Simple amplifier schematic for my tiny 4 Ohm speaker?

[xorophone]

Hello! I'm trying to amplify my guitar signal to drive a small 2.5" 4 Ohm speaker and since I'm just going to use it for some testing, I'd like to use the parts I already have at home (if possible). The only op-amps I've got are LM358 and TL072 and the transistors I've got are 2n3904, MPSA13 and MPF102. Is it possible to make something out of those? I tried this schematic: https://lowvoltage.wordpress.com/2011/05/21/lm358-mic-amp/ , excluding R1 and using a 10k resistor instead of 100k for R5, but I got a really distorted, extremely quiet signal. When hooking it up to another amplifier instead of the small speaker, the signal is only slightly distorted, so the only big problem is the volume.

If it isn't possible to do this with my very limited collection of components, please share your favorite amplifier schematic that should work with my speaker. I'm sorry if this is a dumb question, but I have never used one of these speakers before.

Thank you!

[GGBB]

Try the Ruby: http://www.runoffgroove.com/ruby.html.

[xorophone]

Try the Ruby: http://www.runoffgroove.com/ruby.html.

Thanks for the link! I'm guessing it's not possible to use the op-amps I've already got then. Is that right?

[GibsonGM]

Try the Ruby: http://www.runoffgroove.com/ruby.html.

Thanks for the link! I'm guessing it's not possible to use the op-amps I've already got then. Is that right?

Not really.  Those are voltage amplifiers (ok, the transistor work on current, but...)....they can't really transfer that voltage into power to drive a speaker. 
Anything you could make that MIGHT do it, would be more complex in the end than just getting an LM386 audio amp chip!

[xorophone]

Try the Ruby: http://www.runoffgroove.com/ruby.html.

Thanks for the link! I'm guessing it's not possible to use the op-amps I've already got then. Is that right?

Not really.  Those are voltage amplifiers (ok, the transistor work on current, but...)....they can't really transfer that voltage into power to drive a speaker. 
Anything you could make that MIGHT do it, would be more complex in the end than just getting an LM386 audio amp chip!

That makes sense! Thank you for the explanation. I'll have to stock up on them. They seem very useful.

[GibsonGM]

Yup, they're pretty useful....you won't get wondrous booming volume levels out of them, but for test equip., headphone amps and low-vol practice amps, they're a very simple and cheap option!

[GGBB]

Thanks for the link! I'm guessing it's not possible to use the op-amps I've already got then. Is that right?

Whoops - my bad - sorry. When I read LM358, I thought LM386 and immediately thought of the Ruby - plus you have an MPF102. Close but no cigar.

[GibsonGM]

Thanks for the link! I'm guessing it's not possible to use the op-amps I've already got then. Is that right?

Whoops - my bad - sorry. When I read LM358, I thought LM386 and immediately thought of the Ruby - plus you have an MPF102. Close but no cigar.

S'ok tho, he will want to build a Ruby after he gets his 386's, so good 'pointer'!

[slashandburn]

Another vote for the Ruby from me!

Unless the OP wants to sound like Clapton, in which case just ditch the electronics and start reciting some Enoch Powell quotes.

[anotherjim]

Actually, there have always been schemes to boost an op-amp into being a power amp. You do need a least 1 PNP transistor to got with an NPN.


Ruby is far better option.

[GibsonGM]

Ruby is far better option.

Yeah, LOL     Altho maybe a fun project later on...

[Renegadrian]

or buy a frekin' cheap tda 2822 and you're good to go!!! I frekin' love those chips!!!

[Rixen]

LM358 suffers from crossover distortion... a consequence of it's output transistors being biased almost completely off to reduce quiescent current.

[slashandburn]

or buy a frekin' cheap tda 2822 and you're good to go!!! I frekin' love those chips!!!

With the circuit from the datasheet? I tried to get one of these going on the bb a while back and couldn't get it going. Ended up playing with a tba820 instead (which was cool, but seems to need more juice).

Can you recommend a circuit for the 2822?

[Marcos - Munky]

for test equip., headphone amps and low-vol practice amps, they're a very simple and cheap option!

For simple and good sounding distortions too!