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Amp in a Computer Case?

Started by Muthauzem, February 15, 2009, 10:46:19 PM

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Muthauzem

Yeah... I've ripped apart almost everything from an old computer and ended up with a nice empty metal case...
I wondered, what now? Then, almost instantly, I thought that maybe I could build a Guitar Amp in that.

I'm an electronics student and I've built some stomp boxes and power suplies before, so I'm kinda familiar with everything. But never dealed with amplifiers... I wanted something that sound good but is still simple.. So I choosed to go with SS in istead of Tube.

The question is, is it possible? Like, Is there any way to fit the speaker and circuitry inside the case? Is there any problem in it being all metalic, acousticaly speaking.

Also, I haven't started my researchs yet, so I'm completely lost about what circuit to pick. If you guys have any sugestion for me to begin with. I was thinking in something like 30 Watts - 8 Ohm...

Thank You, Already

J M Fahey

Hi Mauthauzen.
An LM3876 or 3886 can give you around 30W into 8 0hms, and are more powerful than what you need; that´s good because then you have a safety factor built-in.
TDA2050's can deliver almost 25W into 8 , but you are stretching them a bit.
There´s a lot of preamps to pick , or you can consider Mansur´s excellent Mesa Preamp (if you like heavy stuff) which he posted here.
Making neat holes into iron sheet (the computer case) won´t be very easy with homebuilder tools.
Try to get some aluminum sheet which is easier to work , doesn´t rust neither need paint, etc.
Good luck with your project.

Fahey

teemuk

I thought this idea once and didn't find it very appealing in the end. Besides the bottom plate and the plate that mounts the motherboard the metal sheets of the chassis are very thin. They flex annoyingly and can't be trusted supporting moderately heavy components like a (fairly big) transformer or PC boards that can break from excessive flexing. Because the chassis is steel it's also hard to puncture holes through it.

A "pizza box" –style computer chassis (or a rack-mount) would be great for projects but most of those ordinary PC chassis are too big and if you want to get rid of the plastic front part it's difficult to craft something nice to replace it. When you strip most of the unimportant parts off, the chassis is left with plenty of untidy holes and stuff. If you want to make that thing looks something else than stripped computer chassis you have to do a lot of work and likely craft a lot of custom parts. The simple idea is starting to get fairly difficult...

The thing pretty much qualifies as a head cabinet only. Mounting speaker to a PC chassis is not a good idea unless you are willing to go through the trouble of damping all the stuff that could resonate. So yes: It's an acoustic issue. And there will be a lot of those ugly resonances in a case built out of thin metal sheets. I trust that you have experienced that even a computer fan or a "speeding" CD drive can make plenty of ugly noise in that box - so just imagine what a speaker will do. If it's for "humour value" and you don't mind the sound quality then it's naturally a different issue.

Then, at least I happen to live only few kilometres away from a local junkyard where I can buy a cheap aluminium plate with almost no price at all. Bending it to L or U-profile doesn't require special tools and it provides a much tidier and compact chassis than a PC case. It's sturdier and easier to shape. And you can get it in correct size to begin with. So, I simply decided not to bother myself with those computer chassis... I also came into similar conclusions with various mini stereo and monitor chassis. They almost always seem to be poor platforms for something built out of scratch and turning them into something different usually just involves too much "unnecessary" work.

Even if you don't have a scrap metal yard near you, you can likely find a place that sells various types and sizes of aluminium "industrial enclosures".

Not to say your idea isn't plausible (on a contrary).

Muthauzem

Wow... Thank you VERY much Fahey and teemuk.. I Couldn't expect better answers than yours :D

Since it's my first project, I won't try messing with thinks that can easily go wrong :D
The "humour value" was really in my mind, but it makes no sence if it doesn't satisfies it's main function, which is the audio part.
Well, I never looked for this type of enclosures here, where I live, but I'll see what I can get.

I'll take a look at those chips you've said Fahey. Just a few question. They are AmpOps... What should I do with them? A Basic buffer configuration? Follow datasheet sugestions? And, Do they do it all? Like, is it just "plug in" a preamp before them, the speaker after, and you're ready to go?

Thank you, again.

J M Fahey

Hi Muthauzen.
Homebuilding is fascinating.
To keep it a pleasant activity, most suggest following a step by step scale.
Make first, say, an LM386 amp , even simpler than a Ruby: just the chip, 2 or 3 extra parts, a couple jacks, a piece of perfboard, 9V battery, some junk speaker. Not even case or pots! (control it from your guitar); just the application from the datasheet. It works!!
You´ll feel happy and have something to show your friends.
After that "pimp it": build a Ruby or similar, with CD play along input, headphone jack, the works.
The next step would be, say, some TDA20xx ; basically the same from 4 to 30 W circuits, allowing you to re-use the same basic PCB or perfboard design.
From there on, the sky is the limit.
Don´t rush straight into "difficult " designs; (well, the same applies to guitarplaying and 1000 other activities as well).
Download and start reading (at your own pace) Teemu´s impressive book about SS amps,it´s all there.
Good luck
J M Fahey

Muthauzem

Yeah.. you've made up my mind... I started reading datasheets and everything and yeah.. it's a little too much for me now.. I'll start slowly =)

Thank you, one more time. See ya!