BASIC Amp

[Somicide]

Well, after looking at schematics for nearly a whopping year now, I want to know:  If I wanted to make a SINGLE transistor amp (not feasible) using say, a 2n5089, how would that look?  I mean, I understand basicly whats going on with my stuff, but, i've never seen a schem of something like this.  I want to use this new bit of knowledge to try and design my own stuff.

[RDV]

Like this:
http://www.geocities.com/tpe123/folkurban/fuzz/snippets.html
Scroll down to Ultra Class A Superdrive Power Amp.
I've got one. It's fun with a fuzz, just not real loud.
Get the transformer at RS(I did).

RDV

[brett]

Can I restate that to see if you're saying what I *think* you want.

A single transistor amp.  To drive an 8 ohm speaker?  Or as a pre-amp?  If it's for 8 ohms, that's a max of about 0.1W if you get say 20% efficiency out of it.

Are you sure you don't want two transistors?  A 2N5089 (for voltage gain) and a BD139 (for current gain)?

Any more clues?

[Somicide]

Well theoretically, yes.
see brett, I just want to see what the schematic would look like for a very minimal amp, ie, barebones.  So the 2 transistor would probably be better, yes.  I'm trying to further my education here, and have wondered this since the physics course in electronics.  Thanks for the responses!  Oh RDV, that dealie looks interesting!

[smoguzbenjamin]

So what you're asking is "how do I set up a transistor as an amplifier" regardless of gain/loudness? More like the principle than the application, in that direction?

Well.. uhm... think of it this way: you're passing current through Collector and Emitter, and you can vary that current by applying current to the base. In NPN transistors high base current means either hgih or low C-E current, not sure. In PNP trannies it's the other way around.

[RDV]

Oh RDV, that dealie looks interesting!

Try a bunch of Tim's circuits. They're an education all on their own. The Ugly face is quite popular. Check the samples too.

RDV

[Somicide]

ben, thats it!  exactly.  I just am not so good with phrasing whats in my head (ask my girlfriend...)  but yea, thats what i meant.

[smoguzbenjamin]

No problem, I have that kind of blackout all the time

Well, as I stated in my previous post, try and think of what the transistor actually does, and experiment. I don't have time to write down all I know, my girlfriend just got out of the bath and will be nagging for me to come downstairs any minute Besides I think R.G. or someone like that will be far more qualified to answer your question. But think of it as a canal in which you can slow down or speed up the water flow by adding or subtracting flow from a sidestream.

[Somicide]

I see, but the 'sidestream' in question would be the E or C of the Transistor, yes?  and I could adjust current or voltage with a resistor, if i'm not mistaken.  Am I getting close?

[smoguzbenjamin]

The sidestream refers to the base, while the main canal is the C-E junction. When a signal is applied to the base of the tranny, the big flow changes with it, but in a bigger fashion. Filter the DC out of this and you've got a bigger signal Remember that bipolar (normal) transistors are current-controlled, so the voltage doesn't matter that much, I don't worry about it anyway and I've had a problem only once

Creativity always helps so when something's not working on your breadboard; take a look and think of what's happening, then change stuff accordingly. You can also guess but it takes a little longer. :mrgreen: