Scope Probe to Soundcard Input?

[outoftune]

I use a sound card and Spectrafoo analysis software for troubleshooting and repairs as well as an old school scope.

I'm wondering if anyone has experience or a circuit for connecting a scope probe to a sound card input. Is it as simple as chopping off the BNC adapter and adding an XLR to connect it to the sound card input? And add a cap to prevent voltage from hitting the card.

What I'm looking to do is be able to probe various points of the circuit for troubleshooting without having to always fire up my scope. I also want to avoid blowing up my sound card.

 

[JohnRoberts]

A 1x probe will have 50-60 pF of capacitance, A 10x probe will have 10M in series.

Other than that no problemo.

JR

 

[Khron]

I'd go with a 10X probe, but wired to go into an instrument input (with the associated 1M input impedance, just like most scopes do).
Mic inputs (XLR) usually have under 2k input impedance, which wouldn't leave much signal amplitude.

No real need to bother with a DC blocking cap, there's bound to be one inside the sound card anyway.

 

[Bo Deadly]

No real need to bother with a DC blocking cap, there's bound to be one inside the sound card anyway.

Maybe. But what voltage rating?

For some reason I always find myself making probes for the QA400 (pretty much same as soundcard but with fancier software). Usually it's because I want to attenuate by just the right amount so that, with the QA400 output at 0 dBV, the output of the device being tested is just below clipping (assuming there is gain - if not, maybe amplification is necessary!). Then the input probe also has an attenuator so that the QA400 reads 0 dBV and thus get the best possible signal into the QA400. Throw in some caps if necessary and it's pretty much impossible to make a universal probe. You just have to tailor make them.

 

[outoftune]

all great advice thanks everyone

 

[outoftune]

I've ended up with a working solution.

I used an existing scope probe, cut off it's BNC end and put it onto a 1/4". I connect this to the DI input of a preamp and adjust the gain for unity on the 10X probe setting. Working great for signal tracing. I should note I'm mainly using this to probe stuff that is solid state with PSU of +/- 15 VDC or similar. For tube stuff I will still use an old fashioned scope, wanna avoid sending 400-500 VDC to my DI input