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I need serious critique and advice.....

Guys n Gals, I would like to have those of you interested in helping me clean up a published instructable ( my Latest, in a long while ) as I seem to be at a bit of a loss as to how to make it look less "disorganized".

Maybe it is that I am still not fully recovered from the surgery, or whatever, but it does not look like it is quite "right" yet, to me. Thanks for any help given...

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xACIDITYx9 years ago
It doesn't seem like it has a real ending. Like a final thoughts or Use.

Now I read that For now, this is a step in the right direction, and only (I hope) needs a bit of tweaking to be added as I have time. Does that mean you will continue to work on said project or will continue to work on the 'able?
Goodhart (author)  xACIDITYx9 years ago
Well, I do want to solve the "interference/clipping" problem, and I can add that to the end of this -ible later on. I somehow felt this one wasn't as detailed as the others, and I am not sure how to fix that (because it took me so long, and the time in between "working on it" times, was pretty significant. *sigh*
gmoon Goodhart9 years ago
Glad you're feeling well enough to "putter" (as my wife would say.)

There probably a lot of ways to reduce the distortion in that 386 circuit, but you'll probably loose some gain...(maybe try different speakers to get a bit more volume afterward.)

Also, does it distort at all input levels, or when the signal is largely un-attenuated?

-- Gain of 200 is might large, especially if the unmodified output is normally driving the speaker itself. Maybe reduce the gain setting (1 + 8) by adding resistance in series with the 10uF cap? 550 to 1.5K ish?

-- Add a negative feedback loop between the output (5) and the inverting input (2), removing the ground from pin 2. Try resistances for the NFB loop anywhere between 10K and 1M (or use a pot.)

You could also tap the source of the NFB at the speaker.. (instead of the 5 pin.)

-- Play with the coupling cap values for a different freq response.

-- Add some hi freq roll-off caps on the signal (0.001 uf - 470 pf), in addition to what the .05 and 10 ohm resistor is doing...

-- lastly, from the 386 datasheet:

When using the LM386 with higher gains (bypassing the 1.35 kW resistor between pins 1 and 8) it is necessary to bypass the unused input, preventing degradation of gain and possible instabilities. This is done with a 0.1 uF capacitor or a short to ground depending on the dc source resistance on the driven input.

I.E., try the 0.1uf cap instead of the grounding the inverting input. It's worth a shot...

The last sentence also implies the input impedance could be played with a bit--adding an initial series resistor (10K - 100K), and changing the volume pot to a larger value.
Goodhart (author)  gmoon8 years ago
Looks as though you were right about the 200 X amplification overdriving the speaker. I put in a slide volume control and it needs to be way down near the low end to sound good, but it is still quite loud :-)
gmoon Goodhart8 years ago
Cool, I'm glad it's working (better.) There's probably a sweet-spot somewhere between attenuating the input, and lowering the gain. Could have a real effect on the signal / noise ratio...

There's also likely more distortion at the high-gain setting. The 386 datasheet should have some gain vs. distortion charts...

'Course, if it's working well...if it ain't broke..don't fix it.
Goodhart (author)  gmoon8 years ago
It is adequate. It doesn't need to be "concert hall" quality :-)
Goodhart (author)  gmoon9 years ago
Thanks, that will give me even more to play with as I look this thing over.
Goodhart (author) 8 years ago
I have added quite a few more steps....it is not "quite" to my liking yet, but we are almost there :-)
Goodhart (author) 8 years ago

sorry all !


But this is taking me a LOT longer then I thought to "make pretty" and still keep it functional. But it is coming along ! :-)
Goodhart (author) 9 years ago
I have updated it a little. Some minor adjustments so far, nothing really major, but replacing the Mic helped tremendously. I should have made an audio file so you would know just how badly it sounded before. Now, although it is not concert quality, it is much MUCH better.
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