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Circuitbenders Forum => Links => Topic started by: Circuitbenders on June 08, 2007, 05:37:41 PM

Title: Simple mic and speaker to line level circuits
Post by: Circuitbenders on June 08, 2007, 05:37:41 PM

Theres smple circuits for interfacing just about any mic, speaker or line level signal with anything else you might come accross in circuitbending here:

http://www.epanorama.net/circuits/#audiocir

including a HiFi video audio input attenuator, Connecting speaker signals to line level inputs, Line level signal to microphone input adapter, 20 dB PAD for line to electret microphone input  (handy for voice changing megaphones), and all kind of other good shit.

Title: Re: Simple mic and speaker to line level circuits
Post by: phlogister on October 06, 2021, 01:05:19 AM

This is how i did it, headphones output to the computer's microphone input, one channel. Well, better do it on cardboard and never more than two wires crossed. The resistors are 100 k and 150 ohms (a typical output resistance of a microphone), the capacitor is 0.47 uF (makes a high pass filter 3 Hz and up, to remove the microphone's power voltage). The sounds, rhythms and demos of the tlf-3215 toy keyboard recorded  https://sndup.net/8xjh . Likely also bf-430a1 and many others have the same chip. Only a noise removal was done. Headphones output was made out of its microphone input, with a 8 k resistance in series. Weirdly it also had a switch, that switches the keyboard's speakers off when headphones are connected. In case there is any use of it for anyone, thanks.

(https://i.postimg.cc/gj0VLSJT/airsolder2.jpg)

Not knowing that much about it, i would say, headphones output is not line out that corresponds to some standard. And there are two standards, some 1 V and 0.5 V, something for 600 ohms output, the computer line in i guess is the latter. I think 1000:1 voltage divider for microphone input is enough for low power devices. But may not work for all headphone outputs. If they are just attenuated by one resistor, it is good enough for headphones but may not be much for high resistance input.

The problem with headphones output is that it is not a general output, it is only for headphones. So i guess that it may be a good idea to add a resistor parallel to the headphones output, with a typical headphones resistance, say 50 ohms. Then one gets the voltage that goes to the headphones, which supposed to be mostly not more than 2 V. So 10 times attenuation should then be enough to line out, and further 100 times to microphone input. Who knows more, correct me please thanks.