Amp not getting enough power?

[cheatcode]

I hate to ask for help. I've been googling my face off reading/researching/etc and I can't figure it out. I've come to the conclusion that my amp isn't getting enough power but I don't think there's anything wrong with my power wire/fuses/blocks/terminals/grounds. The signal coming out my HU is clean and it's clean going into my amp.

Here is my current setup

Signal going into my amp

Here is what happens when I try to set my gains

[ShadeTreeMechanic]

Your calculations are off because the impedance is not the same as resistance. All you can do is set it to max clean signal.

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@155db, thanks for the reply. What calculations are you referring to? If I set my gains to the correct voltage the signal will clip. On my subwoofer outputs I can't even set it to the correct voltage (40v) as it won't reach that high.

[ShadeTreeMechanic]

How do you know what the correct voltage is? Set it to max clean signal. That's all you can do.

[cheatcode]

It's called simple math.

[ShadeTreeMechanic]

Ok I get it. You are using resistance when you should be using impedance which changes depending on frequency and driver loading.

The bottom line is that your amp doesn't put out what you think it should. Turn it up to max clean signal. That's all you can do.

If you want more power then get a bigger amp.

[audiofanaticz]

A speaker is a variable impedance, once power is applied to the speaker the impedance changes, a lot and frequently!

Its nothing like a resistor that stays at the same resistance when power is applied.
Just because the speaker is 4ohm, and you wire your amp to 4 ohm, does not mean your amp is playing at 4 ohms.

There is a thing called impedance rise (which is what happens when the impedance of your speaker is fighting the voltage coming from the amp), and that means your 4 ohm speaker maybe playing at 6 ohms or even 10 ohms depending on frequency.
Unhook a speaker once and connect it to a multimeter, with the multimeter on the ohms setting you will see roughly the ohm of the speaker. Now start pushing the cone up and down gently with your hand and watch the numbers that pop up and notice how it changes compared to the resting reading that you just seen prior to moving the cone by hand.

This is similar to how your amp is seeing that impedance.

Using voltage to determine your amps output is a flawed and failed method and simply does not work. Your testing proves this.

[audiofanaticz]

Also your RCA cables seem to be garbage, maybe part of the problem.

The Kenwood KDC-x701 claims to have 5volt preouts, if your only getting .64 and .99 volts output at the end of your RCA cables by the amp(s) something is wrong!

Your losing over 4 volts due to resistance caused by crap low quality cables or the deck does not put out 5 volts per channel like claimed.

Before buying new cables however I would suggust pulling the radio out of the dash and testing the preout voltage straight out the back of the unit (with the rca cables disconnected).

If the preout voltage is high in the 4-5 volt range then you know your current rca cables are a huge problem in your system right now!

The resistance in rca cables will cause a loss of voltage from front to back. If the loss is too much you will degrade the quality of your system.

For example it can cause you to use a higher gain setting than typically needed since the voltage from the rca cables going into your amp is so low, and in return will mean your output power of the amp will be maxing out long before it should be like your amp clipping at 20volts instead of 40volts.

Like I said the math method is flawed, and thats why many people use an oscilloscope or a dd-1 to set their gains and ignore the whole output voltage thing, however you should be able to get closer to that 40 volt mark than what you are currently getting! It maybe only 33volts or hell maybe even 47 volts (if the signal is clean and the amp is under rated poiwer wise), and thats why the math method is flawed.

Would you still set your gain at 40volts per what the math says even though your oscilloscope is showing 47 volts to be clean? I know I wouldnt and would want to take advantage of that extra clean power!!!

So like I said, test the rca voltage at the back of the headunit, I bet its way higher than at the end of your cables.

SMD offers some great stupid low resistance cables (thats all I use) www.wccaraudio.com

Soundrive also offers some great cables.
Both are made in the USA with quality connectors, soldered wires, etc.

Cables from companies like knukonceptz Ive had nothing but issues with in the past, and some other companies that are offering cheap china rca cables as well with loosly crimped connectors etc. Just garbage.

[audiofanaticz]

This is just a quick test I did a while ago.

It will show some used smd rca cables that are 3 and 6 foot long compared to a 1.5 foot long Certified Basshead cable which is brand new never used.

Typically the shorter the cable, the lower resistance it will have, but the quality and gauge of the cable and the quality in the connection from the cable to the plug will play a HUGE difference in that.

 

[cheatcode]

All JL amps do rated or more. I'm not quite sure how this relates to my question since I'm not asking about the drivers at all "since they have literally nothing to do with my issue" but I'm well aware the resistance can vary dependent on driver movement and I know how to use a multimeter, but thanks for the tutorial. 

I'm not sure what set of $10,000 cryogenic RCA's you run but JL Premium RCA's are far from garbage. No, nothing is wrong with my HU. It does around 4.7v clean with the volume all the way up. And no, the "math method" is not flawed. If your amp is rated to do 400 watts rms at 4 ohms then setting the output voltage at 40 volts would ensure your "amplifier" is doing relatively close to that.