Amplifier Genius's Wanted!!! - Civinfo
 
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post #1 of 14 (permalink) Old 19th March 2008, 16:49 Thread Starter
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Genius's Wanted!!!

dear all you very brainy fellow members,

I have seen examples of amplifiers being fitted using a loc or high input converter to cater for the lack of pre-outs on the factory radio.

So I thought I would have a go... I done it all BUT cannot power my amp!

I dont want to run power cables to the battery so i thought I was being clever to try and use the 12v socket in the boot to power my amp... BUT sadly it wont turn on!

I then thought because my amp has remote turn on and power connectors that I could split the power cable and run both from the 12v socket.

... STILL NOTHING,

any thoughts,

the last thing I want to hear is ive got to connect to the battery.

replies wanted please.
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post #2 of 14 (permalink) Old 19th March 2008, 16:55
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The 12V socket in the boot is only rated for 25AMPS according to the manual - I doubt your amp will run off that.

Even if it does it's likely to either blow the fuse as soon as you push it or overheat the wiring and set fire to something.

The most likely scenario though is exactly what you are describing - the Amp just won't power on.

You can use it for the remote line to tell the Amp to switch on but it's still not recommended as most cars generate and audible POP through the Sub if they are activated by the accessories switch instead of a remote-on signal from the head unit.

I used an LOC with "signal detect" which has a remote line for the Amp that it activates when it gets sound from the speakers - works brilliantly. (cost me $35AUD for that unit so about £20 UK?)

-H

Last edited by Harlequin; 19th March 2008 at 16:59.
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post #3 of 14 (permalink) Old 19th March 2008, 18:02
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ive just found a speaker line to rca lead converter for £4.99. its an autoleads product and part number is PC1-601 ordered it from halfords on sunday, called me today (wednesday) to say its in.
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post #4 of 14 (permalink) Old 19th March 2008, 20:56
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Quote:
Originally Posted by Mr JP View Post

I dont want to run power cables to the battery so i thought I was being clever to try and use the 12v socket in the boot to power my amp... BUT sadly it wont turn on!

Don´t do this..

You need a proper cable to the battery with a proper fuse!

Worst case you could burn the car...



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post #5 of 14 (permalink) Old 20th March 2008, 01:17
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yeah, its a pain to put a cable in but it should only take a few hours, and cost less than £20!

what current does the amplifier draw? if the amp has anything bigger than a 10amp fuse i would run a power cable. As FWH says above, you could burn your car and possibly with somone in it!!!!!

a company called Celsus make a lot of line out converters i have this 1 Car Audio Direct - Celsus LC2 Adjustable Converter - Accessory
although i havent installed it yet, this is the sort of thing you will need.

and if you buy the power cable from the website at the same time you could save yourself loads of money!
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post #6 of 14 (permalink) Old 20th March 2008, 13:53
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Hey,

As I am considering a Civic for my next car and love my bass, the need to add an amp and possibly a new headunit is making me keep tabs on these type of topics.

Just a question, but I know some manufacturers standard fit radios do indeed have a low level pre-out on them. For instance I think Peugeot do as I have seen an AutoLeads adaptor lead in my travels, has anyone come across anything to say the Civic radio may have this perhaps?
If this was the case using a high-level to RCA converter would not be needed.

Ian
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post #7 of 14 (permalink) Old 20th March 2008, 14:40
 
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Hi there.

Have you tried to put the ignition in "start" position?
My Accord only powers the 12V sockets when the ignition key is turned all the way to "ready to start".

If the Amplifier is properly connected/wired and you checked with a multimeter/tester that it is receiving power, it should work.

Normaly, you only need to connect the + and - from the 12V socket to power input + and - on your amp and connect another wire from + power input to + remote power.

I can see no reason why (if all of the above is met) the amp should'nt work. The 12V boot socket will shurely provide enough Amps to power the amplifier in LOW VOLUME LEVEL. Has it was said in other posts before, the boot 12V socket WILL NOT be enough to power your Amp full volume up.

Hope it helps.
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post #8 of 14 (permalink) Old 20th March 2008, 14:46
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Be cautious.

An amp connected to a high resistance supply like the 12V socket, will see voltage drops as the load increases. The load can increase quite significantly even at low levels, if the bass is turned up.

