am i fucked?

[m0nk3y]

JL 300/4.

Low Ω light stays on, and earlier all 3 lights were on, amp hotter than dogturds on a sunny day.

Any thoughts? Amp is properly ventilated, and my 500/1 isnt breaking a sweat. Also, I'm using only 2 of 4 channels, and rarely ever above regular conversation volume level.

[SickVette]

First what is hooked up to the amp? I doubt the amp is shot since it still works but you will need to find out what the problem is. It could be a shorted speaker wire, a blown speaker, or inadequate power supply.

What is connected to the amp?

[m0nk3y]

2 boston acoustics 5x7's, 4ga power and ground + remote, monster cable RCAs... everything worked fine with the same setup before we took it out of the truck to put in my ex's car.

[SickVette]

Just tow speakers? Odd to have those problems. Disconnect both speakers and see what it does. If it does it again then disconnect the RCA cables. If it does not do it connect one speaker at a time till it does it again. Unless you have a DMM then test the speaker wires for a short and impedance of the speaker.

[GradeA_TireFryer]

double check the ground - i keep saying this - 99% of the time it is bad grounds, engine noise, high amp draw, poor quality sound......
check the ground at the battery also - you should add a ground wire the same size wire you use on your amp...

check your speakers to ground... sound like they may be bad or a wire is shorting out

[TBSpyder]

Simple way to figure out if it's the amp or the speakers...disconnect the speakers and see if it still does it.

[TJElite]

check the ground at the battery also - you should add a ground wire the same size wire you use on your amp...


This is one of the most overlooked areas of a high power install. People use big power wire, and big ground wire from their amp to the chassis, but very few seem to know that they need to upgrade the ground to the battery. Look at most factory battery hook ups. There is usually a relatively fat ground, going to the engine block, which is really only barely bolted to the frame, and usually isolated with rubber mounts. The only ground from the battery to the chassis is usually quite thin, like 16 ga. This is because in the original vehicle design, the highest current draw is the starter. The engineers didn't count on you adding a couple hundred amps of stereo draw, and then trying to ground it to the chassis. I've actually seen melted antenna connectors at the back of the radio, from the amp current trying to find a ground somewhere through the chassis.

Its easy to do. I recommend using the biggest wire you can work with practically...like 1 or 1/0...you're only buying a couple feet, and you'll never have to worry about upgrading that wire again. Find a good clean spot on the chassis within about 2 feet of the negative post on the battery (the closer the better), and bolt it down (there's a whole procedure here, too, but if you don't know how to make a good ground, you need to learn that before you ever get to this step). Attach the other end, along with the factory grounds, to that cool aftermarket battery terminal you bought. Done. While you're at it, you might want to run a couple of extra 8 or 4 ga wires from the engine block to the chassis, as well. Gives good clean path for the alternator (factory wire is usually pretty nasty, and not real beafy to begin with), and actually has some engine performance benefits, as well.

As Tyre Fryer says, grounds are often overlooked problems. In my opinion, the old 'maxium amp ground length of 18"' is not nearly as important as how you make the connections, and what the factory ground scheme looks like. I'd rather see 25' of 8 ga coiled under the seats on its way back to the negative on the battery than some of the 'drywall screw into the flimsy, tack welded, painted bracket' jobs I've seen. The ground wires have to flow the same amount of current as the power wires do. When the main ground can't, things like RCA cables are asked to pick up the slack, and this is not a good thing.

Tomorrows lesson...why caps under about 10 farad are really pretty useless. Also known as 'the most overrated band aid ever put on an electrical system'.

[Notladstyle]

Tomorrows lesson...why caps under about 10 farad are really pretty useless. Also known as 'the most overrated band aid ever put on an electrical system'.

Useless is a little strong of a word.
Maybe a cap wont solve every problem in the world and they are often installed for the wrong reason but even a 1 farad cap will add a tremendous amount of power to peak demands over 25amps that no high output alternator/wiring could rival.

[TJElite]

Useless is a little strong of a word.
Maybe a cap wont solve every problem in the world and they are often installed for the wrong reason but even a 1 farad cap will add a tremendous amount of power to peak demands over 25amps that no high output alternator/wiring could rival.

OK...I guess that's like saying holding a bed sheet over my head as I jump out of an airplane is better than holding a napkin.

I'll use your 25 amp example. Engergy stored in a capacitor is calculated like this:

Energy (watt seconds)=(capacitance x voltage) squared / 2

So, a 1 farad cap, at 14.4 volts is 103 watt seconds. 25 amps at the same 14.4 volts is 360 watts. So, at this draw, the cap will be out of energy after .29 seconds.

So, you just bought .29 seconds of output for how much? And that's only at 360 watts...probably 1/3 or less of the output of most amps people hook these caps up to. This is also based on a 'perfect' scenario, where the cap is installed right at the amp (no wiring resistance), the amp is 100% efficient, and the system voltage is 14.4 volts. None of which is really practical. It also assumes an ESR of 0 for the cap, which is impossible, but since it is really, really low, I'll disregard it.

