setting gains with a DMM help

[rodneypierce 10+ year member]

Alright guys, I finally got my Eclipse CD7200 HU and got it installed this past weekend. I went to set my gains on the amp and when I did set them to what I had calculated, it was very weak. Both the front and rear channels, and the subwoofer. I have the following:

MB Quart PAB5400 Amp.

55w x 4 channels @ 4 ohms (RMS) - front components and rear 6x9's.

300w x 1 channel @ 2 ohms (RMS) - sub

Aura 5.25 Components @ 4 ohms - 50 w RMS

Aura 6x9 coaxials @ 4 ohms - 60 w RMS

MB Quart DWG 254 DVC 10" sub wired @ 2 ohms - 250 w RMS

So according to my calculations I should have set them at:

Fronts - 14.14 volts AC

Rears - 15.49 volts AC

Sub - 22.36 volts AC

I set them at the above voltage with a 1000hz test tone for the fronts and rears, at about 80% of the HU's volume, and a 50hz test tone for the sub. I had all of the speakers unhooked during the gain settings, and was using a Fluke DMM.

With these settings, my gains on my amp were less then half way up (which doesnt make sense considering the amp is rated for pretty much what each speaker is rated for) and the speakers were not loud at all. heck, could hardly tell the sub was even on.

I also checked to make sure that all speakers were wired in phase as well.

So I went and set each gain at roughly 3/4 of the way up, and its MUCH better, with no audible distortion from any of the speakers. (fronts crossed at 80hz, rears at 63hz and sub at 80hz)

Was just curious if I did that right, or what could be the issue??

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[Gregulate 10+ year member]

Your math checks out. How does it sound?

 

[rodneypierce 10+ year member]

Your math checks out. How does it sound?

at the recommended readings it was horrible. I had to turn the HU almost all the way up to get any volume out of it, and the sub was still very faint. Now that I turned them up roughly another 1/4 of a turn, its much much better, and the sub hits fairly well. I think there is still some to be had there, but it sounds much better. No distortion or anything that I can pick up with my ear. Just wanted to make sure I wasnt going to be clipping.

Is it maybe the amp is just that under rated or efficient? I mean, when the total rated RMS power of the amp is being achieved when the gains are only half way up just didnt seem right to me.

 

[ahole-ic]

Alright guys, I finally got my Eclipse CD7200 HU and got it installed this past weekend. I went to set my gains on the amp and when I did set them to what I had calculated, it was very weak. Both the front and rear channels, and the subwoofer. I have the following:
MB Quart PAB5400 Amp.

55w x 4 channels @ 4 ohms (RMS) - front components and rear 6x9's.

300w x 1 channel @ 2 ohms (RMS) - sub

Aura 5.25 Components @ 4 ohms - 50 w RMS

Aura 6x9 coaxials @ 4 ohms - 60 w RMS

MB Quart DWG 254 DVC 10" sub wired @ 2 ohms - 250 w RMS

So according to my calculations I should have set them at:

Fronts - 14.14 volts AC

Rears - 15.49 volts AC

Sub - 22.36 volts AC

I set them at the above voltage with a 1000hz test tone for the fronts and rears, at about 80% of the HU's volume, and a 50hz test tone for the sub. I had all of the speakers unhooked during the gain settings, and was using a Fluke DMM.

With these settings, my gains on my amp were less then half way up (which doesnt make sense considering the amp is rated for pretty much what each speaker is rated for) and the speakers were not loud at all. heck, could hardly tell the sub was even on.

I also checked to make sure that all speakers were wired in phase as well.

So I went and set each gain at roughly 3/4 of the way up, and its MUCH better, with no distortion from any of the speakers. (fronts crossed at 80hz, rears at 63hz and sub at 80hz)

Was just curious if I did that right, or what could be the issue??

You can't say you get no distortion. You can say you do not hear distortion. There is a HUGE difference there. Your gain being well below half means you did it right the first time. The gain knob doesn't indicate what percentage of amp power it's putting out depending on how far you turn it. It is for matching it's inputs to the head unit's output. Once you've matched properly, the amplifier will give full output with no or very little distortion. The problem is, most people perceive clipping as sound pressure. It's just how your ear and brain perceive it.

I see this all the time. I have a tl, and a couple nice fluke meters. I do test and tunes in my area. People will have me set their gain and I meter right then because I know what it going to happen. Upwards of 90% of the time I have to turn their gain way down from where they had it. They tell me it's quieter than before. So I'll meter it how i set it and show them the number. Then they set the gain and I show them how much they actually lost. Nobody can ever believe it. If you want more intense sound that is not distorted in any way, you'll need more powerful equipment. If you want to keep the equipment you've got, keep cranking the gains and it will eventually fail on you.

 

[Gregulate 10+ year member]

Wait, that's a 4 channel amp powering 2 sets of speakers and one sub? That's 5 channels... I'd say, disconnect the rears, or let them be powered off the HU and not the amp and bridge the power going to the fronts and also bridge the sub channel. I've never used a 4 channel this way, but it's how I understand it to work.

 

[rodneypierce 10+ year member]

Wait, that's a 4 channel amp powering 2 sets of speakers and one sub? That's 5 channels... I'd say, disconnect the rears, or let them be powered off the HU and not the amp and bridge the power going to the fronts and also bridge the sub channel. I've never used a 4 channel this way, but it's how I understand it to work.

Its a 5 channel amp.

MB Quart PAB5400 Amp.

55w x 4 channels @ 4 ohms (RMS) - front components and rear 6x9's.

300w x 1 channel @ 2 ohms (RMS) - sub

 

[bubbagumper6 5,000+ posts]

What did you expect with a single 10" sub and 300w? What enclosure is it in?

 

[Gregulate 10+ year member]

Its a 5 channel amp.
MB Quart PAB5400 Amp.

55w x 4 channels @ 4 ohms (RMS) - front components and rear 6x9's.

300w x 1 channel @ 2 ohms (RMS) - sub

You're right. Sonic has it in the 4 channel section.

 

[rodneypierce 10+ year member]

You can't say you get no distortion. You can say you do not hear distortion. There is a HUGE difference there. Your gain being well below half means you did it right the first time. The gain knob doesn't indicate what percentage of amp power it's putting out depending on how far you turn it. It is for matching it's inputs to the head unit's output. Once you've matched properly, the amplifier will give full output with no or very little distortion. The problem is, most people perceive clipping as sound pressure. It's just how your ear and brain perceive it. I see this all the time. I have a tl, and a couple nice fluke meters. I do test and tunes in my area. People will have me set their gain and I meter right then because I know what it going to happen. Upwards of 90% of the time I have to turn their gain way down from where they had it. They tell me it's quieter than before. So I'll meter it how i set it and show them the number. Then they set the gain and I show them how much they actually lost. Nobody can ever believe it. If you want more intense sound that is not distorted in any way, you'll need more powerful equipment. If you want to keep the equipment you've got, keep cranking the gains and it will eventually fail on you.

I guess it concerns me because I had these same speakers running off a STOCK HU. Which is vastly under power compared to what this amp is pushing, and they were quite a bit louder on that (volume wise). Just doesnt make much sense to me..

And yes, I couldnt hear any audible distortion, since I dont have a OS to check it with, I cant say there is none.

 

[rodneypierce 10+ year member]

What did you expect with a single 10" sub and 300w? What enclosure is it in?

more then the output of a 6x9..... Its in a sealed 1.0 cubic ft enclosure. I had this sub in my previous vehicle, in a way smaller enclosure, too small for the sub and it was louder.....

Im not trying to build some 150db system here, just something decent with good sound is all.

 

[Gregulate 10+ year member]

What did you expect with a single 10" sub and 300w? What enclosure is it in?

I had a JL 10W0 powered by 150 watts in a sealed box and it pounded very well for years. I agree it could be the enclosure...

