Why does my headphone amp distort?

[gfiandy]

Hi,

I had a quick look at the LM386 data sheet it does not show any use of feedback from the output into pin 1 only from pin 8 to pin 1. Are you sure that your schematic is correct.

Regadrs,
Andrew

[Speedskater]

Originally Posted by insta

Heh, it's because I'm not home I'll try and build a sine-wave generator to test this thing out with. What should I expect to see on distortion?

Build a sine-wave generator? This is 2009 and almost 2010. Down-load some test tones and burn a CD or copy the tones to a mp3 player.

[insta]

That seems far less useful to me in the long run. Why do you care how I get my audio source?

[MJL21193]

Originally Posted by gfiandy

Hi,

I had a quick look at the LM386 data sheet it does not show any use of feedback from the output into pin 1 only from pin 8 to pin 1. Are you sure that your schematic is correct.

Regadrs,
Andrew

I asked the same sort of question way back, still looking for an answer...

[insta]

Originally Posted by gfiandy

Hi,

I had a quick look at the LM386 data sheet it does not show any use of feedback from the output into pin 1 only from pin 8 to pin 1. Are you sure that your schematic is correct.

Regadrs,
Andrew

Connecting pin 8 to pin 1 with a resistor will provide a universal gain increase. I based my circuit on the 'bass boost' one found at this LM386 site. It worked well enough in my tests.

[Speedskater]

Originally Posted by insta

That seems far less useful to me in the long run. Why do you care how I get my audio source?

Because in the past I have built both kit and DIY tone generators. But now I often find it more convenient to use a CD player to generate test tones. No controls to mess with and greater choice of test signals (like ramps and multi-tones).

[Mooly]

Insta,
I would just measure those voltages first.

Do you have a 'scope ?

As to signal generators, a CD is fine for simple tests but no good for anything else.
This is a 1khz squarewave off CD (Any CD player will produce exactly the same

[Rembrant]

This is probably the best designed lm386 circuit available.
HeadBanger Headphone Amp Construction Kit

Either way it sounds like a cap in backwards or possibly a cold solder joint on one of the caps.

[ricortes]

Old but rookie status due to 30 year layoff.

Forgive me if I am wrong or just need the info for personal reasons.

Why the op amp? I mean it looks like you have it set up as a unity gain or buffer. LM386 has plenty of gain built in for most apps and you are willing to add the parts so the op amps seem unnecessary.

I aggree with Mooly, volume pot between op amp and 386 input tied to ground. Otherwise the internals of the chip may latch up.

Finally if it were me I would just pull the op amp and test the 386 with another source like MP3 player and see how it performs. For that matter, the op amps alone should be able to drive ~10 mamps to power head phones to make sure that stage is right.

Rick