Pico Monica
Non oversampling digital/analog converter

We all know about the advantages of non oversampling converters compared to those 1-bit-mash-bitstream-whatever-converters.
Time to build me one, I thought. ;-)

The converter (top) and the PSU (bottom):

This one is based on Monica 2 by [DIY paradise]. As far as I know, they don't offer Monica 2 anymore, only Monica 3 which has an USB input instead of SP/DIF, but I might be wrong - check out the DIY Paradise website for details. It's worth a visit, anyway.

Monica 2 (left), the current to voltage converter (bottom) and a balancer board (top) which was a left over from a previos SSL 9000 preamp clone project:

The Monica board remained completely as delivered by DIY Paradise, but the current to voltage converter got some additional caps to bypass the lytics. 100nF each:

The PSU is as simple as can be.
The 18V rails have 300 Ohm shunt resistors to ground to quickly discharge the huge caps (2 x 4700uF!) after the rectifier diodes bridge once the mains power is diconnected. The 12V rail doesn't need a shunt resistor since monica draws enough current on the 12V line to discharge the caps this way.
I wasn't able to meassure the remaining ripple after the passive (-> huge caps) and active (-> regulators) smoothing of the voltage, so the PSU seems to be not too bad ;-)
Please keep in mind, there is an additinal regulator plus diodes on the monica board to further smoothen the voltage. I reckon, there is absolutely no point in using batteries instead of mains power after a good regulation.

I truly wanted to have an optical input here, but my parts supplier had no lightwave receivers in stock and ordering them from another supplier would be 5Eur additional shipping costs - that's reason enough to go only for a coaxial SP/DIF input, isn't it? :-)
Pico Monica's back offers nothing unexpected: The SP/DIF input, the two balanced XLR outputs and the input for the supply voltages.

In the end, this converter was always meant to be used with my [Pico Rucksack project] and believe it or not, it's a heavenly marriage. Damn, they sound good, detailed and especially the sound stage is outstanding as expected from good fullrange speakers (with a perfect amplifier and a perfect DAC :-D).
[Here's] more about the Pico Rucksack project.

I'm not quite sure if the requantization distorts the digital signal or not, I haven't done all the meassurements and checks, yet, but the converter still sounds unbelivably good and detailed. I still need to do some checks in the digital domain, they will show the truth.

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Darius Kubarth 2008