# Do I need 10x probes for my DSO Nano?

I purchased a DSO Nano V2 to check my car audio amplifier gains but I’ve never used an oscilloscope before so I’m still figuring things out. Basically the problem I’m having is reading the waveform on a friends amplifier that is 1250watts at 2ohms. As I turn the gain up the waveform gets larger then the screen allows even when I adjust the volts/Div. I didn’t have a problem setting my amplifier gains (75watts RMS at 4ohms, and 800watts RMS at 2ohms) so I’m wondering if I need a 10x probe? Thanks in advance.

Max peak-to-peak voltage for the Nano is 80V (+/- 40V with ground at center) and using the standard probes. The formula to calculate Vrms from amplifier power rating and load impedance is:

Vrms = R * SQRT(P/R)

At 1250Wrms and 2R this should equal 2 * SQRT(1250/2) = 50Vrms. For a sinus test signal, peak-to-peak should then equal SQRT(2) * 50 = 70.71 (+/-35.36V). So in theory you should be just within range. A 10x probe will up the maximum to 800V (+/- 400V). You could apply the same formula to your own amplifier and observe if the measurements agree (look for clipping around the calculated Vrms value).