Running a car amp from computer's PSU?

[Maxxarcade]

This has probably been discussed before, but I need to know...

I am building a dedicated system for providing all audio functions of my digital pipe organ project.

I need a 4 channel amp, and the easiest thing I can think of to use is a car stereo amp. This would also keep size down and allow me to fit all the electronics in the console.

Right now I have a 4x60w Clarion amp hooked up for testing, and it seems to work fine, but drags the +12v rail on this cheap Codegen 300W PSU down to 11.6v or so, and it sounds bad if I try to play it over a certain loudness. Though I think most car amps need about 13.8V to work at full power.

Can I just use a good PSU with dual rail +12v, and use the other rail to power the amp? I assume one rail would be for the motherboard VRM only, and the other would run the drives and also the amp. There is only one hard drive in the system and a CD Rom, so I'm hoping the second rail would have enough power to spare.

EDIT: Damn, I posted this in the wrong section, should have been in the power supply or general electronics section

[Topcat]

Re: Running a car amp from computer's PSU?

I doubt a PC PSU could adequately power that, car stereo amps pull a lot of current especially at startup and when cranked. It would probably turn it on, but it would start clipping when turned up. It would probably run a small one, and if you don't plan on blasting it, but otherwise, I'd find a power source capable of more amperage output.

[starfury1]

Re: Running a car amp from computer's PSU?

although it maybe dooable with a big beefy expensive computer PSU.
(and possibly depend on how they achive the dual rail)
Sounds like you are having some success with it with the 300W

Don't know about car amps but
Audio power amps are best run with an Analog unregulated (soft) psu
(big transformer caps and cost)

I sort of go with TC, a seperate psu for the power amp would be better idea

I dont know how well this would work for you but
Maybe see if you can get from the flea markets decent amperage Amature 13V8 PSU
(bigger the better I think as you will probably be pulling a more constant higher current of it then a rig)

Analog would be preferred but there are SMPSU's of this type
although as TC said switch on surge current maybe an issue

How Regulation might effect the sound is another question and its possibly part of why the 300W is turning to crap when you push it

neither supply type is ideal for what you want to do thought
I think


no first hand experince on this just my thoughts

Hope its of some help anyway

Cheers

[Maxxarcade]

Re: Running a car amp from computer's PSU?

I'm thinking of building my own analog PSU for it, lots of circuits are available online. The easiest uses a 7812 regulator to drive several current pass transistors.

Another possibility is to just build my own amp, probably IC based. I do have two IC's from a receiver that have 3x100 watt outputs each. Problem is I can't get the datasheet from Sanyo

[gonzo0815]

Re: Running a car amp from computer's PSU?

I think it should be possible, with a decent 12v capable psu.
But i would certainely not use the Codegen for anything, as they tend to kill hardware.

Any way, if you going to build an PSu, i would say there is no need to stabilize it. Just put enough capacitors in and let it work.
Most poweramp i know do not regulate the voltage beyond rectifcation and filtering.

[japlytic]

Re: Running a car amp from computer's PSU?

I have modified power supplies for various applications (One of my first was a Seventeam ST-200WV for a variable output of 12-13.8V).
The issue I have encountered is not only the changes in the divider network to Pin 1 of the TL494/KA7500 (or equivalent), but the removal of the overvoltage sensing components in the -5V, -12V and +5V rails (D20, R30, R32, R36, R41, R45, and Q6) causes the overcurrent detection to become more sensitive . To fix this problem, I would replace R33 with a 100R unit with a 10K trimpot. This trimpot would be adjusted to a point just before the voltage drops on a full load (200W).

Units with an op-amp (typically a LM339) often require different modifications, which I will describe in the future when I modify power supplies with that chip.

Although I did this with no rewind of the transformer (I upgraded the high power rectifier), I recommend that the transformer be rewound (with special insulation tape) for 300W+ supplies, as described in the October 2003 issue of Silicon Chip.

Finally, be sure to have a good value of output filter capacitance and inductance...

[starfury1]

Re: Running a car amp from computer's PSU?

Thanks Japlytic

I was going to mention the silicon chip modding one but thought it might be more trouble then it was worth considering the rewind.
(plus you would have to buy the full article.)

I think Maxxarcade hope was to save himself a little time trouble and space by just using 1 psu to do both jobs...I can understand that

there was a site somewhere on the net that had pages on modding them too
(think it was on a specific 200W AT supply) stuffed if I know where the link is in the bookmarks.....if anyone is really interested I'll see if I can find it.

Please if anyone has some good links on how the car amps are put together electronics wise these days I'd be interested.

Just got me curious now...thanks

Cheers all

[999999999]

Re: Running a car amp from computer's PSU?

You "could" but it would be a very bad idea.

Power amp PSRR drops very fast to a bad level when the supply line noise frequency increases. Terribly so, the last thing you want to do is power an amp with a switching supply already coupled to a high current, high current swing system too.

Yes you could do it, but the result would be about the worst (accuracy)performance that amp would ever deliver.

[linuxguru]

Re: Running a car amp from computer's PSU?

You don't need to re-wire the switching transformer, but it certainly helps to re-wire the output inductor in the pi-filter.

1) Unsolder it. Unwind it carefully and find the number of turns in the +12v section.

2) Using the same gauge or thicker gauge of enamelled wire, rewind the only the +12v section with the same number of turns, but double or triple the current-capability using bifilar or trifilar winding.

3) Upgrade the rectifier on the +12v rail to the new (higher) current.

4) Double or triple the capacitance on the +12v rail.

5) As mentioned by Japyltic, disable over-voltage and over-current sense on all other rails (+5v, -5v, -12v).

6) Isolate the +5v, -5v legs of the switching transformer by removing all the corresponding rectifiers.

7) Add additional solder (or solder a copper braid) on the +12v rail sections, on the solder side of the PCB on all sections from the switching transformer/rectifier/pi-filter/output electrolytic to handle the higher current on the rail.

8) (Optional) Change the resistive divider for +12v to the appropriate ratio for +13.6v.

9) (Optional) Modify the output wire(s) to the appropriate gauge to minimize resistance in the power harness to the car power amp.

Note that this mod works best when powering only a single-channel subwoofer power-amp module - the remaining channels are best handled by other 2/4-ch amp module(s), powered by a lower-powered linear PSU.

[cadiman]

Re: Running a car amp from computer's PSU?

I love car amps for diy projects. they are small and pack alot of punch. the problem you have is they work great with a battery. I would use sealed batteries as big as you could fit in your project and then use the power supply to charge them. This works great as long as your not using the charger to run the amp when the batteries are dead. You can find these batteries at a good battery store in all different sizes as well as the charger if your not using the power you have. also the voltage needed for an amp is around 11 to 15 vdc they are not very picky on voltage because these are current amplifiers. They need lots of amps to turn them up. you could also run 8 ohm speakers instead of 4 ohm this would cut amps down as well as output, but will keep you out of trouble. Why do you need four channels? and good luck!

cadiman