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Old 25th April 2009, 11:20 PM   #1
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Default Lm386

I finished building this project

http://www.kitsrus.com/pdf/k17.pdf

It's getting signal but the quality is terrible is there another chip I could replace the LM386 with?

Also I want to replace the trimpot I taught I could use a 10k type A but I think the original trimpot is a type B.
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Old 26th April 2009, 01:06 AM   #2
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The problem is the circuit not the chip. Looks more like a guitar amp than a head amp. 20 gain is too high.

Try this circuit for a good headamp with that chip.
http://www.minidisc.org/headbanger.html
I have one sitting on my desk right now for my computer. It sounds great.
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Old 26th April 2009, 07:10 AM   #3
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So what's supposed to be the gain input range? I tested it with my Qbox at -50db -20db and +4 I'm surprised that I would get signal at -50db
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Old 26th April 2009, 07:10 AM   #4
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Ok I know where the bad sound quality is from, the chip was toast that's good that I bought like 20 of those a few weeks ago. Now it's clean but I really need to pad down the input gain. At line level I'm at around %5 on the pot. How can I pad down the input gain?
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Old 26th April 2009, 04:44 PM   #5
kaos is offline kaos  United States
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Make sure the jumper is removed from C2. If there’s still too much gain then add a 30K (or some optimal value) resistor in series with C1.
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Old 26th April 2009, 10:19 PM   #6
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How could I split the difference between with the jumper and without? Without the jumper is good for line level but too low for -50db
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Old 26th April 2009, 11:54 PM   #7
kaos is offline kaos  United States
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You could put a switch in place of the jumper at C2 for two different gain settings (just don’t switch it while the power’s on). You could also try a resistor in place of the jumper (something around 390 ohms) for an intermediate gain value.
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Old 27th April 2009, 02:12 PM   #8
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The best value I found for a resistor instead of the jumper was 56ohm If I go over I don't get -50db from my tone generator, which brings me to ask what's the minimum db input that little amp can take? I know -50 is mic level which I should use a pre-amp but I can get a signal that low with the jumper on. I was thinking about a switch as well, that's a good idea, what's the reason I cannot switch it when it's on?
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Old 27th April 2009, 02:12 PM   #9
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How should I wire the switch?


Both are working which is weird.


jumper switch

pin1------------------------ 1(Left)
pin2------------------------ 2(Center)
3(Right)




jumper switch
pin1-------------------------1(Left)*
|--2(Center)*
pin2-------------------------3(Right)

*pin 1&2 of the switch are together
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Old 27th April 2009, 03:44 PM   #10
kaos is offline kaos  United States
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If I understand your switch designations correctly, the first option appears to be the correct one. If you switch it with the power on you may get a thump in the speaker as C2 charges. On a low powered amp like this it may not be that bad.
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