light Organ

Discussion in 'The Projects Forum' started by NZMikeV, Jun 4, 2011.

  1. NZMikeV

    Thread Starter New Member

    Jun 18, 2010
    Hi there.
    I am having a bit of grief with this light-organ circuit. It works well, but only at a volume too loud for comfortable listening. I thought it would be fairly easy to improve the sensitivity, but that has not been the case. Aside from experimenting with the resistor values (which achieved nothing other than preventing it working at all) and adding an extra BC547 to make a darlington pair (which achieved nothing other than preventing it from working at all -again! :confused:), Any suggestions? I'm sure it's simply a case of further amplifying the signal before sending it to the triac but my attempts thus far have failed miserably - and I would prefer to avoid op-amps for this circuit. Once I have got that sorted, I'll be adding another lamp and then a filter for different frequencies.
    Any suggestions are appreciated.

    Notes: The circuit did not work until I replaced C1 with a 10uF electro. The triacs suggested in the text aren't available here, I am using a SC141D. My Halogen transformer is rated for 150W so adding more lamps is not a problem, as long as I can drive the triacs.
  2. KJ6EAD

    Senior Member

    Apr 30, 2011
    Increasing the resistance of R3 will increase the gain of T1 but will alter the operating point of the amplifier and may cause clipping of the signal. Remember, the first stage of amplification is a FET inside the electret condenser microphone itself. Make sure adequate DC voltage is being supplied to the microphone.
  3. NZMikeV

    Thread Starter New Member

    Jun 18, 2010
    Thanks for that, I tried but to no avail. Decreasing, rather than increasing R3 helps but I still have to have the stereo volume cranked up and the mic is right in front of the speaker.
    I have a small pre-amp kit that I'm about to make up, which can use an electret mic as an input. Maybe I can use that instead and do away with R1?
    If that doesn't work, I might have to come up with a new circuit that uses a 4-transistor (non-inverting) amplifier, though that seems like overkill? Or could it be that I simply need to decouple the second transistor with a second capacitor? I'm sure the solution is simple - but it's got me stumped :confused:
  4. Adjuster

    Well-Known Member

    Dec 26, 2010
    I would add a single AC-coupled common emitter amplifier stage. That way, you could leave most of your circuit as it is.

    Your preamp kit would be another possible option, perhaps preferable as it is already designed.
    NZMikeV likes this.