Reading Oscilloscope Traces -For Dummies

[jjman]

I’ve done some googlin and searching here but haven’t found a good link to a reference of graphics of typical anomalies that might appear on audio oscilloscope traces. I’d like to learn how to recognize these. Other than amplitude, phase, frequency and clipping, I wouldn’t know how to classify or react to what my scope might show me. I stumbled upon this but it's not comprehensive and not audio specific:

http://support.fluke.com/find-sales/...432735_a_w.pdf

My scope is an analog Tektronix 4 channel (forget the model #.) It’s been a great tool to have since I got it off eBay. The manual doesn’t really help on this particular topic. I’m posting here since I’m mostly interested in tube-related phenomena.

Anybody know of some links or on-line resources that include this?

[boywonder]

I have access to a scope but I can barely operate the thing.

I am keenly interested is this subject also.

[kmaier]

The scope is one of my most used test pieces.. along with a good digital meter. It's not difficult to understand how it works and what you can do with it, but perhaps a basic primer would be useful. Tektronix has their XYZ about scopes available for a free download here:

http://www.tek.com/Measurement/programs/301913X312631/

They also have a free download on scope probes as well.

It may be useful to find an older ARRL handbook from the late 1950's. There is a schematic of a simple X-Y scope in the test and measurements section and shows various scope patterns and what they mean.

Regards, KM

PS - one more good link:

http://www.tek.com/learning/oscilloscopes/

[HollowState]

You might try Pete Millett's site below. Look through:

Troubleshooting with the Oscilloscope,
Oscilloscope Techniques,
Know Your Oscilloscope,
Cathode-Ray Oscilloscopes &
The Cathode-ray tube at Work.

http://www.pmillett.com/technical_books_online.htm

[jjman]

Originally posted by HollowState
You might try Pete Millett's site below. Look through:

Troubleshooting with the Oscilloscope,
Oscilloscope Techniques,
Know Your Oscilloscope,
Cathode-Ray Oscilloscopes &
The Cathode-ray tube at Work.

http://www.pmillett.com/technical_books_online.htm

Thanx ! This one has a nice set of what I was looking for.

http://www.pmillett.com/Books/Middle...leshooting.pdf

Still gotta check the other ones too.

[DigitalJunkie]

I think I learned about 'what to look for' from just looking at pictures of nice clean waveforms in books and stuff. -Familiarize yourself with what a nice sine,square,etc. waveform looks like.

If you're using a signal generator,it's a good idea to take a look at it's raw output,just to get a feel for any anomalies it might produce (PC soundcards used as a function generator usually have pretty 'funky' output waveforms.) This way you'll know what you *should* be seeing (an exact copy of the input waveform,only amplified.) and what you are seeing in reality,if the two don't (closely) match,there's a problem.Anything that varies from the input waveform (except amplitude) is an "anomaly",strictly speaking. There is some degree of 'acceptable' mismatch under some conditions however.(during clipping/overload obviously,at freqs. above or below the audible range,etc.)



(Sorry for rambling,Been celebrating tonight! )

[cliffforrest]

And may I add, after 40 odd years of 'scoping ....

1) Get in the habit of checking probe and channel calibration before you start a session, OR if in doubt at what you see.

More important if using a unknown scope or switching probes, but for me it is automatic, like looking in the mirror before driving off.

2) Don't believe what digital voltmeters tell you without scoping as well.

So many times I have seen techies conclude that the +5v is out, only to discover it has 2Vpp of 100Khz oscillation on it!


I tend to use an free running trace (horizontal line), set at 10V/cm and centered on the screen for all initial measurements . With a bit of experience is is possible to easily eyeball +/- 40V to a couple of volts, and quick move around the circuit.

I feel the pain of those attempting any DIY without a decent analog 'scope .....

[n_maher]

Great thread. I bought my first real scope last week and have been getting to know it a bit and will certainly pour over the links here. So really I'm just stopping in to say thanks.

[boywonder]

So far I have looked at 10Khz sq wave at the output, noise on DC LT and HT. Beyond that, I pretty much a numbskull presently.

What other common parameters are typically analyzed with the scope for amps and preamps?

What techniques do you use to measure these things?

Are there advantages to using a scope instead of a DVM to adjust phase splitter balance?

Are there any basic techniques to measure distortion without using FFT such as inverting a sigal and comparing it to another signal?

Is it possible (and reasonably safe) to measure a B+ of say 350V using a 300V probe?

[JoshK]

Related question. What do people here use and recommend for a function generator? Most people using computer + soundcard or desktop piece?

I am looking to pick up a FG maybe. I do have a soundcard that would probably be up to the task (firewire solo and/or audiophile 24/96 usb), but haven't tried that out.

Great thread. I am ready to start learning how to use my Kikusui 5ch scope.