How To Properly Set Amp Gains With A O-Scope AND By Ear

The number 1 most misunderstood adjustment in car audio is setting the gains on amplifiers. The gain knob is NOT a volume knob, instead it is for level matching, to match the output voltage of the head unit. The correct way to do this is with an oscilliscope.
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Moreover, most head units do not put out a clean signal all the way to the top of the volume knob, especially on the internal power side. Many people believe that you set gains by setting the head unit at 75% volume, but Jefferson shows you why that is not a good plan, as even a high-end Alpine head unit clips the signal BEFORE 75%.
For our tests, we have an Alpine head unit from 2003, a Pioneer 2-channel amp from the same era, and a couple of speaker pods. We are using a 1khx sine wave test tone. You don't want to use music for this test, it is too dynamic and you won't be able to see the actual signal on the scope.
We do play the test tone on the speakers, which is very loud, so be prepared for that in the middle of the video.

[@valecasillas5729]

When i check tha max outputs of my estéreo Kenwood exelon dmx 907s 😅 i used 1 kilohertz testtone and no distorted but when I set my gains of my amplifier dsp audiocontrol D-4.800 they shows distortion?????of my estéreo wy 😂😅 l

[@Reddirtrodz]

You always start at the signal source and then work your way to the amps. Is the dsp output is distorted, then you need to dial it down.

[@BassheadKustomsZambia-kk6ii]

When setting the gain on the amp without the speakers connected does this mean the oscilloscope will be reading distortion at the stability of the amp? What i mean is if you going to use the same amp at 1ohm vs 2ohm will the clip point be the same?

[@Reddirtrodz]

Based on ohm load, the clipping point can change, occuring sooner than without a load. You can make (or buy) dummy loads for this type of test, which is a video I am working on.
This would be a good real-world test to see just how much difference there is between unloaded, 4, 2, and 1 ohm loads.
In most cases, I like to use the scope to determine the max clean input level from the source unit and any processors, then I set the base gain at the amp. For mids and highs, this is usually as far as it needs to go. For subs, you can tolarate a little more distortion (under 10%), but I prefer a zero-distorion system for SQ, so I will test everything with speakers connected and fine tune it.
If you are running SPL or SQL, a lot of installers will build in a little distortion, specifically on the subs. for SPL, we often run square wave for competition, as square is louder due to the fact that the wave has no ramp-up/down, the peak of the wave is much longer than a sinusoidal (sine) wave.

[@valecasillas5729]

And my dsp D-4.800 is already set my crossovers 😅 time alignment and the eq to ???

[@Reddirtrodz]

The levels are too high or you have a issue in the signal path

[@davpart7723]

Should I set my gains with my eq settings already set? Or set the eq settings after the gains. Also should the cross over be off or on HPF for fronts and rear speakers

[@Reddirtrodz]

You want the signal to be as you will use it, at least as close to what you can. Crossovers, eq, etc should all be set. That doesnt mean you can't adjust after, but the idea is to find the max clean volume and then don't go above that point.
Some people tune in 5-10% distortion as it hard to hear, particularly in bass ranges, but that's a person preference.
You can play with it, and once it starts making sense, you will figure out what you prefer.

[@davpart7723]

@@Reddirtrodz right on! Makes sense.

[@WickedwildRC]

How are you hooking up the oscilloscope?

[@Reddirtrodz]

Ground to negative speaker output, probe to positive.

[@djcorewrecked]

If im measuring my stock headunit, should i connect the o-scope after the stock amplifier?

[@Reddirtrodz]

Depends on if you are using the stock amp output. If you are running high-level input, then yes.

[@djcorewrecked]

​@@ReddirtrodzI'm using the stock amplifier for the interior speakers, then I am tapping off the stock subwoofer wire to go into my LC2I pro