oscilloscope hookup for amp/dummy load testing

Thread Starter

Johnny7

Joined Feb 5, 2022
14
The only schematics I can find show only a single channel being tested.

Is it safe to connect the ground clips from each of two oscilloscope channels to the corresponding "ground" (speaker lead negative) end of each resistor?

Does this violate the "single ground" rule - or is it OK since the two channels actually share a common ground?
 

Ian0

Joined Aug 7, 2020
9,489
The only schematics I can find show only a single channel being tested.

Is it safe to connect the ground clips from each of two oscilloscope channels to the corresponding "ground" (speaker lead negative) end of each resistor?

Does this violate the "single ground" rule - or is it OK since the two channels actually share a common ground?
It is, until you find yourself testing a bridge-tied-load amplifier!

With stereo amplifiers where the speakers return to 0V, there may be some errors, proportional to the speaker lead resistance.
You can eliminate that problem by connecting both probe clips to the ground at the speaker output sockets, but than generates a different small error as the load resistance now include the speaker lead resistance.
 

Thread Starter

Johnny7

Joined Feb 5, 2022
14
It is, until you find yourself testing a bridge-tied-load amplifier!

With stereo amplifiers where the speakers return to 0V, there may be some errors, proportional to the speaker lead resistance.
You can eliminate that problem by connecting both probe clips to the ground at the speaker output sockets, but than generates a different small error as the load resistance now include the speaker lead resistance.
Thanks for the response, Ian.
This is not a BTL amp, though the warning is much appreciated.
 

Audioguru again

Joined Oct 21, 2019
6,608
Some cheaply made amplifiers play the momentary levels of music and vocals well, but smoke then burn out when being tested with a continuous high level.
 
Top