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The Mute Audio SkeletonDAC

SkeletonDAC History

Early in 2011, it became apparent that Texas Instruments' decision to NRND (Not Recommended for New Design) the PCM2702 DAC chip was having a significant effect on the price for that chip. The BantamDAC (and AlienDAC before it) was based on the PCM2702 chip. Prices as of this writing (July 2011) have exceeded $18 per PCM2702 chip at Mouser and over $19 at Digikey. At the same time, Texas Instruments was recommending the use of the PCM2704/5 as a "functional equivalent" for the PCM2702. Unfortunately, the pinouts are not the same between the two chip designs. The PCM2704/5 could not be used as a drop-in replacement for the PCM2702.

For awhile now, customer requests had been overwhelming to change the USB Type B connector on the Bantam to a mini-USB. Beezar and DIYForums also desired to re-shape the BantamDAC's PCB into the format established for the GrubDAC (corner notches and mid-lenth mounting holes). This would enable its use with the attractive and economical Hammond 1551HTBU translucent blue, plastic case. It would also preserve its existing use in the onboard-DAC-section of the MAX V1.2 PCB and for the Carrie USB-powered portable headphone amp design. All of these new requirements, however, (particularly the pin-out differences of the PCM2704/5 chip) called for an entirely new design.

Erik Soosalu of Mute Audio (the GrubDAC designer) graciously volunteered to take a look at the new chips (PCM2704/5) and to see if a replacement design could be developed for the BantamDAC. It was also noted that with the GrubDAC already available, and since the primary advantage of the PCM2704/5 was in its all-around built-in features, the decision was made to go as minimal as possible. No separate power regulation, no separate USB or clock interface, and no separate amplification stage would be considered. Instead, the goal was take advantage of all of the built-in features of the DAC chip to the greatest extent possible.

In short order, Erik came up with a new design: the SkeletonDAC. As a bonus, the PCB even made use of the optional SPDIF-out capability of the PCM2704/5 chip. With a slightly different build (mainly larger output coupling capacitors), the built-in headphone amplifier of the PCM2704/5 chip could also be used to directly connect to headphones with the SkeletonDAC. Prototypes were ordered and several were shared with builders who posted their questions and results on Head-Fi in The SkeletonDAC thread.

BantamDAC prototype

Carrie with the BantamDAC

SkeletonDAC prototype
As mentioned earlier, Erik's design preserves the commonality of the SkeletonDAC with the GrubDAC and BantamDAC and its use with the Millett MAX V1.2. The new MAX V1.2 PCB can use a BantamDAC, GrubDAC, or SkeletonDAC mounted directly on the MAX PCB V1.2. This is a further application for the SkeletonDAC, in addition to the Carrie and stand-alone uses.

Millett MAX V1.2 with BantamDAC

Throughout its development, the goal was to make the SkeletonDAC a replacement for the BantamDAC, while preserving commonality with the outstanding GrubDAC. The BantamDAC was an excellent, versatile small DAC that set a high bar for features and performance at a very low price. The SkeletonDAC exceeds that bar with what we believe must be one of the most economical DIY-DACs on the market. We believe the SkeletonDAC is an excellent replacement for the BantamDAC in all its uses or as a cheaper alternative to the GrubDAC, but further - the SkeletonDAC is appropriate for direct connection to small headphones/earbuds!
file last changed:Saturday, August 6, 2011 7:00:00 AM
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