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Using a car amp to power home speakers

DAKSTER

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I've spent a couple minutes searching, but nothing has popped up.

Its just a simple question for you guys who are more electronically inclined than I.

I have a 2x100 RMS Pioneer car amp, which I want to install into a wooden box, with a volume knob, power knob and a power LED at the front and RCA inputs and speaker crimps at the back. I'll run this amp off a computer PSU also built into the box, and have it look like a matching component of my current wooden computer project.

Signal is to come from the PC, the amp is basically intended to be just that.. an amp.

Now I have connected the amp to an old power supply, which apart from the screaming fan on the power supply seems to provide ample power. I'll deal with that issue later, probably by buying a more suitable PSU. I've successfully hooked all this up to the PC, and it works great... with car speakers (Kenwood 7x10s in boxes).

I want to use a set of AR9s which I am rather attached to (70's Acoustic Research speakers) because I prefer the warmer sound of these old (top end stuff at the time) speakers, and I just want to make an amp without bells and whistles that matches the computer box. Not interested in surround sound, subs, or PC speakers at all, just a nice stereo sound using the PC as a source. The car amp is lying around, and it should be no biggie to stick it into a wooden box with a PSU and a volume pot I would have thought.

However, when I try to run my old AR9 home speakers off it, it sounds like crap. The volume is paltry compared to the car speakers, and there is a lot of noise which sounds like the speakers are crapping themselves. Obviously the home speakers are 8ohms, and the amp is nominally 2/4ohms.. I assume this is the problem? Both sets of speakers have similar nominal power ratings, the only difference is the ohms as far as I can tell.

Can anyone suggest a cure..?
 

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The resistance will be causing the issue I am almost certain. You will be over driving the amplifier to no doubt. Not really a solution bar getting the proper resistance. You might be able to wire it so it's 4 ohm but I doubt it will do any good.
 

Tasmaniak

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Normally I would agree although doubling the impedance shouldn't be THAT dramatic. But more to the point, when I googled those speakers I got this website Acoustic Research AR9 on thevintageknob.org and they list the enclosure as being 4ohm.

Perhaps the difference can be explained in their sensitivities? The AR9s are 87db and the Kenwoods 7x10s are usually 93db (I don't know which 7x10s you have to confirm this) But they could explain a loss.

Also is their power handling, the kenwoods are about 80wrms... the AR9s are about 17wrms. You need a bit more grunt to get them moving air at lower volumes.

None of these are definete reasons but they can all play a part.
 

Tasmaniak

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drewVHSS

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at 8 ohms those 100watt rms amps will really be around 25 or so watts rms so they're going to be very underpowered for what you need.
also running speakers at a different ohmage will result in 1 of 2 things depending whether you go higher or lower in resistance : one way will increase low mid and some muddiness in the sound, go the other way will increase treble bias.
(it's been many years since i played with this sort of thing, using higher or lower ohm speakers is mainly a p.a. and guitar amp sort of trick to achieve different results, it's not really something that's done with consumer audio by intent.)

Also , you'll have to stick with older style AT power suplies, ATX power supplies need a "power good" signal to be fed back to them from the motherboard so they'll fire up. With old AT power supplies you'll be struggling to find anything stronger than 250 watt and the main portion of that grunt will be on the 5v rails which is of no real use for you long term with bigger amps that you'll need to drive those speakers at a higher resistance than car amps are designed for. The 12v rails will usually be sitting around 125 watts at best.
(i scour those power supplies to use on various things that originally were powered by 12 plugpaks, i.e. some cheap import chinese surveilance camera equipment i've installed for a few people that came with weak power packs that failed within 3 months of use) 1 comes to mind for adam the owner of the chinese restarant at gosford whom on that day... backed into my vh ss......

I have successfully had a 250watt at power supply run 1 100 watt rms amp for a 12" alpine bass engine (very old sub which was the equivalent of a DDR drive before they came out) and when pushed to half the amp and subs limit, the power supply would go into protect mode, but it made quite a good rumble pack for my lounge chair playing the playstation at the time... (note a long long time ago!)
Silicon chip has articles on modifying old AT power supplies to remove all the unneeded circuits and only have a 12v rail with a much higher ampereage output and overall wattage. They can be reasonable robust power supplies if modified heavilly.

