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Thread: Need help building VW Monsoon amp input

  1. #1
    Maximum Bitrate kbyrd's Avatar
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    Need basic electronics help! (building VW Monsoon amp input)

    There's at least a couple of other threads about this. I started this one so I didn't hijack the others.

    The audio Monsoon amp in many Volkswagens expects a balanced signal biased to 6 volts. The line or headphone out from the carPC doesn't match that. Also the Monsoon amp doesn't have a separate turn-on lead, it uses the presence of 5-6V on the left front - line to turn on. A few people on here (R32 Juhl, colorless, and alimh, probably others) have figured out circuits to go from PC soundcard to Monsoon in. Here are two diagrams (from others):

    - R32 Juhl -


    - alimh -


    I am so close to having a working system, but I need some help. I have little to no practical electronics-building experience. I've only recently begun soldering, I've done a bunch of reading on electronic components from this site (hey, I remember high-school science!), and I now understand exactly why the circuit above is needed. I even understand the diagram and why we need the voltage regulator. So, I'm not a total loss. But, it's all recently book learned and not hands-on. I need some advice on actually building the circuit above.

    Here's what I have.
    Things I have:
    - 7805 voltage regulator
    - Heatdsink for 7805, some thermal grease and a mounting screw. I'll be feeding the 7805 a 12V line from the M1-ATX power supply so the heatsink is needed.
    - a mini PC board (http://www.radioshack.com/images/Pro...76/276-148.jpg)
    - Some wire (18ga or 20ga)
    - a 1/8" stereo plug (3 conductor, solder connections)
    - A spare Monsoon input plug (the grey connector, part# 1J0-962-624-A), plus matching wires and pins (4 ea. of part# 000-979-131). I bought these from a VW dealer.


    My plan is to follow R32 Juhl's diagram (the top one with a voltage regulator) and build four things:
    1) Monsoon connector: Insert pins/wires into grey connector, group wires into three groups, front/rear left +, front/rear right +, common -. I'll crimp/solder male quick-connects to the other ends of these groups. One quick-connect each for L+ and R+, and two for common - (these are both connected to the same bunch in a Y configuration, you'll see why later). Now I have a Monsoon to L+/R+/common harness.

    2) 1/8" plug: solder (practice makes perfect!) three wires to the conductors of the plug. Crimp/solder 3 female quick-connects to the other end of these three. Now I have a 1/8" to L+/R+/common harness. The L+ and R+ quick-connects go directly to their partners from step 1. The common goes to one of the common connects from step 1, leaving only one open.

    3) PC power Molex 12V: I built this already, I have a 4-pin male molex -> 2 male quick connects (12V+/- only, I'm leaving the 5V alone) This will be my input to the voltage regulator.

    4) The 5V circuit. I'm following R32 Juhl's diagram. So, I need a wire soldered to the input pin of the voltage regulator to my 12V+ quick connect (step 3). I'll solder another wire to the ground connector and connect it to the 12V- also from step 3. Finally I'll solder another wire to the output pin of the voltage regulator with and crimp a male quick connect. This connects to other common on the monsoon connector from step 1.

    This sound good? Here are my questions:
    - How do a phyisically wire up step 4? I have a PC board, and if I let the heatsink rest on the board, the pins of the 7805 go thru the holes a bit. If I bend and solder the pins here, it feels like it'll be pretty stable. Does the bent pins plus solder keep the 7805 in place? I know I'll have to solder my leads to the three pins on the 7805, but how don't I have to secure them physically first? Maybe I hook the wire lead and bend a pin around it? Do I even need a PC board, is there a better way?

    - I've got 18ga wire, it clearly won't fit in the PC board holes, what should I use?

    - On the PC board which way is the bottom? It looks like one side has a conductive ring around each hole.

    - Can I see a picture of someone else's circuit?

    - From the schematic, it looks like the common conductor of the 1/8" jack (and therefore my soundcard) will see 5V. Can I place something between the jack and the 7805 to keep that from happening? I want a one way valve). Would this be a a diode?

    Thanks for any help.
    My worklog.
    Status: VM GTI sold, got out of the CarPC tinkering hobby, but I still think about getting back in.

