High voltage when tuning with DMM

[gbleezy 10+ year member]

Newbie needing help here. So I have an Alpine PDX 1.1000 hooked up to a stock head unit using a line out converter. It's pushing a 12" Kicker L7 in the ported box from kicker (11VS12L72).

I have the gain all the way down, I turned the treble, mid and bass all the way down on my HU, played a 50hz test tone and with the volume not even half way turned up, the AC volts on my DMM is already above 40. When I turn up the volume even more it goes up beyond 50 and 60 volts. With a 750w RMS sub at 2ohms, I'm supposed to set the gain on my amp so that the DMM reads 38.72 ACV.

Am I doing something wrong here?

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[Kangaroux 5,000+ posts]

you sure the dmm isn't faulty?

 

[akheathen Premium Member]

what is your loc set at? it could be too high. also, it helps to clamp a meter on to measure current to account for impedance rise

 

[Buck 5,000+ posts]

What ohm load is your amp seeing?

 

[SQcrewcab 10+ year member]

Correct me if i am wrong, but when setting voltage for the gain..usually you set it with no speakers hooked up.. "Unloaded"

 

[Slayerx 10+ year member]

Correct me if i am wrong, but when setting voltage for the gain..usually you set it with no speakers hooked up.. "Unloaded"

Depends who you ask I think, but I'm pretty sure the majority says with speakers hooked up, to count any impedance rise you may face so you don't rob yourself of some power

 

[Haunz 10+ year member]

Correct me if i am wrong, but when setting voltage for the gain..usually you set it with no speakers hooked up.. "Unloaded"

That would be 100% incorrect...

 

[gbleezy 10+ year member]

you sure the dmm isn't faulty?

I don't think so, I connected it to my battery and it seems right.

what is your loc set at? it could be too high. also, it helps to clamp a meter on to measure current to account for impedance rise

the only settings on my LOC are for LF RF RR LF and those are little dials you can turn, the shop that installed it set these.

What ohm load is your amp seeing?

according to kicker the sub is wired to 2ohms. there's 4 settings on my dmm for ohms, 20M, 200K, 2K and 200. when i set it to 2K it shows 1. when i set it to 200 my dmm starts beeping.

I think I figured it out though. My amp has an input gain selector switch. It was originally set to 0.1v - 1.0v, I set it to 1.0 - 8.0v and when I tried to tune with my dmm, the ACV was around 6. I then set it to around 37 ACV. I remember pulling out my HU in the past looking for the output level but it didn't say so I left it as is. Should it be set to 1.0 - 8.0v?

 

[Buck 5,000+ posts]

I don't think so, I connected it to my battery and it seems right.


the only settings on my LOC are for LF RF RR LF and those are little dials you can turn, the shop that installed it set these.

according to kicker the sub is wired to 2ohms. there's 4 settings on my dmm for ohms, 20M, 200K, 2K and 200. when i set it to 2K it shows 1. when i set it to 200 my dmm starts beeping.

I think I figured it out though. My amp has an input gain selector switch. It was originally set to 0.1v - 1.0v, I set it to 1.0 - 8.0v and when I tried to tune with my dmm, the ACV was around 6. I then set it to around 37 ACV. I remember pulling out my HU in the past looking for the output level but it didn't say so I left it as is. Should it be set to 1.0 - 8.0v?

It should be set to 200. The higher your ohm load the higher the voltage is going to be. I forget the formula but it is something like this:

voltage= ohms * the square root of watts

 

[Slayerx 10+ year member]

Why is it beeping? 200 is what it should be set at, if I'm understanding you correctly.

And yes, it should be set to 1-8v

 

[gbleezy 10+ year member]

I don't have my sub hooked up when setting the gain.

I'm not sure why it's beeping. I played the 50hz test tone, set my dmm to 200 in the OHMs section and numbers just kept changing rapidly on my dmm and it was making beeping sounds, kinda like when you roll your r's with your tongue.

Also, the manual for my box says, "Note: The use of a subsonic filter will significantly increase power handling. The power handling specification in this chart

is calculated using a 25Hz, 24dB/octave subsonic filter."

My amp has an SSF but the only options are Off, 15hz or 30hz...what should I set it to?

 

[Slayerx 10+ year member]

your box is probably tuned high, so set the ssf to 30hz, but 15hz is better than nothing though not too much stuff gets that low, it'll help.

set your gains with the subs connected. The reading should stay almost constant. Not sure why the dmm is beeping and reading sporadically. I'd suggest trying a diffrrent dmm to be safe.

 

[gbleezy 10+ year member]

cool, thanks for all the help.

 

[akheathen Premium Member]

well, when you have it on ohms, it will beep at anything below 10ohms, or something like that, so don't freak out on the part. if it's a fluke, push the button with the curved lines to silence the beep. it's just a continuity indicator. now, on ac, when it's beeping, that means you have it set to measure the wrong way (to indicate when you are hitting min, or max). there should be buttons to toggle peak/rms/etc. what you want it to do is average rms, and not on min/max settings. if you have your manual for the meter, it will be good to read up on the ac settings and what your little icons mean on the screen. and, if you have it "unloaded", then it will put out higher voltage than when loaded, and if you can get ahold of a clamp-on meter to measure amps with the other meter measuring voltage. the subs are not a dummy load, and impedance rise will actually put the wattage lower at your calculated voltage. for instance, your 2ohm load could be actually playing at 3+ohms, which means you are actually getting closer to 450, rather than almost 700...... if you can't get ahold of a clamp, then i would just set it at 40....

 

[Slayerx 10+ year member]

^^^ what he said, I was thinking that as well but forgot to mention, set it to about 40 since you cant clamp it