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CJ
11-14-2006, 12:02 AM
Today I was hooking up an audio amplifier (lm386n) to play with the vocal demos. I was having trouble with the typical capacitive connection (pops, hisses, just not clean sound), but discovered that just having the wire in the row just outside of the DIP next to pin 1 provided a very clean sound without any hookups to the chip directly. all that was hooked to the amp was power, ground, and speaker.


A testament to breadboard Capacitance?

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Who says you have to have knowledge to use it?

I've killed a fly with my bare mind.

Beau Schwabe (Parallax)
11-14-2006, 12:25 AM
"A testament to breadboard Capacitance?"

Exactly!


Try something like this:



1K
Propeller I/O >--/\/\--o------> To pin2 LM386
|
o--||--> GND (Vss)
.1uF


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Beau Schwabe (mailto:bschwabe@parallax.com)

IC Layout Engineer
Parallax, Inc.

Post Edited (Beau Schwabe (Parallax)) : 11/13/2006 6:45:24 PM GMT

Forrest
11-14-2006, 12:26 AM
Are you sure that's a good breadboard? Can you reproduce this on another breadboard with similar results?

CJ
11-14-2006, 12:46 AM
Beau, the inputs for this amp are on 2 and 3, - and + respectively, I get nothing out of it when hooked up per schematic, as it is now, it is the best sound I have ever had out of it, and quite content to keep it this way.

Forrest, I can't see how it wouldn't be a good breadboard, I have continuity where it's supposed to be, and the printed surface on the backing sticker is intact.

I was merely pointing out something cool.

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Who says you have to have knowledge to use it?

I've killed a fly with my bare mind.

Beau Schwabe (Parallax)
11-14-2006, 02:46 AM
Cj,

Since pin 1 and pin 8 control gain, you can affect the output by coupling to pin 1 in the way that you are doing.
Default gain is only 20 for the LM386.· By placing a 10uF cap across pins 1 (+ cap)and pins 8 (-cap)·your gain
will increase to 200.

I changed the pin1 on my schematic to pin2, but it still holds true.· You can use pin 2 (inverted)·or Pin 3 (non-inverted)
it should·not matter in this case, but·whatever pin you are not using·needs to go to GND or·Vs/2.

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Beau Schwabe (mailto:bschwabe@parallax.com)

IC Layout Engineer
Parallax, Inc.

rokicki
11-14-2006, 06:01 AM
Is it possible that the input voltage swing is just too high? That is, if you drive it
directly from the propeller (even with an R/C divider) we're talking about
1V p-p or thereabouts. With 20x gain you're going to be clipping all over the
place.

CJ
11-14-2006, 09:15 AM
It sounded like it was clipping, the way it is now is nice and smooth, and simple to wire

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Who says you have to have knowledge to use it?

I've killed a fly with my bare mind.