  2. #2
    Maximum Bitrate R32 JUhl's Avatar
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    I will have more time to read your post tonight, but I wanted to quickly comment that I will be changing my schematic to show the SOURCE voltage needs to be 12V not 5.
    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. #3
    Maximum Bitrate kbyrd's Avatar
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    Quote Originally Posted by R32 JUhl
    ... but I wanted to quickly comment that I will be changing my schematic to show the SOURCE voltage needs to be 12V not 5.
    Ahh, because the 5V from the PC power supply probably is <5V? I measured with 4.89V this weekend and wondered about that, but I figured you all knew what you were doing. What does the voltage regulator do when fed less than 5 volts, just pass it on? This would show up as noise in the audio signal since the 5V from the M1-ATX would vary based on what the PC was doing.

    I'll edit my post (and my real world wiring) to reflect 12V from the PC. Thanks for any advice you can provide later. I'm so close.
    My worklog.
    Status: VM GTI sold, got out of the CarPC tinkering hobby, but I still think about getting back in.

  4. #4
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    As far as R32's diagram, you will most probably need to install a capacitor between where the 5v connects to the - line and the output of the soundcard. If you have it without the capacitor, you will notice that when you turn your computer off it will automatically turn off.

    The best way to test (wihtout soldering) is to buy a breadboard (radioshack) and just plug your wires and capacitors in.

  5. #5
    Maximum Bitrate kbyrd's Avatar
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    Quote Originally Posted by alimh
    If you have it without the capacitor, you will notice that when you turn your computer off it will automatically turn off.
    I don't understand, what will automatically turn off when I turn my computer off? What does the capacitor do?


    The best way to test (wihtout soldering) is to buy a breadboard (radioshack) and just plug your wires and capacitors in.
    That's a good idea, I'll probably do that, but I'll need to build the real thing eventually too and I still have questions about how to mount,place,secure things.
    My worklog.
    Status: VM GTI sold, got out of the CarPC tinkering hobby, but I still think about getting back in.

  6. #6
    FLAC
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    Have you guys thought about using an unbalanced to balanced singal converter? The monsoon is expecting a balanced signal. Wouldn't that eliminate any noise?

  7. #7
    Maximum Bitrate kbyrd's Avatar
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    I've heard of these, but couldn't find one for sale anywhere, I probably don't know what I'm looking for. Also, I think most balanced signals are biased to 0 volts, with the actual voltage swinging posative to negative, we need it biased to 6 volts, going from 0-12v.
    My worklog.
    Status: VM GTI sold, got out of the CarPC tinkering hobby, but I still think about getting back in.

  8. #8
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    Quote Originally Posted by kbyrd
    I don't understand, what will automatically turn off when I turn my computer off? What does the capacitor do?
    Sorry for the unclear post...

    This is what happened to me:
    I would turn on the computer without the 5v connected. Everything would startup fine but no sound (obviously).
    Then I connected the 5v (with the computer still on) and "pop" the computer would shut off instantly.

    What was happening was the 5v was going back into the (-) channel of the soundcard which was grounded to car ground. So putting 5v right to ground would mean the circuit is shorted.

    A capacitor only lets AC pass through. The higher rating it is, the more and more low frequencies it blocks. A DC signal (in our case, the 5v) is a signal with 0 frequency (the lowest of the them all). So any size capacitor would stop that 0 frequency DC from passing back into the soundcard.

    Now, in your case, your soundcard may not be grounded right to car ground, but may be grounded to a reference (called signal ground). In any case, there is no harm in putting a really small capacitor (1 nF) between the output of the sound card and the point where the 5v touches the input signal (see my diagram) to be on the safe side.

  9. #9
    Maximum Bitrate kbyrd's Avatar
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    alimh, thanks for explaining about the capacitor. Do you have any advice on how to actually construct the circuit? How about a picture?
    My worklog.
    Status: VM GTI sold, got out of the CarPC tinkering hobby, but I still think about getting back in.

  10. #10
    Maximum Bitrate kbyrd's Avatar
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    Two things:

    - Bump (R32 Juhl said he'd give me some advice and I'm hoping Zip-lock has time to tell me where to get a balanced line converter)

    - Can people with newer 2004/2005 GTI/Jetta/R32 Monsoon systems give me a double check on the wiring of the grey monsoon amp connector? I'm aware of the wiring diagram on vwvortex, but it doesn't feel right. Mine has 4 pairs with 4 blacks. I assume black is "-". But, the black isn't on the same "side of the connector. It alternates. For example:
    Pin 24 isn't black, but the vwvortex post (on adding a sub to a monsoon amp) has pin 24 as RF-. I know these systems have had wiring goof from the factory, does this still happen? Should all my "-" wires be on the same row (pin 24, 21, 18 15) because they're not now with the stock connector.
    My worklog.
    Status: VM GTI sold, got out of the CarPC tinkering hobby, but I still think about getting back in.

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