Digital audio in hi-fi certainly often comes from a music streamer, yet the usefulness of Bluetooth cannot be understated. So the next step was to include a high-fidelity Bluetooth module and automatic switching for it. I did have a stand-alone BT unit before, but none that covered LDAC, currently the best technical standard for streaming audio over Bluetooth, and it would be nice not to have to go through remotes and input changes each time. As I’ve noted before, my main DDC board has two inputs, so I’ll use those together with relay switching and module signaling to switch between them.

But including a noisy Radio frequency module also has its issues, here I made a thick copper tub for it to go in, itself mounted at the very top of the chassis, and the antenna only ever external.

Switching is not something I want to have to do manually, as you can see from the previous post there I have it setup so a trigger signal from turning my media streamer on, automatically turns this unit on, I want something similar with the Bluetooth option. To get there I noted that the Module had an “EN” pin, a pin that goes to around 3.3V when the  module is connected to another unit. So here I have a signal that can drive an indicator LED, but also it can send a signal to a relay to switch.

I chose a DPDT, double-pole, double-throw, relay since the dip switches to select input was configured such, so some quick and dirty tiny soldering later, hooked to a relay module this should in theory switch to Bluetooth once someone connected to it. I did find a note saying the unit in question should trigger on minimum 2.8V so should be fine.

This rebuild I also added a number of tweaks not mentioned before, as before I included local filtering on the new modules, a couple of caps close to them for good measure, but also included ferrite beads on each of the three main taps from the power supply, DDC-board, USB, Bluetooth. The relay’s get a 1Ohm resistor instead, nothing more really needed.Other notables include using star-grounding, having each of the units, and connection to case have their own dedicated return to power-supply ground, to minimize noise. And lastly to use the box without the media streamer on, which powers the whole unit remotely by sending it a 5V trigger signal over USB, I need a switch. To do this i have an on/off/on Single pole double throw switch, it connects two lugs together in each end

Custom DDC: 1 Digital to Digital Converter; USB to l2s over HDMI; S/PDIF; AES