Checking gain adjustment

[grocery getter 10+ year member]

My mono sub amp gain knob has min to max, no numbers. Is there a way to check how many volts I have it set at so I can match my input volts from preamp? I have a dmm. Also, it's adjustable from 0.3v to 6v, and what does 2v/45k with the ohm sign mean?

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[LosIsATool 5,000+ posts]

You dont set gain by the pre outs

http://mobile.jlaudio.com/pdfs/gainSetting.pdf

 

[grocery getter 10+ year member]

I know the way to adj an amp is with an oscope. I dont have one. My understanding is to adj. gain/sensitivity to match incoming volts from the HU. When I use 50hz 0db test track, and HU settings are at 0 and subw at highest level. Im only getting .6v at best to the amp, with vol between 75%-80%. My output volts to the sub is only around 16v. Im suppose to get 28.28v max output to equal 400 watts. Should I get a line driver?

 

[LosIsATool 5,000+ posts]

Setting the gain has nothing to do with your HU, so you dont know how to do it right.

You dont need a oscope. Did you go to the link I put for you?

 

[audioholic 5,000+ posts]

Setting the gain has nothing to do with your HU, so you dont know how to do it right.

If you think adjusting gains has nothing to do with the h/u, then you dont know how to do it right. The gains match the input sensitivity of the amplifier to the output signal voltage from the h/u.

 

[vaiboy 10+ year member]

My mono sub amp gain knob has min to max, no numbers. Is there a way to check how many volts I have it set at so I can match my input volts from preamp? I have a dmm. Also, it's adjustable from 0.3v to 6v, and what does 2v/45k with the ohm sign mean?
I know the way to adj an amp is with an oscope. I dont have one. My understanding is to adj. gain/sensitivity to match incoming volts from the HU. When I use 50hz 0db test track, and HU settings are at 0 and subw at highest level. Im only getting .6v at best to the amp, with vol between 75%-80%. My output volts to the sub is only around 16v. Im suppose to get 28.28v max output to equal 400 watts. Should I get a line driver?

The 2v/45kΩ is the input for the preamp, it means the maximum voltage for input signal is 2v and the output impedance of the source needs to be 45kΩ or less.

A preamp is a line driver, it would help if we knew what preamp you have. If you are only getting .6v output after the preamp you need to adjust the gain on the preamp before you mess with the gain on the amplifiers. It would also help to know what amplifier you are using.

 

[grocery getter 10+ year member]

Thanks guys, when I said preampi meant my hu preamp outputs. Thats why I was mentioning a line driver. I have a Dual xhd7720 hu and a jvc arsenal 7001 mono amp.

 

[BlactimusCrime 10+ year member]

is that jvc amp rated 400rms or 400 max?, because that could be the issue here

 

[grocery getter 10+ year member]

400rms

 

[vaiboy 10+ year member]

Thanks guys, when I said preampi meant my hu preamp outputs. Thats why I was mentioning a line driver. I have a Dual xhd7720 hu and a jvc arsenal 7001 mono amp.

What are your LPF and Subsonic Filter settings on your amp?

Try setting the LPF to 300hz and the Subsonic to 20hz on your amp, then the volume to about 35 with the subwoofer set to 12 on your head unit. Set the amplifier gain to minimum and put your DMM probes in the speaker output. Play your test tone and slowly increase the gain adjustment until it reaches 28.28 VAC if it maxes out below 28.28 then something is definitely wrong.

The headunit output seems a little low at .6v but technically your amp should be able to reach full power with that input voltage.

 

[LosIsATool 5,000+ posts]

If you think adjusting gains has nothing to do with the h/u, then you dont know how to do it right. The gains match the input sensitivity of the amplifier to the output signal voltage from the h/u.

Not being sarcastic but where does the square root of RMS*OHM=voltage have anything to do with the head unit

 

[Kangaroux 5,000+ posts]

Not being sarcastic but where does the square root of RMS*OHM=voltage have anything to do with the head unit

The higher the preout voltage is, the lower you need to set your gain to reach the desired AC voltage. most amps say "level" and have 0.2V and 6.0V as a setting. setting your gain to the preout voltage of your HU will give the maximum potential for your amp without putting it into clipping

 

[audioholic 5,000+ posts]

Not being sarcastic but where does the square root of RMS*OHM=voltage have anything to do with the head unit

You've lost sight of the forest through the trees. Setting your gains is merely the action of adjusting the input sensitivity of the amplifier's input stage, with the output signal voltage of the headunit. So obviously the statement that setting your gains has nothing to do with your h/u, and backing that up with Ohm's Law, is invalid.

Im not trying to be an ass here, but with such a vague statement from you originally, I wasn't sure how to contradict you specifically as to how the h/u plays a role in gain adjustments.

 

[LosIsATool 5,000+ posts]

I know that but like I said earlier, you are adjusting to a voltage from that equasion. So it really has nothing to do with the HU. You dont adjust gain to the pre out

(you do but not like that) in the formula

 

[LosIsATool 5,000+ posts]

You've lost sight of the forest through the trees. Setting your gains is merely the action of adjusting the input sensitivity of the amplifier's input stage, with the output signal voltage of the headunit. So obviously the statement that setting your gains has nothing to do with your h/u, and backing that up with Ohm's Law, is invalid.
Im not trying to be an ass here, but with such a vague statement from you originally, I wasn't sure how to contradict you specifically as to how the h/u plays a role in gain adjustments.

Thats what I dont understand. The formula doest can what pre out voltage you have