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setting gain with oscilloscope

Printed From: the12volt.com
Forum Name: Car Audio
Forum Discription: Car Stereos, Amplifiers, Crossovers, Processors, Speakers, Subwoofers, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=95710
Printed Date: October 31, 2024 at 6:31 PM


Topic: setting gain with oscilloscope

Posted By: kungwaz
Subject: setting gain with oscilloscope
Date Posted: July 18, 2007 at 9:18 AM

I have a oscilloscope that I can use, but how do I set the gain with it?

I have read that you put your HU level at 3/4 and then you shall increase the gain, is this correct?

Now to the question about the oscilloscope; How do I wire it correct? at the terminals at the amp parallel to the speakers? (I guess the speakers should be connected when I set the gain). Then just increase the gain until I see the clipping?

// Kungen



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// KungWaz



Replies:

Posted By: Alpine Guy
Date Posted: July 18, 2007 at 4:46 PM
My guess would be to test your Headunit outputs first and see where they clip and go down a few notches, then hook the headunit up to the amp and turn the gain up until the output almost clips. But im sure there is a far more detailed method.


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Posted By: jmelton86
Date Posted: July 18, 2007 at 7:11 PM

Alpine Guy wrote: test your Headunit outputs first and see where they clip

Will the RCA ouputs clip at the same volume as the speaker outputs? I've always wanted to know this.



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Posted By: aznboi3644
Date Posted: July 18, 2007 at 7:57 PM
if the rca outputs are clipping than you will be able to tell by hooking up the scope to the amps outputs...they will be clipped also




Posted By: kungwaz
Date Posted: July 19, 2007 at 1:19 AM

Ok, so I only have to use the scope on the amp?

What level should I have on the HU, 3/4 ?

// Kungen



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// KungWaz




Posted By: DYohn
Date Posted: July 19, 2007 at 10:03 AM
The quick way to set unity gain with an oscilloscope: start with scope connected to amp output and input gains all the way to minimum.  Play your test tone CD and slowly turn up HU volume until you start to notice the waveform being clipped.  This is your max HU volume setting before the onset of clipping.  (Note that some high quality HUs today will not clip their outputs at all.  In this case, simply set the HU to about 80% of whatever it's max might be.)  Now slowly increase the input gain setting on the amplifier until you reach the target output voltage for the amp's power rating into your speaker load, or until the waveform starts to clip whichever comes first.  You can actually go a bit past this setting and introduce a small amount of clipping (no more than 10%) as most people will never hear this and it will allow a bit more usable output from the amp.  If you want to be more precise, you can also scope the line level outputs from the HU and set the volume for max rated voltage output level before you scope the amp.  After you have set this basic level, change the CD to play some frequency sweeps or pink noise and re-check the amp output.  If you notice significant clipping, reduce the gain setting until it clears.  The real power of using a scope comes from being much more precise than a volt meter, and also a scope makes it much easier to adjust settings to match the output levels from multiple amps.

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Posted By: mjwood0
Date Posted: July 20, 2007 at 7:15 AM
Wow DYohn -- That's a great explanation. Very helpful. I was wondering how this worked and that cleared it up!





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