Replies to This Discussion

Permalink Reply by Scott aka Farmer Ted on March 14, 2016 at 1:17pm

Yeah, noticed that too. Also realized that the speaker negative is connected to pin 5 of the opposite IC.

Permalink Reply by Paul Craig on March 14, 2016 at 9:17pm

Correct, the 386 chip pin 2 is (input -) and pin 3 is (input +).

  One chip has  (input -) to pin 2 and output pin5 goes to (speaker -). Making up the negative side of the bridged amp.

The other chip has (input +) pin 3 and pin 5 output to (speaker +). Making up the positive side of the bridged amp.

I've noticed several schematics for the 386 chip amps that will use either pin 2 or pin 3 for input on single chip amps.  But as for the battery input, pin 6 is always battery/power positive. Which is why these chips will fry if the battery/power polarity is reversed.

Permalink Reply by Scott aka Farmer Ted on March 14, 2016 at 8:50am

Not sure what CON1 & CON2 are, but presume that they are contacts on a pre-made board?

The C8 and R10 combo is common on many LM386 amp circuits, but I don't use them on mine. C9, the 1000uF cap is the filter cap relative to the battery/wall wart power source. It smoothes out the dc "ripple" to eliminate background dc noise. Notice how it connects to "ground".

R1 (4K7 ohms, or 4.7K) can be anything from 330 ohm to 4.7K ohms, and is more dependent on the color of LED used. Some LED's need higher resistance, others need less to avoid burning out the elements.

Permalink Reply by John Sawyer on March 14, 2016 at 9:19am

I have used quite a few of these: http://www.ebay.com/itm/Low-Voltage-Audio-Amplifier-Module-Kit-NJM3...

It has a very similar circuit to what you present here, runs great on a 9v battery, even better on 6 aa, c or d cells...

This circuit is functionally no different than the 1w Aztec amps that you see sold in many places. The jumper selects 20x or 200x gain: if you wire a 1k pot across the jumper, you have adjustable gain... I find they sound better if you insert a .022uf cap across the input leads.

YMMV

Permalink Reply by John Sawyer on March 14, 2016 at 11:54am

Your mileage may vary. Btw, if you don't have the paper that came with it, you have to be careful to not reverse polarity on the battery or you smoke the whole thing.

You should still have my email, ping me if you need any help.

Permalink Reply by Paul Craig on March 14, 2016 at 8:56pm

The first version of this amp that I built got smoked from the walwart polarity being accidentally reversed. I'm going to have to rebuild mine.

Some of these small chip amp will be okay if the polarity is reversed, but most of them will be toast.

Permalink Reply by Scott aka Farmer Ted on March 15, 2016 at 1:40am

True, being careful about the wall wart polarity saves a bit of frustration.

Permalink Reply by Paul Craig on March 15, 2016 at 7:55am

The only way is knowing the pin designations of the chip(Google Search), and following the circuits on the PCB.

Permalink Reply by Paul Craig on March 15, 2016 at 12:27pm

386 pins would be this.

Permalink Reply by Scott aka Farmer Ted on April 2, 2016 at 10:15am

If you mean polarity of the wall wart, it will be marked on the same side where the specs are (voltage in/voltage out/millamperes, etc).

it looks like this:  (in this example, center is negative, as with many effects pedals)

Permalink Reply by Paul Craig on April 2, 2016 at 7:22am

While waiting for funds to order the speaker, I went ahead and labeled all the controls. I used some rubber letter stamps and ink. Not the best job, but I think it adds to the rustic fell of this cabinet.

Permalink Reply by Paul Craig on April 13, 2016 at 7:06pm

I ordered the WGS 10" Veteran speaker. Can't wait to get this done.

Wanted to kill my cat yesterday. Little *&^% got in my office/project room and knocked a book off the top of the bookcase that fell right into that Utah speaker and tore a big hole in it.

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