O-scope problems with 0db

[adulbrich 5,000+ posts]

Ok, so we tried to set my gains with this scope tonight:

Portable Arm Nano DSO201 Oscilloscope Mini Storage LCD Digital Pocket Sized Kit | eBay

It's my understanding that lots of you have this scope. Several people recommended it to me.

I downloaded a 40hz test tone that was supposed to be at 0db. First, I wanted to see what volume my headunit clipped at. From previous setups, I guessed was at 22/35. Kept turning it up more and more. Maxed out the HU at 35, with the sub level at +15. Wave was still perfectly clean. I was a little surprised that it didn't show any clipping, but moved on anyways.

Connected RCA's to amp (after turning everything off, of course). Then we tried to set the gains on the amp with the scope. Ended turning the gain dial all the way up, and the signal coming out of the amp was still perfectly clean. At this point, I knew something had to be wrong. No way I had a completely clean output signal with HU and amp gain both all the way up.

I re-connected a sub to test the settings. Turned the head-unit all the way down to zero, then started some music that I normally listen to. Then, I slowly rolled up the volume until the clipping light started to flicker on the remote gain knob. It was clean up to 17/35. At 18/35 it occasionally flickered. Anything higher and it flickered bad.

On a song with long bass notes, we tried to look at the waves and set gains based on that, but the window wasn't big enough. Couldn't zoom out or put sensitivity low enough to see the whole waveform.

I'm guessing the test tone I downloaded is at a recording level much lower than 0db.

Where can I download a true 0db sine wave for 40hz or 50hz? Also need one for 500hz and 5,000 hz.

Also, what's the biggest or most powerful amp you guys have used this scope for? Couldn't see the full waveform close to full output //content.invisioncic.com/y282845/emoticons/frown.gif.a3531fa0534503350665a1e957861287.gif

Any useful tips or advice is appreciated.

Click to read more...

 

[wew lad 5,000+ posts]

I'm wondering if you might be using it wrong(it happens), i know they usually have different settings for the input. Have you checked the manual and tried updating the firmware? I want to get one of those too but I'm not sure I've seen the problem you're having.

 

[Umbra]

The tones I used I got from this thread: Test Tones and Tuning Tutorial - All New Links, Again! - Tunez - All things music related - SMD Forum

It's possible that even at max volume there's no clipping from the RCAs on the HU. If you were testing the speaker wire outputs I'm sure the signal would clip much sooner.

You should definitely be seeing clipping on the amp outputs. It's possible the signal from the HU to the amp is too weak to register, but if music works fine it's probably the test tone.

I haven't done it in awhile, but I seem to recall getting easier to read graphs by flicking the switch on the probe to 10x.

Try another test tone. One more thing to check, make sure the LPF on the HU and amp isn't filtering out the tone you're using.

 

[Jeffdachef 5,000+ posts]

Create one from audacity. However I get the feeling something else is off here.

 

[adulbrich 5,000+ posts]

I'm wondering if you might be using it wrong(it happens), i know they usually have different settings for the input. Have you checked the manual and tried updating the firmware? I want to get one of those too but I'm not sure I've seen the problem you're having.

What would be out of date that needs updating? I's not like waveforms get outdated. We tried both sensitivity settings.

The tones I used I got from this thread: Test Tones and Tuning Tutorial - All New Links, Again! - Tunez - All things music related - SMD Forum
It's possible that even at max volume there's no clipping from the RCAs on the HU. If you were testing the speaker wire outputs I'm sure the signal would clip much sooner.

You should definitely be seeing clipping on the amp outputs. It's possible the signal from the HU to the amp is too weak to register, but if music works fine it's probably the test tone.

I haven't done it in awhile, but I seem to recall getting easier to read graphs by flicking the switch on the probe to 10x.

Try another test tone. One more thing to check, make sure the LPF on the HU and amp isn't filtering out the tone you're using.

Didn't even think about the low-pass on the amp attenuating the test tone I was using. Thanks!

Create one from audacity. However I get the feeling something else is off here.

Downloaded audacity last night, and was planning to use that to make some test tones. I took a recording class at school, and we used it a lot, so I'm somewhat familiar with it. May still need some pointers though.

 

[wew lad 5,000+ posts]

Is there any setting that will automatically adjust the chart? Does it show voltage in? Is it correct? Does the entire waveform still show (not off the graph)? I recall one of those oscopes having custom software that's better for them but I think it was an older model.

 

[ChaseinBass]

Only settings you gotta mess with is X and Y settings and you can Make the wave taller or shorter y =voltage x= time it's looking I am no electronics expert at all lol and I figured it out I will post a pick so maybe you can copy settings but mine is older model View attachment 26552406View attachment 26552407

Sent from my iPhone using Tapatalk

 

[adulbrich 5,000+ posts]

[quote name='mitchell0715']Is there any setting that will automatically adjust the chart? Does it show voltage in? Is it correct? Does the entire waveform still show (not off the graph)? I recall one of those oscopes having custom software that's better for them but I think it was an older model.[/QUOTE]


Not that I know of. Everything but the top fit on the graph

[quote name='ChaseinBass']Only settings you gotta mess with is X and Y settings and you can Make the wave taller or shorter y =voltage x= time it's looking I am no electronics expert at all lol and I figured it out I will post a pick so maybe you can copy settings but mine is older model View attachment 26552406View attachment 26552407


Sent from my iPhone using Tapatalk[/QUOTE]

Made Y as big as possible, I think.
@av83; can tell you guys more information. He was showing me how to use it.

 

[Austin175 10+ year member]

Did you have the probe set on x1 or x10 an here exo has links for good test tones in the description

 

[adulbrich 5,000+ posts]

Did you have the probe set on x1 or x10 an here exo has links for good test tones in the description

Tried both x1 and x10

Going to use a USACI tones disc on Tuesday night, to rule out my computer not being able to burn things correctly

 

[av83 10+ year member]

Tried both x1 and x10
Going to use a USACI tones disc on Tuesday night, to rule out my computer not being able to burn things correctly

i'm pretty sure that's going to be the fix, btw. see ya later

 

[adulbrich 5,000+ posts]

i'm pretty sure that's going to be the fix, btw. see ya later

Yup, sounds good!

 

[The Camry]

So what ended up being the issue

 

[noble brown]

I have one too. If you go to both the Xn and Yn on the side and hit M it will give you fit options for both scales. In Xn you will see "y ranges" this will adjust voltage scale. Allow you to see the whole wane form. You must also set the probe to 10x and under the Xn menu change "probeatt" to ten also. To get rid of that annoying purple line go to Ex and press left arrow till it disappears. You may notice your wave is offset, you can center it by going to Yn and highlight "ViewPos" and left or right arrow to adjust that. There is more I can help with if you have q's

 

[adulbrich 5,000+ posts]

So what ended up being the issue

Could have been one of two things:

1. The tone was not actually 0db. May have been -10, because there was a big difference when we used the USACI disk tones

2. I set the subsonic filter all the way down, and high pass filter all the way up, so I knew the input signal was not being attenuated

Changed both at the same time, so I can't say for sure