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Old 10th September 2011, 08:02 AM   #11
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Just to note, the 100k stereo pot was chosen because it was/is a stock item at Radio Shack. I think the Headbanger was 100% Radio Shack sourced.
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Old 27th October 2011, 03:25 AM   #12
fubar3 is offline fubar3  Canada
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Quote:
Originally Posted by PhantomBox View Post
Has anyone else tried out the "Headbanger" headphone amp, based on the LM386 opamp?
Complete schematics and description is at "www.minidisc.org/headbanger"
I did it just a view hours ago. It sounds really crispy but has ahellofalot noise in it.
Volume seems to be ok, although it distorts a bit when the 100k pot is fully open.
I used the headphone-out of a small Mackie console, because I need to make a headphone distribution amp with 1 in and 6 outs. Power is supplied by a 15VDC 1amp wallwart.

One thing I noted: It is somehow not clearly stated how to connect the separate grounds but on the bottom view of the amp board they are clearly connected together. A corresponding image is available at the link mentioned above.

Any idea of how to control the noise? Maybe by using lower input voltage, perhaps 9 - 12VDC?

Phantombox
The headbanger is a practical DIY project. The LM386 is often used in minimal-parts configuration where there is high-gain and high distortion. But the headbanger designer has adjusted the circuit for minimal distortion and pleasing sound. If it does not sound good, there is something amiss in the circuit or the input source. All grounds should converge to a single point.
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Old 28th October 2011, 01:59 PM   #13
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I have builtb a couple of these amps. There is a trick with a bit of a trade off, to minimise the hiss.
Send me your email and ill explain.
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Old 28th October 2011, 07:39 PM   #14
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...Use an output series resistor?

I did a bit of simulation using the LM386 model you find in the LTspice group. I don't think this is particularly accurate, but then again, real-world '386s seem to vary considerably, too! The model rather seems to represent the junky ones. Even that gives reasonably acceptable distortion into 32 ohms in the Headbanger config (gain = 20 dB). A good version would seem to be performing reasonably well, though still at fairly high noise levels.

I don't think LM386s are terribly attractive for headphone amps any more. Gain-hacked TDA2822Ms or equivalent make better single-supply cheapies, and NJM4556D equipped Cmoys don't exactly break the bank either.
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Old 28th October 2011, 11:17 PM   #15
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Now look at that, I just managed to improve the simulated LM386's distortion performance quite dramatically by cranking up its gain to maximum and using it like an ordinary opamp, with an ~10x non-inverting gain using feedback Rs of 100R and 1k.
Click the image to open in full size.
At ~5vpp into 32 ohms (~100 mW), 1 kHz harmonic distortion for the standard Headbanger circuit simulated as dominant 3rd (closely followed by 4th), with 3rd @-66 dB.
With the circuit above, it turned into dominant 2nd @-76 dB, with 3rd and 4th at ~-85 dB.

Hmm, AC analysis showed some high-frequency gain peaking. A 100p (ceramic NP0) in parallel to 1k feedback resistor R5 took care of that for now. Distortion is virtually unchanged.
Click the image to open in full size.

Bandwidth now is really wide, so you may want to include some input RC filtering to keep RF out.

The circuit didn't blow up in simulation, so it may not do in real life either. Sure seems worth trying.
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Old 29th October 2011, 12:10 PM   #16
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As with any "magic tweak", there had to be a downside, and that's stability with capacitive loads. The original Headbanger circuit is utterly unimpressed by capacitive loading. This one will do 22 nF max, which is about 10 times the amount I'd ever expect from a headphone cable.
Click the image to open in full size.
HOWEVER, a measly 1 ohm resistor in series with the load - which is plenty low for cans, and it's not like you'd want to use the kind of super-critical IEMs on a noisy LM386 output anyway - will tame even the critical 47n..100n region.

Distortion at 5 Vpp into higher-impedance loads is a bit higher numerically but very well-behaved - 2nd @ -65 dB, 3rd @ -75 dB, 4th @ -85 dB and quickly dropping further. (That's about 10 dB better than the Headbanger circuit.) I also tested with 10 kHz, and results are almost the same. Distortion does rise noticeably for 32 ohm loads - 2nd @ -66, 3rd @ -77, 4th @-79 dB. This trend continues at 20 kHz.

Last edited by sgrossklass; 29th October 2011 at 12:28 PM.
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Old 14th April 2012, 04:39 AM   #17
3n2323 is offline 3n2323  United States
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Quote:
Originally Posted by sgrossklass View Post
As with any "magic tweak", there had to be a downside, and that's stability with capacitive loads. The original Headbanger circuit is utterly unimpressed by capacitive loading. This one will do 22 nF max, which is about 10 times the amount I'd ever expect from a headphone cable.
Click the image to open in full size.
HOWEVER, a measly 1 ohm resistor in series with the load - which is plenty low for cans, and it's not like you'd want to use the kind of super-critical IEMs on a noisy LM386 output anyway - will tame even the critical 47n..100n region.

Distortion at 5 Vpp into higher-impedance loads is a bit higher numerically but very well-behaved - 2nd @ -65 dB, 3rd @ -75 dB, 4th @ -85 dB and quickly dropping further. (That's about 10 dB better than the Headbanger circuit.) I also tested with 10 kHz, and results are almost the same. Distortion does rise noticeably for 32 ohm loads - 2nd @ -66, 3rd @ -77, 4th @-79 dB. This trend continues at 20 kHz.
a newbie question, will a small 8 Ohm speaker, instead of high impedence headphones, make the above any different?
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