# Subwoofer Output low if Gains are not "almost-maxed-out"



## abhipuru16 (Dec 15, 2010)

abhipuru1.6'S ICE- Ford Fiesta 1.6S- First Steps towards THE WORLD OF PURE MUSIC - Team-BHP

Hey guys!
This is my setup.


And this is the problem I am facing-



> Please help me solve this peculiar problem in my newly installed ICE. The problem is that we took pre-outs from inside the stock HU. Now, the front channel gains are set at around 50% giving out 23V (sqrt (130X4)), which is good. The problem is with the rear channel where the subwoofer is connected. There is literally no output from anything below 90% gains. Right now, the gains for the subwoofer are almost set 100% at which the DMM reads 38.2V (desired 40V) at full clip of the gain pot.
> The voltage as well as the output from the subwoofer decreases rapidly if I go below "almost full gain". All this at full Headunit Volume.
> What could be the problem?
> Please note that I hear no unwanted noises or whines maybe because the subwoofer gain is set so high and not the front components'. Please help.
> ...


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## tanakasan (Sep 8, 2007)

Fader setting centered?

Robert


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## abhipuru16 (Dec 15, 2010)

Everything is bang in the middle, centered.


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## tanakasan (Sep 8, 2007)

I looked at the link for your build. Since you're running the passives, why not split the known good front signal? Sounds like plenty of output voltage. Are you using amp x-over for the sub? Amp settings good? Proper inputs used? Not HP by accident? Subsonic filter set correctly? Did you take a measurement at the rear RCAs for voltage?

Try fading to full rear and see?

India! Cool!

Robert


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## abhipuru16 (Dec 15, 2010)

Hi
Thanks for taking interest in helping me. 
While measuring the voltage obtained on playing a 0db 50hz test tone across the speaker terminals I couldn't get more than 38volts even at full gain. All this while, everything was a big zero on both the Headunit and the Amplifier. 
No, I didn't check the voltage in the input RCAs to my amplifier. Can you help me with the process?

Moreover, could it be a case of faulty RCAs? Say, they maybe pinched? 

There is an input selector switch and an output selector switch on the amplifier, can I use this to split the front channel signal without physically changing the connections? Apart from this, is it possible that these two switches themselves might be set the wrong way causing all this drama?
The input selector switch has two options- 2ch or 4ch and the output selector switch has two options- 1+2ch or 3+4ch. 
And yes, I am from India, what is so cool about it?


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## [email protected] (Nov 7, 2010)

Do you have better subwoofer output if the volume on the radio is at say 1/2"

I am wondering if your headunit has built in compensation that reduces the amount of bass as the volume is turned up?


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## abhipuru16 (Dec 15, 2010)

Better as in sonically or something else?
The volume on the Headunit ranges from 0 to 34. As far as I could figure out, the voltage across speaker terminals only increased from 24 to 34.


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## [email protected] (Nov 7, 2010)

If you have the radio on like 20 is there more bass than if you put it on 32?


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## abhipuru16 (Dec 15, 2010)

No, at volume 25 to 26 the bass is loud enough to refrain me from turning up the volume further.


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## [email protected] (Nov 7, 2010)

So, if there is plenty of bass, what is the problem?

You have the single subwoofer bridged on the rear 2 channels of the amplifier?


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## abhipuru16 (Dec 15, 2010)

^^^^^The gains for the sub channel are set to "almost" full. This is what is worryinng me, whereas, the gain for the front channel are at 50% giving the desired voltage.


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## abhipuru16 (Dec 15, 2010)

Okay Guys!
Here is an update. Today, I played a 50Hz test tone and measured the voltage in the RCAs coming to the amplifier from the Headunit at full volume and TADA!
All the 4 RCAs showed the same voltage. It was 0.5~0.7V in all of the input RCAs.


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## Ianarian (Dec 20, 2010)

abhipuru16 said:


> Okay Guys!
> Here is an update. Today, I played a 50Hz test tone and measured the voltage in the RCAs coming to the amplifier from the Headunit at full volume and TADA!
> All the 4 RCAs showed the same voltage. It was 0.5~0.7V in all of the input RCAs.



Hey man,
You have to slow down a little bit and see why Mr Knapp is asking questions. He is trying to get at something.... TADA? So your voltages are the same....cool....so now is the problem solved?


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## abhipuru16 (Dec 15, 2010)

Ianarian said:


> Hey man,
> You have to slow down a little bit and see why Mr Knapp is asking questions. He is trying to get at something.... TADA? So your voltages are the same....cool....so now is the problem solved?


My gosh!
You sound so serious!
I mean, I know the problem is not solved yet but I am happy because one of my doubts is cleared, hence the "TADA" thing. I am happy that the RCA cables are not damaged because I spent a large sum of money on Rockford Fosgate Wiring. 

@Mr. Knapp
Yes Sir, I use a SVC (Infinity Ref1240SE) through the bridged rear channels of my amplifier. What keeps bugging me is the fear of damaging equipment because to reach the desired voltage of 40V (sqrt(400X4)) I have to turn up the gains to 100% and even then I get nothing more than 38V. 

At 50% gains it sounds like there is no subwoofer at all, it just doesn't play. 

I am more worried about the voltage part. 

Back in my mind, I keep thinking that I am not utilizing the amplifier's potential to the fullest and even if I am getting close to that potential with 100% gain (38V as opposed to the desired 40V), I am seriously risking the subwoofer.


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## Ianarian (Dec 20, 2010)

> What keeps bugging me is the fear of damaging equipment because to reach the desired voltage of 40V (sqrt(400X4)) I have to turn up the gains to 100% and even then I get nothing more than 38V.


This makes no sense at all. Why do you think you need 40v? How was your tech able to intercept 4 channels separately out of the inside of the unit? If you are getting .5-.7 on each rca, thats 1.4v per stereo pair, 2.8v total for 4 channels? Thats pretty low considering some sources go 4.0v/stereo pair(L+R). If we cut it down: the amp inputs are .3v-8v I think, no quote. If what I think is right, and you're saying that your voltages are as indicated above, does it not make sense that you'll need full gain to match the signal? Matching signal is all your gain is, no matter where that sensitivity is set, the amp is going to give you full power. The gain does not determine how much power the amp will put out.


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