If the voltage drops, then the amp will clip the output wave. Clipped output can and will trash speakers, even when driven well below their rated output!
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post #9 of 14 (permalink) Old 21st March 2008, 12:55
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Quote:
Originally Posted by Pottsy View Post
Be cautious.

An amp connected to a high resistance supply like the 12V socket, will see voltage drops as the load increases. The load can increase quite significantly even at low levels, if the bass is turned up.

If the voltage drops, then the amp will clip the output wave. Clipped output can and will trash speakers, even when driven well below their rated output!
Nothing to add here, except maybe a capacitor. A decent capacitor does flatten the load-peaks, but still...
I don't think it's wise BTW to draw 25 amps from the rear power socket over a longer period of time, although I must admit that I haven't seen the cable that runs to the socket. But it has to be VERY thick, with as few connectors as possible on the way.
Another way to avoid high current, especially for subwoofers, is using an 8 ohm speaker. I know that in theory can have more watts from a 4 ohm speaker, but taking in account the power losses, that shouldn't be much of a worry. And speaker efficiency is just as important: a speaker at 92dB only needs half the power of a 89db chassis to reach the same soundlevel.

K.
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post #10 of 14 (permalink) Old 21st March 2008, 13:30
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Quote:
Originally Posted by Koen View Post
Another way to avoid high current, especially for subwoofers, is using an 8 ohm speaker. I know that in theory can have more watts from a 4 ohm speaker, but taking in account the power losses, that shouldn't be much of a worry. And speaker efficiency is just as important: a speaker at 92dB only needs half the power of a 89db chassis to reach the same soundlevel.

K.
Hey,

Just going to jump in here a bit as I have dabbled in high power ICE systems in the past. If your interested in seeing it check here :

MainPage Then click on the S16 Page.

I wouldn't be entierly convinced your idea of using an 8ohm subb woofer will necassarily help in reducing the current draw down the power line. While good in theory the amp is still going to pull it's required amps regardless of what is connected at the end of it, only then when power is at the amp will the amp itself then run cooler through the 8ohm subb loading it up a bit more and not allwoing the power to flow so freely.

Just thinking about this somemore (it's been a while since I've had to think of this) an 8ohm load is going to add more resistance to the amp, hence power will backup. A 4ohm load allows the power ffrom the amp to flow more freely.

Lets not forget an 8ohm subb connected to the bridged output of an amp will be seen as a 4ohm load at the amp anyway, load ~ divided by 2 (as it's on the bridged output) = 4 ohms at the amp.
A 4ohm subb will present a 2ohm load at the amp, current will flow more freely and the RMS power goes up.

In the 306 I had above I was using 2x 8ohm 15" JL Audio subbs, I went 8ohm as the original Calibre amp was not capable of running 2 ohms bridged mono. As you can see though I still ended up going to a Phoenix Gold ZX500 after blowing 3 Calibres up!
I was also running 1/0 gauge power cable & a 1 farad capacitor to smooth the power delivery.

We need to bear in mind that electricity does not flow in the wires but along the out side of it, hence good quality audio power cable has multiple thin strands of wire which increases the surface area of the wire compared to it's size.
Even though the car cabling will be of good quailty it wont have a high strand count and as amps are pulled it will not be as capable of delivering them as well as a multi strand cable.

For safety I'd say fit an 8 gauge power cable minimum from a fused connection under the bonnet to the boot. It's a pain but will be safest and should you have a fire your insurance company cannot say it was the faulty ICE install.
Pulling major amps down a thin wire will make it heat up and it's near plastics & carpet.

Ian

Last edited by coolice; 21st March 2008 at 13:37.
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post #11 of 14 (permalink) Old 26th March 2008, 22:37
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Sorry, but I have to respond to this. As an electronics engineer and fanatic, I can't help it, I just have to.

Quote:
Originally Posted by coolice View Post

I wouldn't be entierly convinced your idea of using an 8ohm subb woofer will necassarily help in reducing the current draw down the power line. While good in theory the amp is still going to pull it's required amps regardless of what is connected at the end of it, only then when power is at the amp will the amp itself then run cooler through the 8ohm subb loading it up a bit more and not allwoing the power to flow so freely.
You have a bit of a strange idea about power, current, and so on.
An 8 ohm load draws only half the current of a 4 ohm load. You say that the input current is about just as high. Well then, where does the rest of the current go then? And more, since
U = R x I (voltage = resistance x current)
and
P = U x I (power : current x voltage)
we can derive
P = R x IČ

That would mean that, if indeed the current would be constant, the 8 ohm speaker delivers twice the power of the 4 ohm...

