How can we see, on a scope, the switching noises of an any amps output stage ?

[gaetan8888]

Hello

How can we see, on a scope, the switching noises of an any amps output stage ?

Btw, since few weeks I have a new and much better scope, a Sencore SC61 , it have lot of fonctions, I buy it used for a very very low price.

If it can be usefull to know for that test, here a web page with the specs of my scope ;

http://www.tucker.com/java/jsp/produ...6297_condR.htm


Thank

Bye

Gaetan

[h_a]

One way is to use another function generator to generate a sine with the same peak voltage as the amp output and subtract it from the amp output. You see then essentially a straight line with spikes at the positions of the null-crossing.

Have fun, Hannes

[gaetan8888]

Hello Hannes

You mean that the other sine signal would be inverted in phase ?

And I just adjust the scope frequency to see the spike ?

Thank

Bye

Gaetan

[multisync]

on many 2 channel scopes you can add or subtract the 2 vertical inputs from/to each other. What you will see is the difference. So subtract the input from the output, if the phase and time delay are very close you will see distortion, and other components. I used to set up bias on amplifiers by turning up the gain on the vertical amplifier inputs so that the crossover region was visible. All I would see was a diagonal line across the screen and a little step around the crossover area. I would adjust the bias for the smoothest /straightest line while monitoring the bias current. This was for amplifiers that would later measure around .05% distortion on an analyzer. hope this helps a bit.

[Elvee]

Another possibility is to connect the primary of a small audio transformer between the test generator output (thus the input of the amplifier) and a medium power resistive divider connected to the output.
The ratio of this divider must be identical to that of the feedback network of the amplifier. You can make it slightly adjustable to fine-tune the rejection.
You visualize the result on the secondary.
The only residue left (apart from the distortion) will then be caused by phase errors.

PS
This assumes the amplifier is non inverting, which is generally the case. For an inverting amplifier, you don't even need the transformer.

[destroyer X]

Here is the Sencore picture.

regards,

Carlos

[jackinnj]

So once you have one, or all these suggestions set up -- run the test while adjusting the bias potentiometer -- and you can see the switching effects as the bias changes.

Some Pass owners complain to Nelson that they hear a thump when the amplifier goes from Class A to Class AB1. Such are the foibles of folks who can afford amps milled from a solid block of aluminum.