Well, I Got My First Oscilloscope?

[The Ballzz]

xtian,
I sure hope the other members of the "dark sciences/magicians' guild" don't come down on you too hard for sharing that very clear, concise , simple and easy to understand tip! I'm certain that will help some of us greenhorns get started. FWIW though, I did measure the signal from my iphone and certainly noticed the wave form to be pretty darned ragged! Still a great place to start.
Thanks Again,
Gene

[xtian]

I did measure the signal from my iphone and certainly noticed the wave form to be pretty darned ragged!

Ragged? Doesn't sound good. You will often get ugly looking wave forms if you do not ground the probe to the signal ground. Your probes have the tip, of course, but they also come with a little alligator clip that serves as the ground, and you have to use it!

[wyatt]

For the beginner, books like this usually have several pages on how to use an oscilloscope, They'll cover the horizontal (Volt/Div) and the vertical (Time/Div), Triggering, AC and DC settings, etc. and can get you started with basic audio troubleshooting....

http://www.amazon.com/How-Diagnose-Fix- ... 0071744223

[img:260:324]http://ecx.images-amazon.com/images/I/5 ... 3,200_.jpg[/img]

[vibratoking]

This stuff is all over the net for free. Scope manufacturers, at least the good ones, want you to use their stuff. You may learn about waveforms while reading this as well.

[John_P_WI]

VK posted a good read.

The most troubling settings for newbie users to understand IMO are:

Coupling: AC, GND, DC. I expect you'll almost always use AC as you will be using sine waves and audio, it strips away the DC component if one is present (op amps with dc bias for example). GND displays a flat line and is good for aligning the waveform displays of the 2 channels (sets the baseline for lack of better terms).

Channel Display: Which probes are showing on the display, 1,2 or chop (both).

Triggering: Which signal do you want to trigger off of (Use the channel your signal generator is hooked up to as a trigger source). As I said in a different post use a couple of BNC cables and a Tee to connect your scope, function generator, and circuit under test to ONE channel of your scope - use this for triggering. Remember, that the volt/div setting has to display a large enough waveform on the display to trigger. Some scopes have rising, falling and delayed triggering - for audio "rising" is OK.

Cal'd "knobs" these will add gain or change the sweep timing. You cannot use your display for accurate measurements IF they are not "clicked / fixed" in the Cal'd position. You can use the measurements against others for comparison, ie 3 divisions against 4 divisions, but cannot measure volts / div since it is off of the cal'd position. It is good for viewing waveforms in other words.

Analog scopes, in general, are not too good at showing square waves. You'll see a series of offset dashes. But, it can be use to view triggering of latching circuits etc IF they are fed a square wave.

I think the biggest challenge to learn is where to put the probe ground clip and why... Remember, it is at earth ground. For example, don't put the probe and ground across a resistor like you would a dmm. That resistor will now be at earth potential! Poof...

Finally, invest in GOOD probes and BNC cables. No one has time to troubleshoot / second guess their test equipment. Learn how to connect your DMM to the scope and use as a frequency counter if it has the ability to.

That is about 90% of getting up and going on an analog scope...

[lord preset]

Just beginning to figure this thing out. I am trying to troubleshoot why i am getting nasty buzzy distortion on a recent Small Special build. The attached pics show a 1khz square wave as seen at v1b and on one side of the PI. In both I have the reference signal on Channel 1 and the test on Channel 2.

As a reality check, my reading so far makes me think that I am seeing a pretty clean if not flat signal at V1B but at the PI the squiggles (EE technical term) at the top of the wave indicate parasitic oscillation. Am I on the right track here?

[John_P_WI]

Why a square wave?

[xtian]

Hey, what a good looking scope!

I think you're seeing slew rate distortion. The square wave contains frequencies higher than the guitar amp can reproduce. You should be testing with 1 sine wave at about 1KHz.

[lord preset]

Why a square wave?

I was going off the article link earlier in this thread
http://r-type.org/articles/art-125.htm

[lord preset]

Hey, what a good looking scope!

I think you're seeing slew rate distortion. The square wave contains frequencies higher than the guitar amp can reproduce. You should be testing with 1 sine wave at about 1KHz.

I understand that square waves aren't just square, but I'm not sure I understand why the "squiggles" would be visible at the PI but not at v1B where the signal has already gone through two triode stages.

When I use a 1khz sine wave I don't see anything of note. The waves look fine until the amp starts to clip, but this is way past the point that the distortion I am trying to track down starts to be audible. So maybe a guitar source can produce behavior that a uniform wave source cannot? Before I got a dummy load I had the amp connected to a speaker and it got very loud without any noticeable distortion using a sine wave, but the guitar produced the undesirable distortion at much lower volumes. I know neither the guitar nor the guitar cable are the culprit as they are fine with other amps. Am I barking up the wrong tree trying to see this kind of problem on a scope?

[martin manning]

Yes I think you are seeing a parasitic oscillation. Maybe try placing a small cap across the PI plates?

[lord preset]

Yes I think you are seeing a parasitic oscillation. Maybe try placing a small cap across the PI plates?

Thx. What value(s) should I try?

[martin manning]

50p-100p is typical.

[lord preset]

I tried a cap across the PI plates and voila! No nasties! Then it occurred to me that maybe what fixed the problem was just that I had touched the solder joints - so I removed the cap and indeed that was the case. I could have sworn that I had already retouched those pins but hey Ill take it.

My naive faith in the magical properties of oscilloscopes is restored.