Making mobile audio work at home

[Nikita] made a great find while cleaning out his garage: a set of audio amplifiers from a 1986 Volvo. After a bit of testing, he dislodged a stuck relay and set out to use these amps for a home audio system. He grabbed some left over brackets from his TV mount and used them as rail mounts. On the back he wired standard speaker connectors and RCA connectors to the wiring harness for the amplifiers. The final aspect is powering up the device, for which he used his ATX psu previously modified as a bench supply. 130-Watts of power for the cost of a few connectors.

We surprise to find we haven’t covered this common ATX bench-supply conversion before. What we have seen is an adapter to use one as a bench supply.

Comments

  1. jh says:

    Old AT power supplies are even easier to use for this… no adapters needed for the power switch. Just wire up a molex to your power and grounds and plug into the power supply.

  2. bikegeek says:

    Hmmm… I should have thought of this… now I have a purpose for my old McIntosh amp from my car audio days.

    My dreams of a kick-ass car audio systems were dashed when my son came along… don’t need 1000W of clean power to play rocknocerous.

  3. Ken says:

    I’ve used a car radio powered from a power supply in my garage for years, have one setup for the hot tub as well.

    Also using one to control the low voltage lights around my pond.

  4. IluvBread says:

    This.
    Not too advanced, yet interesting and totally doable, for me alot of the things here at hackaday.com is out of my reach.
    My coding is crap and I don’t have all the tools I would need / want (I don’t even have a dremmel..)

    But this, I really enjoyed this article. =) Thanks.

  5. Mike says:

    A classmate of my brother did something similar in the 80’s with his car system. He built a case for his residence room so that he could bring his system in with him and have a system in his room as well.

  6. sp00nix says:

    I wanna do this with the amp form my 1990 Volvo. Its a nice little 15×2 amp

  7. fartface says:

    Um wow… HAD = Stuff we did in the 80’s….

    next hack : How to use a shaver or TV in your car! What a Uber Hax0r!

    Or better yet, Add a subwoofer to your moped…

    Come on guys, cant we get some real hacks instead of someone hooking a power supply up to some old car junk?

  8. guest says:

    +1 IluvBread

    Thanks HAD!

  9. osgeld says:

    I used to work in a car audio shop, we had a 12v supply that was the size of a 15 inch CRT computer monitor

    didnt matter once you hooked up a 3kW (or larger) amp on it though, we had to use some giant (like 100lbs each) led acid batteries to supplement it or it would start to smell funny

  10. osgeld says:

    led = lead

  11. Ryan says:

    I’ve actually wanted to learn how to do this for some time now. It’s something that someone can do easily, especially getting the parts (scrap or goodwill). Thanks HAD, this was relevant to me!

  12. fdawg4l says:

    I’d worry about safety in (the possible lack of) proper grounding. Some cars had floating grounds which may work well with the ATX supply, but do bad things when tied to earth ground.

  13. Wobble The Hutt says:

    reminds me of when i made a sirius sattalite radio bag unit out of car parts before they released smaller more module units. ran it off a gamecube power supply. (great little 12v 3.25amp psu) also when i worked at a local computer shop my cd player for my workbench was an old ATX power suppply with a paper clip jumping a couple pins to turn it on, some crappy computer speakers and a computer cd drive with a play/trackskip button.

  14. Fallen says:

    I’ve done this 5 times before. :P
    Although my last one was 4 in parallel through 4 beefy FETs. As they heat up their resistance goes up, limiting the current from that PSU. It ensures even current sharing. The tricky part was getting one potentiometer to adjust all of their voltages accurately.

    I used it to power a 4kWrms car audio amp, while troubleshooting it(It shuts down if the internal bank of caps dont charge up within a reasonable amount of time. A car battery charger couldn’t do it. The inrush current is immense.)

    One down side is switching frequency, at least in my case, needed to be raised, since it was audible. It was around 15-20kHz before.

    ALSO REMOVE THE LOWER VOLTAGE RAIL COMPONENTS. I forgot, and blew up some caps on the 5V rail hahaha.

  15. D_ says:

    Nice way to make use of stuff not being used at all. I’m a graybeard myself and it annoys the hell out of me when other graybeards post a bitch, about a posted hack was something back when. Some of use where doing similar in the’70s. I recall dad doing so in the 60’s with a tube type under dash mount AM radio he bought in the 50’s for $100. Ignore we graybeards HaD, continue posting those things similar to that where done long ago.

  16. Shadyman says:

    As far as using an AT/ATX power supply, I’d be more interested in finding out what kind of filter caps would be needed for a proper filtering job on the power to prevent buzz, etc (as previously mentioned by Fallen).

    I’m a little wary about the fact that my 300W amp has a massive-gauge wire, and the ATX’s is so small. Maybe that’s just me :x

  17. oldschooller says:

    Great things can be done when people aren’t afraid to bring the 12V world into their homes…. the only suggestion I would make on this would be to add a couple of 5600uF 16VDC or 6300uF VDC caps to stabilize the output of the p/s for transient peak draws. Nice to see people making use of otherwise “useless” things!

