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Old 22nd February 2013, 08:24 PM   #1
Big Gig is offline Big Gig  United Kingdom
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Default USB DAC & headphone Amp with 3D Printed Enclosure

Having considered purchasing a USB DAC and headphone amplifier for my system I found that I couldn't quite find a product which met all my requirements. Then about 1 year ago I was inspired by a National Semiconductor chipset (as have a few diyers on this forum) to build a small desktop DAC and headphone amplifier to meet my own specification. The sound quality was so good that I took the design from basic prototype through to proof of concept and even got to grips with 3D CAD software to design the plastic enclosure. The results of which I have attached to this thread.
You can see more pictures here
Headphone Amplifier - a set on Flickr

Functionally the unit is powered by the USB 5V supply from which I generate a split rail using DC Converters. I then clean up the analog power with a Super Regulator (thanks to Walt Jung). USB audio is handled by a TI PCM2906 which outputs to a Wolfson WM8804 SPDIF transceiver with jitter attenuation. The DAC is a low power Wolfson WM8718 device. The product also has a mini optical toslink input with analog audio option and system management is handled by a programmable logic device (Lattice). The analog amplifier section uses TI LME49720 op-amps coupled to BUF634 unity gain high speed buffer. Power supply decoupling is handled by Wima SMD capacitors and some higher capacity Nichicon KA and FG series components.

I made a handful of units which I've shared with family and friends and I thought I would now post to the DIY Community. Thanks to Steve Soibelman for pointing me in this direction.

I call this Project Jaina.
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File Type: jpg Jaina_amp1.jpg (134.4 KB, 555 views)
File Type: jpg Jaina_Amp2.jpg (240.3 KB, 527 views)
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Old 22nd February 2013, 08:29 PM   #2
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Does it fly?
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Old 22nd February 2013, 08:44 PM   #3
Big Gig is offline Big Gig  United Kingdom
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Mach 1
Sounds great! I haven't been able to test with an Audio Precision or Dscope yet but using my sound card and RMAA I get encouraging results.
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Old 23rd February 2013, 10:48 PM   #4
Big Gig is offline Big Gig  United Kingdom
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RMAA results attached.
I think I am seeing the limitations of the sound card used to capture this analysis rather than the USB DACs true performance. Only an audio tester can resolve this to better precision
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File Type: gif freq_resp.GIF (24.9 KB, 476 views)
File Type: gif noise.GIF (12.3 KB, 431 views)
File Type: gif thd.GIF (11.8 KB, 433 views)
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Old 24th February 2013, 01:36 AM   #5
qusp is offline qusp  Australia
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nice work!, hey did you give one to Steve? I've been (more than) a bit slack sending him some (gifted as I wont build them) O2 headphone amp PCBs for him to build with his daughter. Hes helping me with a baffle design for a set of DIY speakers.

you must be boosting the voltage a fair bit with those DC-DC convertors, the superegs are not exactly low dropout and the buf634 not exactly efficient. well done, may I ask specifically which boost convertor?

Last edited by qusp; 24th February 2013 at 01:53 AM.
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Old 24th February 2013, 07:54 PM   #6
Big Gig is offline Big Gig  United Kingdom
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Cheers qusp! I just connected with Steve on a LinkedIn discussion on the Audiophile Forum regarding this project and he suggested I open this design up to the diyaudio community. So no he doesn't have my product...yet. He did mentioned he's actively involved in speaker design which is interesting. DIY speakers are great fun, I had a go about 15 years as a joint project with a friend using some Lowther drivers and their Fidelio cabinet design.

Regarding the DCDC converters on Jaina, I'm using:
LMR64010 Step Up Boost Converter to provide +6.4V
LM2611 Cuk Converter to generate -6.4V

I then regulate to plus/minus 5.75V using off the shelf LDOs (LT1963 & LT3015).

The Super Regulator has a dropout of ~1V so I added a bit of margin and run the clean analog supplies at plus/minus 4.50V

I could maybe run the amps with a slightly higher voltage and just stay within the 500mA USB limit, but with this arrangement I draw ~400mA with everything running.

My initial idea was to run from a battery so that's one of the reasons the supplies are designed for efficiency.

Anyways I attach a copy of the power supply schematics for reference, which some may find useful.
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File Type: pdf Jaina_Power_Supplies.pdf (87.6 KB, 99 views)
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Old 24th February 2013, 09:38 PM   #7
agdr is offline agdr  United States
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Big Gig - impressive project! Both the electronics and that custom case.
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Old 25th February 2013, 02:38 PM   #8
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Very nice!
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Old 26th February 2013, 08:47 AM   #9
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Ian,
Nice to see you made it over here. I think you will be in much better company here than over on the Linkedin site. Qusp and others will at least be able to ask an intelligent question and offer suggestions if you want or need them. Just for the rest of you, Big Gig is from the wonderful world of Invidia. I spend no real time on the LinkedIn site as that is more of a war about cables and nonsense than anything else. I do however post on certain composites and other groups there were my expertise does come in handy and others are also from the professional side of things. Somebody here may want to produce some of these headphone amps if Big G is willing to share the artwork for the pcb. Welcome to the group Big G.
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Old 27th February 2013, 09:41 PM   #10
Big Gig is offline Big Gig  United Kingdom
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Thanks Steve, I'm more than happy to share the Gerber files if anyone is interested to take a look at the layout. The design does have some gotchas so it does need a re-spin to fix a couple of issues. Most passive components are 0402 and there is one leadless package and 1 package with exposed pad which requires a good heat gun or ideally a reflow machine.
I would also change the DAC to the Wolfson WM8740 because the WM8718 won't lock to the WM8804 96KHz 24 bit output without a software write to DAC's internal registers. I mostly listen to CD or FLAC at 44.1K so this isn't really an issue for me. A Wolfson FAE acknowledged the problem but they don't make this hardware mode incompatibility obvious in the component datasheet.
Maybe I should build a DIY variant? Or release the casework data with PCB dimensions for DIYers to put their own electronics inside? I'm open to ideas of how to improve this design and happy to answer questions and requests for further info.
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