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FAQ: Connecting your soundcard to a Volkswagen Monsoon Amp

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  • FAQ: Connecting your soundcard to a Volkswagen Monsoon Amp

    Many Volkswagen owners have the Monsoon Sound System as a factory installed option. Part of this upgrade includes the "Monsoon Amp". It's a strange beast and differs in a few important ways from an aftermarket amp.

    First, it is a "line level" amplifier. That means that it can take in an already amplified output from the headunit rather than a very low signal one such as the "line output" you find on many audio systems and computers. The monsoon amp then amplifies and splits this signal into different components such as bass, treble, midrange, and routes it to the proper speakers in your car. Trouble is, some of theses speakers differ in their resistance values. Removing the amp and replacing it with an aftermarket amplifier would requires enough knowledge to buy/build a proper crossover network.

    Second, the monsoon doesn't have a "turn on" signal wire. Most amplifiers have a signal wire that is connected to the accessory or ignition wire of the car to sense when to turn the amplifier on and off. The monsoon does not. It has a special circuit that senses voltage on one of the speaker wires to tell it when to turn on or off.

    These differences make it difficult to hook up a soundcard's output jack and get audio to your VW OEM speakers. This may seem like a really specific subject for a forum-wide FAQ, but it appears many people have the VW Monsoon sound system and run into the problem of hooking it up to a soundcard's output.

    There's a bunch of background about balanced vs. unbalanced input and the exact signal we should be sending the monsoon. That's for a different thread. This circuit certainly doesn't mimic the OEM head unit's output exactly, but it does play your soundcard's output thru your speakers and I don't notice any difference in quality. I'll skip all that and go right to the solutions.

    How do I turn on the Monsoon amp on/off?
    The Monsoon amp does not have a separate remote turn on lead. It uses the presence of 5-6V on the left negative audio input as a signal to turn on. So, you have to inject 5-6V DC into the negative line of your audio signal. Since the 1/8" headphone plugs that go into soundcards have a common negative conductor anyway, I've tied all the negative input lines on my Monsoon amp together.

    Here's the circuit:

    The RCA jacks on this end
    are where you plug in the
    sound from your soundcard
    or computer headphone out.

    The cables on this end go
    to the Monsoon amp

    You'll need to main parts to do this:

    1. A 5 or 6 volt regulator. I used a Radio Shack 7805 5 volt regulator (part #276-1770), price: $1.59.

    2. A Ground Loop Isolator (GLI). I used a Radio Shack GLI (part #270-054), price $16.99.

    The idea is to use the 5 volt or 6 volt (5V is much easier to find) regulator and splice it's output in with the negative line of the audio signal as shown in the circuit diagram.

    The ground loop isolator serves two purposes. First, you don't want the 5-6V DC going back into your audio source (your soundcard) so the ground loop isolators act as a DC filter. This protects your soundcard or audio source from being fried by the voltage of the regulator. Second, you need it to act as a ground loop isolator and noise filter so the audio is clean. The 5 volt regulator takes 12V from your car and converts that to 5 volts for this circuit. That 12V can introduce noise and your soundcard is probably grounded to a different place than your amp which could introduce "whine" into the audio.

    There is an input side and an output side to this circuit. Only the bottom RCA jacks will have the 5V applied, that's the output side. Here's a couple of pics of the completed thing in a project box:

    Here's a pic of it installed in the hatch of a GTI:

    It's on the left, that rubber strap came with the car, it makes a perfect place to mount this.

    One last, but important point about this circuit. You have to be able to switch the 5V on and off somehow, to signal the Monsoon amp to turn on and off. What that really means is switching the 12V line that feeds the 5 volt regulator. Some people use a 12V line from their power supply unit (PSU), since it automaticlly turns on/off with the car.

    I chose to feed my 5V regulator from the same 12V source that powers the amp. (you can see the washed out tap splice in the bottom center of that last pic), this is a constant 12V so I control it with a relay (mounted above the amp in the last pic), the relay is controlled by 12V line from the my PC's power supply.

