Bad amp? Bad headunit? bad math?
Thread Starter
Le Mans Master
Joined: Aug 2005
Posts: 7,392
Likes: 218
From: Merritt Island, FL
Bad amp? Bad headunit? bad math?
OK, so I've been trying to set the gains properly in both of my vehicles. In my vette, everything went as planned, using the calculations I found online, for the expected output AC voltage based on amp rating and impedance of the speakers.
However, in my truck, I calculated an expected output voltage of around 15 V, and yet even with the gain maxed, I can only get around 6 or 7 volts. Is this likely to be the amp, or the headunit?
FWIW, I have a Pioneer DEH-P6700MP headunit, supposedly 2.2V pre-outs... it's a few years old. The Amp is a Pioneer GM-6300F, it's about a year old, not the greatest amp but it's what I had... It's rated for 60W RMSx4 at 4 ohms - I have the rear 2 channels bridged to provide 120W to a 10" sub, and the fronts go to Polk 5 1/2" speakers, @ 4 ohms.. If I am doing the calculations properly, that should mean 21.9V on the output for the bridged sub channels, and around 15V on the front speaker channels. I can get the sub outputs tweaked properly, but the fronts max out at about 5 or 6 volts, I can't get anywhere near to 15V.
However, in my truck, I calculated an expected output voltage of around 15 V, and yet even with the gain maxed, I can only get around 6 or 7 volts. Is this likely to be the amp, or the headunit?
FWIW, I have a Pioneer DEH-P6700MP headunit, supposedly 2.2V pre-outs... it's a few years old. The Amp is a Pioneer GM-6300F, it's about a year old, not the greatest amp but it's what I had... It's rated for 60W RMSx4 at 4 ohms - I have the rear 2 channels bridged to provide 120W to a 10" sub, and the fronts go to Polk 5 1/2" speakers, @ 4 ohms.. If I am doing the calculations properly, that should mean 21.9V on the output for the bridged sub channels, and around 15V on the front speaker channels. I can get the sub outputs tweaked properly, but the fronts max out at about 5 or 6 volts, I can't get anywhere near to 15V.
Drifting
Joined: Jul 2005
Posts: 1,484
Likes: 27
From: Torrance Calif
Some meters don't have very good frequency response above 400hz, and some of the cheap ones anything above 120hz.
The more important part is: can you turn the level up enough to drown out the sub?
The more important part is: can you turn the level up enough to drown out the sub?
Team Owner
Joined: Feb 2000
Posts: 51,504
Likes: 6
From: Sacramento CA
Remove speakers, test amp outputs
sqrt(RMS*Impedence)
ex
Sqrt(150*4)
150watt amp, anticipating a 4 ohm load.
head unit at 3/4 volume
And use a 0db 50hz sine wave to measure.
ALSO
Make sure ALL OF YOUR CROSSOVERS ARE TURNED OFF.
IF you play a 50hz tone and have your 80hz 12db amp crossover turned on, you aren't going to get what you are lookin for.
sqrt(RMS*Impedence)
ex
Sqrt(150*4)
150watt amp, anticipating a 4 ohm load.
head unit at 3/4 volume
And use a 0db 50hz sine wave to measure.
ALSO
Make sure ALL OF YOUR CROSSOVERS ARE TURNED OFF.
IF you play a 50hz tone and have your 80hz 12db amp crossover turned on, you aren't going to get what you are lookin for.
Last edited by Kale; Aug 18, 2009 at 11:27 PM.
Thread Starter
Le Mans Master
Joined: Aug 2005
Posts: 7,392
Likes: 218
From: Merritt Island, FL
Remove speakers, test amp outputs
sqrt(RMS*Impedence)
ex
Sqrt(150*4)
150watt amp, anticipating a 4 ohm load.
head unit at 3/4 volume
And use a 0db 50hz sine wave to measure.
*************
Did exactly all that, worked as planned for the subs. The full-range speaker output, I was never able to get it over 7 volts (needed around 15)
**************
ALSO
Make sure ALL OF YOUR CROSSOVERS ARE TURNED OFF.
**************
Pretty sure they were, but I will try again today. I'll post my results later
***************
IF you play a 50hz tone and have your 80hz 12db amp crossover turned on, you aren't going to get what you are lookin for.
sqrt(RMS*Impedence)
ex
Sqrt(150*4)
150watt amp, anticipating a 4 ohm load.
head unit at 3/4 volume
And use a 0db 50hz sine wave to measure.
*************
Did exactly all that, worked as planned for the subs. The full-range speaker output, I was never able to get it over 7 volts (needed around 15)
**************
ALSO
Make sure ALL OF YOUR CROSSOVERS ARE TURNED OFF.
**************
Pretty sure they were, but I will try again today. I'll post my results later
***************
IF you play a 50hz tone and have your 80hz 12db amp crossover turned on, you aren't going to get what you are lookin for.
Thread Starter
Le Mans Master
Joined: Aug 2005
Posts: 7,392
Likes: 218
From: Merritt Island, FL
I think so -- the Pioneer headunit has several different ways to screw with some of the settings, and maybe I missed one -- I unplugged the headunit for a few minutes, so everything reset to default, and then when I reconnected everything again, I was able to get the required voltage. SO thanks for pushing me in that direction 
