Oscilloscope probe guitar cable.

Started by Buffalo Tom, March 01, 2021, 05:01:44 PM

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Buffalo Tom

Hi. I wanna make a guitar cable with BNC to guitar jack.  So I can plug the output of guitar pedals into my oscilloscope. Oscilloscope probes seem to have some resistance and capacitance built into them. My Rigol PVP2150 passive probe has 1M and 50pf on the x1 setting. Should I include 1M series resistor and 50pf between tip and sleeve of the "guitar cable" Im making?

PRR

Quote from: Buffalo Tom on March 01, 2021, 05:01:44 PM...Oscilloscope probes seem to have some resistance and capacitance built into them.....

1X probes do not. (That 1Meg is in the 'scope, isn't it?)

10X probes do; but there's little reason to do 10X on guitar-level stuff. The voltages sure are not too high. Guitar cords are a lot of capacitance already so not essential to pad-out for lower C.

I would just find a half-bad guitar cord, a half-bad 'scope cable, amputate, and twist the good parts together.

(Or as I did on my Allen B DuMont 'graph-- just use a 1/4" jack input.)
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antonis

#2
It isn't so simple..
(beyond the fact that 50pF cap may not be needed due to guitar cable length..)

x1 probe designation actually refers to the factor by which oscilloscope input impedance is multiplied by the probe..
By adding 1M series resistor you actually make  a x2 probe designation..

https://www.electronics-notes.com/articles/test-methods/oscilloscope/scope-probes.php

edit: Paul said it more comprehensively.. :icon_wink:

"I'm getting older while being taught all the time" Solon the Athenian..
"I don't mind  being taught all the time but I do mind a lot getting old" Antonis the Thessalonian..

iainpunk

no need for any components there, i have cut off the tulip end of a guitar to tulip cable, and added a BNC connector, works like a charm, but its nice to have 2 of them, so you can plot the in vs out graph, and see some cool shapes and stuff!
if i were making cables again, id make one cable a 3 way split, male TS and female TS with really short cables and a long cable to the BNC

cheers
friendly reminder: all holes are positive and have negative weight, despite not being there.

cheers