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Headphone Amp

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redart

New Member
Hi All,
I'm looking for any kind souls out there who know a thing or two about designing amps to offer some critique on the following headphone amp I've built. The design is a cut down hybrid of two (strangely similar) designs I found on the web at Headwise http://headwize.com/projects/eaton_prj.htm, and Rod Elliott's ESP site http://sound.westhost.com/.
This is my first attempt at building at amplifier, so I'm happy to say it works, and sounds pretty good too, despite being built entirely on a 2.5" x 6.5" breadboard (including the PSU!). I'd include a picture of it but it looks too horrible.
As I'm a beginner at this sort of thing I'm hoping to get some ideas on where the design may be lacking, and what sort of improvements I might look at making. Anyway, here's the schematic. Thanks for looking.
 

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dknguyen

Well-Known Member
Most Helpful Member
Would using MOSFET's make an improvement? (I am just putting the idea out there).

ANd..what is the left circuit supposed to do? Is that the power supply? What does an LM3771 do?
 
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redart

New Member
Hi,
I had originally planned to use MOSFET's, but the store was sold out of them!. The LM317T and LM337T are voltage regulators.
 

Oznog

Active Member
You don't usually need a dual power supply for headphones, and certainly not of this amplitude. It'll make too much heat for the transistors to lower it back down. An iPod for example puts out about 2Vpp. Normally you'd bias the output to Vdd/2, and put a large polarized cap in series with the headphones to filter out the DC.

Making a drive stage like that is unnecessary. An LM386 will work but is not the best of quality. A BUF634 is a great high power unity gain amp, but you'll want to put a high gain op amp like a TL082 around it.
 

redart

New Member
Thanks for the feedback.
The phones I'm using are Sennheiser HD420SL's, with nominal impedance of 50 ohms I believe. I'm probably one of the few people on earth who doesn't own an iPod, but I'm guessing the bud type earphones that come with such devices would have a much higher impedance?.
I originally tried using just the TL072 by itself, but it quickly ran out of steam and into distortion when asked to go loud. You mentioned the TL082....the spec sheet looks almost identical to the TL072 I'm using. Also Burr-Brown amps are like hen's teeth here in Oz. I like the simplicity of using a power amp for current boosting, so in the absense of a BUF634 I might try the LM386, unless you can suggest a better alternative.
 

Dr.EM

New Member
I tested the headphone amp on this page once and found it rather good, even though I was only using a TL084:

http://www.mp3forkidz.com/mic/circuits.html

It just uses op-amp buffers in parallel with current sharing to drive the load. Add more buffers for more power, though I could hear a non-distorted sine wave quite clearly on the other side of the room using just the 3.
 
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