TBH you're better off finding an old class a-b amp from the late 70's to really bring those speakers to life, I've always felt something is lacking in new sound systems compared to my old marantz gold series amp and my thorens turntable.
 

DAKSTER

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Decided to read some stuff on your speakers. Interesting to note... everyone seems to say you need GRUNT and lots of it.
Acoustic Research AR9 Floorstanding Speakers Reviews

Yeah been doing the same thing. Maybe my Yamaha amp has more grunt than I gave it credit for..
You said 17W RMS lol.. the back of speaker says 175 nominal.. not sure what the Kenwoods are I will have to unscrew one and have a look.

Just assumed they were 8 ohms, shouldnt assume things ;)

So I guess I need a bigger amp... really want to keep them they are awesome.
 

Tasmaniak

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Lol yeah oops! 175 nominal.

From what I read they seem like a fair weapon!
 

DAKSTER

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at 8 ohms those 100watt rms amps will really be around 25 or so watts rms so they're going to be very underpowered for what you need.
also running speakers at a different ohmage will result in 1 of 2 things depending whether you go higher or lower in resistance : one way will increase low mid and some muddiness in the sound, go the other way will increase treble bias.
(it's been many years since i played with this sort of thing, using higher or lower ohm speakers is mainly a p.a. and guitar amp sort of trick to achieve different results, it's not really something that's done with consumer audio by intent.)

Also , you'll have to stick with older style AT power suplies, ATX power supplies need a "power good" signal to be fed back to them from the motherboard so they'll fire up. With old AT power supplies you'll be struggling to find anything stronger than 250 watt and the main portion of that grunt will be on the 5v rails which is of no real use for you long term with bigger amps that you'll need to drive those speakers at a higher resistance than car amps are designed for. The 12v rails will usually be sitting around 125 watts at best.
(i scour those power supplies to use on various things that originally were powered by 12 plugpaks, i.e. some cheap import chinese surveilance camera equipment i've installed for a few people that came with weak power packs that failed within 3 months of use) 1 comes to mind for adam the owner of the chinese restarant at gosford whom on that day... backed into my vh ss......

I have successfully had a 250watt at power supply run 1 100 watt rms amp for a 12" alpine bass engine (very old sub which was the equivalent of a DDR drive before they came out) and when pushed to half the amp and subs limit, the power supply would go into protect mode, but it made quite a good rumble pack for my lounge chair playing the playstation at the time... (note a long long time ago!)
Silicon chip has articles on modifying old AT power supplies to remove all the unneeded circuits and only have a 12v rail with a much higher ampereage output and overall wattage. They can be reasonable robust power supplies if modified heavilly.

TBH you're better off finding an old class a-b amp from the late 70's to really bring those speakers to life, I've always felt something is lacking in new sound systems compared to my old marantz gold series amp and my thorens turntable.

The PSU is a 500W thermaltake ATX, I just bridged the connector and fooled it into thinking it was on a motherboard.

I have to agree about the older amps, much warmer sound, which matches the speakers. I might have to find one or build myself a DIY amp I guess. Just trying to cheat and stick a modern amp into a wooden box, to save messing around with things I have limited knowledge about. Oh well its a learning curve :).
 

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best amp I ever owned was a playmaster 120, was a make your own kit amp but once you built it yourself you had a fair idea on how to modify it to achieve the sound you really wanted....
Granted i built mine when i was 14 and learn't the hard way that 1/2 farad caps don't like being wired backwards and got covered in electrolyte and had to spend some extended time being hosed down by dad followed by having to patch a hole in the shed roof...... fun times.......
 

DAKSTER

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OK now thats instilled me with a vast amount of confidence in building my own... not :rofl2:

I guess now the hunt starts for an old amp I can strip... or buy a much gruntier car amp, whichever works out cheaper. An old amp would be a nicer sound, a new amp is going to be much easier to mess with.
 
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