D06: solid state bass amplifier from JBL subwoofer

The D06 is a Bass Guitar Amplifier built on top of the solid state TDA2030 IC.

The project starts from a salvaged JBL subwoofer. The enclose was in wood, front and back cover in plastic. the woofer cone was inside. I decide to check if it works... and it of course works. The speaker was a good 8ohm 8inch subwoofer.

I can't leave the speaker inside the case, so I decide to cut the case in the middle, where the wood that holds the speaker is glued. Now that the case is cut, the speaker can see the sun.
The case was wrapped with plastic, that I have to remove cause it was ruined even before I cut the case.

Once removed I had to cut an hole on the front plate, just over the speaker. There I will install the amplifier controls.

Hole done, now it's time for the plastic holder for the controls, but that was simple.
The back of the amplifier too it's as simple as a piece of wood with some hole for the supply plug and the handle.

One problem I have to figure out was the speaker hole, it was done in such a way that the speaker has to be mounted from the outside of the case, but I don't want to see screw, so I've 3D printed an adaptor, that will also be the holder for the mosquito net I'm using to protect the speaker.

Last but not least is the case finish, I've used a texture glued with vinyl glue.

Inside the speaker I've build a new electronic.

The amplifier main supply it's a 230V to +-14V AC. Rectified to +-18V and 9V. I'm using the dual rail supply for the amplifier IC and the single rail 9v supply for the preamplifier.

The preamplifier circuit first stage is based on J.Tillman Discrete FET Guitar Preamp (http://www.till.com/articles/GuitarPreamp/). JFET used is J201.

The three tone stack can equalize Low, Middle, High frequencies and it's based on a design found in Peavy amplifiers from 80's. After the tone stack a new preamplifier stage is needed in order to mitigate the loss of the previous stage.

I've added here a simple distortion stage, enabled with a switch. It's simply a capacitor that increase the gain of this second stage and a couple of diodes to clip the signal.

The power amplifier it's base on the TDA2030 IC in a simple dual rail configuration.

One interesting thing I've added it's an optical compressor. It's based on the VTL5C7 optoisolator driven by the output of the preamplifier stage. The optoisolator drive a voltage divider that is used to reduce the output signal of the amplifier.

Now here we came to the sound.
It's pretty good, tone stack also sounds good. Volume is not so high of course, we are speaking of a 14W amplifier but it sounds good to my ear.

Hope you find this project interesting. You can find all the schematics and information below.

Notes

• read risk disclaimer
• excuse my bad english