A long time ago, I rather naively bought a Monica DAC from diyParadise. Looking at it now with more experience designing DACs and boards in general, it’s easy to see it’s an awfully badly designed board and the TDA1545 chip used should never be used unbuffered as it is. As the parts are fairly rare and of good reputation, I decided to put together a project that would hopefully take all the good bits of DAC designs available, and combine them into one board. The result is the Nothing New DAC (NoNe DAC). Just to quickly run through the design:
- Differential S/PDIF input is taken through a transformer, and then buffered using Jocko Homo’s input design
- S/PDIF decoding chip is a CS8412, with improved PLL filter design (I’m afraid I’ve lost the link)
- DAC chip is a Philips TDA1545 non-oversampling continuous calibration DAC
- Active I/V is taken from rbroer’s simple single rail discrete design
- Output capacitors were (eventually) taken off-board due to the large size of decent polypropylene caps
On board power is first smoothed by a CRC Π-filter, and then split to two separate LM317 linear regulators; one is for the low voltage IC section (10 V), and one is for the higher voltage I/V stage (15 V). Both can easily be bypassed if a decent off-board regulator is used. The IC voltage is then further regulated by 3 separate TL431 shunt regulators, which power the digital and analog sections on the CS8412 and the TDA1545. Each current source delivers 100 mA, which leaves ample headroom for the chips.
A board was ordered from BatchPCB (in 2009!) and you can see it above, with my rather old Nokia there for scale. It looked good, but I ran out of time/motivation to actually build it up. So, this year I’ve finally got round to making it up. It’s a mixture of PTH and SMD, so the build was fairly straight forward, with only a few niggles regarding component placements.
Two big problems, however, were significant. The 74HCU04 used for the input buffer had its inputs on one side wired back to front, which was easily fixed with some jumper wire. There seemed to be a problem with the board manufacture, as it’s not connected to the receiver chip in any way. As the trace responsible is under the chip, this required some more drastic surgery. The other problem was the connection to FSYNC (WS) and SCK (BCK) – they were the wrong way around too.
Given the above problems, the files won’t be uploaded as it’ll take some fairly major changes to fix. The board has been re-done, and I’ll post the results up in the next post with a full write up.