Oscilloscopes: safe use and testing

[sluckey]

Do not try this test on a cap that's installed in any circuit.

[pompeiisneaks]

From my best understanding of this, in guitar amps, most of the noise problems are caused by bad lead dress, bad solder connections or bad heater wiring placment/installation.

Doing this WILL reduce noise in the amp, but so little that it will be almost imperceptible when the amp is being played at any volume other than whisper quiet.

Many people take the effort to do this, and it will make the amp noticeably quieter at idle. This is very good/important/useful for HiFi where you have classic music being reproduced through the amplifier and you want those super quiet sections to be clear and not swallowed by noise.

On a guitar amp that is played loud in most cases (and by loud I just mean loud enough that it swamps the noise this range covers) it's somewhat moot.

Any current model production amp has components either placed by a robot or by a person that has no time to try and ascertain the foil direction since manufacturers mostly stopped indicating this a long time ago, and rarely do you get an amp off a mass production line with noise problems that cause someone to complain/return the product.

I think a lot of boutique builders and people like us that build for fun like do to this and hear the dead silent amp at idle... But at what benefit? It will add at least another 30 mins to an hour of time in the amp build, and if that's worth it to you, do it.

The technique is pretty straightforward with a scope, I've noted the larger the capacitor the more this actually seems to be detectable. Tiny ceramic, silver mica or even film caps around .005 and below seem to barely differ from side to side to me... 0.1 and the other huge ones are very obvious.

~Phil

[Stephen1966]

Do not try this test on a cap that's installed in any circuit.

Understood. I'll leave them as they are. And Phil has a point, any noise from caps picking up RF is probably negligible given the usual suspects: lead dress, solder connections and heater wire placement. I am curious though, are we talking about the potential for shock here? In any case, to reiterate, I won't touch them but the test is worth saving for next time before the caps are installed and charged.

[xtian]

Do not try this test on a cap that's installed in any circuit.

Understood. I'll leave them as they are. And Phil has a point, any noise from caps picking up RF is probably negligible given the usual suspects: lead dress, solder connections and heater wire placement. I am curious though, are we talking about the potential for shock here? In any case, to reiterate, I won't touch them but the test is worth saving for next time before the caps are installed and charged.

If you have properly discharged your filter caps, and the amp is not plugged in to AC, you can freely poke around with no worries. But use a multimeter and CONFIRM that the filter caps have been discharged.