Mini-stack (part 1)

Not exactly the most challenging builds ever undertaken, but still…

More or less since I originally built my passive preamps I have wanted to build more components in the same form factor. Here is the beginning of a “mini-stack”, namely a USB DAC and a passive pre, which should then be supplemented later by (at least) a power amp in the same small chassis (a GX143 from modushop.biz, so 124x40x73mm). That isn’t ready yet, but I do have a few ideas for what to do 😀 As for what is ready:

The passive pre is based on a Noble 10k pot that I happened to have lying around – not much more to say about that really 🙂

The DAC is based on an “off-shelf” module from ebay. It uses the SA9023 USB receiver/ES9023 DAC chipset so that it can accept up to 24/96 input signals. The module is powered from the USB connection. It is possible (and possibly recommended) to use an external supply instead, but since the preamp is passive I wanted to keep the design “cordless” except for the USB. Obviously that won’t work for the power amp… My only little piece of hacking here was to wire an “USB on” LED on the front panel instead of relying on the on-board SMD one.

The ES9023 DAC chip from ESStech is a highly respected performer and used in quite a few designs such as the AudioQuest DragonFly (albeit there with a more complicated/advanced USB front-end) and quite a few others. It is voltage output with a built-in charge pump to avoid capacitors in the signal path and it is actually capable of driving headphones directly, so the 10k load here isn’t really an issue.

The sound quality of the board is quite a bit ahead of the older PCM27xx-based designs as well. The sound from this little combo is actually quite good and the fact that no external power suppliers are required makes it a bit more interesting.

My idea for the power amp is to use a class D chip powered from an off-board switching supply. I have looked at both the TPA311x and the TDA749x chips but I am still exploring options here so nothing definite yet…let’s see what happens 🙂

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