Sorry man, wrong there...
Quote:
Just thinking about this somemore (it's been a while since I've had to think of this) an 8ohm load is going to add more resistance to the amp, hence power will backup. A 4ohm load allows the power ffrom the amp to flow more freely.
What does "power run freely" mean? An output stage of an amp delivers some current to the load, and depending on the output impedance (which should be as low as possible) that results in a voltage across the load, and some voltage across the output impedance, called "loss". That's why them things get hot!
Keeping that in mind, you will understand that the loss is lower when the amp is loaded with 8 ohms instead of 4 ohms.

Quote:
Lets not forget an 8ohm subb connected to the bridged output of an amp will be seen as a 4ohm load at the amp anyway, load ~ divided by 2 (as it's on the bridged output) = 4 ohms at the amp.
A 4ohm subb will present a 2ohm load at the amp, current will flow more freely and the RMS power goes up.
That's not how it works, however going deeper into this would take me far into schematics and theory.

Quote:
We need to bear in mind that electricity does not flow in the wires but along the out side of it, hence good quality audio power cable has multiple thin strands of wire which increases the surface area of the wire compared to it's size.
Even though the car cabling will be of good quailty it wont have a high strand count and as amps are pulled it will not be as capable of delivering them as well as a multi strand cable.

For safety I'd say fit an 8 gauge power cable minimum from a fused connection under the bonnet to the boot. It's a pain but will be safest and should you have a fire your insurance company cannot say it was the faulty ICE install.
Pulling major amps down a thin wire will make it heat up and it's near plastics & carpet.
It is indeed ALWAYS better to install power supply cables as thick as possible, with as low resistance as possible. Even a very low resistive loss costs power at the end. Suppose that the cable from battery to amp has only 0,1 ohm resistance, which is not bad at all! For a 240 watt RMS amp it would carry 20 amps, meaning a loss of 2 volts! So your amp wouldn't be getting 12 volts, but only 10... (Simplified calculations). That's also where these big electrolytic capacitors come into play: they flatten out the load peaks, so the current in the supply cables is less peaky, and you'll have a more steady supply, and less loss.

K.

K.
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post #12 of 14 (permalink) Old 27th March 2008, 17:03
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Quote:
Originally Posted by Koen View Post
Sorry, but I have to respond to this. As an electronics engineer and fanatic, I can't help it, I just have to.

You have a bit of a strange idea about power, current, and so on.
An 8 ohm load draws only half the current of a 4 ohm load. You say that the input current is about just as high. Well then, where does the rest of the current go then? And more, since
U = R x I (voltage = resistance x current)
and
P = U x I (power : current x voltage)
we can derive
P = R x I²

That would mean that, if indeed the current would be constant, the 8 ohm speaker delivers twice the power of the 4 ohm...

Sorry man, wrong there...

What does "power run freely" mean? An output stage of an amp delivers some current to the load, and depending on the output impedance (which should be as low as possible) that results in a voltage across the load, and some voltage across the output impedance, called "loss". That's why them things get hot!
Keeping that in mind, you will understand that the loss is lower when the amp is loaded with 8 ohms instead of 4 ohms.

That's not how it works, however going deeper into this would take me far into schematics and theory.

It is indeed ALWAYS better to install power supply cables as thick as possible, with as low resistance as possible. Even a very low resistive loss costs power at the end. Suppose that the cable from battery to amp has only 0,1 ohm resistance, which is not bad at all! For a 240 watt RMS amp it would carry 20 amps, meaning a loss of 2 volts! So your amp wouldn't be getting 12 volts, but only 10... (Simplified calculations). That's also where these big electrolytic capacitors come into play: they flatten out the load peaks, so the current in the supply cables is less peaky, and you'll have a more steady supply, and less loss.

K.

K.
Hello Mate,

I see where your coming from and indeed I am worng in some areas, I did mention it's been a while & I'm probably not using the right words to get across what I am trying to say, but so to are you in some assumptions with speaker loads seen by the amp.

