signal from pmt and sound card

[ChrisRadium2023]

Hello everyone,

There's something puzzling me about the signal I get from the pmt and the sound card :

When I read the pmt pulses on my oscilloscope ( through a resistor located just after the coupling capacitor (in series) , the signal car be "elongated" depending the value of the resistor I use. For a 100uS lengh or mode the resistor has to be around 1M . If I use higher value the pulses period gets even longer.

I 've seen another video on youtube where a guy just linked his pmt straight to the sound card and could still get a spectrum!! All he did was to had a coupling capacitor to get the signal and link it to the sound card via a jack.

The weird thing is that when i can get some pulses on theremino they dont look like at all what I get on the oscilloscope and their lengh is always 50-80 uS ....not like my readings on the oscilloscope.

The fact that I could see that my cheap sound cards seemed to block most of the signals and superimpose some inner noise on the signal I'm trying to read with Theremino leads me to wonder If in the end It would be much better to buy a proper good quality sound card such as the card I can find on amazon that are meant to record @ 24bit 192kHz sampling and that have a preamp included... Will it be better ? will there be less noise ?

Chris.

[Sesselmann]

Chris,

It seems like you have re-discovered the RC constant, In electronics resistance times Capacitance equals time (Ohm * Farad) = Seconds.

A cool trick, you can use Google to calculate it 😉

Steven

google.png

[ChrisRadium2023]

thanks but i know what RC constant is and about RC filters :)

it doesnt explain why what I get on the oscilloscope isnt what I observe on the MCA Theremino. Do you have an explanation ?