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/download/asset/2432735_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?
http://support.fluke.com/find-sales/download/asset/2432735_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?
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/
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/
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
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
HollowState said:
Thanx ! This one has a nice set of what I was looking for.
http://www.pmillett.com/Books/Middleton_troubleshooting.pdf
Still gotta check the other ones too.
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!
)
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!
)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 .....
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 .....
Several misc scope questions
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?
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?
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.
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.
Re: Several misc scope questions
Speaking of probes - would any one care to make some recommendations? Hopefully that isn't too much of a threadjack since I think it's a pretty common topic among scope newbies. Personally I'm looking at one of these - http://www.tequipment.net/CalTestCT2674A.html.
You could run the full set of RMAA tests on it. There is a free version of the software available for download.boywonder said:
I would not recommend exceeding the parameters the probe. Let's say you got a measurement, but damaged the probe. How would you know for sure? I'd just buy a HV probe if you expect to be measuring things that high on even an occasional basis.
Speaking of probes - would any one care to make some recommendations? Hopefully that isn't too much of a threadjack since I think it's a pretty common topic among scope newbies. Personally I'm looking at one of these - http://www.tequipment.net/CalTestCT2674A.html.
Re: Several misc scope questions
With the scope you can use the "add" button to sum the two probed outputs of a sine wave. Since they are out of phase you want to see a horizontal line as the sum. I checked this in one of my amps, with a LTPI and it was surprisingly balanced.
I also used it to fine tune a tremolo oscillator for speed and strength. Lotsa fun things you can do.
I built a cheap signal generator from a kit that works well except that I later discovered it has 4.5vdc on its output. This matches what the spec sheet says for the chip inside it. So I put a cap in there to block it.
boywonder said:
With the scope you can use the "add" button to sum the two probed outputs of a sine wave. Since they are out of phase you want to see a horizontal line as the sum. I checked this in one of my amps, with a LTPI and it was surprisingly balanced.
I also used it to fine tune a tremolo oscillator for speed and strength. Lotsa fun things you can do.
I built a cheap signal generator from a kit that works well except that I later discovered it has 4.5vdc on its output. This matches what the spec sheet says for the chip inside it. So I put a cap in there to block it.
Re: Re: Re: Several misc scope questions
Sure - http://audio.rightmark.org/index_new.shtml - that's the place. Just click on the download section and you'll see where to go.
boywonder said:
Sure - http://audio.rightmark.org/index_new.shtml - that's the place. Just click on the download section and you'll see where to go.
Here's an inexpensive one that does go on sale periodically:
http://www.mcmelectronics.com/product/72-490
Output max is about 2V rms sine wave.
You would be hard pressed to get a better sine/square generator than an old Heathkit IG-5218 unit... (IG-18 is the older version). They are usually reasonably priced on ebay and can deliver very low distortion output with a wide signal and frequency range. There were some modifications made many years ago that reduce distortion and improve overall quality. I still have the one I built over 30 years ago and it still performs flawlessly.
Regards, KM
Regards, KM
IMO it is important to have a function generator that can go well above the audio frequency range, particularly when dealing with circuits involving negative feedback and multiple coupling capacitors. You could have a frequency in the ultrasonic range where the phase shifts through 180 degrees and there is still appreciable gain that will cause ultrasonic oscillations, and with a function generator that tops out at 20khz you'll never know about it other than that your amp performs like 
.
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