That's basically it. The best way to do it is to find out where the signal from your hu starts to clip. Most good hu's will be able to go to full volume without clipping. So if your 4v preouts can actually put out 4v after traveling through 16+ feet of rca cable (which I doubt) then you would set the amp gain to 4v. There is always some signal loss in the rca's though. This is why quality rca's are a must. On top of that you would want to set your amp gains with an o-scope but most people don't have one so you could improvise with a dmm which is really frowned upon by some but has always worked for me. Most music is recorded at a lower level so using a 0db test tone may not give the volume that you are looking for which is why some people use a -5db tone to set gains. I use a line driver is one of my systems and that allows me to keep the gain on the sub amp at absolute 0. It keeps noise to a minimum while making the bass deeper and more dynamic. So the line driver is doing the work amplifying the signal and there for the sub needs to work a lot less. Hope this helps.

 

I'm with you except for a couple of points. RCAs will have an almost negligible voltage drop over a 16 ft run. That would be the least of my concerns for picking a good RCA. It's a low current signal and even your most basic RCAs will transmit the signal adequately. I've demonstrated that countless times to know that it's more important to keep the RCA away from obvious sources of radiated RF energy. In my personal system I use RCAs that I scavenged from boxes of old gear pulled out of customer vehicles. These are nothing more than 2 pairs of jacketed 24 gauge wires surrounded by a metal braid; very old school and no mystery marketing BS. I would have pulled them out instantly if I felt they were a weak point.

The second issue I disagree on is that a line driver results indirectly in making the sub work less. The sub is going to do what it does according to the AC voltage coming out of the amp. Whether you get that voltage from an 8V input or a 4V input, the sub is doing the same amount of work. The voice coil might in theory take on a little more energy due to distortion at the lower voltage(this coming from the gain adjusted higher), but the cone is going to move the same amount.

 

Rca's can have an impact on signal transmission. And that's just it, it's a low level signal traveling down a long run of thin wire. If the copper is impure or the connectors aren't very good it will add resistance to the signal. I'm not talking about dropping the voltage by 50% or anything but maybe .2-.5 volts. Why lose that if you don't have to. It's getting to the geeky point but it is true.

Damn my mistake on that. I meant the sub amplifier has to do less work. Thanks for catching that.

 

If the goal is and it should be, to set a specific output voltage / power from an amplifier then a 4v deck verses a 2v deck will not make the amp work any harder.

For instance, you’re setting the output of the amp to 25v. Using the 2v deck the gains are set to ¾ max. Using the 4v deck you achieve the same 25v but the gains are only set to ¼ max. Your amp is working just as hard with either deck.

 

I posted something in a similar thread.

http://www.diymobileaudio.com/forum/1316593-post26.html

Cranking the amp gain to max makes it work harder faster. Meaning, it doesn't take many steps (or turns) on the ol' volume control to reach full output.

By the way, a clipping amplifier is more efficient - so it's actually working more efficiently while you cook your speakers.

 

If the amp put out 100w, then it puts out 100w. Where the gains are set have no bearing on what out will put out. It only has to do with when it will do it on the volume knob.

Sent from my Motorola Electrify using Tapatalk 2

 

That's not entirely true. I'll bet I could get my 500w rockford to put out 10,000 watts at 99% thd. If i cranked the gains up and applied a 30v input signal. How do you think those companies that sell 5,000 watt amps for 100 bucks get their "max" power ratings?

 

Yikes. Spyke, you need to quit while you're ahead.

 

Quit while he its behind

Sent from my Motorola Electrify using Tapatalk 2

 

Damn it. I just tested it. I must have been doing something wrong or with bad cables the last time I did that. O well, At least I learned something.

 

:thumbsup:

 

This is just my thoughts, but if you do have a HV head unit that means your gain on your amplifier will more than likely be all the way counterclockwise (towards the 2v-5v setting) if your head unit is less than 2v then the gain will be more towards the clockwise (2v-.2v setting).

Either way you will end up with the same amount of output (amplified signal) from the amplifier.....CORRECT OR WRONG? Having a HV head unit will not make your amplifier have HIGHER OUTPUT, the amplifier will still have its limits.

The thing is a lot of people think of the gain as a volume control, so they think if I go higher (towards the .2v setting) my amp will put out more power----- WRONG it will clip the output singal and damage several things.

If am wrong please correct me.

 

This is just my thoughts, but if you do have a HV head unit that means your gain on your amplifier will more than likely be all the way counterclockwise (towards the 2v-5v setting) if your head unit is less than 2v then the gain will be more towards the clockwise (2v-.2v setting).

Yes.

Either way you will end up with the same amount of output (amplified signal) from the amplifier.....CORRECT OR WRONG? Having a HV head unit will not make your amplifier have HIGHER OUTPUT, the amplifier will still have its limits.

Correct

The thing is a lot of people think of the gain as a volume control, so they think if I go higher (towards the .2v setting) my amp will put out more power----- WRONG it will clip the output singal and damage several things.

If am wrong please correct me.

I'm not sure about this. I agree that when you crank the gain up distortion will increase. What I don't know is if the power output from the amp will also increase. I imagine it would to a point though. When I set my gain and am looking for 40v, I can turn the gain up(just for demonstration purposes) and reach 100v which translates to 2500w. Way higher than the amp is rated for obviously. Also note that this is being done with the sub disconnected. I am not in anyway saying that you can or should increase gains to get more power out of your amp.

