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ncc74656

cheap basic o scope

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I'm looking for a very basic usb scope to plug to my laptop, perhaps with X10 or X100 shunts. id be using it for basic clipping testing on RCA up to maybe 1000w amps. I'm looking for sub 100.00 price range, this thing does not need to be fancy at all.

 

anyone have any suggestions?

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That purpose has no purpose.  Complete waste of money don't do it.

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i picked up one of those jtec build your own o scope kits, it was quite fun to build. I'm playing around with that little guy, cost me 25.00. coworker bought a 4500.00 o scope for this but that is just insane to me...

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Just don't use it for clipping tests.  Even the $4500 unit is a fail for that.

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what do you use for checking the quality of input signals? MECP hoots and hollars about scoping every single line, the scope would be able to tell you where a factory amp's "cleanest" power output is, no?  we had a harly in the shop a while back that showed up to about 1/2 volume a clean sine but anything past that looked more like a damn PWM signal...

 

I'm using my scope on an old orion 2500.1 amp that I'm trying to fix, my first delve into doing that kind of circuitry work (I'm expecting it to end in fire...)

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MECP has all sorts of useless information.

Cleanest is a farce.  Train your damn ears.  The variation in the recordings you MUST account making any measurement tool COMPLETELY useless.

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my ears are too f*cked for that stuff, i mean i know when i hear distortion but I cant hear shit in the higher frequencies. i would prefer a way to visually see whats going on rather than trusting my ears. 

 

 

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So if you have music sources that have 12dB in variation where do you set it?

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yea i get that... i make a point to use the customers music so at least to start with its reasonably set but yea your right that once that changes the "tune" is irrelevant.   idk, i guess it comes down to we charge to do things to amps for "tuning" and id like to actually DO something worth while there, ya know?

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So what are you measuring and why?  

NEVER use customers music.  Use what you HAVE and KNOW.

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It is a complete waste of time to set your gains like this.  You can't fully control voltage drive upstream, especially if someone else is controlling the source material, therefore it is pointless to do this.

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Posted (edited)

i use the customers music and source to control variables. i get what your saying, when we do an install and set things up with scopes we can say the subs are with in spec under present conditions. if they change source, turn up gains, add bass boost, etc. and blow up their subs we can say it is not covered and would not have happened had they not done this.

 

we operate under MECP which dam near mandates using scopes to setup systems like this

 

coworkers and myself have setup gains on amps with test disks and every time i hear a system setup this way it sounds like crap, the subs sound WAY under worked which they are as the drivers can always handle more dynamically than static test tones... 

i have scoped many aftermarket radios and have never seen a clipped rca signal out of the HU even at max volume (on any name brand anyway) so i personally don't think the radios play a large role in sending bad signals into an amp but rather the source of the music is what does this. so you scope an amp with say a -3db tone and get what? a point at which the CD or USB input with a static load will clip on the output and then we stop... but even mecp states you want distortion, up to 10% they claim on a sub output as you cant hear it and you will get more output. wouldn't it make more sense to just tune until you can hear the music sounding crappy and pull it back a bit from there? maybe simply play the system for 15 min or so at this level and see if any of the components are getting hotter than they should, wouldn't this be a more real world way to test if things wont blow up down the line?

its worth noting that 90% of our installs are not trying to balance one driver to the next, its just adding subs to be as loud as possible or replacing a couple speakers here or there... in an ideal world id like to replace everything and then the scope/amp power/power handling wouldn't be the limiting factor but rather the next driver in the line, balancing the transfer from midbass to mid range to tweet so as to not have a smooth transition between all this. in the last 3 years ive only had 2 customers spend the money for such a setup however. the rest just want it as loud as it can go

if it were you... how would you setup systems (assuming the operator will NOT turn things down if it sounds shitty) for clients on basic builds. most of what we do is not 3 way active with DSP but rather coax or 2 way component on 2 channel amps off a factory HU. 

 

 

Edited by ncc74656

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1 hour ago, ///M5 said:

So what are you measuring and why?  

Is the above rambling an attempt to say you don't know why?  If not, then MECP has failed even more than I thought.