  18. oldschooller says:

    Sorry —- 6300uF 16VDC

  19. Masta Squidge says:

    @oldschooller. There shouldn’t be any buzz assuming it is all hooked up right. I mean I can understand how it might occur, but in a car as long as you avoid a ground loop there should never be any noise.

    Of course filtering as you say can’t hurt.

    As for why the PSU’s wires are so small, it’s because you don’t need the wire to be as heavy for the short distances. 6-10 inches inside a case is nothing compared to 12 feet in a car. But I’m sure you know that.

  20. Masta Squidge says:

    Oh, to clarify, a car has tons of noise in the system from the alternator, a bit of noise from a PSU shouldn’t be any different.

  21. Masta Squidge says:

    And oh god I hate to triple post as it were but it states on the page something about limited voltage and whatnot altering the output of the speakers.

    This is true at the end of it all but in between its not the input voltage that matters. “Internal system resistance” is a non issue and saying “If we have only 12 volts to drive into a speaker” is misleading.

    The actual voltage output of the amp should be much higher than 12 volts, and as long as your power is within range the amplifier will perform its rated output (within said range of course).

    ALSO, I believe most stock speakers in cars, especially older ones, are in fact 8 ohms anyways. A higher load on the amp, in most cases, results in somewhat cleaner sound at the expense of volume. It also makes it easier on the amp as well, with less heat generated and longer lifespan.

    Wiring down to 4, 2, 1, or any load in between places the amp under more stress. Some amps will overheat in moments if ran below its lowest stable impedance.

  22. Sp`ange says:

    jh: lemme tell you, there’s nothing quite like listening to the Disney Princesses CD with a reference Infinity 10″. ;)

  23. Kaijuu says:

    To those who bitch and moan:
    While it’s clearly not rocket science (which is why I never posted my rig of using-a-car-amp-with-a-beefy-psu-as-an-inbetweener anywhere), there are tons of people out there who need an amp like this for something or other, but fail to think out of the box.
    The circuit itself is as straightforward as hooking up a light bulb, but the rig as a whole makes it HAD-worthy.

    As long as these kinds of “hacks” do not show up every single day, I see nothing wrong with articles like this.

  24. Troy says:

    I pulled the “Aktiv” stereo system out of my VW Corrado back in the mid 90’s and did the same thing for my garage stereo, well, sort of. I used the wire harness from the VW and used an AT power supply. The speakers were from the Corrado as well, they have small powered amps on the door speakers that rune those and the front dash speakers. I ended up making small boxes for the door and dash speakers and a separate set of boxes for the rear speakers. So far I have replaces the dash speakers with a set of Bostons and the AT power supply with a lab quality variable power supply. The system works great to this day. I have a 2003 Passat that was totaled back in 12/09 that I have thought about taking the Monsoon out of and updating my garage system with.

  25. Per Jensen says:

    Using this Car-amplifier inside with nominally 8-ohms speakers is not a good idea, you’ll only get a half the wattage out of the amplifier, compared to a 4 ohm speaker, or even a 2 ohm one…

  26. Kaijuu says:

    Per Jensen: Technically you’re right, but it’s not like he’ll draw the maximum output continuously; a couple of Watts output is enough to make your ears bleed.

  27. Josh says:

    I had a setup like this strapped underneath an old computer chair with speakers on the top left and right as the rear channel on my PC. worked great since there was nowhere behind me to install them.

    nice build!

  28. Andrew says:

    Hmm, couple things I’m wondering…

    What do you suppose the rated power of that PSU is? I know on my 350W supply, the 12V rail will do slightly less than 120W (9.8A @ 12V).

    Second, if he’s cutting the impedance of the speakers in half, he’ll get 133% current, but only 66% of the voltage, right (ie, 88% of peak power)? Or do these amplifiers not have internal impedance in the way I am thinking of them? Wouldn’t he just be better off leaving them impedance matched and not using “full power”?

  29. osgeld says:

    “” I believe most stock speakers in cars, especially older ones, are in fact 8 ohms anyways””

    i dont know about old cars, but no 4 ohms is the norm, although you can get less, or you can get more, you just have to check what the amp can do

    Ive seen car amps rated from a quarter ohm to 16

  30. Per Jensen says:

    Older stock systems is usually 2 to 4 ohms since the amplifier only have 12 volts to power the speakers. High end amplifiers today is outfitted with switch mode step up circuit, so the voltage it can feed to the speakers are more than 12 volts – so thanks to ohms law, more power can be put out. I have never seen 8 ohms speakers in any car myself.

