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I use a stereo jack to rca cable


and then I connect the signal to the rca's signal (pin) and ground to the rca's ground (the round metal rim).

It is the simplest, cheapest and most crude way to use an audio card oscilloscope. The fidelity of the signal will be mediocre due to losses caused by the connections and the cables. Not to mention that if you apply excessive voltage you may destroy your sound card (or more...).

The proper way is to build a circuit like this.

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That's a good interface circuit to protect the sound card from damage, except its output voltage swing of up to 11V positive or negative might still cause damage. Check the absolute max input voltage spec for your sound card. The circuit will also work fine with a positive 5V and negative 5V supply.

The TL082 dual opamp is noisy. A TL072 is a low-noise version and costs less.

The TL082 and TL072 dual opamps oscillate at a very high frequency when they directly drive the capacitance of a shielded cable. Therefore I recommend adding a 100 ohm resistor to the circuit's output (the pot's slider) in series with the shielded output cable.

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  • 5 weeks later...

Anybody cares to explain how does the "150V input protection" part work?
I am thinking of building a similar circuit for my computer. I don't care about output amplification and adjustment, I just want to increase the input impedance and protect my computer's soundcard from burning.

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Anybody cares to explain how does the "150V input protection" part work?
The article explains pretty well how it works.
D1 or D2 conduct if the input voltage exceeds the power supply voltage by a forward diode voltage drop (0.6V) and clamp the voltage at the output from exceeding +12.6V and -12V.
R2 limits the current when the input voltage is too high. The 1/2W rating for R2 occurs when the input voltage is 150V.
C3 couples high frequencies around R2 so that they are not attenuated by the lowpass filter caused by R2 and the capacitance to ground at its output. ;D


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  • 1 year later...

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