    However you control the regulator's 12V source, one thing is critical. You must switch the 12V+ line, not the ground. If you switch the ground connection to the regulator, the amp will not turn off. Since the amp draws about 1 amp just sitting there with no audio signal, that's no good for your battery.

    Wiring your sound to your Monsoon amp

    Ok, I've got this box with RCA jacks, how do I feed this from my PC and to the Monsoon amp?
    The PC side is easy, assuming you have a 1/8" headphone jack on your soundcard (most do) get a 1/8" male to RCA female adapter. They're a couple of bucks. Still confused? Read this FAQ.

    For the Monsoon side, it's not tricky, you just order a wiring harness from a Volkswagen dealer. Here's what I ordered:

    - 1 of 1J0-962-624-A. This is the grey connector itself, no wiring.
    - 6 of 000-979-131. This is wire with female pins that lock into the connector. I only needed 4 (see below) but bought extra.

    My total including tax was $24.30. I made this:

    Gather up all the lines into four groups, L+, L-, R+, R-. Now attach two RCA female plugs one for the left side, one for the right.

    Finally, find two RCA male-male patch cables (these are really common) and connect one from the PC to the "monsoon box" input side and one from the "monsoon box" output side to the monsoon input. Some people may not want all the extra RCA connections and patch cables. It's your choice. I like this because it turns my monsoon, my car PC, and my "moonsoon box" into standard components that are easy to connect and disconnect.

    If you're really paying attention, you'll noticed I didn't list a pinout of which input to the monsoon is "front left +" or "rear right -". That's because it is different in different model years (gotta love Volkswagen) There are some posts on that list pinouts for the monsoon grey connector, but they were different from mine. How do you find out yours?
    <TODO: I need to good instructions on how to determine the grey connector pinout here>

    Thanks to Alimh, Bugbyte, colorless, WebDog, and R32 Juhl (and whoever else I missed) for their help in developing this solution, I'm just the messenger.
    My worklog.
    Status: VM GTI sold, got out of the CarPC tinkering hobby, but I still think about getting back in.

  • #2
    Okay Boss! Looks good. Our R has been in the bodyshop since 9/20 and we just got it back last night. Out went any grandiose plan I had previously made about using my Xmas break to work on the car! Nonetheless, tomorrow I'm going to FINALLY take a stab at using all the work you've put into this and see if I can offer any further assistance afterwards.

    Thank you for taking the time to do all the research and then taking the time to write the FAQ!
    My first attempt at a carputer.

    PM me if you're interested in a monitor faceplate for your '99-'04 Golf or Jetta. My Vortex ID is NorthAtlR32 - you can IM me there, too. Go here for more information.


    • #3
      My plan is just to use the Blitzsafe CD changer to Aux input adapter and keep the stock stereo. I don't have a Monsoon system though.
      MP3Car Forums || FrodoPlayer || Ogg Vorbis || PN User Feedback || Heatware


      • #4
        Voom PC case, M1-ATX, EPIA M10000, 512mb RAM, External 5.1 audio, Alpine 50w x 4 amp, 7" Lilliput in dash, WinTV USB TV/FM, RR, Autoroute & Infomap Navigator 4, Gatso Hunter.


        • #5
          Originally posted by MV54
          ...and your point is?
          My worklog.
          Status: VM GTI sold, got out of the CarPC tinkering hobby, but I still think about getting back in.


          • #6
            There is an easy way to determine the pin-out for the connector. I haven't tried it but it just came to mind while reading this. I work in the home audio and integration industry and have a tool called a "toner". Some may know what this is but for thoes that don't it's a tool that allows you to send a "tone" over a wire. This allows you to find the wire carrying the tone where ever it runs in a house by using a tool called an inductive amplifier.. it's a little wand with a button on it.. real simple.

            If the wire leads you are hooking the toner up to are attached to a speaker, the speaker will reproduce the tone. sound like .. deeedle deeedle .. over and over again. I use this method to test a driver out of the box and to identify speakers installed if the wire isn't labeled. You can get one of these things at home depot and they can be costly.