A 10 farad cap is good for 10368 watt seconds at 14.4 volts. Now your 360 watt load is upheld for nearly 30 seconds. and a 1000 watt load is upheld for 10+ seconds. Now that's probably useful.

Factor in a 65% efficient system (amp inefficiency plus wiring resistance) and a 13 volt system, the 10 farad cap still give about 5.5 seconds of power to that 1000 watt amp.

Add to this the fact that you eluded to...most caps are installed wrong, and for the wrong reason (my lights dim when my bass hits), and I say that caps less than 10 farads are useless and a waste of money.

There's also another school of thought that says they are actually harmful, as they are just another source of drain to the battery. Again, the system is not perfect...the cap has an internal resistance and the wiring to and from the cap has resistance. Since in this case, resistance is electrical waste, a small cap could be doing more harm than good. Further, a discharged cap is basically a direct short to ground. Since electricity follows the path of least resistance, your cap is going to get charged before your amp gets more power. I think all of this would be minor, in any case, but goes to the argument against having them, in my opinion.

Small caps can play a valuable role in voltage stabilization at much lower current draws, though. This could be usefull where sensative electronics are installed (like an in car PC), but this is a different end goal.

I guess we got to tomorrows lesson early.

[TBSpyder]

I guess we got to tomorrows lesson early.


:lol:

[m0nk3y]

...and for an update-

fucked! the amp has to go back to JL for repair... UGH.

[Notladstyle]

OK...I guess that's like saying holding a bed sheet over my head as I jump out of an airplane is better than holding a napkin.

I'll use your 25 amp example. Engergy stored in a capacitor is calculated like this:

Energy (watt seconds)=(capacitance x voltage) squared / 2

So, a 1 farad cap, at 14.4 volts is 103 watt seconds. 25 amps at the same 14.4 volts is 360 watts. So, at this draw, the cap will be out of energy after .29 seconds.

So, you just bought .29 seconds of output for how much? And that's only at 360 watts...probably 1/3 or less of the output of most amps people hook these caps up to. This is also based on a 'perfect' scenario, where the cap is installed right at the amp (no wiring resistance), the amp is 100% efficient, and the system voltage is 14.4 volts. None of which is really practical. It also assumes an ESR of 0 for the cap, which is impossible, but since it is really, really low, I'll disregard it.

A 10 farad cap is good for 10368 watt seconds at 14.4 volts. Now your 360 watt load is upheld for nearly 30 seconds. and a 1000 watt load is upheld for 10+ seconds. Now that's probably useful.

Factor in a 65% efficient system (amp inefficiency plus wiring resistance) and a 13 volt system, the 10 farad cap still give about 5.5 seconds of power to that 1000 watt amp.

Add to this the fact that you eluded to...most caps are installed wrong, and for the wrong reason (my lights dim when my bass hits), and I say that caps less than 10 farads are useless and a waste of money.

There's also another school of thought that says they are actually harmful, as they are just another source of drain to the battery. Again, the system is not perfect...the cap has an internal resistance and the wiring to and from the cap has resistance. Since in this case, resistance is electrical waste, a small cap could be doing more harm than good. Further, a discharged cap is basically a direct short to ground. Since electricity follows the path of least resistance, your cap is going to get charged before your amp gets more power. I think all of this would be minor, in any case, but goes to the argument against having them, in my opinion.

Small caps can play a valuable role in voltage stabilization at much lower current draws, though. This could be usefull where sensative electronics are installed (like an in car PC), but this is a different end goal.

I guess we got to tomorrows lesson early.

The discharge slope for a capacitor is

V(t) = (v) (e^(-t/rc)

I will use a more realistic 13.8 volts and a peak demand of 500watts

Ohms = (v^2)/w = (13.8^2)/512 = .372 => rc = (o)(c) = (.372)(1,000,000uf) = 372000

V(t) = (13.8 )(e^-t/372000)

V(.08 )= 11.13volts

That means that the capacitor will maintain a voltage above 11volts for about 1/10th of a second in the real world. Now lets look at logic for a moment:

How long does it take the alternator to transmit that same current ~16 feet from the front of the vehicle to the rear? The electrical current(mine you not the electron itself) travels at 2384x10^5 ft/s with no resistance. It would take nowhere near .08 second to complete the journey even after you factor in the resistance of the wire the capacitor would still be well above 11 volts before the supply current was restored.

There is no need for any more capacitance over that because the supply current is infinite and therefore the capacitor is nearly instantaneously recharged and no the capacitor does not add any extra load onto the circuit because since it maintained a >11v throughout the circuit, the current demand is minimal.

Without the capacitor the instantaneous circuit voltage at the amplifier would immediately drop to below 11v and cause clipping before the alternator could resupply current.

That is why 1 farad is all you need.

