Sound To Light Box help

[stuee]

Hi, i have a sound to light box that has a internal mic, the box is for 240v out to 8 lights, it has sound to light or chase functions. I now have a rack mount and put this in but the mic is useless for picking up the audio.
Would it be atall possible to remove the mic and wire it to the line out of my mixer. or is the voltage too high and damage it?

If anyone can help i would most appreciate it.
Thanks
Stu

 

[audioguru2]

Hi Stuee,
It might be Very Dangerous!

The lightbox might be cheaply designed without an isolation transformer. The mic might be connected directly to one side of 240VAC.

 

[stuee]

I dont think it is, ive touched the mic when it was turned on. its one of them tiny mics. with the tiny solder pads o nthe back.

 

[audioguru2]

Maybe you weren't grounded when you touched it.
Maybe the mains receptacle it was plugged into was wired correctly (they all aren't).
Without an isolation transformer it is deadly to connect anything to it.

 

[stuee]

What if i stick my meter on it and check the voltage?

 

[audioguru2]

Today you might measure 0V to ground on the microphone. Next week, with it plugged into a different mains receptacle that is wired incorrectly, the microphone might measure 240VAC.
Mains powered devices must have an isolation transformer if you want to connect them to anything. Maybe it already has a mains transformer. Look and see.

 

[stuee]

i am unsure of the situation, im not that clever
Ive put a image on my server if you could look and see what you think,
Thanks
Stu


www.geelongcarmods.com/images/board.jpg

 

[trigger]

I agree with Audioguru.

Especially you don't know much on the circuit.

 

[audioguru2]

The circuit has a 9V isolation transformer probably because the box is metal. But the microphone could still be connected directly to 240VAC because I don't see opto-isolators driving the BTA08 triacs.

 

[stuee]

what would one look like?  opto-isolators?
Thanks
Stu

 

[audioguru2]

4 or 6 pins dual-inline for each triac.

 

[MP1]

stuee,
It is doubtable that the mic has 240 volts on it. I have never seen a color organ or similar circuit that did this. Close view of your picture shows a foot print for the mic; The traces look like they connect to some ICs on the board and some capacitors and resistors; Verify this and you will know. Check the value of the capacitor connected to the mic. If you have 240 volts here, these components would have to be rated accordingly. This will tell you if the mic has high voltage on it.
In other words, follow the traces from the mic connection to the next component and/or all components connected to this trace and look at it's rating. Even with this, some manufacturers use highly rated components because they do not stock several different ones. But the caps on your board look like small packages and are most likely part of the 9 VDC circuitry. If the mic traces connect to either of the ICs on the board, you can look at the data sheet from the number printed on the ICs to determine what the maximum voltage range is. I am going to guess these are op-amps to amplify the low level of the mic to a useable level that will trigger your light circuit.

MP

 

[stuee]

Thank you MP that is very heplful.
All the caps that inline with the mic are either 16v or 25v. looking at the bottom too, the main power (the thick track) come in onboard and goes stright to the 3 pin transitors then out to the power blocks at the back.
So back to my orig question, if this is a low voltage mic, is it possible to conect it to my lineout from my mixing desk, I know i mught have to add a resistor or something but not sure what.

Thanks

 

[audioguru2]

Hi Stuee,
My old TV didn't have external audio jacks and its chassis was connected to one side of the mains.  The microphone and circuit of your colour organ is connected to one side of the mains through the gates of the triacs. I used an audio transformer to feed audio from my TV with isolation and you should use a transformer to feed audio to your colour organ.

 

[Alun]

MP,
Just because the microphone and asociated components only have a small potential difference across them it doen't they aren't floating at a high voltage. It could be possible that they're connected to the neutral side of the mains and while this might perfectly safe under normal conditions if the neutral becomes dsconnected or the socket is miswired it could be a very big safety hazerd.

A good way to test for isolation is to measure the resistance between both of the microphones connections and both the live and neutral connection, do this with both polarities (swap the +/- terminals on the meter) also try the diode checking setting on the meter, if the resistance is >1M then you'll be fine.

But I always think it is best to be safe rather than sorry and use an audio isolation transformer, if you use a 1:1 transformet connected to a speaker jack it will overload the circuit. You could always try a small 6V mains transformer, connect the 230V side to the audio source and the 6V side to the microphone.

 

[Alun]

what would one look like?  opto-isolators?
Thanks
Stu

You can get multiple opto-isolater modules, they are often packaged in 8, or 14pin DILs.