To not use the bias voltage you'd have to solder another TRS plug and socket. That will cost you money and some solder joints. Just removing one resistor is easier.

If you don't want to use bias voltage, there are two ways without damaging the sound card itself. 1. Use TS plug to connect. This way the bias voltage will be grounded. 2. Use TRS plug to connect and do not ot use ring connection on it. The above methods do not require SMD soldering, do not reduce the sound card functionality and do not need any extra components.

These are mono microphone inputs.

You certainly could, although the bias voltage would create a 'thump' noise through capacitor when you fist turn it on, also the bass response would be reduced.

@@TrystansWorkbench The thump could be got rid of by a couple of diodes.

@@goingnowhere7845 So removing the bias resistor looks a neat idea after all. All the best Richard, thank you for your comments.

Damjan, the datasheet for the CM108 chipset is here: rats.fi/wp-content/uploads/2016/04/CM108_DataSheet_v1.6.pdf

They would just drift in the same direction I suppose, so the relative drift would be zero. So remove the crystal from one board, and feed the oscillation from the other board to where the crystal would be? What application do you have in mind?

@@TrystansWorkbench I was just wondering if you could create a multi channel sound card with the inputs. I have been using things like MAX9814 with electrets and admp404 mems on a Pi for voiceAi. But generally seem far better than bias driven passives. Even line ins.

Yes, almost certainly.

Hi Webpunk, well you would need to remove the bias voltage as in the video, then get a 1/4" Mono to 3.5mm adapter for your guitar lead to go into. You might have to experiment with your guitar's output level, but it should work.

@@TrystansWorkbench whow, big thanks! It should sound like a guitar connected to line input? I mean input impendace of soundcard would 50k, but output impendance of the guitar is 500k, would it work in this way?

@@webpunky I didn't realize a guitar had such a high impedance. If I'm not mistaken, the impedance of the CM108 chip (without the bias circuit) would be in excess of about 200k. It could be that the mismatch may mean that you won't get enough drive from the guitar. These things are very cheap though, it's probably worth trying. Keep shredding!

@@TrystansWorkbench Hahah, big thanks for the answers, i will!) I think i will write to you when i make this mod)

@@webpunky Heh, no worries. The other thing I've realized after 'sleeping on it') is that the MIC input is a TRS (Tip Ring Sleeve) stereo socket, but Tip and Ring are connected together. So if you put in a Mono 1/4" guitar lead into a 1/4" to 3.5mm adapter you would not get a signal as the ring Ring and Sleeve would be shorted out. So you'd need to make a lead up to isolate the Ring of the 3.5mm MIC socket, or try to remove that connector on the sound card itself (possibly by cutting the PCB track between Tip and Ring might be easiest) - or it could be better to be done with it and remove the 3.5mm socket at wire in a 1/4" mono socket.

After this mod, add your own bias voltage for your condenser microphone.

But for condenser it needs power....so I think i don't have to remove this resistor!

Yes, that's correct if it the right bias voltage for your condenser microphone.

I can't increase bais voltage.. because USB ports max 5v..i think.

Yes, USB is 5v. Typically a condenser microphone would want less than 2 volts. Take care.

Perhaps an external crystal is more stable than the internal oscillator? Who knows!

@@TrystansWorkbenchhi , trystan , probably the designer of the chip ... i have been working and testing different cm108 cards , including the fake ones .. for me the cm108B has less quality audio compared to the cm108 and cm108AH cards , tested with grado ps1000 . the best audio card ever is no longer being produced , a cm108 with extra lobs pinout , the negative output from the lobs pin makes the audio quality stunning , and no output capacitor was used ... even when used on youtube! the new cards are not that good , the output and power capacitor sound not as good , and the layout and other capacitors are less good , but for the price we cant argue , i hope the old ones come back , i would buy a 100 instantly !

Yes, very often newer versions of boards concentrate on value engineering rather than absolute performance unfortunately. I imagine not having an output capacitor gave it improved low frequency response too

@@TrystansWorkbench hi , trystan , the whole audio became "live" and even emotional , the difference in a bad and good upload was very easy to hear . i have a audioquest black card , it was no match for the old cm108 card!