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Onvinyl 28th December 2006 08:14 PM

What do I see on my scope?
While checking an amp, feeding it with a pure sine wave, I can see that sine wave in ok shape but painted in a thick line. What should that tell me?
Without a signal, the amp shows only background noise,

pinkmouse 28th December 2006 08:23 PM


Onvinyl 28th December 2006 09:21 PM

Argh, always my darkest dreams come true :rolleyes: :dead:

pinkmouse 28th December 2006 10:39 PM

It may not be as bad as you fear. That kind of problem with low level oscillation may well be solvable by lead dress or better PSU decoupling.

davidlzimmer 28th December 2006 10:40 PM


pinkmouse 28th December 2006 10:47 PM


Originally posted by davidlzimmer
Possibly. Crank up the time base on the scope and see if you can resolve a waveform. If it's harmonics then it will likely not be that much higher in frequency. Harmonics will also change with the input frequency, wheras oscillation is unlikely to. However, I personally have never had a problem like this due to harmonic distortion, but there's always a first time! :)

SY 28th December 2006 11:46 PM

Depending on the test frequency, it can also be hum/ripple. Try synching to the line and play with the trigger level to see if there's some low frequency stuff in there.

I_Forgot 29th December 2006 04:16 AM

It may also be a crappy scope. A lot of old scopes get fuzzy as the capacitors in their power supplies go bad. A good scope will display a thin, sharply focused line. Does the scope have a 1 kHz square wave calibration signal you can look at?


Pano 29th December 2006 04:43 AM

If it's a Class-D amp, it the switching RF! :D

audio-kraut 29th December 2006 05:41 AM


What do I see on my scope?
most likely a trick question.


What should that tell me?
easy - somethings wrong somewhere

sorry, hard to refrain with question like these....

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