Another RTZ SDM (DSD) DAC

[Thermionic Idler]

Had some fun and games with the sigma22 board (bottom right) where R10 had to be desoldered and replaced with a different value. Turns out getting solder out of a through-hole with a simple solder sucker is nigh on impossible if it's connected to a ground plane on both sides, which acts as a nice little heatsink.

I sometimes use a micro drill bit and a pin vice to avoid delaminating the copper foil.

Yeah at one point I got the Dremel out but all the drill bits were too big.

[Thermionic Idler]

Quick update - the build is finished, but the Beaglebone isn't starting up Too tired to do any troubleshooting, I'll come back to it next week. Build pics will follow.

[Thermionic Idler]

Right then - so it seems that the Beaglebone isn't powering up because the linear power supply I've installed for it has a 'soft start' - after some Googling I discovered that if I unplugged the barrel connector and then plugged it in again, the Beaglebone booted up and worked normally.

So it needs a 'not soft-start'.

Best way to achieve this? I'm thinking a solid state relay rather than a mechanical one because of the lack of switch bounce - BUT... I think also the SSR may have some noise / in-line resistance of its own, hand-plugging the barrel connector was OK so I'm leaning towards a mechanical relay.

Thinking about it, it also should not be triggered too early i.e. before we near 5 volts, in case the BBB power management chips pulls the same shenanigans at whatever voltage pops the relay. So maybe we need a Zener voltage reference in there somewhere as well.

EDIT - I think it would actually be more sensible to have a time delay relay that kicks in after half a second - so a time rather than voltage monitor, getting a zener accurate enough to kick in at exactly 4.75V (the minimum required voltage for a BBB) when your power supply is 5.05V is going to be cutting it a bit fine.

[Thermionic Idler]

Things have been on a bit of a hiatus the last month or so, as I've been busy migrating my desktop over from MacOS to Linux. KiCad in particular took quite a bit of config work as I always get into a bit of a mess with my own symbols / footprints, so I was migrating those and doing some housekeeping along the way so that they hopefully stay in some kind of order going forward.

After finally getting that all set up, I designed a small PCB which uses a zener and BC546 to trigger a relay when the BBB supply voltage is around the 4.7 - 4.8V mark, hopefully that will satisfy its power management system. I've purchased several values of zener - the spice model predicted 3.9V should get closest taking into account there's also 0.7V or so at the transistor, but I will also test the circuit with 3.6V and 3.3V values.

[Thermionic Idler]

It's finally done! Actually I got it finished around mid-September but I've been busy with rebuilding my desktop OS (twice) so hadn't got around to updating this thread.

Anyway, the first attempt at solving the BBB power issue failed as it cut in at too low a voltage for the power management chip to respond. So I did what I probably should have done in the first place and sat the thing behind a relay controlled by a 555 timer set to click on after 3 or 4 seconds.

That worked. Finally I now have a functional, and superb sounding, Roon endpoint / DAC.

Picture of partly completed build with the 'extra' unplanned timer PCB in the foreground switching the power to the BBB and its DSDit cape:



Rear view of the finished item:



And same from the front:

[Ray P]

Good work Dave, perhaps even shoddy!

[Tony Moore]

Nice work! Looks great and I bet it sounds excellent.