Without acutally measuring the amps current draw in a given setup I'd be inclined to say that no matter what load on the output side the amp itself, running full volume would try to pull the amps it needs to produce it's RMS figure.
Of course this most probably will change if using an 8ohm speaker as below.

An 8ohm speaker/load will not stress the amp so much and that is a fact, the lower the impedance the easier it is for the amps power to flow though into the speaker. Crude way of explaining it but thats a simple term.

Some ampifiers are not rated to a 2ohm load on the bridged output, as the lower the speaker impedance the more amps/current will flow through the amp. This you can see from the amps load tests/specifications, an amp connected to a 4ohm load will give X amount of power while the same amp connected to a 2 ohm load will give Y which is more RMS power.

A 4 ohm speaker delivers twice the power of an 8ohm dont you mean? You may be refering to what I have possibly come across as saying.
4ohm is less of a load on the amp compared to using an 8ohm speaker, the amp will produce more power connected to a 4 ohm speaker than an 8ohm one.

In essence you do not want the lowest impedance rating you can get, unless of course your amplifier is capable of running down to 1 or 0.5ohm even. This is how the top boys get mega bass from small amps, if the amp is stable down to really small impedances then you can configure a group of subs to load the amp down to say 0.5ohm and inturn it will produce lots of power.

The lower the speaker impedance the higher power output you will get from the amp as there is less restriction to the power output.

Another crude example is a hose pipe with a bung in the end, with the end of the pipe blocked up the water pressure behind it builds up.
If it can burst the pipe it will, no restiction to flow means the water will flow more freely. The same results happen with amplifiers if the impedance is to low for it to handle, this I know first hand.

Quote:
That's also where these big electrolytic capacitors come into play: they flatten out the load peaks, so the current in the supply cables is less peaky, and you'll have a more steady supply, and less loss.
I can agree that they smooth power once inside the amplifier yes, but will not necassarily smooth power into the amp from the power cable.
In this instance you will need a dedicated smoothing capacitor of 1 farad or above, a clue to needing one of these is your lights dimming with the bass hits. That and a high output alternator or better battery.

When it comes to working out current draw for a give power supply or output this maths is beyond me so your experince here is invaluable.
But when it comes to ICE & speaker wiring I do know a lot as I have been there blowing amps up which are not loaded correctly.

Also, when connecting a 4ohm subb to the BRIDGED output of a 2 channel amp you are halving the 4ohms across 2 outputs of the amp. Hence the amp will be running @ 2ohm's bridged mono.
Dedicated MONO amps are different again.
Subb wiring diagrams explain in most cases the various ways of wiring up 1 or more subbs to provide a given impedance value for the amp to see.

Of course there are some amps that regardless of load on the speaker side will give the same RMS power if it was driving an 8, 4, 3 or 2 ohm subb. JL Audio amps are one such make.

On the basis of amps running hot, an amp running a 2ohm load will be hotter than the same amp running a 4ohms load.

If MR JP can give us the specs of his amp then you could probably work out it's current draw and recommend the correct size cabling he needs?

This is cool, I'm having to remember what I've done myself in the past.

Ian

P.S. Just found this : Home Toys Article - Speaker Impedance, Your Amplifier And You.

Another : OHM SWEET OHM

Good reading and the first one makes references as I do to a water hose pipe.
I'm not 110% on my electrics, I used to be an electrical/mechanical engineer but didn't do much sutdying in electric circuits more wiring and programming.

Last edited by coolice; 27th March 2008 at 17:16.
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post #13 of 14 (permalink) Old 27th March 2008, 19:15
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I have the alpine microsub with built in amp and all i have done is wire up a cigarette lighter to it and plugged it in to the socket in the boot and it works fine and does not generate any heat in the wires i have also wired the remote cable in to the cigarette lighter aswell so it will power on without fear of it being on all the time as the sockets do not power up untill the ignition is on.

If you are using a stand alone amp such as an Alpine MRP-T220 Amplifier then i would advise running the appropriate wiring from the battery and having an inline fuse on it aswell.
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post #14 of 14 (permalink) Old 27th March 2008, 23:05
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not all amps are 2ohm stable. in this mode it puts extra draw on the +12v cable and what ever amp you use, keep the earth as short as possible, and nice n thick.
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