condenser and electret mics

[Audioguru]

Your new circuit has Q2 turned on fairly hard most of the time. You removed the trimpot to ground at its base (which reduces how hard it is turned on) so its sensitivity depends on the current gain of the transistor that can vary a lot. Some 2N2222 transistors will be sensitive and others will be less sensitive. You added a series trimpot which can adjust the sensitivity only a little and reduced the value of C2 so that it responds only to very high audio frequencies.

I bet there are millions of high frequency sounds that will activate the circuit.

 

[FrozenTear]

From this circuit,
https://obrazki.elektroda.pl/85_1293084480.jpg (lower sensitivity circuit)
the 1nF capacitor and 10k resistor that i circled out will be my high pass filter, but how to calculate the gain of that high pass filter? and what's the cut off frequency of that filter?, Can somebody please teach me on calculating this? Thank you.

 

[Audioguru]

Q2 is not biased properly. It will be saturated if the current gain of the transistor is high and it will be almost cutoff if the current gain of the transistor is low. The amount of conduction of the transistor will also be affected by its temperature.
Q2 needs a base resistor to ground making a voltage divider and a bypassed emitter resistor.

If Q2 is biased properly so that its collector voltage is at half the supply voltage (at 4.5v) then the collector current of Q2 is 0.96mA and its input impedance is 4k ohms. C3 applies a lot of positive feedback which might cause Q2 and Q3 to be an oscillator.

The highpass filter should be fed from a low impedance but instead it is fed from the very high 470k output impedance of Q1 which R3.
Then the 10k trimpot R15 will have almost no effect and the highpass will have a cutoff frequency of (1 over 2 pi RC) 330Hz. The filter has only a single order so its dropoff is very gradual.

The very high output impedance of Q1 driving the fairly low input impedance of Q2 causes a signal loss of about 53 times at high frequencies.

None of the links in this thread go to the correct thread here. They all go to a power supply thread instead.

 

[sergiosparks]

Re: polarity of mic condenser

hi
i wanna make this clap switch
but i only have a condenser mic
can i use it instead of using the electret mic in the circuit?


thanks a lot

Added after 5 hours 53 minutes:

HI


reporting
i built this with a condenser mic
and the result is weird
it says it is on when i clap once
then it turns it off when i clap again
the result is diff
i clap and it turn on and it stays on for a very short time and it goes off automatically
( i cannot clap to turn it off)
then i can clap to turn it on again hmmmmmmmmmmmm the same process continues


here is the link

**broken link removed**
can any smart fellows in this forum clear my doubts?
Thanks a lot

Ps: I connected exactly like the circuit

Hi Simon,i am replying to an old post but any way try a 'higher gain' transistor
for your microphone preamplifier you can check them using datasheets usually given free my their manufacturer.Maybe the 'clap' part of the audio output is still too weak to 'trigger' the preceding circuit.