Code Practice Oscillator

Dear Friends,

I have designed a CPO and would like to know whether the schematic is in order before I build the circuit. Please give your views.

Thanks
Ravi
Colombo
Sri Lanka

Hi Ravi,
1) You don't need C3, it would make the gain of the LM386 too high.
2) You should add a 0.1uF coupling and DC blocking capacitor between the output of the 555 and the volume control.
3) You should pass the output of the 555 through the switch to the coupling capacitor added to the volume control. You are switching the ground pin of the 555 now, which makes it sound funny and with a "pop" each time it starts running.
4) You should change the values of R1 and R2 to be 47K each. With their existing 100 to 1 ratio, the output would be very narrow pulses that sound buzzy.
5) I hope you are using a volume control with a logarithmic audio taper. A linear pot would make it too loud unless it was turned almost to zero.

Hi audioguru

Thanks very much for the views.

1). The Cap,C3 is to have a high gain of around 200 times of the normal gain. Instead can I have a POT to control the gain?

2),3),4) and 5) - Agree

As you know the output of LM386 is below 1W. If I use a high output amp, will there be a problem in the oscillator side?

Have a nice day!
Ravi

Ravi said:

As you know the output of LM386 is below 1W. If I use a high output amp, will there be a problem in the oscillator side?
Ravi

Click to expand...

1 watt is PLENTY. You only really need a few milli watts for comfortable listening.

JimB

Hi Ravi,
The output of the 555 is about 7V peak-to-peak. If you amplify it with a gain of 200 times it would try to be 1400 volts! You use C3 on an LM386 when a low-level microphone is feeding it.
Using a logarithmic audio taper pot for R3, its volume control, even at half-setting of the volume control it will still be too loud with a normal LM386 gain of 20.

Sure, use a higher power amp if you are deaf and want to shake the floor!

Hi audioguru,

Many thanks for your suggestion. Over the weekend I've built this ckt and it is now working perfectly.

Thanks again.

Ravi
Colombo
Sri Lanka

Hi Ravi,
Good, it's perfect.
I am glad that I've helped you.