a journey you went on - but I guess it’s part of the hobby! glad you managed to find a solution that pretty much sorted it out for you and thanks for sharing! how are you enjoying the sounds now?

Too long explanation

You're probably not going to not want to hear this, but a lot of your issues are from using cheap Chinesium components. They make those down to a price point, and as such, they leave out a lot of careful design considerations such as basic noise rejection.

No one made you read it. 🙈🙉🙊 There won't be an end-of-chapter quiz.

Blaupunkt wasn't considered a "cheap" component in the past. Are there any non-Chinese-made components? MacIntosh? The issue with alternator noise and the Boxster/Cayman is well documented on the web. IMHO, it's primarily caused by a design issue - the mid-mounted engine and the front/frunk mounted battery - require a long wire running the distance between the two. That wire is run inside the cabin of the car, not hidden in a tunnel or other shielded area. I'd have to guess since Porsche , BMW and Mercedes also used a digital data link (MOST bus) that they were using "cheap Chinesium components"? Especially for their higher end systems like the Burmester in my old Cayenne Turbo? Or the Bose systems in the 987? Most of the problem could have been avoided by Porsche providing a filter capacitor at the alternator , which used to be common practice. Eliminate the electronic noise before it ever gets to the wire leading to the battery. When I added one there, the noise was greatly reduced. Routing of the cables was also critical. The noise level would change dramatically by moving the connecting cables just inches in where it was run. What I tried to present here is two fold: 1. A connection technique that eliminates electronic noise pickup 2. A connection technique that also eliminates having to run cables through small spaces, grommets, around the battery compartment. Plug and play baby!

I'm really loving them. With the lack of noise, I can increase the volume on the rear speakers a bit, and that really helps hearing music with the top down. And I only get bored with cars when there isn't anything in mind to do to them.. I still have a few ideas for the Boxster that I have in the planning stages right now. It's been very reliable as far as repairs, so most of the ideas are along the line of improvements of some sort.

Ah good point, when the top is down I can’t really hear much of the music on the move… even with the Bose system ( 718 ). what else are you planning for the sound system?

Nothing immediately. There are rumors of a new improved version of the Chinese headunit. Depending on what's improved and the cost I might consider that..