            You can acheive the same effect by using a 9 volt battery and "poping" the speaker, you'll hear a pop at the corresponding speakers. Be careful, it is possible to damage a speaker if you leave the battery on for a while, but doubtful. If you are really worried about it, slap a resistor in line to the battery.

            So that's my input. Like I said I've yet to attempt this on my own monsoon system and I am also new to carputers. I am in the process of putting together my first carputer. If anyone sees a flaw in this process on this system please inform me!


            • #7
              this may seem like a silly question, but does any of this apply to a monsoon amp in a pontiac? i know that the pinouts are going to be different, but how about how it turns on and off? any info would be greatly apprectiated.
              Car Pc progress meter:
              [-5%-------------------] Carpc build #2. So far, 20$ deep! I love recycling!

              "The car is the closest we will ever come to creating something that is truly alive" -Sir William Lyons
              My worklog


              • #8
                Just thought I'd point out that GM uses these Monsoon systems, most notably the 2003 Buick Regal has them available and they are almost forced onto you by the dealers in the 03 Regal.

                Off-topic: GM also used the same head gaskets on the 1998 Chev Lumina as VW did on the 1998 Passat. That was a lovely repair bill for the Lumina (oh, it's got a VW head gasket, only GM parts are covered by the warranty)


                • #9
                  Just a thought... but you should be able to achieve the same +6v offset using capacitors instead of the bulky, expensive ground-loop isolator.

                  I just put this circuit together in a simulator and it seems to work, and the distortion seems to be pretty low... with a 5KHz signal through it, distortion was 110dB or more down... and increasing the value of the caps a little more would make it even better. I would be willing to bet that it has better frequency response than the transformer in the ground loop isolator, anyway. (this represents one channel... RCA output would be taken across the resistor terminals, with the ground terminal being the one at the regulator output, and V1 represents the RCA input)

                  I don't have a monsoon amp, but maybe someone else would be willing to try this out. total parts cost is less than $1, minus the regulator circuit, or maybe a few bucks at radio shack prices.
                  Attached Files
                  But don't take it from me! here's a quote from a real, live newbie:
                  Originally posted by Viscouse
                  I am learning buttloads just by searching on this forum. I've learned 2 big things so far: 1-it's been done before, and 2-if it hasn't, there is a way to do it.


                  • #10
                    Here are some diagrams for the GM one


                    • #11
                      quick question: where did you get the box, where in canada can i get a similar one, and how much?


                      • #12
                        Originally posted by evandude
                        Just a thought... but you should be able to achieve the same +6v offset using capacitors instead of the bulky, expensive ground-loop isolator.
                        In fact, the original circuit I installed did use caps, but I like the isolator ($15 at Radio shack) better and I actually had some whine the caps didn't get rid off.
                        My worklog.
                        Status: VM GTI sold, got out of the CarPC tinkering hobby, but I still think about getting back in.


                        • #13
                          Originally posted by peterbrowne
                          quick question: where did you get the box, where in canada can i get a similar one, and how much?
                          The black box is just a plastic box from Fry's Electronics. They're local to California and maybe Arizona and Nevada. But, it's a black project box. Most electronics stores (like radio shack) should carry them. If you're really stuck, I'll send one to you, but you'd probably pay more in shipping than the box cost.
                          My worklog.
                          Status: VM GTI sold, got out of the CarPC tinkering hobby, but I still think about getting back in.


                          • #14
                            Hey thanks for the DIY write up. 3 quick questions.

                            Can the existing monsoon harness be tapped into to?
                            Did you splice the wires together L and R or separate them with RCA Y cable?
                            Do you need a heat sink for this setup?


                            • #15
                              I agree... awesome write up. I am in the beginning stages of getting everything I need for my puter. Once that is accomplished, I will be visiting this thread again!
                              My Shadow used to look like this. She's better now!