I'd like to interface my Mackie 802VLZ4 mixer's line inputs and outputs with my phone and my ThinkPad by way of their TRRS jacks.
Doing this with TRRS-to-dual-TRS adapter cables has some problems:
- Horrific electrical crackling and chattering noise at the mic input when feeding the mic input from the aux send or the main outputs. My guess is that the mic bias voltage is interfering with the signal.
- Distortion. The signal level at the aux/main outputs of the mixer is far too hot for the mic input and requires running the output fader/knob at the lowest end of its range, which is less than ideal.
- Mono/Stereo. The mic input on a TRRS connector is in mono, which is fine (the first two problems notwithstanding) if I want to feed it from a mono aux, but problematic if I want to use the stereo bus, which will have to be summed to mono first.
For the record I've tried the adapter cable only with the ThinkPad and not my phone, yet.
I decided to build a little adapter box to solve the three problems.
I took a little inspiration from some videos on YouTube
and came up with this:
https://docs.google.com/drawings/d/1ovtH-qWSbTdVd8ZfaA4Itoj1b5tdtmYiYpHW9GAHVBk/edit?usp=sharingMind you, while I have decades of experience making my own audio cables and occasionally troubleshooting and fixing PCBs, and while I have a pretty good basic understanding of electricity and electrical components... I have never before built an electronic circuit from scratch, so this is my first project... ever. I'm in my mid 40's.
Therefore while I have a basic grasp of what the above circuit does, I have no idea why those specific component values were chosen, and whether or not they'll work in my application. I've got a resistor kit and some capacitors coming in so I'll be able to tweak the circuit.
What I'm hoping to find at this forum is some guidance, and advice should the device not operate as expected at first go.
I've already received the project box, connectors and other components from AliExpress and have started assembly. Image attached.
Thanks for reading.