Solid State Guitar Amp Forum | DIY Guitar Amplifiers

Greetings all, hoping you can offer some advise to a newbie (really I don't know anything about amps) So I found a cute little amp in the trash and it followed me home, an old solidstate garnet stencil amp. It looks like it's based on an lm380n ic, so from what I can tell that's 2.5 watts of gut wrenching power!!

k, here's my really newbie question.... I think it must have gotten wired up to a second external speaker at some point, because coming off the board I have a white wire connecting to the white wire of a speaker in a pretty ugly fashion... but speakers have two wires, and I'm not sure where to connect the other one.  :duh I've looked at the board and don't see an obvious signs of 'wire goes here'. any really obvious suggesting off the bat I don't know about? I can post pics of specific areas/parts etc, if that would help too.

My thought is, check it's unplugged, and just start toying with locations for the other wire till it goes.  My fear is that every amp page out there has big flashing warnings of doom...  but at 2.5 watts do I really need to have any concerns? Can i just "try, plug it in, unplug, try again, repeat" till it makes some noise?

That method can very quickly lead to the sudden death of that amplifier - although I'm pretty sure it's dead already. Before even thinking about connecting the speaker properly you should measure if the output IC is still working or if there are any other serious faults (e.g. shorted power supply or something similar).

Don't start poking around unless you know what you are doing. 2.5W is not much power but the circuit can still shock you nastily. Most likely you just touch a place that will make the speaker (and/or the amplifier) say BANG and emit smoke. Keep you fingers well away from that mains wiring side: It has exposed high-voltage parts.

Finding the proper place to connect the speaker wire should be rather easy: I'm pretty sure the guys who designed the amp didn't try to reinvent the wheel and have simply followed the app note circuit of the LM380. That is, one wire from the speaker goes (through a coupling capacitor) to the output pin of the chip. The other speaker wire connects to the ground. You should of course verify this, but I'm pretty sure you'll find this configuration. Whichever the missing speaker wire is, its connection spot should be easy to find after few minutes of tracing the circuit.

However, I stress it again: If the output chip is faulty or if the amp has some other severe problems connecting the speaker will likely do a lot more harm than good. If faults such as this exist you gain nothing by connecting the speaker. So, first, make sure everything is intact and working properly, only then think about the speaker.