*Quick* Audio Probe Question

[audiolife]

Going to build an audio probe for the first time tomorrow. Going to go with the original found here:

http://www.diystompboxes.com/pedals/debug.html

My question:

The TS connector goes to the input of my amp, and I use the one lead of the cap to probe around the circuit? I'm not understanding how there is signal being generated in this scenario so maybe I'm wrong... don't wanna blow my nice little testing amp.

If this has been covered before sorry, I've used the search.

Cheers!

[facon]

You plug your guitar into the input of the pedal. Reach over and strum it while you're probing.

[petey twofinger]

i really use this tool a lot , one of my " highly highly recommended builds "

http://www.youtube.com/watch?v=6X7VrcYwKM4

there is a part two with the probe and a demo as well .

have fun !

[audiolife]

Simplicity itself. Thanks so much for the insight guys!

One last thing...

Can I use a polarized .1uf or does it have to be non? If so, which end goes on the cable and which to probe?

[ashcat_lt]

It should by rights be non-polar so that you can test signals which are referenced to ground without reverse biasing the cap on the bottom half of waveform.  That said, it will work (at least for a while) with a polarized electro.  If you're testing a negative ground pedal then anything which isn't wiggling around ground must be more positive than the amp input.  With a positive ground I think you'd be safer turning the cap around.

But, you could take 2 x 0.22uf polarized caps and connect their - ends together and then use the two remaining leads as one non-polarized cap.  Really, the value isn't too critical either.  2 x 0.1uf would roll off another octave of bass, but probably work in most cases.

[petey twofinger]

the only thing that i ran into was initially the cap i used was a higher value capacitance  ( its in the video , maybe part two though )  it cut the signal level too much . too quiet / unusable , so i switched it out to a lower value .

the cap blocks any voltage from the test amp , so make sure the VOLTAGE on the cap is higher than the voltage you will be working with . 50 volts may be a good choice as opposed to 16 , but , ymmv .

http://www.youtube.com/watch?v=SF0ZjDsYKas

[ashcat_lt]

That sounds ackbasswards to me.  A bigger cap should mean it lets more bass freqs through.  Haven't watched the video, though.

[audiolife]

I want to use the value that will give me the most accurate representation of the signal.

Could I use a single .22uf non polarized? I seem to be out of all the values called for...maybe I'll have to run to rat shack