mic insert vs piezo transducer?

[Neil Groves]

ok i just built a sound to light circuit (colour organ) and works fine with line in, i hooked up a mic via a pre amp and no signal, i then tried a different design of pre amp and still no signal, i breadboarded a 3rd design pre amp and no signal, i thought this is really odd, i went out and bought another mic insert, STILL no signal so in desperation i ripped the mic off the board and fitted a piezo transducer i had laying around and hey presto, gallons of signal at the output, so my questions are thus..........

Can i use a piezo transducer in place of a mic insert?, why would a tranducer work and not a mic insert? is the tranducer as efficient as a mic insert?

the mic insert i tried is from the velleman sound to light unit kit, the transducer is from radioshack, the circuits i tried for the pre amp were an op amp design, a bipolar transistor design and a f.e.t input design, none of which work with the mic.

any idea's please?

Neil.

 

[Reloadron]

Hi Neil

Could be the type of microphone used. This would likely go better if you could post a drawing?

Ron

 

[audioguru]

A "mic insert" can be a dynamic mic with a coil and magnet like a tiny speaker, an electret mic that must be powered (they are 2-wires or 3-wires and both connect differently) or a condenser mic that needs a 48V power supply.
The mic in the Velleman #103 Sound to Light kit is a 2-wire electret mic that is powered through a 10k resistor from +9v. Its metal case connects to 0V and its other pin connects to the 10k resistor that powers it and to the input coupling capacitor of the mic preamp.
An electret mic will not work if its pins are connected backwards.

Attach the schematic of your mic preamps for us to see if they have enough gain and are biased correctly.

A piezo transducer has a horrible peaky frequency response that sounds like a whistle. Its output level is higher than any other mic.
An electret mic has a very wide and flat frequency response.
A dynamic mic peaks at about 4kHz to 5kHz to make voices sound closer.

 

[Neil Groves]

Thanks audioguru, i think that clears it up, i have no power going to the mic °√°

Neil.

 

[audioguru]

An electret mic is a condenser mic with 48V stored in its electret material. The moving diaphragm changes the tiny capacitance and forms a capacitive voltage divider which has an extremely high impedance. So it has a junction FET inside to reduce the impedance. The FET must be powered.

A dynamic mic or piezo mic generates its own output voltage.