Hey all 🙂 Here's a project I'm calling rgba - reasonably good bluetooth audio.
It's a very small Bluetooth audio receiver, DAC, and amp that is meant to attach inline to the cord of a pair of IEMs (or headphones, though for my current purposes it's targeted at a pair of high sensitivity custom IEMs I have--you could adjust the OpAmp feedback network to tune it for other devices fairly easily). It aims to provide as high-quality audio as possible while retaining reasonable battery life and its tiny form factor.
It's based around the TI PCM5242 DAC and OPA1662 op-amp, with necessary power regulation and filtering circuitry and a Qualcomm CSR8675-based Bluetooth audio module that handles Bluetooth audio communication and charging the 3.7v LiPo cell.
Here's a couple of renders of the front and back of the current version of the PCB, which comes in at about 5x3cm total
Also here's a couple of images of the board layout. It's a 4-layer stack up, with PWR/Signal on layers 1 and 4 and two ground planes on the middle layers. I tried to prioritize the cleanliness of the signal path, then the power train going into the analog side of the DAC, then power into the opamp and everything else fits in around those.
Finally, you can check out the schematic rendered as PDF here: rgba/rgba.pdf at master * termhn/rgba * GitHub
and you can also check out the KiCad files and BOM in the Git repo here: GitHub - termhn/rgba: Reasonably Good Bluetooth Audio - A tiny, inline Bluetooth audio receiver for IEMs.
This is my first audio circuit design... it's based a lot around TI reference designs and application notes about HiFi audio/headphone amplifiers from them. Let me know what you think 😀
It's a very small Bluetooth audio receiver, DAC, and amp that is meant to attach inline to the cord of a pair of IEMs (or headphones, though for my current purposes it's targeted at a pair of high sensitivity custom IEMs I have--you could adjust the OpAmp feedback network to tune it for other devices fairly easily). It aims to provide as high-quality audio as possible while retaining reasonable battery life and its tiny form factor.
It's based around the TI PCM5242 DAC and OPA1662 op-amp, with necessary power regulation and filtering circuitry and a Qualcomm CSR8675-based Bluetooth audio module that handles Bluetooth audio communication and charging the 3.7v LiPo cell.
Here's a couple of renders of the front and back of the current version of the PCB, which comes in at about 5x3cm total
Also here's a couple of images of the board layout. It's a 4-layer stack up, with PWR/Signal on layers 1 and 4 and two ground planes on the middle layers. I tried to prioritize the cleanliness of the signal path, then the power train going into the analog side of the DAC, then power into the opamp and everything else fits in around those.
Finally, you can check out the schematic rendered as PDF here: rgba/rgba.pdf at master * termhn/rgba * GitHub
and you can also check out the KiCad files and BOM in the Git repo here: GitHub - termhn/rgba: Reasonably Good Bluetooth Audio - A tiny, inline Bluetooth audio receiver for IEMs.
This is my first audio circuit design... it's based a lot around TI reference designs and application notes about HiFi audio/headphone amplifiers from them. Let me know what you think 😀
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Sent first run of boards off for fab thru OSHPark 🙂 Will order a few sets of bom soon... then to test!
This morning I finished assembling the first prototype and... evidently forgot to order the battery connector, and I haven't actually tested listening to it yet because I still need to program it a bit first but... ITS ALIIIIIIVE! (And no excessive heat or magic smoke!)
Also, in the time since I ordered rev 1.0, one of the regulator ICs went out of stock everywhere and won't be back in stock for several months. Made a rev 1.1 featuring new 3.3v regulator chip, even smaller size (shaved ~10mm off each side, now 40x21mm), and a new interactive BOM hosted on GitHub pages that you can check out here: Interactive BOM for KiCAD
Here's renders of the new board, will be ordering a set plus the necessary new IC and new battery connector soon after I confirm things are working on rev 1.0.
Also, in the time since I ordered rev 1.0, one of the regulator ICs went out of stock everywhere and won't be back in stock for several months. Made a rev 1.1 featuring new 3.3v regulator chip, even smaller size (shaved ~10mm off each side, now 40x21mm), and a new interactive BOM hosted on GitHub pages that you can check out here: Interactive BOM for KiCAD
Here's renders of the new board, will be ordering a set plus the necessary new IC and new battery connector soon after I confirm things are working on rev 1.0.