 

hi folks,

just read thru the thread and learned a lot. thanks to the pros for that. iam more or less noob here, so still need some clarification.

1) i have a 500wrms @ 2ohm mono. its cea 2006 rated. does this mean it will always provide this kinda power? (provided i match gains with input voltage using a dmm)

2) some was saying, 'this amp will produce 500wrms @2ohm no matter where the gain settings are'

if this is true, how come i can use my 300w woofer with this system? what i generally do is set hu volume just below clipping point and set voltage to what ever would correspond to 350wrms and leave it there. iam i doing anything wrong?

cheers

 

1- Yes it will put out 500 watts when the input signal level and gain setting ask it to.

2- That's a true statement but it needs to be qualified by saying that it will put out that power IF the input voltage corresponds to the gain setting you have the amp set to. IE counter clockwise at say ~5 volts will put out the rated power IF you input signal is ~5 volts. Turn the gain up to .3 volts and all you need then is .3 volts of input voltage. So yes "it will put out rated power no matter the gain setting"

(This is also assuming the amp works as it should and does put out rated power at its labeled gain settings)

 

I also would like to point out that when I set my gains, I always use a -5db test tone. I do this because music is usually recorded at less than a 0db level. If you set the gains using a 0db tone and never exceed the hu level where you set the gains, your amp will not reach full output under most circumstances.

 

Ok ok let's back up. Line 1. I was being sarcastic. I calculate power and set it according to voltage.

Line 2. Again, being sarcastic. Notice the boldface on the words might

Line 3. Reread and notice the boldface on the word unloaded.

Me and you are on the same page. I am in no way shape or form saying that you can get rediculous amounts of power by turning up the gains. I also think that setting gains using a scope is by far the safest and most accurate way to set gains. On the other hand, if you can get it in the ball park using a dmm and aren't stupid with the volume knob you won't have problems either. I have been doing this for 16 years and have never once blown an amp, sub, speaker, or tweeter.

 

Trust me I know you were being sarcastic, but the young fellas reading this will take it seriously. Before you know it everyone will do your way "formula" and come up with crazy numbers - you forgot to plug in AC current. Just throwing that out there.

 

you and I

 

Shut up Chad.

 

Hey, since this is a grammar lesson now. What is the correct way to word this sentence?
1. My car needs to be washed
or
2. My car needs washed

I vote 1.

 

WTF even my 4year old knows which one. You probably meant "My car needs a washing" on #2, but thats just my guess.

 

I define random.

I can make anything blush.

 

Ok Guys a simple question.

I have an ABC HU and XYZ Amp.

Lets suppose XYZ HU puts out 8 unclipped volts @ 50 volume (this is max volume). And ABC amp takes input from 8 to 0.2 v and puts out 100 x 4 W RMS.

Lets see XYZ HU gives 6volts @ 40 Volume and the gain pot on ABC amp is at 8 volts (lowest). Now i match the voltage to 6Volts. The speakers will get louder right ? As the voltage is matched.

Now when i turn the Gains knob down why is there a drop in output / speakers are not loud ? Amp is still putting out 100 x 4 right ?

 

No, it's not putting out rated power then. It is putting out ~56 watts.

If you have the head unit set to 6 volts out and you move (ie lower) the gain from 6 volts to 8 volts it will lower the output because you are setting the amps gain knob (ie trim pot, ie volume knob...not master volume knob) to a point where it needs more input voltage (ie 8 volts) to put out rated power. The lowest gain setting (ie most counter clockwise position) requires the largest input voltage to put out rated power, as indicated by the label. And vice versa.

 

Because the gain control IS a volume control. No, seriously. It's a potentiometer in a voltage divider circuit. We call that a volume knob.

You turn it up, things get louder. You turn it down, things get softer. It doesn't add distortion, it doesn't make the amp work harder. Some of you guys are overthinking things.

Here's a diagram:

CD -> HU volume knob -> amp gain ctrl -> amplifier

The last stage ("amplifier") has a constant gain (let's say... x 10). It also has a maximum output. Manipulating the two volume controls in front of it allows you to achieve that maximum output. That maximum output never changes. Doesn't matter where any of the volume knobs are, or whether it's a head unit, ipod, or sine wave generator providing the input signal.

You can keep the HU volume knob at a fixed setting and go to your trunk and turn the gain knob to control volume, but that's a pain in the ass. So people usually keep the gain knob at a fixed setting and use the HU volume knob to control volume. Makes much more sense.

But make no mistake about it. It's a volume knob. I think when people begin to realize this, they'll have a much easier time understanding what they're doing when they turn that gain knob.

 

I agree with t3sn4f2, atleast thats the way I see it. I dont like to think that the gain is a VOLUME......for me its more of a attenuator that goes for my radio too, lol.

I know we were just using examples but in reality HU can claim up to 8v output signal, but it will usually be half of that and only reaching the peak (8v) in milli-seconds if not nano seconds, lol.

 

I love this one. If you say the amp must work harder, then we can speak in Joules, which is a defined measure of work. A Joule is the energy expended in applying one Newton of force through one meter or in passing one amp of current through a resistance of one ohm for one second. For electricity, we can simplify that to one watt for one second. So, if our amplifier puts out 100 watts for one second, it does 100 Joules of work.

Doesn't matter what the input voltage is, so long as it puts out 100 watts.

Simple.