Super Low Watt Guitar Amp

[tonyharker]

It depends which 386 you are using. LM386N-1 LM386M-1 and LM396MM-1 max voltage is 12, LM386N-4 max voltage is 18v

[Mark Hammer]

I think the JRC386 is also rated for a little higher output wattage.  I don't know if the various suffix 386s are different internally, or whether they simply represent different batches that can tolerate passing different amounts of current, similar to the way that an A,B, or C designation on a transistor indicates different hfe ranges of a same device.

[Vivek]

Test for maximum tolerable current could be destructive,

But hfe test is not destructive

[kevinng]

This is the smallest size I have seen for "full range" speakers that could be expected to reproduce the entire audio spectrum.  A guitar only goes down to 82 Hz so you do not need audiophile or "hi-fi" components but you want something that makes your guitar sound like it would in a system you would use on stage.

Yes. But you definitely will not be needing a "full-range" speaker for guitar amp. Yes, the loudspeaker doesn't need to produce bass frequencies below 80 Hz BUT generally we also don't want it to produce higher frequencies above 5 kHz either. Especially distorted tones will sound nasty and fizzy if the speaker reproduces all the high order harmonics. Clean acoustic guitar can sound tolerable.

In my experience the issue with little loudspeakers is not only their limited low frequency response (that makes them sound thin and boxy) but also their broader response towards higher frequencies (that makes them sound shrill and fizzy). The latter is heightened by their broader dispersion of HF: When big speakers may sound ear-piercing in their on axis "beam" the little speakers sound ear-piercing even off axis.
On top of that, some of the little speakers (especially those found from cheap car stereos or ghettoblasters) have dust cap designs that artificially try to to increase the high end response. They are probably the most awful devices ever for reproducing a distorted guitar tone.

Thanks a lot. I plan to filter out some lows to save energy at the advice of forum-mates in another topic since the speaker might not be able to produce them. I understand that putting a cap directly to the speaker will filter out the lows. Do I put a line to ground with a cap to filter out the highs at the same point?

[anotherjim]

You can get more out of a small speaker by using the boundary effect.
Sound from a source wants to radiate globally. Placing the source against a boundary causes the rearward waves reaching that surface to reflect back to add to the waves going away from the boundary. The distance from the source to the boundary is critical - it has to be as short as possible otherwise there will be phase differences at different frequencies (due to having different wavelengths) that can cause either cancellation or addition.  The reflected sound is treated as from a "Phantom Speaker" that is located the same distance behind the boundary as the real speaker is in front of it. If the real speaker is 1 metre from the boundary, the reflection is coming from 2 metres away. The only sound that escapes the effect is those high frequencies whose wavelengths are too short to wrap around behind and can only radiate forward on-axis.
If the speaker is placed on the floor in the corner of a room, it gets x3 boundary boosts - the floor and 2 walls and x3 phantom speakers.

[Paul Marossy]

What's wrong with building a 1W Amp and driving it with less signal with a volume control ?

That's my approach. Works for me...

[Paul Marossy]

You can get more out of a small speaker by using the the boundary effect.

Good point. When I made my Little Gem MkII years ago I built it as a little combo amp with a sealed speaker cabinet. I used (2) 4" speakers I picked up at a thrift store. It didn't sound too bad, but it sounded better when I ported the cabinet later with a small hole appropriate for the volume of the box. Actually has a pretty decent bass response. I also added a tone control which further helps to shape the "tone". I'd say it sounds similar to a Lab Series L5 at low volume, with no reverb.