I'm a bit over the moon at the moment. I built a really simple LM386 amp, added a couple of <3inch full range speakers and housed it in an old watercolour paint box with a cigar box label and old computer fans protecting grills and it's magic.

Never satisfied, I added a switched output jack and ran the power through a stereo input jack so it only powers on with the lead inserted and I can play it through my home made cabinet with 2 1960's 12" Celestion Greenbacks. It roars - although there's more residual hum when I do that.

I've been using a Christmas present I gave myself - David Eric Nelson's book Junkyard Jam Band for circuits and ideas and also built his Mud'n'Sizzle preamp. The preamp seems to work really well at overdriving the 386 and I can get either a clean or deep and muddy overdrive. I just wish I could play !!

I want to be able to run the amp off a wall wart as well as battery, and I've got a socket for the 9v wallwart which seems to be switchable in that there are 3 connectors on it, one for the center +ve, and the other two which are connected then the wall wart isn't plugged in and not connected when it's not. Can I just  run the negative that the stereo input jack switches to those two terminals, so that then there's no wall wart, and the jacks in, I use battery power, and when the wall wart is connected, I use it instead? Is a little knowledge a dangerous thing, or am I onto a sane idea?



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I have to admit I did feel a bit guilty about the lack of evidence. Will try to get some pictures taken over the weekend. Sound will take longer.

Thank you my conscience!!

This diagram shows how to wire up the wall wart jack. Take note of the stereo jack on the left, which is set up so battery power is only used when the guitar plugged in, and the wall wart is unplugged.

The V+ from the wall wart jack goes to the on/off switch on your amp.

The 2.1mm jack is designed/wired so that the red+ tab receiving the battery positive lead disconnects the battery when the wall wart plug is inserted. Also, the negative lead from the battery to the 2.1mm jack, and the ring of the stereo jack act as the "battery disconnect".

I wanted to go that route on my amp build but it wouldn't work with the power jack that I had. So i just used a 2-way toggle to switch between battery and walwart.

Walwarts are convenient and last all day compared to a battery, but some walwarts can cause noise in your amp if they have an internal problem or they're cheaply made.

Lets see some pics Dennis. 

True about wall wart noise. Best choice is a "fully regulated" wart, like those used with effects pedals, etc.

a "fully regulated" wart    Is there medication for that?

Thanks Scott. That's fantastic. Now I know how to wire the 3 pole double throw stomp box switches I got from ebay - which look just like the Stewmac one and feel really solid except I got 10 from China for less than the price of one from Stewmac and it was free postage and packing and arrived in the UK in 8 days.

What software did you use for that diagram? I really like it.

Thanks again


Just search "10PCS 9-Pin Stomp Foot Switch" there's a few of them. The one's I got are those with the blue body to the switch.

What I usually do is have a quick look at what other stuff each of the vendors have. Sometimes that swings me in to direction of one of them.

This one was  the guy with the speedy delivery to the UK, but that's not where you are, is it? When I ordered them, I thought he was the only one who had them, but not any more.

OK, so here are pictures of the amp.

And the Mud'n'Sizzle preamp.

I will try to get some audio, but it won't be soon


Nice amps. I've found that these little 386 chip amp sound great through big speakers. Made a Ruby amp and put it into a Behringer practice amp using it's 6" speaker. An built my own dual chip bridged amp with a 10" speaker. The bigger speakers move more air and they sound surprisingly good.

Thanks Paul,

What I love is the amp with the preamp through the 2*12 cabinet. The overdrive/distortion I get though the small speakers of the amp itself is OK, but through the larger speakers if sounds so good. It's really hard to believe it's just a 1/4 watt driving it.

The most powerful amp I have is a 5 watt tube Fender Champ clone that was heavily modified by someone who knows what he's doing (unlike me). I haven't tried the preamp through that yet. There's just so much to play with and explore.

I've also got a couple of Chinese 18watt power amps that I want to try. They are small enough to live in the same small tin box as the preamp, and I just love the bizarre idea of having an 18watt amp that can play clean or distorted in what's essentially an Altoids tin.

The trouble with doing this stuff in the summer is that there's so much to do in the garden, and "she who must be obeyed" has no idea of the power of addiction!!

My dual chip bridged amp has loads of distortion at 1watt . I can use it as a preamp with a old Radio Shack 20watt PA amp, but I need to get some new speakers for it.

Old PA amps can be found for cheap and make great power amps with the right preamp or pedals.


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