Custom USB Microphone difficulty level? - Page 1
Forum section: electronics / beginners

author: joeyjoejoe
author_rank: Frequent Contributor
timestamp: June 23, 2018, 06:29:12 pm
content: I currently have this mic:I opened it up out of curiosity, and it had rather few components, and an AK chipset. I believe it would be comparable to the AK5371, which has everything built-in mostly, including the ADC and USB interface.I'm wondering how difficult it would be to design a custom USB microphone?1) I want to integrate a physical mute switch and indicator - many lack this.2) I want it to be cheap(er) then some of the options on the market.3) Perhaps most importantly, it would be a fun project.Some of my concerns1) I'm a bit worried about the audio quality, but then when I think about it, this Logitech mic probably has a 1$ condenser at the tip anyways.2) Unsure about USB design - from what I've seen, I think PCB design is a bit harder, traces must be equal length.3) Audio is another world for me, but if I can copy existing schematics or reference design... also no clue about which MIC element to pic, impedance matching, etc.Finally, I can't actually find any of these AK components very easily.. but I did find the AK4571 in stock at Digikey. Perhaps this is the successor? Or perhaps there's other companies as well I should be eyeing?Any tips or discussion is appreciated!

author: wraper
author_rank: Unknown
timestamp: June 23, 2018, 07:13:19 pm
content: Quote from: joeyjoejoe on June 23, 2018, 06:29:12 pmThey are functionally different ICs, both very old and AK4571 is the older one.

author: floobydust
author_rank: Super Contributor
timestamp: June 23, 2018, 07:13:54 pm
content: It's not hard to make an "OK" microphone for speech, very but difficult to make a really good one.It really depends on your budget. Some PC blog mics are crazy overpriced and silly art looking for what you get.Best mic signal processing includes a low noise differential preamp, some filtering, compressor/limiter- not just a simple preamp going to an A/D.TriedMaxim MAX9814but found it to be noisy, distorted crap.Best fidelity signal processing IC's with compressor/limiter are fromTHAT Corp.but more expensive and complex to design (lots of fun though). Many of their parts suitable for professional musicians.Low cost electret condenser modules are very good, flat response and different radiation patterns (cardioid/omni) available. Just they have low output so amplifying this with low-noise and rejecting AC hum pickup can be a challenge. Then you have to filter things within voice limits and lower dynamic range so an A/D can handle it.

author: joeyjoejoe
author_rank: Frequent Contributor
timestamp: June 23, 2018, 09:10:09 pm
content: I think I'm OK with a mediocre result, as I'm more then happy with what is inside the Logitech mic, and it's nothing special at all. This is just for voice for Skype/Discord - nothing fancy.

author: JS
author_rank: Frequent Contributor
timestamp: June 23, 2018, 11:16:07 pm
content: Why not to mod one? If you want better quality you could upgrade the capsule and even add a gain stage...Add a switch and led and be done with it...JS

author: joeyjoejoe
author_rank: Frequent Contributor
timestamp: June 24, 2018, 12:04:02 am
content: I want it to be smaller and sit on top of my monitor.

author: JS
author_rank: Frequent Contributor
timestamp: June 24, 2018, 12:06:01 am
content: Reatyle it, or would you get a smaller pcb and useful parts cheaper, considering your time, than the ones in the mic.JS

author: Audioguru
author_rank: Super Contributor
timestamp: June 24, 2018, 03:57:12 am
content: An electret mic works best with filtered 8V to 10V feeding a 10k bias resistor to give the 0.5mA to the mic. The MAX IC gives a voltage too low so the mic produces clipping distortion.You probably do not want the compression and AGC in the MAX IC that suddenly drops the gain way down if there is a cough or "plop" you dropped something.You never "match" the preamp input impedance to the mic impedance because if you do then you are throwing away half the signal level. Use a 27k preamp input impedance that is 10 times the 2.7k electret mic impedance with its 10k bias resistor.