Audio line level to PCB microphone level

Thread Starter

AVMoos

Joined Nov 11, 2022
7
Hello everyone!

Im having a problem... I got nice lighting installed in my new studio, but the lighting of my laser is controlled by audio with an onboard microphone.
This is annoying because i want the laser to work also when my music isnt that loud. inside the laser is a tiny microphone on a PCB.
What a want is to create a jack input on the laser so i can take the 0dB output of my audio interface and send that directly to the laser.
does anyone know how i can get the line level down to the level of the PCB mic so i can solder the jack input on the laser to the + and - of the microphone?

Would be lovely to get helped <3
 

Dodgydave

Joined Jun 22, 2012
10,591
A simple volume control will work with an isolation transformer,can you post any pictures of the circuit board, ?
 
Last edited:

Ian0

Joined Aug 7, 2020
6,713
Not quite so simple, as you will end up connecting your quiet audio ground to a power ground. Find a small step-down transformer - even a mains transformer will do, as the laser will mainly be triggered by the bass.
 

MisterBill2

Joined Jan 23, 2018
13,805
I also recommend an isolation transformer, but you may also need a voltage divider because that microphone signal is just a few millivolts while the line output may be over a volt.
But even worse, the power source in the laser package may not be isolated from the mains adequately. So the voltage divider, unless you choose to use a variable potentiometer, would be a series combination of a 100K ohm resistor and a 1K ohm resistor, with the common point being the free end of the 1K resistor and the 100K going to the line output. The output to the laser would be across the 1K resistor.
 

Thread Starter

AVMoos

Joined Nov 11, 2022
7
Hello everyone!

Im having a problem... I got nice lighting installed in my new studio, but the lighting of my laser is controlled by audio with an onboard microphone.
This is annoying because i want the laser to work also when my music isnt that loud. inside the laser is a tiny microphone on a PCB.
What a want is to create a jack input on the laser so i can take the 0dB output of my audio interface and send that directly to the laser.
does anyone know how i can get the line level down to the level of the PCB mic so i can solder the jack input on the laser to the + and - of the microphone?

Would be lovely to get helped <3
Looks like a LM358 op amp input, can't see the other 8 pin chip, the ULN chips are DC output drivers.
Gonna make a picture better in a few minutes
 

Ian0

Joined Aug 7, 2020
6,713
At least that tells you that 0V isn't connected to mains live!
I'd still recommend an isolating transformer to keep the ground noise of your studio quiet ground.
 

MisterBill2

Joined Jan 23, 2018
13,805
Did anybody examining the circuit board, or other data, get any clue about the required audio level? I am thinking that the 100:1 attenuation that I initially suggested may be more than required. I agree that an isolation transformer is still a good idea, possibly with a step-down ratio of 10:1?
 

Thread Starter

AVMoos

Joined Nov 11, 2022
7
Did anybody examining the circuit board, or other data, get any clue about the required audio level? I am thinking that the 100:1 attenuation that I initially suggested may be more than required. I agree that an isolation transformer is still a good idea, possibly with a step-down ratio of 10:1?
i tried to measure the voltage of the audio signal from the mic, multimeter says 0,8V at the peaks, and normal audio level is 1v. starts to look like not an complicated situation
 

MisterBill2

Joined Jan 23, 2018
13,805
OK, measuring 0.8 volts is amazing there must be a high output mic cartridge, or an internal amplifier. Or a DC component in the signal. So "0 VU" output would be close to the right level. But I still recommend an isolation transformer.
 
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