A high quality probe is essential, and isn't necessarily included when
you buy a 'scope. You want a 10x probe if you're going to look at the
internals of circuits, so as to minimize the loading effect of the
probe, which becomes a part of the circuit and changes it to some
degree. If you've got two channels, you should use them, so you'll need
two probes. The purpose of looking at two signals is to view their
relationship, triggering on one of them and seeing what the other is
doing at the same points in time.
Become familiar with the triggering options and controls. You normally
want to use internal triggering from one of the two inputs.
When looking at a signal, switch around to a number of different
frequency ranges, and tune the brightness down to get a clear, sharp
image. One of the most useful things you can discover with a scope
looking at audio is ultrasonic high frequency oscillations (known as
parasitics) riding on top of the main waveform. You don't want these!
They cause distortions of the bad kind (as opposed to the good sorts
that we all love). If you find parasitics and make changes to fix them
(usually by adding a small capacitor in the feedback loop of an op amp),
the scope tells you if your fix worked. The scope opens up a world of
visualization of what's happening.
I give another example. I recently built a pair of CGS Tube VCA
modules. Looking at their output on my Veeblefetzer LED displays showed
that the outputs were skewed into the negative voltage region. I
thought something was wrong, because the output is AC coupled. I
expected the signal to be centered. A quick look with the scope showed
what was going on. The wave shape was a non-symmetrical pulse wave with
the energy concentrated in the negative region. Nothing was wrong. The
Veeblefetzers are great, but cannot show the detail a scope can.
-Richard Brewster
http://www.pugix.comBen Stuyts wrote:
> On 24 Mar 2007, at 01:43, jneilyahoo@... wrote:
>
>
>> For example, is there a reference standard for calibrating these
>> things?
>> Or should I just send a full-strength signal out of the modular and
>> tweak
>> things until the waveform fills the screen? Right now I'm not seeing
>> enough amplitude, and I'd rather keep an amplifier out of the input
>> path
>> if I can.
>>
>
> I'll give this a try...
>
> I usually keep the vertical scale at some calibrated value. A lot of
> scopes have a separate gain setting for each channel, separate from
> the V/div setting. I keep it at the default ('calibrated') setting,
> so that I can read off the waveform's amplitude from the screen.
>
> Keep in mind that some probes have a 10:1 attenuation built in. If
> your scope has a 5 mV/div max sensitivity, this will become 50 mV/
> div. Some scopes might show some noise (up to 0.2 or 0.4 div on your
> screen) on their most sensitive setting, so it is best to avoid this.
>
> This makes it difficult to focus on low-level signals. Use a 1:1
> probe, or a switchable 10:1 / 1:1. However, you will need the 10:1
> probe if you need to measure on a high-impedance circuit. For the
> analog inputs and outputs a 1:1 probe will do just fine, and you can
> set your scope to something like 1 V/Div to start with.
>
> It is kind of odd that you have trouble filling the scope's screen
> (if I understand you correctly) with the output of an MOTM module. It
> really shouldn't be a problem. Have you checked your probes?
>
> With kind regards,
> Ben
>
>
>
>
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