[TJElite]

Wow, .08 seconds? I was taking some best case scenarios, and giving you .29. Let's look at your example.

If it takes nowhere near the .08 seconds for the current to travel down the wire, then why do you need the cap? The battery would supply the current needed. Right? Well actually, not quite. What you'd now be comparing is the ESR of the battery vs. the ESR of the cap, plus or minus wiring resistance, depending on where the cap is. The cap is nearly zero, and the battery is pretty close (around 7 milliohms), and wiring resistance, while several times greater, still doesn't amount to much. So, your .08 seconds just became a whole lot less.

Now, I don't know if 'clipping' is the technically correct term to what might happen here. Realistically, there won't be any harm to the amp, nor will you hear anything over the span of .08 seconds (probably much less). You will probably lose some output power, but how much? A 500 watt peak demand works out to about a 325 watt RMS output (65% efficiency on avg.) at 13.8v. Lets assume output current is limited to this 36 amps (unlikely, but worst case). Now, your voltage drops to 11. Now your 500 watt peak is down to 366, which is 237 RMS, or about 25% down. Since we all know that a 50% reduction is 3db, and 3db is considered the avg. resolution of human perception, I'll say this won't be noticed. Add in the fact that it will last .08 seconds or less, I'll guarantee it.

Most voltage protection circuits on amps don't react until around 10.5 volts, and even that is over the span of several seconds.


I will agree that the additional load of the capacitor will be negligable...I discounted that theory in my last post, but it is not nothing...a cap that needs to be recharged will take some load from the factory charging system, albeit not much.

And what alternator give you 'infinite supply current'... I want one of those. :-)

As for 1 farad being all you need, I also disagree. In your 500 watt example, you certainly don't need more than 1 farad (you don't 'need' any), but at bigger current draws, and in specific situations, capacitance can play a real role.

In my Caprice, I have a 275 amp alternator, 1/0 wire running back to two Stinger SPV70 (70AHR 850CCA) batteries. From there, a pair of 4 ga go to the Crossfire VR2000d 2000 watt (at 12.5 v) amp, via a Lightning audio 25 farad cap. At full tilt, this amp has a measured draw of 185+ amps. At that kind of current draw, the difference in ESR becomes much more important (voltage drop across a resistance is current dependent). When we take this thing to DB contests, we are sometimes forced to run it with the engine off, or at best, not reving it. This takes the big alternator out of the equation, since the output is severely diminished below 2000 rpm (this is a fact of nearly all alternators, btw.) For these contests, we usually use a sine wave of about 50hz, and often play it for 20+ seconds. This is about the worst case for an amplifier...having to deliver its full RMS rating for 20+ seconds. Here, every .1 DB matters, and we need as much voltage, for as long as possible. In back to back pulls, we've seen as much as 1.3 DB less without the cap. Again, not perceptable to the human ear, but in this case, the capacitor can be the difference between 1st place and also ran. Also, this 1.3db was based on peak measurements, which usually a couple seconds into the burst, so the .08 seconds (which would be nearly zero at 185+ amps) best case above wouldn't help.

I stand by my opinion that any cap less than 10 farad is useless. Now, I'm not above learning, so bring me a real world, measurable, or even audable (by the average person) example of a 1,2, or even 5 farad cap making a difference, and we'll discuss it. Personally, I think if you do find this example, the cap will still just be a bandaid stuck over the real problem.

I'll even go far enough as to say that for the average enthusiast, even the big caps are probably not necessary. When I listen to regular music in my caprice (it is very musical), I doubt I'm getting any audible benefit from the cap.

Dalton, right? I hope you don't take this as flaming or anything...I acutally have quite a bit of respect for you. You formulated a good argument. I'm not sure how old you are, but I'm betting you are quite a bit younger than me (hint, I first met JJ when he was selling gear out of his house. I worked for him off an on back about 1988, when his store was up on Klosterman). I'm also betting that you know a lot more about this than I did at your age. This is a fun discussion, and I hope we can continue it, and others, either here, or better yet, in person. Perhaps we'll meet at one of the upcoming events, or something.

[TJElite]

...and for an update-

fucked! the amp has to go back to JL for repair... UGH.

Other than the time and shipping charges, that's not always a bad thing. I had to send a 500/5 back to them once. Not only did they fix the problem, they also updated some other circuits to 'current spec'.

[Notladstyle]

The time needed to supply current to the rear of the car is so small its near instant BUT that instant with a lack of power will cause the amp to clip.

A 1 farad cap can supplement current spike around 50 amps for long enough to be restored by the alternator and since the amplifier will only have that peak demand for an instant the capacitor can recharge without inturrupting supply.

This is why SPL measurements show no difference because the demand is steady and a capacitor will only improve performance during extreme transients. on paper and in reality thats what it will do. I do think anything over a 500 or 600 watt peak should have a higher value capacitor to keep the discharge curve above 11 volts.

Im 20 and im in my second year towards my EE from usf.

[mbanks21]

Whered you get the amp from?