AC Volts vs DC volts

[Nestacle 10+ year member]

Hey guys,

My friend and his dad set the gain on his alpine mrp-m500 amp awhile ago using a DMM. Now i know you are supposed to have the voltage on AC when using the DMM to set the gain, but what would happen if it was set to DC volts? Because when he was done the process of setting the gain, his gain knob was quite a bit higher than the "nominal" marker on the amp gain knob (it is alittle higher than the 0.5 volts marker), which to me doesn't seem right (you would think the gain would come out closer to the nominal position). His dad was the one who set the DMM and hes pretty sure he told him to set it to AC but what if it was on DC volts?

thanks

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[loopkiller 10+ year member]

There usually is a fuse that would pop in the DMM. If no fuse, then the DMM will pop.

 

[Lakota 5,000+ posts]

Using DC voltage is incorrect since music is AC current. Reset the gains w/ either using AC on the dmm or just totally forget the dmm method all together. To be honest, the dmm method isn't necessary, I never do it that way.

 

[Gebrochen 10+ year member]

It would just read an inaccurate measurement. It wouldn't blow the fuse unless you were measuring current and exceeded the limit. It would have been very obvious something was wrong if you had it on DC measuring AC voltage.

[edit] the reason it wouldn't pop the fuse is because measuring a negative voltage is just as valid as a positive one. The DMM would just show confusing updates of random crap as the voltage swung between +85V and -85V (or whatever the real AC reading should have been). Totally pulling it out of my ***, but maybe some meters would interpret that you wanted to know the DC offset. Never seen that, though.

 

[BumpinTypeR 10+ year member]

hey im the one who nestacle is talking about. i reset my gain, and this time the knob ended up not being turned nearly as far as it came out to be last time....it actually raqched my desired voltage right at the nominal marker on the amp...any ideas why it would be different? could it be because i had my HPF on 125hz and LPF on 100hz while setting the gain? keep in mind this is a sub amp wired to a single 12" type r.

thanks

 

[scoob8000 10+ year member]

With your DMM set to DC, you should see nothing. If your seeing DC coming from the amp speaker outputs you got some nasty clipping going on, or you have something wrong with your DMM.

FWIW, I have this same amp behind a Clarion HU with "5.8v" preouts. I have to set my gain to nearly it's max to get rated power..

 

[BumpinTypeR 10+ year member]

ok so i set my gain with a DMM and was shootin for 31.62 volts because that = 500RMS at 2ohms. Im runnin a 12" dvc 4ohm alpine type r sub. I did the whole gain setting procedure and the gain knob reached 31.6 volts right in the middle (at the "nominal marker") how come it didnt end further up like yours did?

The first time i set the gain i had my src-lv adjust setting on my HU at 0...then i realized when i turned this up my music was louder and not being drowned out by the subs, which i liked. And the first time i set my gain the knob ended up being much higher up (alittle past 0.5) when i reached my voltage.

so the sedond time i set my gain the src-lv thing was all the way up, and my gain knob was turned alot less further than before after i reached the desired voltage.

should i have set my gain with that setting at 0 or all the way up?

thanks

 

[Buck 5,000+ posts]

There usually is a fuse that would pop in the DMM. If no fuse, then the DMM will pop.

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