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Old 30th November 2006, 01:08 PM   #1
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Default Needed: Small efficient headphone amp(no SQ requirement)

Hello,

I'm in need of a small(as small as possible) headphone amp. This amp will be for a hearing impaired person so hi-fidelity is not required. It only needs to be small and efficient. The phones to be driven are 25ohm 115 dB/1.0 mW.

I'm competent enough to physically build most circuits and even etch my own boards, but I lack the knowledge to actually come up with a circuit of my own.

Any help will be greatly appreciated.
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Old 30th November 2006, 01:58 PM   #2
paulb is offline paulb  Canada
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How about this? Plenty more at this site.
http://headwize.com/projects/showfil...=cmoy2_prj.htm
You can probably use an SOIC package to make it smaller.
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Old 30th November 2006, 08:21 PM   #3
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Thank you, that looks simple enough for me.

Will a TL072 work for this? I only ask because I have a bunch of them.
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Old 30th November 2006, 08:26 PM   #4
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A tl07x will have a bit of a hard time driving 25 ohms, according to

http://tangentsoft.net/audio/opamps.html

There're quite a few other suggestions there. Good luck!
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Old 30th November 2006, 09:51 PM   #5
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Hi There,

I'd use something like this:

http://focus.ti.com/docs/prod/folder...icingpackaging

Very efficient, very simple to implement, very small, low voltage, and free samples. Check for other devices on Ti.com as they have many high quality, efficient headphone drivers and most of the time, a few samples are free.
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Old 1st December 2006, 12:25 AM   #6
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Quote:
Originally posted by DCPreamp
Hi There,

I'd use something like this:

http://focus.ti.com/docs/prod/folder...icingpackaging

Very efficient, very simple to implement, very small, low voltage, and free samples. Check for other devices on Ti.com as they have many high quality, efficient headphone drivers and most of the time, a few samples are free.
Thank you, that chip looks like it would be perfect for my application.

I'm sure the cmoy circuit probably sounds a lot better, but thats not an issue here.

I was just in the middle of putting a board together in Pad2Pad and the dang thing froze up on me after I spent nearly 45 minutes on it.

I was almost done.
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File Type: jpg cmoy.jpg (49.4 KB, 133 views)
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Old 6th December 2006, 12:55 PM   #7
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OK, I have some samples of TPA6111A2 and I need some advice.

The output of this chip requires fairly large capacitors for decent low end response. Is it possible to bridge this chip and avoid the capacitors?

Also, what is a good gain for use with the average MP3 player?

Attached is a pic of how I'm guessing I can bridge the chip.
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Old 6th December 2006, 03:54 PM   #8
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You should be able to bridge this with no problems. The chips are fully protected and rated down to 8 ohms, so I don't see a problem there. Distortion will be higher, but you already indicated that was not a problem. You may want to reduce the gain by half as there will be a 4X power increase when bridged. Supply current too will be higher, but you could still get good life with 3X AA or C batteries. Very nice project!

Paul
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Old 6th December 2006, 09:45 PM   #9
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Quote:
Originally posted by DCPreamp
You should be able to bridge this with no problems. The chips are fully protected and rated down to 8 ohms, so I don't see a problem there. Distortion will be higher, but you already indicated that was not a problem. You may want to reduce the gain by half as there will be a 4X power increase when bridged. Supply current too will be higher, but you could still get good life with 3X AA or C batteries. Very nice project!

Paul
Solve one problem; create another. I seem to have overlooked the simple fact that If I go BTL in dual mono it can't be used with common ground headphones.

Thats OK though, I decided to just go ahead and use output decoupling caps. 100uf tantalums are relatively small.

It won't play flat down to 20hz with only 100uf; but thats probably a good thing. The end user in my case can't hear that low and will be less likey to overdrive and blow their headphones.

Here is my final board. I'll post a pic of the real thing after I put it together.
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