Need help creating a sound amplifier

[kleanthisky]

I wanted to make a sound amplifier and I found this schematic on google.

 

I have several questions about this. 

 

1.Can I use a 12V~800mA Power supply i have instead of the battery?

2.Can i ground pins 2 and 4 without the C6 Capacitor? or just ground pin 2 only and use connect pin4 to both C7 cap and ground

3.Can i remove the Gain Potentiometer and use just the cap between pin 1 and 8? 

 

[rhyseyness]

9 minutes ago, kleanthisky said:

I wanted to make a sound amplifier and I found this schematic on google.

 

I have several questions about this. 

 

1.Can I use a 12V~800mA Power supply i have instead of the battery?

2.Can i ground pins 2 and 4 without the C6 Capacitor? or just ground pin 2 only and use connect pin4 to both C7 cap and ground

3.Can i remove the Gain Potentiometer and use just the cap between pin 1 and 8? 

 

-snip-

1. Yes power supply will be fine, as long as the voltage is the same as the battery would have been.

2. No, C6 is necessary.

3. You can't replace a resistor/cap network with a just cap, and why would you want to... never want to adjust the gain? If so, just used a fixed resistor, but I can't think of a reason you'd want to do that. You're going to need to adjust the gain to test when you first set it up anyway.

 

Not really sure why you're asking about removing/changing these random components.

I'd learn a little about electronics before you start this.

What are you planning on using it for?

[kleanthisky]

12 minutes ago, rhyseyness said:

1. Yes power supply will be fine, as long as the voltage is the same as the battery would have been.

2. No, C6 is necessary.

3. You can't replace a resistor/cap network with a just cap, and why would you want to... never want to adjust the gain? If so, just used a fixed resistor, but I can't think of a reason you'd want to do that. You're going to need to adjust the gain to test when you first set it up anyway.

 

Not really sure why you're asking about removing/changing these random components.

I'd learn a little about electronics before you start this.

What are you planning on using it for?

I found other circuits that only use the volume potentiometer and have only the Cap between pin1 and 8

 

I want to test it on some speakers i have

[mariushm]

1. Yes, you don't need to use a battery, it will work with a DC adapter. Make sure the voltage rating of that C4 capacitor is larger than the maximum input voltage from the adapter.

 

Download the LM386 datasheet : http://www.ti.com/lit/ds/symlink/lm386.pdf

 

As you can see on page 4, the maximum voltage for the LM386N-4 version of the chip from TI is 18v, but other versions or chips from other manufacturers may work at only up to 15v or 12v

 

2. Don't remove components from a circuit. They're there for a reason.

 

3.  A potentiometer is like two resistors that change their values depending on the potentiometer position. It's  [start ... wiper ... end ]  ... in the circuit you have a connection between whiper and end.

So once you figure out the best gain value you like, you can remove the potentiometer from the circuit , measure the resistance between the wiper pin and the end pin and you can then use a simple resistor with a value very close to that measurement.

Leave the capacitor to that value.

 

See page 8 in datasheet :

 

The chip has a minimum gain of 20 , so if you leave pins 1 and 8 unconnected the chip will have the gain set to 20. If you put a 10uF capacitor between pins 1 and 8 you make the gain to the maximum of 200. If you want something in-between you add a resistor in series with that capacitor - that's what the potentiometer does. For example, the datasheet shows a 1.2 kohm resistor setting the gain to 50.

 

9.2.1.2.1 Gain Control
To make the LM386 a more versatile amplifier, two pins (1 and 8) are provided for gain control. With pins 1 and 8
open the (my note:internal) 1.35-kohm resistor sets the gain at 20 (26 dB). If a capacitor is put from pin 1 to 8, bypassing the 1.35-kohm
resistor, the gain will go up to 200 (46 dB). If a resistor is placed in series with the capacitor, the gain can be set
to any value from 20 to 200.

 

In general datasheets have plenty of information ... try not to get scared of all the graphs and numbers and formulas and jump o "Detailed description" and the following sections in the datasheet, they explain why those values are needed and sometimes suggest alternative values which can tweak the behavior

 

[rhyseyness]

4 minutes ago, kleanthisky said:

I found other circuits that only use the volume potentiometer and have only the Cap between pin1 and 8

 

I want to test it on some speakers i have

I'd leave the resistor there, it makes sense to have it so you can adjust the level of gain (useful for an amplifier).

What speakers are they?

 

This amplifier will work, but will not perform anything like an off the shelf solution.

There's a reason a good speaker amplifiers are expensive.

 

It'll be a fun little project, but do not expect it to sound anything like a decent proper amp.

 

EDIT: and don't forget to heatsink the f*** out of that chip, lol.