I've got a nice pair of 4" speakers salvaged from a junked keyboard that I'd like to make into a little device to plug iPods into. I've never made an audio amp before. Any favorite circuits?
Just make sure that whatever IC you pick can handle a 2.5-ohm load. That's pretty low impedance.
Yeah, that confuses me. I'm assuming they're 2.5 ohm because the speakers say "2.5 Ω 5 W " on the back, but that does sound surprisingly low. The 7052 chip that people on that other thread recommended has 8 ohm loads in the sample circuits. I know exactly zero about how this works.
Ideally, for maximum power transfer you'd want the amplifier's output impedance to match the speaker's impedance. Realistically, the impedance of the speaker will change in operation due to mechanical issues.
So, you shoot for the "nominal" impedance - in this case, 2.5 Ohms.
That said, if you have an amp designed for an 8 Ohm load, it doesn't mean it won't work with a 2.5 Ohm load. What it does mean is that more output current can flow than for which the amp is designed resulting in distortion and possibly overheating if you have the thing cranked up.
If you're only dealing with a couple watts, and are not intending the outcome to be "high fidelity", then give it a shot and let your ears (and finger for temperature testing) decide.
and we happened to use the LM2N3904 and MPF102 JFet transistors. Those gave us the cleanest sounds, but we've done an audio amp with a LM386 before as well: http://www.tymkrs.com/forum/viewtopic.php?id=17
For examples of how they sound:
MPF102 High Impedance:
Comments
i think this may help
-Phil
Yeah, that confuses me. I'm assuming they're 2.5 ohm because the speakers say "2.5 Ω 5 W " on the back, but that does sound surprisingly low. The 7052 chip that people on that other thread recommended has 8 ohm loads in the sample circuits. I know exactly zero about how this works.
So, you shoot for the "nominal" impedance - in this case, 2.5 Ohms.
That said, if you have an amp designed for an 8 Ohm load, it doesn't mean it won't work with a 2.5 Ohm load. What it does mean is that more output current can flow than for which the amp is designed resulting in distortion and possibly overheating if you have the thing cranked up.
If you're only dealing with a couple watts, and are not intending the outcome to be "high fidelity", then give it a shot and let your ears (and finger for temperature testing) decide.
Struck the above 'cause evidently I'm incorrect.
Back to the cave...
http://www.tymkrs.com/forum/viewtopic.php?id=21
http://www.tymkrs.com/forum/viewtopic.php?id=24
http://www.tymkrs.com/forum/viewtopic.php?id=20
and we happened to use the LM2N3904 and MPF102 JFet transistors. Those gave us the cleanest sounds, but we've done an audio amp with a LM386 before as well: http://www.tymkrs.com/forum/viewtopic.php?id=17
For examples of how they sound:
MPF102 High Impedance:
LM2N3904 High Impedance:
LM2N3904 Low Impedance:
Let us know if you have any questions
OK - please elaborate?
http://www.soundandvisionmag.com/blog/2011/11/14/output-impedance-show-and-tell
OK - thank you, that was iinteresting reading.
The first link explains why moden-day, integrated amps are low impedance. I was speaking from a tube-based amp postion.
The second link reiterates my original post, albeit for headphone applications.