Using an Oscilloscope to Set Your Gains for Around $50

An important part of getting your stereo set to sound its best is to have your gains set correctly. The reason behind this is you want the most gain as close to the source as possible to reduce/eliminate any static/distortion in the system.

I spoke with a JL Audio tech about this a while back and he had a good quick explanation:
"For example if you are watching a movie through a DVD player and pause it, but turn the volume on the receiver up, you create a slight hiss because it is trying to replicate a signal that is not there [or barely there]."

This is why you want to be able to have the gains on your amplifier set correctly so you can eliminate any hiss/distortion.
For Reference, my system is: Kenwood Dmx1037s, Helix Dsp Pro Mk2, Two JL Hd900/5 amps. Your system may be a little different, but should be the same process (If you aren't using a dsp, just skip that part).

Equipment Needed:
Cheap Amazon Oscilliscope:
https://smile.amazon.com/gp/product/B081ZPMKJ5?ie=UTF8

There's about a dozen different models/colors but they are all the same, just buy the cheapest one you can find that looks like the one above (there are grey options too). I believe i got this one for $37

Optional Equipment:
A great thing about these portable oscilloscopes, is that they can be run off a 9v battery to make them portable so you aren't running an extensions cord out to your truck if its not in the garage. I remember i calculated something like 3hrs of use on a 9v battery (something like that).

Grab one of these 9v to barrel connector to make things easier:

$8 DAIERTEK 10pcs 9V Battery Connector 9 Volt Battery Snap Clip I Type with 2 Pairs of Alligator Clips and 2.1mm X 5.5mm DC Male Power Plug

https://smile.amazon.com/gp/product/B07YBYL7HH?ie=UTF8


A BNC to RCA adapter makes life a LOT easier instead of messing with alligator clips sliding off the end of an rca cable.

$2 Monoprice BNC Male to RCA Female Adaptor - Gold Plated

https://smile.amazon.com/gp/product/B006VK8IEI?ie=UTF8&th=1


Test Tones:
Head over to the Kicker website and go to the "KXMA and KMA Amplifier GAIN MATCHING" section:
https://www.kicker.com/test-tones
We will be using the 50hz 0db, 50hz -5db, 1khz 0db, and 1khz -5db. I put them on a flash drive, you could also stream them from your phone.
I have these downloaded if kicker pulls them down or changes the link, just pm me if you need them.

The Procedure:
Since we want to have the most gain closest to the source, we will be starting at the head unit. Use the 0db test tones for the head unit (and dsp if applicable) and the -5db for the amp adjustments. The -5db at the amp ensures that there wont be any clipping at the amps.

Head Unit:
Start off my making sure that there is no sound curve adjustments (needs to be flat) to the eq or any enhancements applied. Also check to make sure that the S/W level is set to 0 and no bass boosts are applied. On the scope there is a flip switch that changes from AC/DC, set it to AC.
Grab the RCA's that are coming out of your head unit and disconnect them from your dsp (or amp). Plug one of the rca's from the NON-S/W output (i used the red one on all my adjustments, but it doesn't matter) into the scope and fire up the 1khz 0db test tone. MAKE SURE TO SET THE TRACK TO REPEAT JUST THAT TONE.
Start turning up the volume until you can start to see the sign wave on the scope. Use the buttons and dial to adjust the wave so you can CLEARLY see 1 or 2 complete waves.
Keep turning up the volume until the peak and valley of the signal starts to clip, meaning its no longer a smooth curve.
For my head unit this is at 38 of 40 on the volume:


And when i go to 39 volume this is what happens to the curve:


So, we have established the absolute maximum that the head unit can go to and we will be using 38 on the volume for all the coming tests.
Tip: You can press and hold the OK button and it will remove the data from the top of the screen so you just see the sign wave with the grid.

Next do the same procedure, but use the S/W output RCA and the 50hz 0db test tone. Set your head unit to the max volume you just found, and find the s/w gain setting on your head unit. Try to adjust it until it starts to clip. On my head unit, i found that that i can add +1 to the S/W Level before it clips. I dont have a clip picture at +2, but i remember that it had a diagonal edge at the peak/valley (maybe i'll update it in the future to have the clip picture).
Here's what it looks like at +1:



Note: See how its a little harder to see the peak/valley of the sign wave? I should have adjusted the SEC/DIV so that i could only see 1 or 2 complete waves.

Here's a good video of the procedure/explanation on a slightly different head unit, but resulted in the same settings.


DSP:
(You can skip this step if you are not running a dsp)
First thing: If you are using a bass knob or volume knob, set those to the max or you could just unplug the
Isolate only one channel so that only that channel will be outputting sound and use an rca cable to connect to that channel of the dsp:

Next Bypass all the Highpas/Lowpass filters and the adjustments at the bottom so that your sound curve is flat on the dsp. Make sure that you have muted all the other channels, since you are deactivating HPF/LPF filters (RED), you could easily cook a speaker if you sent the wrong signal to the wrong speaker.


Play the 1khz 0db test tone at your max head unit volume you found before and start to move the Channel Gain & Output Level slider over (Yellow) and see what your scope looks like.
Now this procedure is a little bit different from the head unit, at maxing the gain adjustment, i wasn't able to get a clipped signal, so instead of going for the max additional gain on the dsp, we will be using a target voltage. You need to figure out what the max input voltage your amps can handle. My JL Hd900/5's can take up to 8v input from the RCA's.
Just to incase i needed to adjust anything in the future, i went through and did all the channels at 5v, 6v, 7v, 8v and Max gain. I'll be using the 7v values for my adjustments to leave a little bit of headroom.

