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-   -   Build a Loud, Simple & Cheap amp for a friend (http://www.diyaudio.com/forums/car-audio/121585-build-loud-simple-cheap-amp-friend.html)

EWorkshop1708 19th April 2008 02:11 AM

Build a Loud, Simple & Cheap amp for a friend
 
Hello, the goal of this is to build a car amp as cheaply and easily as possible, while still providing decent power to satisfy the average person. :cool:

Approx 150W-300W RMS total in stereo is the goal, although actual wattage isn't a major concern. :att'n:

A younger friend of mine is interested in me building a car amp for him, but he's not spending huge cash on a system, but still wants good sound that's loud. I also want to make some money on such a project, the other reason to go cheap. I found some large efficient heatsinks for only $20 a piece, so to keep it cheap and simple, I want to build the whole amp & SMPS as a whole on only one heatsink and circuit board

I don't need to build the amp as beefy as a regular overbuilt DIY amp I'd build myself, I just want it to perform with minimal parts, and be easy to build, and also repair if needed.

I had a few ideas:

1. Single pair of MOSFETS for SMPS 75N06 or similar. (75A)
2. Two audio channels rated @ 2 ohm each using a single pair of NJL0281/0302 thermaltrak to reduce usual costs and complexity of using a VBE transistor and mounting to heatsink for temp comp
3. Use SMPS transformer from old recycled computer power supply, and use in reverse as stepup (worked great on an SMPS I just made so far) to get amps voltage rails.
4. Use a few small cheap capacitors in parallel, or just use a single pair of larger caps for the power supply
5. Use TL494 PWM IC with a socket for easy & fast replacement if IC blows, and no voltage regulation, and simple 2N3904/3906 totem poles to drive the mosfets from IC
6. No snubbers on SMPS to save space and cost since they are not necessary for operation

What ideas/components, placement, etc, would you recommend in the building of a cheap DIY amp???? :)

theAnonymous1 19th April 2008 02:29 AM

Here is an option for a small TL494 supply (if you plan to build your own)......

http://www.electronics-lab.com/projects/automotive/012/

Perry Babin 19th April 2008 03:23 AM

Why not find a commercially available amp (used) that's relatively good quality as is and tweak it. You'd have the sink, board, transformer/core and virtually all of the other parts you'd need.

The class B amps (most of the budget amps) have little or no bias compensation so they shouldn't present any problems if you want to use those transistors.

EWorkshop1708 19th April 2008 04:12 AM

Quote:

Originally posted by Perry Babin
Why not find a commercially available amp (used) that's relatively good quality as is and tweak it. You'd have the sink, board, transformer/core and virtually all of the other parts you'd need.

The class B amps (most of the budget amps) have little or no bias compensation so they shouldn't present any problems if you want to use those transistors.

Interesting. I'll look around, but I haven't found any used/broken amps lately. If I could get one cheap and fix it, that's cool too. That would also save a lot of time and effort in getting a cheap amp for him.

I still want to see if the DIY is possible being I have most of the parts, but don't want to use all my good parts because I will build other things too. No paralleling with the transistors, and using single pairs gets a working amp with mimimal complication and parts. I also thought about just using a single pair of 6800uf capactors for the amps power. 2 caps makes things easy.

I remember an old BOSS 250W :rolleyes: max amp I fixed a long while back had only one pair of transistors for the SMPS, and each channel, and a simple TL494 with two pull-down PNP's. However, the amp was built with cheap sucky transistors, and weak mosfets.

I figured I could try and build a better cheap design of my own, by using much better transistors, that's even simpler in circuit complexity and more reliable than something like that old cheap BOSS.

dangus 19th April 2008 06:16 AM

Last week I bought a made-in-USA Rockford-Fosgate 4 channel amp for $44. The case was a bit corroded, but the innards look fine and unmolested, and it works. Not the kind of deal I come across regularly, but I was holding out for something "nicer" than average, and that sure qualified.

While I'm sure it would be a great learning experience to build an amp, in terms of the time and money cost you'd be better off trolling pawnshops and yard sales for a good used amp. Or just buying something new off eBay or some online megastore, if you can figure out which ones are worth owning.

jol50 19th April 2008 04:53 PM

I bought a 2x200/1x500rms at 4ohm insignia for <40 TMD. It was an unused return (new) and tested, even fan cooled. Just happened upon a good auction. It is huge though and unless a friend of mine wants it not sure what I will do with it. I'm sure some people here have old amps around for that. I might have one soon that is 360x1rms insignia with bad outputs, case is beat up some but fan cooled also.


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