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The Mute Audio SkeletonDAC


What is the SkeletonDAC?

The Mute Audio SkeletonDAC is a ground-referenced, USB-input high-fidelity audio DAC. When assembled properly and attached to the computer via a USB 1.1 port, it will be natively detected in Windows, OSX and Linux without the need of any add-on drivers. Once recognized and setup by the operating system, it can be utilized as a high quality audio output device. You can then use your choice of media player to play .wav, .mp3, .flac or other audio files. Output can be connected to your choice of 3.5mm, 1/4", or RCA jacks depending upon what you wish to attach to the board. It can also be used to directly connect to low-impedance, efficient headphones or earbuds (see below).

The SkeletonDAC represents one of the smallest layouts yet offered to the DIY community for a USB DAC board and adheres to the standard planform established by the famous GrubDAC. The two-sided board is approximately 1" wide by 2" long and includes notches and screw mounts to fit the popular and economical Hammond 1551HTBU plastic case. The design utilizes the USB-interface, onboard 3.3V regulator, heapdhone amplifier, and optionally - the SPDIF output sections of the Texas Instruments' PCM2704 or PCM2705 DAC chips. The use of the PCM's chip onboard regulator ensures a quality power source to the digital sections of the DAC chip while requiring an absolute minimum of supporting parts. The on-board USB connector is of a Mini-USB type, allowing for use of mini-USB cables which are becoming standard in the industry.

Despite its small size, the SkeletonDAC utilizes the built-in amplifier of the TI PCM2704/5 to allow direct connection to low-impedance, efficient headphones and earbuds. You must use properly sized output coupling capacitors to prevent loss of bass (see the Tweaks and SkeletonHeadphoneDAC pages on this website) and also include a small 3.5mm headphone jack (barrel-type recommended). Power output is approximately 12 mW at 32 ohms. This is enough power for many smaller earclip or earbud type headphones and perhaps enough power for some very efficient, low-impedance full-size headphones, too. However, output is sufficiently neutral to also provide line-out capability for connection to an external amplifier.

Like the BantamDAC and GrubDAC before it, the SkeletonDAC can also be built as a CableDAC. In this configuration, the on-board USB connector is bypassed using a pig-tailed USB cable soldered directly to the board. This configuration provides an amazing combination of convenience and versatility for quality listening.

In addition to all of these features, the SkeletonDAC also has an option on the PCB to include an audio signal transformer, enabling a SPDIF output for coaxial cable. This means the SkeletonDAC can serve as an inexpensive, self-powered USB-to-SPDIF convertor device for higher-level DACs.

The SkeletonDAC can be built for as low as $25, depending on case and connector selections. The basic PCB can be populated for $20. We believe that makes the SkeletonDAC perhaps the most economical Do-It-Yourself DAC on the market.

(prototype PCB)

(prototype PCB)

What's needed ...
Basic construction and parts selection is covered in detail within these web pages. Other than the parts in the Bill of Materials, you will need a soldering iron and solder, sufficient for SMD PCB work. This is not as intimidating as it sounds - just be sure you have a low-power soldering iron with a small chisel tip and good solder (eutectic recommended) that is thin and easy to use. A Hakko 936 with a T-0.8D tip or equivalent will go a long way in success of building the Bantam, but is not strictly necessary. Solder should be on the order of 0.025" diameter or smaller, although smaller diameters can be difficult to use (lots of breakage). Eutectic solder is best - a blend of 63/37 tin/lead with a rosin flux core (non-corrosive). Besides the miscellaneous tools used in PCB work such as needle-nose pliers (smooth jaws), flush cutters, DMM, and wiring tools - strippers, wire cutters, heat shrink, etc., there are a couple of specialized tools that can make the difference between success and failure with building SMD projects:

Tweezers - These should not be from your mother's, wife's, or girlfriend's makeup kit. Instead, if you invest in only one tool for this project, a quality pair of SMD tweezers is it. There are many to select from and can be found at Mouser, DigiKey, Allied, Newark, and even Fry's. Try to buy one that's specific for SMD and not from a combination kit, unless the kit is specific for SMD work (in which case, it's probably way too expensive for this project). I purchased some #7 stainless-steel, non-magnetic curved tip tweezers:

These were somewhere around $10 for an off-brand copy (GoldTool at Fry's) and have worked fine for me, but be careful that you get good-quality ones with tips that do not flex and are as sharp as a pin, almost. Xcelite makes good ones (shown) and Wiha makes outstanding versions. Others go for the straight tweezers, but I find the curved tip is more natural for me. It is the only tweezer I use.

Flux Pen - These are unbelievably helpful with SMD work, and also unbelievably sticky - so be careful. Used liberally, the flux from a flux pen can almost glue the part down. It can get a bit troublesome if you get it on the tip of your tweezers, though.

Helping Hands - These are more or less obvious. I use ones that are only $1.99 at Harbor Freight, but you shouldn't have to spend more than about $5 almost anywhere that carries them. The board is way too small to hold with your hands while soldering. (Use some electrical tape to protect the PCB surface from the alligator clips.)

How to get help ... has more than enough information to help you complete the SkeletonDAC. Besides these web pages, the forum itself provides ample opportunity to search for answers or for asking direct questions. Most of the SkeletonDAC designers and prototypers are all very active forum participants and will do their best to get your problem solved. In addition, there are many other builders that post and answer questions at: Head-Fi. We hope you enjoy building and listening to the Mute Audio SkeletonDAC!
file last changed:Saturday, August 6, 2011 7:00:00 AM
Please contact the SkeletonDAC webmaster for questions about these web pages.