Will this circuit work?

It works, but are there any problems with it that might fry the chip or something? Also, I didn't know if audio ground should be connected directly to the amp ground, and I saw one schematic that had a 10K resistor in between so I just did that.

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gmoon6 years ago

Yes, all the grounds connect together. That's why ground is referred to as "common."

It won't work without a coupling capacitor between the output pin and the speaker. Amplifiers have a DC bias offset voltage (unless it's removed internally), and the coupling cap blocks that, so that only the AC signal reaches the speaker. Replace the 50 ohm resistor with the cap.

That cap value also sets the cutoff frequency for the speaker (forms a low-pass filter), so use something larger than 200uF IF you want bass response.

You can drop the 100k ohm resistor across the speaker--it's less than 1/10000 of the load resistance, and will have no appreciable effect.

Remove the 10K resistor on the - input. Incoming ground should connect directly to LM386 ground.

The cap on the input may or may not be needed, and it's usually appropriate to add a resistor to ground for a reference (like 10K to 100K for the 386).

Look at the Datasheet, as frollard suggests...
7654321 (author)  gmoon6 years ago
On the datasheet all the examples show the 386 directly connected to ground. They do however show a cap in series with the speaker like you said. Oh, and the 100K resistor kept the others from getting hot... but if replace it with cap like you said I guess it wont matter.
gmoon 76543216 years ago
There's a good chance it's the DC that's causing the overheating.

Are you sure it's 100K, and not 10K? I don't think the 100K would do much, but the 50 ohm series resistor would block a LOT of current. In fact, it would block a lot of the signal, too.

The Little Gem shows how to add an adjustable attenuator to a 386. First the coupling cap, then a 25 ohm rheostat (NOT a pot, these can take current) as a voltage divider.

You can replace the rheostat with fixed resistors, if you like. But they should be in the range of ohms, not Kilo-ohms. Unless you want to loose most of the signal.
7654321 (author)  gmoon6 years ago
Ok I changed it and it now looks like this. Also, if I replaced the rheostat with fixed resistors, they would be basically in parallel with the speaker right?
circuit.png
7654321 (author)  76543216 years ago
now instead of using a whopping 70 mA, it only uses 5 or 6 :D
gmoon 76543216 years ago
Cool(er). Should sound better, too.

Wire two fixed resistors just like a rheostat or POT--the divided voltage is tapped between the resistors.

Like the pic below.

Just choose the resistor "ratio" to get the volume you want. Use the Little Gem schematic as a guide, and don't use more than 25 or 30 ohms total for both resistors. Like a 5 ohm and a 20 ohm... They need to be at least 1 watt resistors, too.
Resistive_divider.png
It might work, its not right.
Why have you got resistors feeding the speaker ?
There is no need for a FIXED resistor at the input, but it might want a pot, as a volume control.

7654321 (author)  steveastrouk6 years ago
It was too loud without them and the 386 got very hot, but a pot sounds good...
You have a fixed gain of 20. The easiest way to turn the input down is a pot.
frollard6 years ago
What does the datasheet for the '386' say?