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here is my understanding. you measure the output of the radio to know how loud it can get before the signal gets clipped, then you have a basis for clean input to the amps. or dsp. you measure the output of the amps to ensure the speakers are not being over driven, you are setting a base level of maximum output, then during the rest of the setup you pull things back from there in your tuning. 

so you scope to ensure speakers are not damaged and clean signals are going to components 

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You are missing one monstrously critical step.  You are NOT measuring output of what is being measured.  How do you then choose your "settings" and why?

Think, don't egurgitate.  It will make you question a bunch of what MECP has "taught" you and that is a great thing.

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measuring output? you mean voltage? i feel that my brain may be turned off to some of this...

so say i measure off an rca preout and see a clean signal, that signal is .8V max lets say. i then go to the amp and turn its gains up until its signal is not clipped or clipped to 10 ish % or until the voltage out matches what the "rated" power of the amp ought to be. 

 

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First off your scope doesn't measure clipping.

Yes, you are measuring output voltage...but I want to know why YOU ARE and what you do with that information.

I realize you feel I am asking an obvious question, but I am trying to help you think about this differently.  You have been brainwashed by MECP nonsense which is solely setup for the least common denominator and not useful at all.  If you want your installs to be solid you need to UNDERSTAND what you are doing not just go through the paces...in particular when you are pacing in the wrong direction.

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i get it, just trying to follow.  ok so i measure on the oscope and when it goes flat it is "clipping" right? so the intent is to measure this so you know that the signal is clean and no distortion from clipping is affecting music quality.  if i am scoping a factory radio that shows a square wave at half volume i would know to setup the amps (gains) to match the mid way point of the radio.

i measure output voltage to know the power I'm pushing, size of wire needed, know if a speaker might get damaged, etc.  some times we set gains via target voltage?

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Be real specific on what you do with the voltage.  Currently from above you haven't measured anything worthwhile.

As for the square wave.  What is the difference between a square wave and a pure sine wave?  And when you find it what do you do?

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And we are going somewhere.  I manage a testing lab with at least 4 $40k scopes and 10 or so $15k scopes.  I've NEVER once used them to measure gain.

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yea i remember you telling me years ago about your crazy equipment. some day id live to sit down and pick your brain about audio, i feel like the field I'm in is so muddied with information that its hard to see which way is up some times.

a pure sine wave has a smooth wave form, it has the best clarity of audio possible. a clipped wave is when the peaks/vallies are flat. the amp does not have enough VA to keep the driver excursion power linier or to stop the drivers inertia from carrying it out of spec with the signal source. this can lead to audible distortion and also can thermally overload a transducer if too much clipping is allowed. 

 

when i find a clipped wave i consider what type of driver it is, what the amps max output is intended to be and also what the source is. e.g. if I'm using a -10db test track and i get clipping then i know there are times the customers music may extend the equipment farter than i am while testing. if they like normal country music and have a driver with some thermal head room it may not be an issue and perhaps i use a -3db or a 0db test but if they like dubstep with +20db preboosted bass and what amount to 30 second long test tones in the music; i would consider either recommending upgraded equipment to get them more bass or keeping the gains lower on this setup to prevent failure of the sub. (this given that mecp allows for up to 10% distortion on a sub) if testing for mids/highs the starting tone attenuation would change.

 

after using these test tones i would play with the customers music and see just how much clipping there actually is and readjust from there if needed

 

as for pure voltage its one or the other at the shop, if we scope tune clipping gains then we don't use voltage but if we measure voltage we use that to place the amp at about the output its rated at. (target voltage). most of who i work with consider target volting an amp an incorrect way to setup a system and oscoping to be the only real way to configure amp gains

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You are skipping the fundamental.  How do you know it is clipped?  How far clipped is clipped?

The o'scopes are the cheap part of the NVH gear I manage.  Have over $3M of NVH gear...

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when the wave form is no longer smooth its clipped right? when its flat on the top and bottom the signal is clipped

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9 hours ago, ncc74656 said:

when the wave form is no longer smooth its clipped right? when its flat on the top and bottom the signal is clipped

How not smooth and how clipped is that?  Why do you care if it is clipped?  ie, what are the ramifications that you are trying to avoid at that particular point in time that allows you to make a decision on what to do with the gain knob?

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2 hours ago, ///M5 said:

How not smooth and how clipped is that?  Why do you care if it is clipped?  ie, what are the ramifications that you are trying to avoid at that particular point in time that allows you to make a decision on what to do with the gain knob?

Audible distortion perhaps. :D

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