  31. osgeld says:

    no we rarley sold them too, usually big subs so they could put a pile of them on a cheap amp and keep a 4 ohm load on a channel

  32. Nikita says:

    Thanks all for your interesting comments.(some do really make me LOL)
    The setup works equally well with 8 ohms and 4 ohms. The sound is crisped and clean: There are no hums and only a slight hiss. Because these are purely amplifiers the quality of sound output rest on the quality of sound input. As expected the amplifiers ran a little hotter in 4 ohms mode, that’s the reason for those big fins!

  33. Reaper says:

    I was going to do this once, where I had left the PSU stock and was using some modified connectors to plug in. I accidentally fried the PSU when I plugged it in because I grabbed the wrong connector :( 500$ PSU down the drain :\ It did 90A on a 12v rail. It’s in my pile of things to take apart, on the off chance some of the circuitry is still good.

  34. Dustin says:

    I made one of these about 6 months ago. I’m running an Alpine deck, 2 amps, 4 speakers, 1 subwoofer, 3 atx power supplys. Great little garage stereo. Had 0 issues so far.

  35. Dustin says:

    On ATX power supplies you need some kind of a load on the 5 volt rail to keep them from shutting down and also to make the Power supply last. I don’t know if this adapter does it or not but I used a resistor to accomplish this.

  36. jeditalian says:

    I, too have bridged a couple pins on a very old power supply, (AT was before ATX right?) wired it to a car amp, ran the wires from the back of my computer speaker system, and wired up big ass speakers in my bedroom. pretty sure i brought my 6cd changer out of my car too and ran it off the power supply as well. but i got bored with it and installed it in my car bc my paperclipped power supply was for making old hard drives spin with their case open.. & stuff like that. i wish i still had those old power supplies. have no idea how to trick a new one into thinking it is plugged into a mobo.

  37. Per Jensen says:

    jeditalian: Short the green wire with one of the black ones, or even the case of the power supply (GND) and i turns on.

  38. cgmark says:

    No need to change the speaker setup because it is powered off 12vdc. Most external car amplifiers in the last 10 years use boost converters or voltage doublers to convert the input power to much higher voltages, some as high as 160VDC internally and others with split -45 and +45V supplies inside.

    The downside of powering it off 12VDC is it will draw more amps than it would if powered by a car. That will generate more heat in the power supply section because the switcher has to handle more current. Depending on how hard you push the amp it can result in the power supply section burning out if they were cheap on the components and used ones close to the current limit.

    Make sure to use a heavy enough wire from the power supply to the amp so not to lose current in the wire. An easy way to test if what you have is enough is to turn up the amp really loud and measure the voltage at the power supply and compare it to the voltage at the power screws on the amp. If it drops or goes up and down a lot then get a bigger wire.

    The only difference in the amplifier in a car and the one in a home is the car converts the DC to higher voltage DC and the home converts AC to DC.
    Everything past that point is basically the same.

  39. skater_j10 says:

    If you’d like to move up to a 200W, 12V power supply, just use an Xbox 360 power Brick. The first generation bricks are rated for 16Amps. Check out this ible to convert one to your needs: http://www.instructables.com/id/XBOX-360-Power-Supply-to-12V-Accessory-Adapter/

  40. Masta Squidge says:

    You get half the wattage, but if your equipment is any good you dont need very much. You do realize just how loud a stock car stereo will get, when it only puts out MAYBE 15 rms.

    Wiring it at 8 ohms is in no way, shape, or form a BAD idea. Halving your wattage is only one half of the equation, the other half is that it results in far cleaner output.

    As far as speaker impedance, my 98 cavalier had 8ohm 4×6 speakers in the front, and 8ohm 6×9 in the back, as stock.

    A fiero, off the top of my head as an example used 10 ohm speakers. I dont think all four were, but I know for a fact at least one pair is.

    Especially, as noted above, you are only running at +/- 12v, as opposed to 13-14 as would be in a car. This results in less heat being generated, less current draw and leaner sound.

    Unless you have horribly inefficient speakers, running it at 8 ohms isnt losing you very much. You do realize that doubling your power only gains you 3db. Granted that is technically twice the volume, its not THAT noticeable in reality.

    Going from say, 100db, to 97 db is not much of a loss.
    There is no reason that setup cant perform well at 8ohms.

  41. Masta Squidge says:

    Oh, and I would love to see any stock system that is ran at 2 ohms per channel. it doesn’t happen. Stock head units could never handle that kind of stress and the heat involved would fry them in the dash.

    The only exception to that rule would be certain premium sound packages, but those include external amps mounted somewhere in the vehicle.

  42. Masta Squidge says:

    Oh, that is not to say that it doesnt work @ 4 ohms. It is just that the “halving your wattage” thing is trivial.

  43. Nikita says:

    Masta Squidge : I agree, I have since tested the setup at 2 backyard barbecues and the difference is not really noticeable when wired for 4 ohms vs 8 ohms, or so I have been told my test subjects…err listeners. The bass response with 8 ohms do seems a little tighter or much better – not sure why, I was expecting the opposite.
    Look out for my youtube video rocking a house party with with heavy bass reggae!

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