Instrument amp powered only by the sun. This is an amplifier that was inspired by a little high school punk/jazz band that plays in the summer near a farmer's market close to home. They are always playing acoustic instruments and I thought what if they could play electric instruments at a reasonable volume without a generator. Thus the solar powered amp was conceived. It took all summer but I finally finished the guitar amp of the set. The bass amp will follow since I found a set of stereo speakers really cheap. I am trying to finish the bass amp this winter so if the group shows up next summer I can see if they'd play through them. I love the retro look of the speakers.

The amp is meant to be used outdoors in the sun so there was no need for a battery. Also even if I charged a 9VDC battery it would only last about 15-20 minutes inside anyway.

Comments as always are very welcome. This is my first time powering anything with the sun.

Step 1: What You Need

A single speaker in a cabinet:
I found these speaker boxes at a rummage sale, they cost me $4 for both. What a deal!! You should be able to use any detachable speakers for this. great if you have a dead boom box or have scrounged the parts out of one, say to use a tape head for a tape delay. (instructable coming soon as i can scrounge enough tape heads)

Amplifier circuit:
LM386 Amplifier chip
5K linear potentiometer
1M audio potentiometer
100uf capacitor
.1uf capacitor
.047uf capacitor
10 Ohm resistor

Solar panels/power section:
1N4001 diode
2 x 2200uf electrolytic capacitors
I found 9VDC at 100mA seemed to be the magic number for me. I got mine through American Science & Surplus at 4.5 VDC by 50 mA you need 4 of these.
A sheet of plexi to mount the panels to
A hollow ball joint to feed the power wires from the inside of the speaker housing

Step 2: Prepare the Speakers

Remove the back of the speaker. Mine just had screws attaching it, if yours is glued or heat sealed together you may need to get inventive.

Locate the positive and negative sides of the speaker setup.

I wanted the amp circuit to be inside the box so i cut back and stripped the end of the wire giving myself enough room to secure the circuit anywhere I wanted to inside the amp.

Unfortunately for me, the wood was so thick, the pots and jack couldn't mount to the wood itself. I happened to have a metal plate that I used for a guitar pedal that didn't work out like I wanted, so I decided to just mount the parts to that.

I mounted the plate where i wanted it and drilled out holes to know where the parts would mount. Then I used the router attachment for my rotary tool to route out the holes big enough to fit the entire pot and jack through. NOTE: you really owe it to yourself to get a rotary tool with a good set of attachments, it just makes everything so much easier.

Finally I mounted the parts to the metal plate.

Step 3: Make the Amplifier Circuit and Wire for Power

The circuit is very similar to the Make crackerbox amp, the little gem from Run Off Groove and about a million others. I don't remember what bassis I used for this or if it was the datasheet.

I just used a Radio Shack PCB for this project because i had it laying around and there were so few parts it was easy to lay out on this board to use the traces. This reduced the amount of point to point wiring and soldering that had to be done.

The solar panels push higher than 9VDC, highest I saw was 11VDC, in direct sun but since the 386 can handle higher voltage than that I didn't feel the need for a regulator.

The diode is in the circuit just to stop some of the back feed from the caps

the 2 2200uf caps are used as a battery with infinite recharge cycles. I figured why use batteries if you don't need them? This amp is intended for outside daytime use.

I added a volume knob later because it was just so loud when I ran an ipod through it. I attached the potentiometer input pin to the input signal before the .1uf cap going to IC pin 2, the wiper to the cap and the third pin to ground.

Perfboard layout done with Inkscape and the Perfboard template came from Run Off Groove Templates. Red dashed lines are for runs on the underside.

Step 4: Install the Power

Now it's time for the power.
Because I am using 4.5VDC 50mA panels and
I want to get to 9VDC 100mA I need to wire 2 sets of 2 panels in series to get 9VDC 50mA and then wire those 2 sets in parallel to get my 9VDC 100mA. These were mounted on a piece of plexi I had lying around.

For mounting I wanted to be able to swivel the panels towards the sun. I used a welding ball joint setup to make the swivel top because it was hollow and I could run the wires through it. I later discovered that the power gain for doing this did not really matter with the panels I have. I won't do it for the companion bass amp.

I just drilled a hole and routed out enough for the two ends to screw together.

Step 5: Final Assembly and Thoughts

Connect all wires to their controls and add knobs for the pots.

Screw the back on and set it in the sun

Audio sample - Setup: Karma K-Micro mic into Griffin GarageBand Cables into Griffin iMic into GarageBand and a Michael Kelly Hourglass Tribal Sun guitar plugged into the amp

It's pretty gloomy out today so the amp tends to get a little bitey. The first part of the sample is Gain 20% and Vol 80% last part is Gain 100% Vol 80%

Final Project thoughts:
The swivel, while a neat idea in theory didn't add anything to the project except cost. There is very minimal power gain gotten through tilting the panels from straight up to facing the sun.

There is no preamp on this project and while it sounds OK, it could sound better.

I am a little worried about the power if I add a compressor for the bass version that will be the companion to this amp. I may need to add more panels and that could add unsightly bulk.