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 www.vwvortex.com 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.