Re: need help please..

[audioguru2]

A log potentiometer is a volume control.
If you use a linear pot then most of the volume change will be at its low end and from half to max will make very little difference in volume.

 

[ungastm]

i bought that linear pot because its hard to find that log potentiometer.
if there is only a little difference maybe i'll should go to this linear pot.
thanks sir!

 

[audioguru2]

There is a big difference if you use the wrong type of pot as a volume control.
Steal a volume control log pot out of an old radio or cassette player.

 

[ungastm]

oh..
im very sorry sir..

i'll find/steal a log pot for that..
is it ok if i find a log pot from the range of 20k-30k?

 

[audioguru2]

The pot is supposed to be 22k. 20k to 50k will be fine and 10k and 100k might work.

 

[ungastm]

what will be the effect if i use a linear potentiometer?

 

[audioguru2]

With a log pot, when the control is turned from max to half-way then the audio level drops -20dB so it sounds attenuated.
With a linear pot turned from max to half-way the audio level drops only -6dB so it sounds almost the same.

At the low end the log pot adjusts the low level volume.
The linear pot suddenly switches the sound off then suddenly fairly loud.

 

[ungastm]

it's not working sir, i used tda7052a and bc547b and for R7 i used the 22k carbon resistor instead of the trimmer.

 

[audioguru2]

R7 must be a potentiometer and is adjusted for a null in your voice that goes to your speaker. Your station's output audio amp is connected to its slider.

Look at the datasheet for the TDA7052A to see how to connect its DC volume control at pin4.
I think the gain is max (+35.5dB) when pin 4 has a low leakage 1uF capacitor to ground.

The polarity of C4 is shown backwards.