using DMM

[fazio93 10+ year member]

I have a 400 W RMS Kicker @ 2ohms

The HU is at max volume and the amp gain is about halfway.

If the multimeter is reading ~15V, do I increase the gain until it reads ~28V (max rated power)?

Thanks

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[Maxipads 10+ year member]

1. turn your HU down to 3/4

2. Half way doesn't mean anything

3. Are you using a 50hz tone?

4. Did you do the equation correctly

 

[RJesus 10+ year member]

yes, you should turn your headunit down to 3/4 power. The volume on your headunit increases/decreases the 'preamp output voltage' of the headunit.

Basically, it increases the signal. Then your amp takes that signal and amplifies it (multiplies it).

So if your headunit is at full volume and puts out 5v, the amp sees that 5v, and times it by the gain you set it to.

If your headunits at 3/5 volume it would put out 3v, and you would set your amp's gain higher to compensate for the difference.

You do not want to put your headunit at full volume, because it causes 'clipping'. The rule of thumb is to set your headunit's volume to 3/4, and don't ever go past that. Because your headunit 'stresses' itself to putout the extra power, and the signal isn't as clear as it is at lower volumes. This is particularly bad, because your amplifier amplifies all of the mistakes found in the preamp signal.

Play a 50hz test tone, with the sub speaker wires NOT plugged into the amp. I like to play a few tones to adjust the subsonic filter, low pass, and just to adjust the gain.

30hz tone to set my subsonic filter, once the voltage your DMM sees starts dropping, your filter has reached that tone (30hz).

60hz for the lp.

you can mess around with it and do what you feel comfortable doing. your voltage shouldn't go over your amp's RMS. Don't go by max power, ever. Completely discard any max power rating you ever see. As its a useless number that represents nothing.

 

[fazio93 10+ year member]

yes i was playing a 50hz tone.

i did the equation correct [sqrt root(400 RMS * 2 ohms)] ~28V

also, i have a JVC head unit with stock speakers. there is an 'amp gain' feature on the head unit:

Amplifier Gain Control: When you are using this head unit with factory speakers (or those rated to less than 50 watts peak), the Amplifier Gain Control can limit the amount of power being sent to those speakers. When the Amp Gain Control is set to low, the volume control ranges from 0 (minimum) to 30 (maximum). When using speakers rated higher than 50 watts peak, you can set the Amp Gain Control to high, and the volume control will range from 0 to 50. The internal amp can also be turned of when all the speakers are powered by outboard amplifiers.

I have it set to low power because I'm not sure how much my stocks can handle. I can't decide whether to set it to high or low power. if i set it to high power i can crank it up to about 40 before it starts distorting (when playing my mp3 player, AUX in) but I can only reach about ~25 with a regular radio station. i have the aux accessory volume control up to max (0-5, set to 5) but my radio stations are always louder. so when i set the gain, either i wont be able to reach my amp's full potential b/c i will not be able to increase the volume as much on a radio station, or i will overpower the amp if i have to crank the head unit volume up when using my mp3 player.

so by max I meant is was at 30 (out of the max 50).

thanks

 

[smoka 10+ year member]

You do not want to put your headunit at full volume, because it causes 'clipping'. The rule of thumb is to set your headunit's volume to 3/4, and don't ever go past that. Because your headunit 'stresses' itself to putout the extra power, and the signal isn't as clear as it is at lower volumes. This is particularly bad, because your amplifier amplifies all of the mistakes found in the preamp signal.

If you are only using a DMM, then you have no choice but to assume that there is clipping. If you use an O-scope, you will realize that most newer quality headunits do not clip at 100% volume.

But either way, you still want to do your testing at 3/4 volume because most people listen to MP3's etc and you will want to have some room to adjust the volume depending on the quality of MP3's.