50w or more solid state amp using lunchbox as case and 5" speaker

[milanb]

I only want a volume knob, nothing else, can I just run some transistors in a row and put some high ohm pot at the end for volume? The idea was to make a portable, loud enough to gig amp with a pedalboard for all EQ, distortion and effects.

[milanb]

Just realized I posted this in the wrong section, sorry, someone please move this  xP

[J M Fahey]

Don't worry, everybody will see it here.
The "bunch of transistors" you mention does exist and is called a "chipamp".
There are some 50W, LM3886 based kits available (search this very Forum and elsewhere).
That means you'll get a PC board, all necessary parts, maybe they can also sell you the power supply, including the power transformer.
You'll make the cabinet, some kind of chassis, mount the chipamp and speaker there and merrily play your bass afterwards.
If you have never built anything before, start by building a Cricket (LM386 based) 9V battery powered, 1W chipamp, just to get your feet wet.
It's fun too !!
Many around here have done so, there's even an annual contest , where the prize is usually ..... a 50W chipamp !!! Go figure!!!
Search around, read many posts, you'll find them interesting and useful.
Welcome to SS land.

[teemuk]

I'd also like to make a point that in this kind of system it is extremely rare and even more inconvenient to try to fit the pot "at the end for volume".

Done this way the plain Ohm's law tells us that a "high ohm pot" will ensure that the amplifier is pretty much developing only milliwatts of output power; or alternatively, a "low ohm pot" will waste about all the power and has to be some huge industrial load box to dissipate that power safely.

Secondly, "transistors in a row" do not qualify as a power amp. You need plenty of more than that. In fact, transistors in a row is not even indicative of anything design-wise.

Judging by your post, you have A LOT to learn and until the basics are clear to you I'd dearly avoid a project such as building a "50W or more" amp. In such project there is plenty of stuff you need to know and nail right, otherwise the end result with your skill level won't be what you're looking for - it might even be catastrophical and downright dangerous.

J.M. Fahey's suggestion to start with a low-power, battery-powered circuit is right on point. Start safely with a simple project and it will teach a thing or two of what makes an amp. I really wouldn't hop to building a high-power, mains-powered circuit before having a slightest clue of what is involved. A failing 1/2W battery-powered project won't cost an arm and leg if it goes out in smoke, it can't shock you lethally and most likely won't introduce explosions or flashy arcs when things go wrong. You can also build one with "half-assed" skills and it will work decently, instead of being a high-power oscillator that kills your $$$ speaker and climaxes to a puff of smoke and failed $$$ parts. All that, on the other hand, has a very good probability when you try to assemble 50W amp without knowing what you are doing and why things must be built certain way.

[milanb]

Thanks for the replies.

Yea, I realize I have to learn a bunch, I am gonna do a battery powered amp first with a speaker I found on an old walkie talkie. But I don't see how theres a risk of getting shocked if I always work on the amp unplugged. Correct me if I'm wrong though.

My experience is basically 2 fuzz pedals that don't work quite right, but well enough that I don't care.

[teemuk]

Yes, without following proper safety precautions you can indeed get shocked when working on an unplugged amp. In some cases capacitors can retain charge for a long time. 9VDC - 12VDC is much less hazardous than 60VDC - 100VDC potentials, common to higher power amps. Shorting capacitor bank storing 60VDC charge does a nice arc, which has a serious potential of destroying fragile components or making inconvenient burn scars.

Not to mention, there's always a chance that some things are wired wrongly, which can have very unpleasant effects when you eventually plug the amp. With that in mind, plugging to low-voltage battery is a heck lot safer than plugging to mains, which is what higher power amps pretty much require.

Don't get me wrong, all this stuff is not hard to learn but what I'm merely implying is that I seriously advice you not to get involved to such projects until you can handle at least the basics and have a clear idea of stuff involved in working with moderately high voltages, very high currents and mains-powered circuits, not to mention delicate systems such as a high-powered amp circuits.