stereo power amplifier

[devgorkha]

I start new project name as "digital display sterio woofer". we can supply a signal from audio source and from MIC too. we add equalizer for each signal and mix signal of sterio(audio and mic input). so that it become complicated.i use bjt as preamp of mic and to mix signal i use buffer using op amp741,equalizer also using opamp 741. this circuit work properly but problem is in power amp, i use sterio ic 2822 as power amp i also work in audio input but it makes very noisy sound when its connected to MIC input. i thing mic peak noise or problem in power amp part so pls .... suggest me where i have to change ???

one confusion !!! can we drive sterio ic as mono mode by using single switch?? but loudness of speaker must not change.

 

[davenn]

Hi the, welcome to the forum

what does the noisy sound sound like ? is it a squeel of feedback ? is it a hum of an earthloop ?
show us your circuit schematic and we may be able to help point you in the right direction

some/most stereo chips can be used in "bridge' mode, have a look at the datasheet for the IC and see what suggestions it makes. put the IC number into google and get a datasheet

cheers
Dave

 

[devgorkha]

thanks dave,
i think... it is not squeel of feedback & hum of an earthloop effect. but it might be the problem
of noise of op-amp 741. i will change it by opa134 ic and i will inform you.

i attach block diagram of my project, this is my own block diagram...i will attach ckt diagram later. it is not perfect .
pls... suggest me how can i make it better.

 

[davenn]

yes I was going to suggest a change of Op-Amp, the 741 is very very old design and quite noisy. just about anything else is better.
OP(A) 27, TL081 for example of modern low noise FET op-amps
Had a look at that OPA134 looks a very good choice
saw some example ideas in the google search as well

Also ensure you have decoupled your DC supply lines to all op-amps correctly to filter out any noise on those supplies.

cheers
Dave