How to parallel a lm386 chip - Electronic Circuits Projects Diagrams Free

joecool85 · 25th February 2006, 03:58 AM

I'd like to run a 4 ohm load using 2 lm386 chips in parallel. Would I just do it like normal and then split the input to go to both chips, then hook both positives together on the output to go to the speaker?

audioguru · 25th February 2006, 07:04 AM

You can't connect the outputs of amps together and expect them to drive a load equally. One will have a slightly higher gain than the other and it will hog the load until it fails.
Equalize the gain of two amps by adding a resistor in series with the outputs. Maybe 0.22 to 0.33 ohms from the output of each amp to the load is suitable.

joecool85 · 25th February 2006, 12:38 PM

Hmm. When paralleling lm3886s, which are way larger, 50w a piece, you use 0.1 ohm resistors. Here is a schematic for them:
http://chipamp.com/lm4780.pdf

Well, thats actually a 4780, but a 4780 is two 3886s in one chip. Do I need the part with the 2.7 ohm resistors/cap to ground?

audioguru · 25th February 2006, 12:59 PM

Quote:

Originally Posted by joecool85

Hmm. When paralleling lm3886s, which are way larger, 50w a piece, you use 0.1 ohm resistors.

0.1 ohm resistors are used because the gain of each LM3886 is determined by 1% resistors, and the power in a higher value resistor would be high, requiring them to be big and expensive.
The min and max gain of an LM386 is made internally and isn't spec'd. Since the power from two LM386 amps is so low, 1/4W 0.33 ohm resistors are fine.

Quote:

Do I need the part with the 2.7 ohm resistors/cap to ground?

The LM386 uses a 0.05uF cap in series with a 10 ohm resistor to ground as an output load to prevent it from oscillating when the inductance of a speaker load results in a high impedance at high frequencies.

joecool85 · 26th February 2006, 12:41 PM

Ok, so higher powered paralleling requires smaller ohm resistors then?

audioguru · 26th February 2006, 02:58 PM

Quote:

Originally Posted by joecool85

Ok, so higher powered paralleling requires smaller ohm resistors then?

The gain of the higher power amps is determined by accurate 1% resistors. Therefore their gains will be closer so smaller value and size resistors can be used.
The lower power amps have their gain built-in but don't have a min and max gain spec'd, so higher valued resistors should be used to equalize their different gains.

joecool85 · 27th February 2006, 04:30 AM

Ah, ok. I get it now.

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode

25th February 2006, 03:58 AM	(permalink)
joecool85	How to parallel a lm386 chip I'd like to run a 4 ohm load using 2 lm386 chips in parallel. Would I just do it like normal and then split the input to go to both chips, then hook both positives together on the output to go to the speaker? __________________ Life is what you make it.

25th February 2006, 07:04 AM	(permalink)
audioguru	You can't connect the outputs of amps together and expect them to drive a load equally. One will have a slightly higher gain than the other and it will hog the load until it fails. Equalize the gain of two amps by adding a resistor in series with the outputs. Maybe 0.22 to 0.33 ohms from the output of each amp to the load is suitable. __________________ Uncle $crooge

25th February 2006, 12:38 PM	(permalink)
joecool85	Hmm. When paralleling lm3886s, which are way larger, 50w a piece, you use 0.1 ohm resistors. Here is a schematic for them: http://chipamp.com/lm4780.pdf Well, thats actually a 4780, but a 4780 is two 3886s in one chip. Do I need the part with the 2.7 ohm resistors/cap to ground? __________________ Life is what you make it.

26th February 2006, 12:41 PM	(permalink)
joecool85	Ok, so higher powered paralleling requires smaller ohm resistors then? __________________ Life is what you make it.

27th February 2006, 04:30 AM	(permalink)
joecool85	Ah, ok. I get it now. __________________ Life is what you make it.