Attempting to set gains with DMM, but can't reach desired voltage...

[JohnKimble]

Hello,

I've run into some issues setting the proper gains on my mono sub amp. I've set all levels, phase align, bass boost, subsonic crossover and low pass crossover to as far counter clockwise as I could. I also left the remote gain controller in the middle setting, as I've read to do.

My amp is pushing 240w to my single 12" at 4 ohms. My sub is also 240w @ 4 ohms. After doing the math, I came up with 30.98v.

While running a 60hz tone, the maximum voltage I can get to display on my dmm is around 5-6v (this is with my gain maxed). When I change the low pass crossover to around ~100, I can get the voltage to bump up to around ~20v. It's not until I adjust the remote gain controller to maximum, I can get the desired ~31v.

Should I calibrate my amp with the gain controller on maximum, instead of in the middle? Is there anything I may be missing? All settings on the head unit are at 0, bass boost is off, loudness is off. Power at the amp reads a solid 12v, with the car running it's at 14.Xv.

Thank you.

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[Side Show 10+ year member]

do another search on this forum on how to set up an amp..... your almost there. turn the headunit up to the level you want it tobe the loudest then turn the gain up till you start to hear distortion at that volume. fine tune it from there with the DMM

 

[bbeljefe]

Always set gains with the subwoofer knob at full, the crossover turned off or as high as it can be set and with the head unit at it's highest unclipped level. If you don't know that level, set it at no more than 80% if you're not using the internal amp and 55% if you are.

Set bass amps with a 40 Hz tone and if you want to compensate for music with low bass levels, set it with a tone that is recorded -5 or -10dB.

 

[beech2000]

Hello,
I've run into some issues setting the proper gains on my mono sub amp. I've set all levels, phase align, bass boost, subsonic crossover and low pass crossover to as far counter clockwise as I could. I also left the remote gain controller in the middle setting, as I've read to do.

My amp is pushing 240w to my single 12" at 4 ohms. My sub is also 240w @ 4 ohms. After doing the math, I came up with 30.98v.

While running a 60hz tone, the maximum voltage I can get to display on my dmm is around 5-6v (this is with my gain maxed). When I change the low pass crossover to around ~100, I can get the voltage to bump up to around ~20v. It's not until I adjust the remote gain controller to maximum, I can get the desired ~31v.

Should I calibrate my amp with the gain controller on maximum, instead of in the middle? Is there anything I may be missing? All settings on the head unit are at 0, bass boost is off, loudness is off. Power at the amp reads a solid 12v, with the car running it's at 14.Xv.

Thank you.

Same here. Not sure what's the deal. Click the following

http://www.caraudio.com/forums/amplifiers/596396-matching-head-unit-alpine-mrp-m500-using-fluke-dvm.html

Good luck.

 

[JohnKimble]

I did forget to mention I set my head unit volume to 26 (75% of my maximum).

I will attempt it again tomorrow with the head unit at 26, low level cross over at maximum (250hz), remote at maximum and a 40hz tone at either -5 or -10db.

Thanks again for the help.

 

[Side Show 10+ year member]

Always set gains with the subwoofer knob at full, the crossover turned off or as high as it can be set and with the head unit at it's highest unclipped level. If you don't know that level, set it at no more than 80% if you're not using the internal amp and 55% if you are.
Set bass amps with a 40 Hz tone and if you want to compensate for music with low bass levels, set it with a tone that is recorded -5 or -10dB.

heya champ, why would you have the low pass filter turned off when your tuning your sub amp? do you tune your amps this way?

 

[JohnKimble]

I forgot, in order for me to reach my 31v I have to increase my bass boost to around +6db (with a range of 0db to +12db). I though I shouldn't need to adjust the bass boost at all?

 

[Side Show 10+ year member]

think you are getting confused with bass boost on the headunit and bass boost on the amp

 

[JohnKimble]

I'm sure I am. Can you elaborate for me?

 

[Side Show 10+ year member]

I don't use bass boost at all, specially not on the amp. why are you aiming at this 31V?

 

[bbeljefe]

heya champ, why would you have the low pass filter turned off when your tuning your sub amp? do you tune your amps this way?

Because you want to make sure that there is nothing attenuating the waveform you're sending the amplifier. And since it's near impossible to know exactly what frequency the crossover is set to or to know how accurate the setting is, the best thing to do is bypass or turn it up all the way.

And yes, I set my amplifiers and the amplifiers I set for customers in that manner. I don't dispense advice I don't follow.

 

[JohnKimble]

I've been told the proper way to set my amp with a dmm is to multiply the wattage by resistance, and square it. 240x4 = 960. sqrt of 960 is 30.98.

Without cranking up the bass boost on the amp, I cannot reach a 31v reading on my dmm.

 

[Side Show 10+ year member]

cheers man, I've learnt something today cheers.... do you change the crossover back down once the gains set?

 

[bbeljefe]

cheers man, I've learnt something today cheers.... do you change the crossover back down once the gains set?

Yes.

 

[bbeljefe]

I've been told the proper way to set my amp with a dmm is to multiply the wattage by resistance, and square it. 240x4 = 960. sqrt of 960 is 30.98.
Without cranking up the bass boost on the amp, I cannot reach a 31v reading on my dmm.

Your math is correct. If you do the things we talked about here and you still cannot get the amp to produce 31 volts, you can turn the bass boost knob up to about half way and then set the gain. That's not the norm but it's also safe to do in most cases.

But again... try what we talked about first. After all, you were trying to achieve an output from a 60Hz tone while at the same time having the crossover set to block all frequencies above ~40Hz. It stands to reason you could barely get a reading. ;-)