Portable Headphone Amp

[Myren]

Hello,

I got a new MP3 player and its mighty quiet. Too quiet. I need to build a portable headphone amplifier for it and my Grado SR 80s (and occasionally my Senn MX-500 earbuds which are even quieter).

I'd really like to design and build an amplifier, but I need recommendations for chips to base it off of. I did some Op Amp work a while ago in school, I still have my old texts, but I need some silicon to start from. If there's pressing need to go away from simple to do Op Amp systems, please elaborate. I'm listening.

Efficiency is a concern. Size would be nice.

Sound quality is semi-nice, but I dont plan on taking extrodinary measures in this project, given that my mp3 player itself doesnt produce the best sound. I'm hoping that it provides good sound at lower volumes, produces less clipping, and that a good pocket amplifier will give me better volume with better sound.

I'm assuming I'll need a very efficient dc-dc converter as well. my mp3 player uses a single aaa battery. i'm probably going to rip it out of its shell and use an aa battery, maybe go dual aa if the amp warrants it.

I've been checking HeadWize, but most of that seems to be non-portable systems. My searching here has resulted with a similar lack of starting place, although I have found a number of interesting in depth discussions. I believe with a starting place I'll be able to do far better research. Thank you for your assistance.

What silicon to use?
thanks
myren

[rickcr42]

I've been checking HeadWize, but most of that seems to be non-portable systems.

the Chu Moy Pocket Amp is a portable design and goes into a lot of detail about the design.

Another good portable amp sit is

http://tangentsoft.net/audio/

and a links page that is more or less headphone amp specific :

http://www4.head-fi.org/forums/showthread.php?t=21563

[Algar_emi]

Check www.headwize.com, projects section:
http://headwize.com/projects/index.htm

The best reference for headphone amps on the net.

Bye...

[jackinnj]

Texas Instruments has a new IC (it's surface-mount) which has high current drive just for this purpose. i was sent some samples, but have not yet burned boards...claimed distortion is in the thousandths of a percent.

[Nisbeth]

Start out doing a simple Cmoy amp based on OPA2132/2134. If you like, you can then experiment with different opamps to see what your prefer (commonly used types for headphone amps are OPA(2)227/(2)228, OPA(2)604, OPA627/637, AD8610/8620, AD823, AD843, AD845 and a few others). If you then want something better, then check out one of the designs from the tangentsoft-page linked above or start digging in the headwize archives for something you think looks interesting. Happy building


/U.


PS: The chip jackinnj is referring to is called TPA6120.

[Dominique]

Don't you think it'll get too complex with a dc-dc converter? It would increase circuit size, also this could introduce switching noise...

For my tiny portable mic preamp, I'm planning to use those hearing aid batteries (Zinc-Air) which exist in several sizes and the strongest are 11.6mm diameter, 5.4mm thick, 1.4V with over 500mAh!! That's a lot of capacity! And the OPA228 works fine with +- 4.2V, which means two times 3 cells, so 11.6 x 32,4mm.

Of course, you'd better estimate how much current the circuit will consume before choosing the batteries.

Regarding the choice of OP-amps, there are a lot, but do you want to build surface-mount or conventional style? Some of the newer OP-amps only exist for surface mounting.

Cheers
Dominique

Edit: I'm not sure if I understand you right:
You want to build the amp in a tiny extra box, do you?

[sonnya]

Originally posted by Myren
Hello,

Efficiency is a concern. Size would be nice.

Sound quality is semi-nice, but I dont plan on taking extrodinary measures in this project, given that my mp3 player itself doesnt produce the best sound. I'm hoping that it provides good sound at lower volumes, produces less clipping, and that a good pocket amplifier will give me better volume with better sound.

I'm assuming I'll need a very efficient dc-dc converter as well. my mp3 player uses a single aaa battery. i'm probably going to rip it out of its shell and use an aa battery, maybe go dual aa if the amp warrants it.

What silicon to use?
thanks
myren

I have been using a TPS61020DRCR STEPUP with a effiency of 96% for a handheld design (Cannot tell you about it... Brandnew hardware for another industry).. And it works like a charm...

It puts out 5VDC from a single AAA cell. and it has a battery low detector.

By the way... Size is 42mm*10mm*5mm on a 1.6mm FR4 PCB.
And it is very simpel to use.

The go for opamp's like AD8027/8028 which can run from singlesupply. Deliver 50mA into a load.
And you can control the crossover region of the input stage...

[Nisbeth]

No noise issues?


/U.

[sonnya]

from the SMPS??

i use 6.2uH inductors from panasonic which is shielded.
Also i use an LC output filter. so i have like 10mVpp at 700KHz.

it is placed in close proximity to a LF trasnponder reader, and this runs with no problem, with no reduction in reading distance.

And they are sensitive to radiated noise.

[Myren]

thanks all!

yes, to confirm, i'm looking to build a small single unit portable head phone amplifier. size is an object, and i'm coincidentally quite eager to start some surface mount work.

one or two aa batteries are my ideal power source: i have a bunch of 2200 mah double a rechargables I payed a mint for, but work excellently. i presume most amplifieres will require a +/- voltage. dc-dc convertors will get me this voltage split, i presume. what other techniques are there? i suppose dual battery is another option.

out of a morbid sense of curiosity, how different are the parameters to turn a headphone post-amp into a mic pre-amp? it occurs to me i have a microphone in need as well.

I'm with you guys through everything else, I have absolutely no idea what any of this means:

it is placed in close proximity to a LF trasnponder reader, and this runs with no problem, with no reduction in reading distance.

thanks
Myren