What headphone amp to build?

[hjf]

Hello,
I bought some headphones (ATH-M50) and I'd like to build a nice amp for them.

I don't care too much about efficiency or heat (it's for headphones! so I'm guessing about 1W MAX should be enough? The ATH-M50 are rated for 1.6W)

What I'd like:

• Simplicity: I like simple, elegant designs that don't rely on multiple stages. My source will be (mostly) my computer's sound card.
• Availability: I live in Argentina, so I can't order fancy or obscure parts, because of import issues and shipping delays (can take up to 3 months for parts to arrive). For example: anything Burr-Brown is out of the question. Also any kind of "fancy" audio-grade capacitors.
• Quality: I would like a simple, undistorted design. This is why I was thinking of Class-A (to avoid switching distortion), or polarized Class-AB. If it needs matched output transistors, that can be a problem (I have loads of BC548 but I doubt these are good for audio).

I might eventually build a dedicated SPDIF to Analog board to get digital audio directly to my headphones, but that will be a later stage. I do have a nice little VS1053 decoder card which I might use as a little dedicated audio player (I have solid knowledge in microcontrollers, but my analog skills are very poor).

I can build PCBs, I have a good knowledge of linear power supplies, so that is not an issue for me.

I found several designs on google. Most of them were based on a single transistor, or push-pull configuration, but always capacitor-coupled, which I'm not really sure is a good thing. Headwize had this design but I don't understand it completely.

I have some opamps in my junk box right now: OP07, OP177, NE5532, NE5534, MC4558, TL07x, TL08x. There's even an LM3886.

Any recommendations would be great. Thanks.

 

[Pacorl]

I would try this:

NP-100v12: DIY 12AU7 (ECC82) Tube / IRF510 MOSFET Headphone Amplifier

 

[hjf]

Thanks guys. I've built the one at Headphone Amplifier and it's been working great.

But i'm really interested in building that 12AU7 amp. These are available and very cheap here (USD 7 for used valves, which will be good enough for testing, then replace with new ones).

Here's the pic of my finished amp:

 

[Vostro]

Hi hjf,
If you build the tube circuit, please let me know.

Thanks

 

[jcx]

if these cans are 99 dB re 1mW then you don't need that much V, I ~ 2.8 Vpk, 72 mApk would give 120 dB SPL

you really don't want that ESP project amp's +23x V gain - just amplifies noise and forces you to use large attenuation with sensitive headphones

I would think even +4 gain would be a bit much with most desktop digital audio outputs giving 2 Vrms

lowering the loop gain makes the loop faster, may give stability problems, could be why Rod goes so high on the gain

I would put a inner loop lead C across the op amp -input to op amp output, calculate the C product with the feedback R for a RC time constant > 2x of the (closed loop amp gain)/(op amp GBW) use radian/s == frequency in Hertz * 2 pi

 

[hjf]

if these cans are 99 dB re 1mW then you don't need that much V, I ~ 2.8 Vpk, 72 mApk would give 120 dB SPL

you really don't want that ESP project amp's +23x V gain - just amplifies noise and forces you to use large attenuation with sensitive headphones

I would think even +4 gain would be a bit much with most desktop digital audio outputs giving 2 Vrms

lowering the loop gain makes the loop faster, may give stability problems, could be why Rod goes so high on the gain

I would put a inner loop lead C across the op amp -input to op amp output, calculate the C product with the feedback R for a RC time constant > 2x of the (closed loop amp gain)/(op amp GBW) use radian/s == frequency in Hertz * 2 pi

the amp itself is very quiet, but i've noticed my phone's output (it was the first thing i tried it with) was quite noisy! but, connected to my computer's motherboard audio (Intel DH67BL) it is very quiet.

The soundcard doesn't really have much headroom. In order for the EQ to work, i really need to turn the volume halfway down. If i use it about 80-90% on the PC, and lower my volume pot, i don't get noise but the bass is lost.
If i turn the volume higher on the amp, and lower on the PC, it sounds much better but noise starts becoming audible. Not annoying, but it's there.

 

[Vladco]

You should visit headwize.com DIYproject section. Simplest one is MOSFET headphone driver by Greg Szekeres. Other option is zen headamp. You can find tons of information on the web including balnced version. Or visit headfi.org diy setion. Lately it become very diy unfrendly but still got tons of information including PPAv2,M3, peter millet hibrid. Or pick JLH kit from ebay but recapping a must. Also you should match transistor or will get big DC offset on start up.
Vlad