 

[ahole-ic]

I guess it concerns me because I had these same speakers running off a STOCK HU. Which is vastly under power compared to what this amp is pushing, and they were quite a bit louder on that (volume wise). Just doesnt make much sense to me..
And yes, I couldnt hear any audible distortion, since I dont have a OS to check it with, I cant say there is none.

I already explained this. Your deck was distorting causing you to think it was louder than what it was. That weak little amp on a meter I'm sure was making them a db or two louder before distorting, but because your ear thinks distortion = loud, you didn't have any idea.

 

[rodneypierce 10+ year member]

I already explained this. Your deck was distorting causing you to think it was louder than what it was. That weak little amp on a meter I'm sure was making them a db or two louder before distorting, but because your ear thinks distortion = loud, you didn't have any idea.

10-4. Ill go back to the old settings and live with it for now I guess. I will have to save to upgrade everything I guess. My problem is very limited space. I have a huge trunk, its in a 98 Grand Prix GTP, but I have to keep room for the stroller considering we have a 5 month old daughter. So Everything is tight to one side of the trunk.

 

[ahole-ic]

10-4. Ill go back to the old settings and live with it for now I guess. I will have to save to upgrade everything I guess. My problem is very limited space. I have a huge trunk, its in a 98 Grand Prix GTP, but I have to keep room for the stroller considering we have a 5 month old daughter. So Everything is tight to one side of the trunk.

I used to have one of those so I feel your pain. You can bump slightly above what you set them at. You will get some distortion so you will think it's "kind of" loud, yet it won't be tremendously hard on your equipment. The thing is you've got 5 channels on 1 power supply. Driving them all into a hard clip is REALLY asking that thing for a lot. So you're wise to turn them back some.

 

[rodneypierce 10+ year member]

I used to have one of those so I feel your pain. You can bump slightly above what you set them at. You will get some distortion so you will think it's "kind of" loud, yet it won't be tremendously hard on your equipment. The thing is you've got 5 channels on 1 power supply. Driving them all into a hard clip is REALLY asking that thing for a lot. So you're wise to turn them back some.

Slap me silly and call me sally. Im such a newb //content.invisioncic.com/y282845/emoticons/furious.gif.fc81ca146dbff91fede3ed290dbc4f4c.gif:furious:! Tonight, I tore the back seat out, to gain access to the speaker terminals. I used a different test tone then the last one, and directly from the USB instead of burned to a CD. Started out measuring everything again, sub was actually very close to where it was supposed to be. The rear's were low, so I brought them up to where they were supposed to be. Ended up about 3/4 of the way up and the fronts were only putting out 1.5 volts..... I checked and checked, and could only get a max of 2.2 out of channels 1 and 2. I looked at the crossover and I had it flipped to high pass, instead of full. Flipped it over to full and bam. 14.8 volts. (again, stupid newb mistake).

Plugged the speaker wires all back in, and turned it up to about 80% of max volume (where I set the voltages at, 65 on the volume control) and could audibly hear some distortion, so backed the gains on channels 1-4 back down about .5 volts under the calculated, and they sound clean as can be! Sub is kicking good as well! Went back through all of the crossovers and reset everything. Spent some time on it tonight.

I have the fronts set at 125hz with a 18db slope, the rears set at 100hz with a 12db slope, and the sub set at 80hz passive. Sounds really good!

Only thing I have to do now is figure out this noise issue. I have a hissing white noise all the time when there is no music. Like in between songs, or at the start of a CD or the USB search. Then I have a horrid alternator whine as well. I regrounded the HU tonight, with a wire from the case, directly to the chassis, and still have both noises. Only thing I can think of it that the RCA's are causing it.

The amp has a dedicated ground on the chassis, by the rear strut tower. I sanded and cleaned the surface prior to installing it, so it should be good to go. Only other thing is the RCA's. They are cheap ones anyhow, so might be time to upgrade them here in the near future, and move them all over to the drivers side, farthest away from the power wire as I can get.