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Old 20th December 2012, 09:04 AM   #11
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Clipping wil produce high frequency harmonics, not DC.

The DC you get on the output is due to the single supply. The output must be at about half the supply voltage so that the amp can reproduce AC signals.
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Old 20th December 2012, 09:12 AM   #12
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The output cap doesn't protect the speaker from clipping.
With a single-supply amp, the output is biased at half the supply voltage. An output capacitor will block this continuous DC flow through the speaker.
When an amp clips, the wave top is chopped off (clipped) and that DC will flow through the speaker.
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Old 21st December 2012, 01:54 AM   #13
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Alright I get it.

So this is what I have so far for a circuit based on my reading.
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Old 21st December 2012, 06:15 AM   #14
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Can I ask what you're reading?
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Old 21st December 2012, 07:57 AM   #15
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Depends on the part. I've been cobbling together the ideas I can find on every subject.

Speaker coupling cap:
ecp audio diy: Some Notes on Coupling Capacitors
Wasn't real sure on this one...

The bypass cap is a bit of a personal decision derived from Figure 5 of AN-69.

Vs coupling cap too comes from AN-69:
"The normal power supply decoupling precautions should be taken when installing the LM380. If VS is more than 2" to 3" from the power supply filter capacitor it should be decoupled with a 0.1 mF disc ceramic capacitor at the VS terminal of the IC."

As far as C1 is concerned as soon as I started to type "I've been scouring the web..." I thought up something new to search and it turned up electrical diagrams of LM380s being used many with C1 as a shunt... something AN-69 failed to example as I was making this diagram. Which I now feel silly because even wikipedia knew C1 was supposed to be shunt upon further inspection.

Last edited by ForeverSka; 21st December 2012 at 08:12 AM.
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Old 21st December 2012, 09:01 AM   #16
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You're learning so don't feel bad.
I took a quick look at the coupling cap link and the formula for the output coupling is there: F = 1/(2 * pi * C * R). The form needs to be changed, though, to C = 1/(2 * pi * F * R) to solve for the unknown cap value C. And you'll need to determine the frequency (F in the formula) -3dB lower cutoff point for your circuit. R is the speaker impedance. So C3 is much too small; it needs to be at least 100 times bigger.

edit: Figure 5 in AN-69 is the power bandwidth of the chip amp. It gives insight to the internal workings of the IC. I look at it as another spec of the amplifier; it doesn't really help with determining bypass or coupling cap values.
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Old 21st December 2012, 09:13 AM   #17
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C1 should not be in series with the power supply, but in parallel.

C3 should be between several hundred and a few thousand F. The link you posted relates to preamplifiers that are loaded with kOhms. Most speakers have 4-8 Ohms and with only 4,7 F you will not hear anything below 4-8 kHz.
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Old 21st December 2012, 05:45 PM   #18
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I see how this works... I need something more like 4700uF. He has a warning that the cap will cause distortion up to 10x the corner frequency. How much should I worry about that? If not much then size considerations would drive me towards a 470uF.
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Old 21st December 2012, 07:12 PM   #19
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Compromise. Use 2200uF.
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Old 21st December 2012, 07:34 PM   #20
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Quote:
Originally Posted by ForeverSka View Post
He has a warning that the cap will cause distortion up to 10x the corner frequency. How much should I worry about that?
Not too much. You are not building a high end system with that IC.

Quote:
Originally Posted by ForeverSka View Post
If not much then size considerations would drive me towards a 470uF.
Sounds resonable.
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