Test Equipment: Oscillocopes

[Brian516]

Well it appears that this was a software issue of some kind. 
I am currently running the "Wave Gen" feature from Visual Analyzer and I am able to detect the PROPER signals perfectly fine.

I will do some more PC FG/Scope testing tomorrow, and possibly make another vid of the performance of the PC FG's that I have and all that.

So, Bill, yes, we can in fact hook directly in to the 3.5mm's output with the scope and measure the traces. It is as easy as that!  
Well, as long as you use the correct playback software and disable all of the "enhancement" features on the PC.  If you would like, I will try and figure out what playback software works best for sending directly out to the scope for viewing. So far, Visual Analyzer seems to work pretty good as a FG, and has many other tools to immerse yourself in.  Seems to be a good program to have in addition to the Soundcard Scope. That prog's FG doesn't seem to be of any use to me, but the Scope part's trace seems to be close to the trace on the Tek 465. However, it is still running on internal loopback, so I won't know exactly how good of a PC scope it is until I make a BNC to 3.5 connector at some point, which will be easy.

Brian

Brian

[picowatt]

There must be an issue with using my computer to put a signal to the scope....
For some reason, the 465 displays the exact same trace no matter what signal I output from my PC. This is the case whether I connect the probe to Left, Right, or Ground. The sounds change in the headphones I wired in, and on proper channels and all that.
If I hook up the 'ground' to the ground out of the PC, it cancels out the signal.

If you cannot connect the scope ground to the HP jack ground (sleeve connection) without killing the AUDIO signal to the HP jack, then you can go no further until you figure out why.  Without the scope's signal ground connected to the laptop's signal ground, you will see all manner of AC noise when connecting a probe/scope input.

I have three different models of laptops here and I do not have any similar issues as what you describe.  I can, using adapters, plug my laptop HP output directly into a stereo receiver's line inputs or into a scope's inputs without any problem.

Some HP/speaker amplifier IC's use circuity to detect when a HP is plugged in, and I believe I have seen one that floats the sleeve to a DC potential to eliminate cap coupling the HP output.  Possibly connecting the scope ground may be messing with that HP detect circuitry.  But again, I have never had a similar issue with my laptops.

If your laptop has a third prong on its AC cord, use your DVM set to low ohms and measure between the HP jack sleeve and the third prong (ground) on the laptop AC cord.  Report back what you measure.

Also, check for continuity between the scope's ground and its AC cord third prong (I am assuming it is not cut off and that the laptop and scope were plugged into the same AC duplex/power strip).

Try running the laptop only on its internal battery (unplug the charger) and see iif you can connect the scope ground to the HP jack sleeve without muting the sound in the headphones.  Also make certain the cord you made up is wired correctly.

What I see when I hook it to the PC out is a crappy looking sine wave trace at 150V.

If you cannot connect your scope ground to your HP jack ground, this "crappy sine wave" is what you will see. 

I tried various different settings - AC and DC coupling show the same trace.
Trigger level does nothing.
Anything but "A" on Horizontal Display makes it extremely bright except for the first half of the sine wave.

I didn't bother switching to one of my Tek probes to see if the sine wave trace looked any better. seems pointless to do.

I also disabled all audio enhancements and DC offset cancellation, etc. It should be 'direct output'.
About to make a quick video to show what I am talking about, then I'm going to figure out how to use the GR Oscillator and see what that looks like on the scope.
https://www.youtube.com/watch?v=E9l-EnME9Vw

Brian

[picowatt]

Well it appears that this was a software issue of some kind. 
I am currently running the "Wave Gen" feature from Visual Analyzer and I am able to detect the PROPER signals perfectly fine.

It seems to have something to do with sending the signal directly to output.  I have to have the "send direct" box checked in the Wave Gen in order to get the proper trace on my scope.

I will do some more PC FG/Scope testing tomorrow, and possibly make another vid of the performance of the PC FG's that I have and all that.

So, Bill, yes, we can in fact hook directly in to the 3.5mm's output with the scope and measure the traces. It is as easy as that!  
Well, as long as you use the correct playback software and disable all of the "enhancement" features on the PC.  If you would like, I will try and figure out what playback software works best for sending directly out to the scope for viewing. So far, Visual Analyzer seems to work pretty good as a FG, and has many other tools to immerse yourself in.  Seems to be a good program to have in addition to the Soundcard Scope. That prog's FG doesn't seem to be of any use to me, but the Scope part's trace actually matches my Tek 465 nearly exactly, so it must be fairly decent.

Brian

Brian

Brian,

Have you tried just playing some music on the laptop while looking at it with the scope?

Keep in mind that the AC levels at the HP jack will be fairly low level with the HP's connected.

PW

[TinselKoala]

Yes, that signal is not coming from the PC's audio output, it's more like a distorted 60 hz hum. I can't see the horizontal scale so I can't tell the frequency of the display on the scope.

But it seems that you now have the issue sorted, by using different software and making some different output settings on the PC.

Selecting other Horiz Display modes than "A" "lock knobs" gets into the delayed timebase features of the scope and we aren't ready to go there yet.

For fun audio display of music try the X-Y setting on the Time/div knob with CH1 connected to the L and CH2 connected to the R speaker outputs. This will give you a complex "Lissajous" pattern instead of a horizontal sweep.

Jerobeam Fenderson:
http://www.youtube.com/watch?v=l8m5L2gqHPw

[Brian516]

Brian,

Have you tried just playing some music on the laptop while looking at it with the scope?

Keep in mind that the AC levels at the HP jack will be fairly low level with the HP's connected.

PW

PW,

I've edited my last post a little since you last read it.   
I don't know what exactly the issue was, but for some reason it seemed to be a software issue with that Soundcard Scope program, since VA's FG is running fine, and I have the reference clip (ground clip) hooked to the 'ground' sleeve of the 3.5mm (well, the wire I ran off of a jack).
I wanted to test it with some simple FG waveforms first. That way I know what I am supposed to see, and know if the scope shows the correct trace or not.
Now that I have it working, and am seeing the correct traces, I will run some music into it while listening tomorrow, and play around some more with the PC FG's I have.  Maybe I'll even figure out what was causing the issues with using Soundcard Scope.

I did notice that the trace drops about 2/3 amplitude when I plug the HPs in. With the output volume at 15% I'm reading about 225mV w/o HPs, and about 80mV with HPs.

Brian