For the most part, the gains on the dsp will be set to mostly +1.25db. If your signal ends up clipping at the dsp, just use that gain level. If not, then you can use the max target voltage that your amp(s) can handle.

Amplifier(s):
If you are using any bass knob or volume knobs go ahead and set them to the max, or just unplug them while taking measurements.
Now we will be using the -5db files for the amplifiers. For this you will be using the alligator clips that came with the scope. Grab a small length of speaker wire that you have laying around and disconnect all the speakers except for the S/W output. Connect your short speaker wire to the amp and the alligator clips to the other side of the wires. Make sure you either mute all other channels on your dsp, or unplug all the other outputs from your amp(s).
If you are using a dsp, make sure you are using your new gain settings, and that you still have the HPF/LPF bypassed and a flat curve. If you aren't using a dsp, you should turn off any filters on your amp.
Play the 50hz -5db tone and look at your meter, most likely it will be clipped to high hell. I dont have a picture, but at my previous amp settings it was almost a 80deg straight line down from the peak of the curve. Similar to this, but more drastic:


Adjust your gain settings on the amplifier, you'll notice that a very small adjustment makes a very large change to the curve. Previously, i had my gains set to about 60%, now i have them set to about 20%.
Rinse and repeat for all the other channels and make sure that you use the 1khz -5db for speakers and the 50hz -5db for the subs.

Your gains are properly set.

 

Reserved

 

I like where this is going, some images not showing up for me though...

 

Thanks for bringing this up to me.

Can another set of eyes confirm if there is an issue with the pictures?

 

Looks like you’re missing 4 images

 

Thanks. I'll update it

 

Fixed?

 

Still missing the one just BEFORE the youtube video.

 

updated for the last time....hopefully

 

Looks good.

Getting my system from Tech12Volts in the next few weeks. Will have to implement some of these. No DSP though. Thought I'd look at what that offers and at $1400... I'm still not sure what I get from it.

 

Not sure what you mean? You spent 1400 at t12v or 1400 for a dsp?

 

When I looked up the DSP you have, the going price was $1400. Wasn't sure what that device does and if it is worth $1400.

 

Ohh, i see. I believe i paid around $800 for it about 2 years ago, may have gone up a bit....but from what i've seen, its still in the ballpark.

If you are running passive component speakers, the dsp isn't worth it. You want to feed your passive components a full range flat curve and let the crossovers that came with the speakers do the work.
The one thing that you would gain is time alignment ability. That makes a big difference.

 

Oh nice! I'm planning to stick with the stock non-JBL head unit and just figured (by ear) the volume before distortion was 46 to set my sub amp gain. But an oscilloscope to test the theory for <$50?

 

Some people say that by ear is the best way using music, but I'd rather take the human factor out of the equation.

 

Do you use a bass remote knob? Where would u position the knob to set the gain? Full tilt or middle?

thanks

 

Thanks for reminding me about this. I need to update the original with this information.

To answer the question, make sure your bass knob is set to the max. You could also just remove it for the time you do your measurements. I ended up having to re-do my measurements the first time because i had the bass knob set to about 75%.

 

If your ever in Oregon swing by and I buy you a six pack and let you go to town on my stereo.

 

Haha! I'll let you know if i head north!

 

Good write up. For simplicity, I'll stick with my SMD DD-1 haha.

 

Those are pretty cool. Pretty nice to be able to see the curve vs just seeing a red light turn on, but shit, if you already have one....no point in spending extra money.

 

So i have a question. I followed all the step minus dsp.
Android radio
Measure hu rca before amp and will clip at 33/36 both at 1000hz 0db and 50hz 0 db. Sub level is at 9/10 on radio. Both zero clipping at 33. 34 will clip right away. So 33 is where i leave it at.

measure amp output to set gain.
1000hz, -50bd. Ok. No problem can turn amp up a tiny and it’s matched gain. Done.

Next, sub

50hz, -5db
Immediately show clipping. Clipping hard. Gain on amp is completely down. Has not turn a bit.
All filter is off.

So? What should i do? To reduce clipping i had to turn the volume down couple notch. Amp gain is still at the lowest possible.
Weird???

amp using is 5 ch pioneer gm-9705

 

Drop it down to 2 of 10 on the sw level of the head unit and you should be able to adjust the gain on your amp. Gonna have to play with it a little to find the right Ballance between the head unit and amp. You want the most gain closest to the head unit, but try to figure out so you end up turning your amp gain for the sw up to around 1/3 up.
Make sure that you have any filters turned off on the amp also.

 

Ok. I’ll give it ago again this evening. Thanks

 

Let me know how it goes.

Whats the model of your head unit?

 

Joying 10” with intel airmont chip.

 

I've read some of the Amazon reviews and it seems that this does not come with the 120v to 9V power supply, is this correct. I have an inverter in my truck and in my mind it would make sense to just power it from that versus using 9V batteries.

Thanks for sharing this, very cool information.

 

The one that i bought and linked came with the 120v adapter.

The inverter would work fine. these meters sip power.

 

Brother this is fire! Well played.

 

Let me know how it goes with the re-test. try to post some curve pictures if you are still having problems.