I fixed the last software bug on this today, so I'm officially calling this project "done". The goal was to create the highest quality, most transparent headphone amplifier possible with little comprimise.
- The signal path is TORX142L or AD8611 -> CS8416 -> AD1896 -> PCM1792 -> OPA4134 -> TPA6120A2.
- There's also an ATMega8L onboard which performs digital volume control - the volume knob feeds the Mega8's ADC a voltage, which digitizes/filters the sample and updates the digital attenuation register in the PCM1792. The Mega8 also handles automatic input selection, swapping back and forth between optical/coaxial inputs until the CS8416 locks.
- Power supplies (3.3V digital, 5V analog, +-12V analog) are regulated using LM1085 regulators. Rails and grounds have solid planes. Analog/digital grounds are connected using a 0-ohm resistor underneath the DAC.
- The oscillator is a cheap 5x7mm SMT XO from CTS. It measures better than any sort of XO/VCXO i've ever constructed.
- I'm using the AD8611 SPDIF circuit I made a thread about a while ago, which uses hysteresis (25mV) for stability whenever there's no input connected. Sorry Jocko
- Other parts... Case is a Hammond 1455L1601BK, front/rear panels are made by frontpanelexpress.com, headphone jack is a slimline Neutrik with gold contacts, and the spun aluminum knob is from Kilo.
How does it sound? Can't say anything bad about it. I love how I can have the volume cranked up all the way in a completely silent room, and I can't hear anything with no input playing. And with music playing, the sound is crystal clear... right now I'm listening to Mule Variations, and I don't know if it's placebo effect but I'm noticing all sorts of different instruments and background things that I never noticed before. Tom Waits makes a great sonic treasure hunt.
I'll test it on the Audio Precision at work sometime, which has better ears than I do.
On with the pictures:
front view:
[IMGDEAD]http://img155.echo.cx/img155/5456/hd117km.th.jpg[/IMGDEAD]
rear view:
[IMGDEAD]http://img155.echo.cx/img155/9333/hd127vi.th.jpg[/IMGDEAD]
4-layer, bare PCB:
[IMGDEAD]http://img155.echo.cx/img155/8062/hd13a3cj.th.jpg[/IMGDEAD]
The assembled PCB, during software hacking:
[IMGDEAD]http://img155.echo.cx/img155/617/headphoneamp8jt.th.jpg[/IMGDEAD]
And finally, here's the entire set of build files (gerbers, eagle files/libraries, etc) - feel free to tear them apart and critique me, or rip them off and build your own. Just don't make a million dollars off the design without buying me a beer.
http://rapidshare.de/files/2470563/HD1.zip.html
- The signal path is TORX142L or AD8611 -> CS8416 -> AD1896 -> PCM1792 -> OPA4134 -> TPA6120A2.
- There's also an ATMega8L onboard which performs digital volume control - the volume knob feeds the Mega8's ADC a voltage, which digitizes/filters the sample and updates the digital attenuation register in the PCM1792. The Mega8 also handles automatic input selection, swapping back and forth between optical/coaxial inputs until the CS8416 locks.
- Power supplies (3.3V digital, 5V analog, +-12V analog) are regulated using LM1085 regulators. Rails and grounds have solid planes. Analog/digital grounds are connected using a 0-ohm resistor underneath the DAC.
- The oscillator is a cheap 5x7mm SMT XO from CTS. It measures better than any sort of XO/VCXO i've ever constructed.
- I'm using the AD8611 SPDIF circuit I made a thread about a while ago, which uses hysteresis (25mV) for stability whenever there's no input connected. Sorry Jocko
- Other parts... Case is a Hammond 1455L1601BK, front/rear panels are made by frontpanelexpress.com, headphone jack is a slimline Neutrik with gold contacts, and the spun aluminum knob is from Kilo.
How does it sound? Can't say anything bad about it. I love how I can have the volume cranked up all the way in a completely silent room, and I can't hear anything with no input playing. And with music playing, the sound is crystal clear... right now I'm listening to Mule Variations, and I don't know if it's placebo effect but I'm noticing all sorts of different instruments and background things that I never noticed before. Tom Waits makes a great sonic treasure hunt.
I'll test it on the Audio Precision at work sometime, which has better ears than I do.
On with the pictures:
front view:
[IMGDEAD]http://img155.echo.cx/img155/5456/hd117km.th.jpg[/IMGDEAD]
rear view:
[IMGDEAD]http://img155.echo.cx/img155/9333/hd127vi.th.jpg[/IMGDEAD]
4-layer, bare PCB:
[IMGDEAD]http://img155.echo.cx/img155/8062/hd13a3cj.th.jpg[/IMGDEAD]
The assembled PCB, during software hacking:
[IMGDEAD]http://img155.echo.cx/img155/617/headphoneamp8jt.th.jpg[/IMGDEAD]
And finally, here's the entire set of build files (gerbers, eagle files/libraries, etc) - feel free to tear them apart and critique me, or rip them off and build your own. Just don't make a million dollars off the design without buying me a beer.
http://rapidshare.de/files/2470563/HD1.zip.html