Thread: Need help building VW Monsoon amp input

Originally Posted by alimh

Here is my thoughts on the voltage regulator and capacitor.

capacitor/diode:
You cannot use a diode because the audio signal that also passes through keeps switching from + to -. THe diode would block out all the -! Instead, the capacitor blocks out DC. Anyway, some soundcards (from what I read) do not use the computer ground so you could potentially hook it up wihtout a capacitor.

Does the one in your schematic say 0.1 microfarads? That is, 1/10th of one microfarad? I'm looking at several at RadioShack that match that:
272-109
272-1069
272-1053

They come in a variety of voltage and percentage ratings. As I understand it. The voltage rating only matters as a limit of the voltage I could run into given capacitor. That is, I'm putting my cap in a 5V-ish circuit so it'll always have 5V at it's terminals.

Also, there are smaller value capacitors, should I use those on the theory that even the smallest value will block DC and a lesser value will have a less chance of blocking the AC audio signal? Any other advice on the various types? (longer leads, etc.) ?

Ok, finally got this monsoon deal undercontrol. Here is what I got.

+12V to the FL- powers up the amp.

Gounding both the FL+ and FL- turns the amp off.

I found that removing he 12V after the amp turns on produces much cleaner sound, there is no noise because there is no source for it.

Here is my plan, I am going to build a circuit that utilizes a relay to turn the amp on and off. This will physicaly isolate the circuit which will ensure there is no noise with out having to worry about capacitors or diodes. I will post my plans. More to follow.

Wierd. I'm pretty sure I've read for vwvortex that the amp looks for 6V on - as the turn on. Removing the 12V provides cleaner sound because the amp is lookng for a signal ranging from 0-12V centered around 6V. 12V probably means max input to the amp.

kbyrd,

Any of those capacitors will work. The only thing that will be trouble are polarized (which those aren't). A smaller capacitor WILL work. I just picked this one because thats what they had at the engineer "store" (place for free electronics, hehe) at my school!

0.1micro (yeah, 1/10 of a micro) will block out any fluctuations from the voltage regulator, if for some reason there are any. Also, its small enough that it won't cut out any audible frequencies.

If you're interested, there is a program called PSpice. It is basically a circuit simulter. There is a free student version. Just google "pspice." Its what we used in our circuit classes.

Either way, if you have any specific questions about your circuit just let me know, I can even pspice-it for you. I wouldn't consider myself an expert by any means, but i have worked with this stuff before...

agentloveless,
What source isyour audio coming from? Your MP3 player? It still works when you take off the 12v? I tried it today, and if I take off the 5v then it will only work if the signal is loud enough... wierd. Let us know what else you find out.

alimh, thanks for the reply. I got a variety, I'll try them.

I have a couple of questions for whoever about the 5V added to the audio signal.
- Should we be adding 6V? Is it easy to find a 6V regulator?

- Regardless of 5V or 6V, shouldn't we be adding it to both + and - lines?

Here's what I'm getting at. The input signal expected by the monsoon is supposed to be a 6V on both lines for no sound and a varying 0-12 on both lines to generate an AC signal. What's the output of the PC soundcard? I assumed it was 0V at ground, and 0-5V (or some small number) on the + line for each of R and L. Does anyone have measurments on what the PC soundcard output is? I'm trying to figure out how to best match the expected 6V biased balanced signal I think the monsoon expects.

The output of the soundcard on my laptop is 1.2v maximum.

I think you should only apply 5v to the - channel. That is what I am doing and it works.

Let me know how it goes with those capacitors.

EDIT: Definately easier to find 5v regulators. I don't think they even make 6v...

What happens if you remove that 5V while the laptop is still on?

My big confusion is how you guys turn the amp off? To turn mine off i have to ground the + and - for the FL. I wonder if you guys are simply leaving your amp on the entire time.

I just tried this today:

I started the computer normally... with the 5v connected. While the music was playing, I disconnected the 5v.

Now, if the volume is loud enough, the sound still plays like normal.

As I decreased the volume, the sound would cut in and out at a medium volume level. I'm guessing this is because the volume of the song fluctuates a little.

When the volume goes below a threshold, the amp turns off and no sound. I knwo the amp turns off because if I increase the volume again there is no sound.

HOpe this helps.

Hmm that is really strange because I can even disconect my source, and as soon as I put it back it plays. Have you tried to use 12V to turn it on in the begining?