The is a VIZZ in the output Sound!!!

[Shahriar]

Hi

I have build an square wave oscillator with LM324(which is a quad opAmp).
I have connected the output to a TIP122(power Transistor) and drive a piezo to creat
a beep sound. but the interesting problem: There is a VIZZ in the output sound. when I
touch the Vcc or GND or some other points of the circuit, the vizz will dissapear. When i
make the square wave with a NE555 there is no VIZZ and everything is OK. I don't think it
is because of noise!!! I connected so many points with a Resistor or capacitor to ground or
put some capacitors between Vcc and Ground but nothing special. I have used one of the opAmps from 4 opAmps of LM324, when I touch the floating inputs nothing happen but when I touch the floating outputs the vizz will dissapear.Few month ago the same thing happened when
I built a preAmplifier with NE5532. there was a small Vizz in the Output which would dissapear when I
touched the GND.
P.S. I have used a speaker choke to drive te piezo. I hope you understood what i meant by a piezo. it is something like a coin and when connected to
a oscillator it sounds like a buzzer. I do not know the exact english name!!!

ThanX in advance
Shahriar

[Guest Alun]

Could you post a schematic?

What do you want to achieve with this circuit?

If it's just a continuous tone I'd recommend a piezo buzzer.

[Shahriar]

Dear Alun

The circuit is to creat a loud Beep. small buzzers can not creat such a loud sound.
when I used a coupling capacitor between the output of opAmp and the transistor Base, the effect of my hand dissapeared, then I remembered that the PreAmplifier I had build, was a DC coupling PreAmplifier (it did,'t have any coupling capacitor). But the thing I didn't understand was the effect of my Hand!!!!!!!!!

Anyway, I changed the circuit and build a sinewave oscillator with opamp and there is no Vizz with or without a coupling cap. ???
but the question still remains: What is the effect of Hand???

ThanX
Shahriar

[audioguru]

Hi Shahriar,
I think that the VIZZ was your circuit oscillating at a very high frequency. Your hand on its ground stopped the oscillation.
An oscilloscope would show the problem and what your hand is doing to it. ;D

[Shahriar]

Yeah, It can be  a possible.
I will check it and tell you.

Thank you very much
Shahriar

[konsempu]

can you teach me how to make an improvised buzzer plz?? its our project anf i have no idea about doing this . Plz.

[Shahriar]

Dear konsempu

This is the schematic I used. I omitted the parts which you didn't need, {Beacuse I was building a Fishing Buzzer}
The schematic you see is just the Buzzer. the Left part is an Sine-Wave Oscillator the right part is the driver. the transformer is a simple Audio transformer. it is there to increase the voltage. you can pull down the base of the transistor with a pot to control the volume. Becarefull the transistor not to get too much Hot. you can use power transistors.

hth - Shahriar