First Project: Stereo Line-To-Mic Adaptor

[floobydust]

OK so I think that circuit is terrible and how do people come up with this to get fame and glory on youtube.

For the mic circuit, you need more attenuation to not overload the Thinkpad mic input. It's about -17dB and I would go to around -35dB. So R3 needs to be much lower, say 150-220 ohms (not 15k). Then another problem is the 1uF cap causes a bass roll off starting around 100Hz, not sure if you want this.

For the line-in circuit, there is usually a resistor to GND on each channel so the Thinkpad thinks headphones are connected. If it has a Class-D output then you will need filtering added to lessen HF noise from getting in the console. I think it's a Class-G headphone out though. I would try add 1k resistors from L, R to GND.

In all of this there is jack-detect lurking, to see if a headset or headphones or even headset button press is occurring. The 1.5k R5 and 1k's I'm suggesting can activate that in the right or wrong way so sometimes experimentation is needed.

[Helmanfrow]

OK so I think that circuit is terrible and how do people come up with this to get fame and glory on youtube.

I don't know if it's fame and glory so much as it's one of three videos that addresses this fringe, niche topic. 😂

For the mic circuit, you need more attenuation to not overload the Thinkpad mic input. It's about -17dB and I would go to around -35dB. So R3 needs to be much lower, say 150-220 ohms (not 15k). Then another problem is the 1uF cap causes a bass roll off starting around 100Hz, not sure if you want this.

How'd you calculate the mic input level?
I don't mind the mic rolling off the low end a little because it's just for voice. I found a rolloff calculator. I'll mess with the values until I find something close to 75Hz.

For the line-in circuit, there is usually a resistor to GND on each channel so the Thinkpad thinks headphones are connected. If it has a Class-D output then you will need filtering added to lessen HF noise from getting in the console. I think it's a Class-G headphone out though. I would try add 1k resistors from L, R to GND.

In all of this there is jack-detect lurking, to see if a headset or headphones or even headset button press is occurring. The 1.5k R5 and 1k's I'm suggesting can activate that in the right or wrong way so sometimes experimentation is needed.

Okay, I'll start making the changes you suggested and report back.