Hello folks,

Last question was answered promptly, perhaps you could help me with this one as well

I'm a little confused regarding the voltage supplied to car amps;
A Soundstream Rubicon 1002 (1000w) should be mine in a few days if all goes well, but according to its spec sheet ( http://www.soundstream.com/manuals/AMP/rubican/rub57102/Rub5027021002.pdf ), it will do 4 and 8 ohms at 12.6v but 2 and 1 ohms at 14.4v.

The amp will be used to build a home stereo amp using atx power supplies, but of course they output 12v on the dot, and i don't like the idea of messing with step up transformers or making custom power supplies

To add to that, i was before absolutely convinced that all car batteries were 12v...

Hence the question is: do amps (this one in particular) really need the 14.4v or will 12v with more then enough amps on it be alright?

Second, if the 14.4v rating is there to make sure that voltage doesn't dip below 12v on transients and the like, the current to the amp will be buffered by 50000uF of 35v high-temp type 500 capacitors, so the psu's should never drop below 12v. Will a 12v supply be ok in that case?

Thank you!

 

Car batteries will show a different charge based on their state of discharge. A fully charged battery shoud show about 12.7-12.9. If your battery is only showing 12.0 their may be something wrong. The current in a car battery can far surpase what those power supplies can provide. The 14.4 represents the charging voltage of a healthy alternator. Normal charging voltages can be from 14.0 to 14.8, allmost no one get's that 14.4 that they advertise because we run fans, wipers,turn signals... etc.
The power supplies will most likely be insufficient because what they leave out is the current draw. For example a amp making a 1000w at 14.4 would be drawing about 70amps(ohms law) at 12 volts it would draw almost 84 amps. That's if your amp is perfectly efficient, which none are that one is most likely a AB amp(I'm guessing cause it's not listed) they're generally about 50% efficient. That means add 50% to those current draw numbers!


It's not just the voltage you have to worry about, it's what voltage and how much current. Your best bet is to buy a quality home theater reciever and leave car audio equipment for car audio!(2 different power sources too hard to convert from one to the other)

 

I am indeed aware of current problems, and i have 4 atx's chained putting out 130a on the 12v line alone, so no worries there. The sub being run is a 12w6 from jl, and only needs 300w rms, or 25 amps x 2 to factor in efficiency. Its a <0.05% THD under 400w @ 2ohms amp, so right up there with modern hi-fi. The plan is to piece all this together in a nice metallic enclosure and make a custom face plate for gain pots, power switch and 12v / capacitor status LEDs. The grand plan is to later sell this as a proper hi-fi power-amp.

Thank you very much for your response!

Question still stands though, will an input voltage of 12v have any adverse effects on the amp? Will it still output its rated values?

Once again, thanks in advance!

 

An input voltage(through the RCA's) of 12v will destroy your amp, most amps accept a maximum of 5-8v. If you mean 12v powering your amp it will not make it's rated power because 12.0v is less than 12.6v you can use ohms law to calculate how much less power, don't forget to account for efficiency!

http://www.the12volt.com/ohm/ohmslaw.asp

 

No worries - go ahead with your plans.

Some companies have "conservative" ratings to make the customer happy when they get more power than advertised (also this allows certain amps to remain in a lower class for competition)

So the ratings at 4 ohms and 8 ohms are the conservative ratings as they are rated at 12V (12v is the power you get when the ignition is off and the alternator is not juicing the system).

But it appears that amp manufacturer also wants it to be known what they can REALLY do with a lower impedance and higher voltage (14.4 is the typical voltage from the alternator when the car is running).

You don't need fancy voltage converters as all cars when the engine is off run on 12v. The only thing that you might notice is 5% - 15% power decrease on the power outputs fated for 14.4v. Since the amp specs intentionally raised the voltage to show what it can do with 14.4V I suspect the increase in power maybe closer to 15% - but this is just speculation. Again, the power difference between 12V & 14.4 will depend on the voltage regulation and other guts of the amp.

But the short answer to your question is you are fine to give that amp 12V - just be sure that your 12V power supply is capable of producing enough current (amps) to closely match the fuse rating of the amplifier.

 

I just read godzillas posts (I was busy with other stuff while replying so I took time).

While his concerns and cautions are valid, I don't believe you are going to try and have that amp screaming full tilt, so the current draw issues won't be that big of a factor.

If I understand you correctly, you just want to know if you can use this amp in a home set-up and the answer is yes.

I've had amps running fine on 10V (I didn't realize my alt died [that idiot light wasn't working' and it was at 10v that everything finally shut down in my car) and no harm was done to them.

 

I of course meant POWER input voltage, this sub's sensitivity is 300mV to 5.0V; i doubt it'd fry though, protection circuitry and all.

I just recalculated my costs and have decided not to use 4 atx's; i'll see if i can find a schem for a 2kW impulse 120vac > 12-15 vdc psu and build one myself.

Apart from that, thank you all for the good input.
Last question, what voltage range will the AMP accept? I don't suppose it uses simple voltage reg's like 7805's that have an input voltage range of +100-1000%? If i could run for example 35vdc into it, a lot of problems would be solved...

And once again thanks!

 

Sorry 14.4 IS NOT TYPICAL, I work in a shop and was curious to see what it really is under real world conditions. I checked using a quality DMM and a battery tester so I will assume my numbers are correct. I checked with daytime running lights on, radio on(low volume) and fan on low(no ac). The typical voltage at idle was 13.8-14.0 In order to get that magical 14.4 you have to shut everything off and rev the engine to about 3000rpm on most cars. In fact alot of cars never get to 14.4, and they're running fine with a healthy electrical system. 14.0+ is considered normal

 

35v would at a minimum would put it into protect mode, it would most likely damage it beyond repair. As for the input voltage(RCA's) if you exceed the rated input voltage you will most definately cause internal damage to the amplifier.

 

Good to know that 14.4 is not typical. My car last time I checked was 13.7 and I thought my alt was on its way out - but since my daytime lights were on, and likely my blower was on, my numbers are likely just fine then.

In regard to the voltage question:
Keep it under 16v to keep it safe. There are amps that can handle 16+v but they typically have been modified.
I would say keep it within 25% of 13 V and you'll be fine.