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#5657 - 11/23/04 08:19 PM Re: Car Amplifier
JT Clark Offline
Desperado

Registered: 10/25/02
Posts: 466
Loc: IL
Oh, you have the amp already? We're trying to help, but we need information. What we're given seems to be confilcting.

400 watts RMS? A converter should be able to do it for one of these amps. 400/120 = 3.33 amps. At full power it might draw more like 5 and put out 3.33 due to the inefficiencies inherent in the conversion. I don't remember off the top of my head who makes better models as I did more research in the other direction.

Quick look , 540 watts @ 4 ohms for $250? No conversion, so no worry about blips in the power supplied. BTW, what sub(s) will this be for? That'll help. I'm curious as to what amp this one is too.

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#5658 - 11/23/04 10:12 PM Re: Car Amplifier
painttoad Offline
Desperado

Registered: 10/25/04
Posts: 688
Loc: peoria il
if i remember right,i have heard nothing 'bout subs.sounds like you want to power mains/surrounds..........but please reconsider!!!
car....====car......home.....===home

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#5659 - 11/23/04 10:26 PM Re: Car Amplifier
painttoad Offline
Desperado

Registered: 10/25/04
Posts: 688
Loc: peoria il
come on,gong....soundhound,we have lots of respect for opinions.....

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#5660 - 11/24/04 03:47 AM Re: Car Amplifier
curegeorg Offline
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Registered: 11/15/03
Posts: 1012
Loc: Raleigh, North Carolina, USA
no support is needed, it is a consensus that car amps in the home are "not the best idea" (to put it liberally). there are things in this world that you sometimes have to accept without explicit proof. we are lucky to have had people smart enough for us to trust, but then again, in a thousand years someone might think Einstein was an idiot...
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#5661 - 11/24/04 06:04 AM Re: Car Amplifier
Sound Killer Offline
Gunslinger

Registered: 04/05/04
Posts: 128
Sorry about the late response.

Painttoad-
Thanks for the info. That was very helpful.

Tekdredger-
No, I don't have one yet. Right now, I am using several QSC RMX amps and Selenium pro drivers in tri-amp mode with some duplicated channels. Would you like to recommend some nice models? I only need some 200W per channel stereo amp.

I also have a question. I am not sure if you know it or not. I went to a local car shop today (Similar to electronic store that kind of car audio demo room) to check some amps and found they were able to power up several of those amplifiers in their demo room instead of cars. How did they do that? Where did they connect their power? Are they also using the power supply? Let me know what you think. Thanks.

JT Clark-
Thanks for the sub amp recommendation. But I need an amp that will do 20HZ~20K so I can use it for mid-woofer and tweeter also. Thanks anyway.

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#5662 - 11/24/04 07:39 AM Re: Car Amplifier
Sound Killer Offline
Gunslinger

Registered: 04/05/04
Posts: 128
Quote:
no support is needed, it is a consensus that car amps in the home are "not the best idea" (to put it liberally). there are things in this world that you sometimes have to accept without explicit proof. we are lucky to have had people smart enough for us to trust, but then again, in a thousand years someone might think Einstein was an idiot.
That's your fu***ng consensus, not mine; and I don't give a shit. Get out of here if you are not interested in this subject. No need to post some depressive, meaningless messages around here. I simply don't want to read.

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#5663 - 11/24/04 09:06 AM Re: Car Amplifier
painttoad Offline
Desperado

Registered: 10/25/04
Posts: 688
Loc: peoria il
come on now, let's not be that way.they have this forum for US. let's not abuse it with language.and we all know curegeorg is going to put his 2 cents in no matter what.i too think this project is a waste i'll say what i can to keep you from doing it but i'll not slam you. the stereo shop would have a good regulated power supply.why not ask them what they paid for it.the response may send you to a home theater store(where i'm sure a lot of people think you should be)

sorry about the "gong" thing GONK

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#5664 - 11/24/04 10:30 AM Re: Car Amplifier
gonk Offline
Desperado

Registered: 03/21/01
Posts: 14054
Loc: Memphis, TN USA
I've stayed out of this debate because the sum total of my experience with car amps is a few friends who have installed amps and aftermarket speakers in their cars. Clearly things have gotten a bit heated here, though, so I'd like to try to offer a few comments.

First, it is technically feasible to power a car amp from 120V AC power. Tekdredger sounds like he has some good insight into the mechanics of this, and you might also get a few leads from the way a custom car audio place does their in-store demos. Doing so will likely pose some challenges, but depending on the goal of the project that may be part of the appeal.

Second, there are likely some inherent differences between the home theater and car audio markets, if for no other reason than the differing power sources and space considerations involved in the two markets. I think those differences need to be focused on before we decide if this project holds promise or not - the "explicit proof" that curegeorg alludes to as not being available. It does appear to be true from glancing at a few online sources (including Parts Express, since that site's already come up here) that the cost per watt range for car audio starts lower than for home theater. For car amps rated at 50W to 125W per channel (4 ohm loads typically), prices seem to start around $0.70 to $0.80 per watt, although you could certainly move up to amps costing $1.50 or $2.00 per watt if you chose to. Any of these costs will then need to be increased to account for the expense of converting from 120V AC to 12V DC to power them in a home setting, of course. This could be compared to Outlaw amps (since we're here) - using 8ohm ratings, the M200 sells for $1.50 per watt while the 7100, 755, and 770 all go for $1.29 to $1.30 per watt. If we keep things "apples to apples", however, and look at the 4ohm ratings for those amps the cost per watt drops to $1.00 for the M200, $0.87 for the 755, $0.86 for the 770, and only $0.78 for the 7100. However you look at it, these prices paint part of a picture. The other part (which I don't know about) lies inside the amps themselves - they all do the same basic thing, amplifying a signal, but are there differences in how it is done? What is the signal-to-noise ratio in a good car amp, as compared to a home theater amp? What sort of THD do you see? What impact does the added power supply issue generate? These are the questions that have not been answered here yet. I don't have the answers, unfortunately. I do understand theendofday's reluctance to discard his plan without getting those answers, and I can see how simply saying "don't do it" without at least some explanation is insufficient for him. Even though I have no plans to try this, I'd like to hear some more concrete explanation myself.

Third, we may need to also address the quality of the amps (as pertains to their intended environment) in this debate. If we are talking about a cheap "bargain" car amp that might be considered the automotive equivalent of an entry-level receiver's amp section, then going through the process of building a power supply is likely at intellectual exercise at best - the results should be no better than simply using one of those entry-level receivers. If we are talking about a good car amp, then the cost and effort involved in building a clean and quiet power supply may be the only barrier - but the audio results may be no better and the overall cost even higher than going with a good, economical home theater amp (either an Outlaw amp or even something used off Audiogon).

I guess at the end of the day, I would prefer to get a good amp purpose-built for the home theater environment rather than taking a car amp (hopefully also a good amp for its market) and trying to transplant it into a home system. On the other hand, I have this weird vision of a mysterious power supply tucked away out of sight and a field of surface-mounted car amps mounted across the front wall of a home theater... eek
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#5665 - 11/24/04 11:45 AM Re: Car Amplifier
painttoad Offline
Desperado

Registered: 10/25/04
Posts: 688
Loc: peoria il
i know that you can hook up car audio in the home and make it sound decent.that is a CAR AUDIO complete system.i have no idea what will happen with home pre-outs driving a car amp(s).i think the x-over from home theater to car theater is getting a bit out of hand.when i'm in my truck i wanna jam not watch a movie.(but that's a different subject)
just remember car audio amps require large amounts of current and if the power supply you buy or make can't cut it then the music turns to mush,then choppy,then quits,then the click of the circuit breaker.....(on the power supply)
i'm gonna head out and talk to my buddy and see what he used on the demo board in his old shop,maybe i can come up with the model of something of good clean power for you.
i have a decent knowledge of car audio , a good grasp of home audio but i just don't know if you will achieve what you are after.
i'll help if i can.
i'd like to see this thread continue,i'm sure even though some of us are against the project, i think we are all curious

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#5666 - 11/24/04 12:13 PM Re: Car Amplifier
JT Clark Offline
Desperado

Registered: 10/25/02
Posts: 466
Loc: IL
It can work, but the conversion gets messy. You're going from AC to DC with the converter and then back to AC in the amp. There are a number of car amps that can have some EXCELLENT quality to them, and there are a lot that are absolute garbage. These will have ratings that many of us that are into car audio call "When lighting strikes" meaning they will only make that much power if lighting strikes. This is not the only value that manufacturers might fudge either. I'd have to know what this amp is to be able to tell if it is good or not, but rest assured that car audio amps can be quite good. smile

With the RCA signal, I think it should be ok as car amps are adjustable and all of them can take from under 1V to several volts of signal strength, depending on the model. The low end tends to be from say 0.2-0.5 V to a higher end of 2.5V-15V. There is no way to correlate better quality to voltage ratings. I know of good amps that are on both ends of that.

I've looked into power inverters more which switch DC power to AC. Those will run from a couple hundred to $600-700 or so depending on how stable you need the power to be and how much power you need. The power converter might be cheaper than that, iirc, but you're not going to pick up a new one of anything approaching decent quality for like $30-40.

Now for the converter output amperage, you will need around 30 amps of output to be able to play 400 watts, depending on the output voltage. If it's an AB amp, then double that value (60 amps)as AB amps are about 50% efficient. If it's class D then figure around 43 amps as they are about 70% efficient on average. Since it's for mids and highs, then the first one sounds more accurate as next to all of those are AB amps.

I can't give any recommendations as to which power converter to use as I just don't know. theendofday can use Google just as well as I can (I would hope smile ) to find a place that sells them. Maybe link them back here and see if anyone finds something suspicious. You want to go from AC power (the wall socket) to DC power (what the amps takes). When searching, don't confuse this with a power inverter which goes from DC to AC. It wouldn't hurt a local audio shop what they use in there demo boards as it should be of appropriate size for what you want, especially if you've dealt with them before. The worst they'll do is not tell you.

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