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Old 7th September 2011, 07:15 AM   #1
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Default Headbanger headphone amp

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
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Old 7th September 2011, 10:28 AM   #2
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I power mine from 4x AAA (6V) and still have a noise issue. To me it isn't much of a problem at normal listening levels; the noise gets buried.
The Headbanger has a lot of gain for a headphone amp, and the 386 does tend to want to break up the HF some, but that's my only complaints with it.
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Old 7th September 2011, 11:35 AM   #3
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I built this amp 10 years ago now and it has worked great ever since! I power mine from a 9V battery and put a .1uf cap across the battery and that reduced the noise a lot. I built mine on perf board from Radio Shack parts in a hotel room so the construction isn't great, the layout isn't great and still it works great! it gets extremely loud but is a bit harsh sounding.

But for me, my goal was to be able to plug it into my laptop and watch movies on a plane over the loud engine noise. so a little bit of hiss and harshness is drowned out by the jet engines LOL!

Zc
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Old 7th September 2011, 03:04 PM   #4
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This one is much better and you can DC couple it :
http://www.national.com/ds/LM/LMH6672.pdf
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Old 8th September 2011, 04:30 PM   #5
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LMH6672 could be a bit of a leap for most building LM386 amps - soic, power pad, 80 MHz CFA - not exactly a socket and perfboard project amp choice - and the OP's 15 Vdc supply will toast the chip

the 1st question for a headphone amp is always - what headphones? - they vary in Z and sensitivity by orders of magnitude - no "standard" like 8 Ohms for loudspeaker

IEM need step down Xfmr to get good S/N, for some 200 mVrms will drive them to 120 dB SPL

"mainstream" circumaural headphones range from 16-600 Ohms
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Old 9th September 2011, 05:16 PM   #6
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LM386s are, in fact, very noisy. Effective input voltage noise is about at 4556 level, but 40 dB of voltage gain is just excessive for headphones. These chips were designed as small speaker drivers and are not exactly hi-fi. The Headbanger amp itself seems to be about as good as LM386 amps get, though I would have used a smaller-value volume pot.

If you're looking to build a very simple headphone amp, I'd recommend a classic Cmoy with a NJM4556 opamp, which AFAIK is pretty much what's inside a Grado RA-1. This will be lightyears ahead of any LM386 amp. Gain should be chosen depending on headphone sensitivity, it'll usually be somewhere between 2x (6 dB) and 10x (20 dB).
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Old 9th September 2011, 06:55 PM   #7
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PS: OK, so upon re-reading the OP wants a headphone distribution amp. I'd go with the suggested bunch of 4556s then. One per channel is fine for general purpose applications, just make sure you have some decently high supplies.

A 15 VDC wallwart isn't exactly ideal, that would mean either many or big coupling capacitors. I'd copy the O2 power supply which only requires an AC wallwart (transformer).
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Old 9th September 2011, 07:38 PM   #8
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The venerable lm386 chip can be made to play ball. That is what the Headbanger amp is all about. I could argue that a gain of 12 is higher than most people would require. But it's all a trade off. It has the power for basically any headphones known to man.

The very first amp I built was a headbanger and in many ways, it is better than the numerous C-moys that I have since built. No Cmoy amp made can power my 32ohm phones properly.

The headbanger could power two sets in parallel with ease. The THD of the 386 based headbanger amp is well within acceptable limits.

However, the problem of the one amp not having enough power for more than one set of phones is only a minor problem here. That is why it is suggested that you use one output buffer for each of the outputs respectively. That solves a host of other problems that will arise if you try to do a one chip output to several sets of headphones at a time.

In the case of a distribution amp, the LM386 will just increase noise and THD where the NJM4556 could do the same job with better results. You will still require one buffer for every output. Why not use a dual supply chip with its advantages? In this case, many.
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Old 9th September 2011, 08:40 PM   #9
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Quote:
The headbanger could power two sets in parallel with ease.
The Headbanger is named appropriately. It could probably power all 6 sets of 32 ohm headphones. The LM386 isn't a first-rate performer, but it has its advantages when used as a headphone amp. These days, a headphone amp is a necessity IMO, and the Headbanger is a great way to dip your toe in the diy waters.
Mine is about deck-of-cards size and will play for endless hours. And it'll make my 16-ohm ear buds scream. I love its portability.
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Old 10th September 2011, 07:42 AM   #10
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To sgrossclass: what value for a volume pot would you have used?
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