Sunday, January 20, 2008

Variable (+/-) DC Supply

I started designing thing with +/- 15V mostly instead of the usual 9 volts I was working with before. I don't have a split supply so i built this simple one. It is variable from about +/- 2 to 18 volts DC.

Its based on the LM337 and 317 of course. The transformer is overkill but the point was to build it out of parts I already had.

The circuit is simple enough to perfboard. It is straight from the application notes (using a 1k pot and an 82 ohm resistor) with 1N4004 diodes protecting the regulator as suggested. The large caps off the transformer are 4700 uF.

There is no display of the output voltage. I monitor it with a multimeter.

Probably not the best supply in the world but more than enough for what I need.

Saturday, January 12, 2008

DIY Bass Repair

At some point I bought this bass online:

"you've got mail!"

Ive never seen something get quite so mangled in the mail. Anyways my money was refunded by the seller and they never filed the claim with usps so i still had the pieces of the bass. I asked some local luthiers about a cost of repair but the cheapest i could find was 80 dollars just for the neck. I contacted Dean and they were willing to sell me a new replacement neck for about the same price. so I decided i didn't have much to lose by attempting the repair myself.

I used wood glue and a bunch of clamps to glue both the neck and the body back together. I just used normal wood glue from the RONA near me and it worked perfectly fine. The hardest part was probably clamping the headstock area but in the end it turned out nicely.

this is the part of the fretboard that was originally cracked

the body "repaired"

various neck shots

Also the pickup was smashed so I replaced it with a seymour duncan "basslines" musicman pickup. It required some sort of preamp so I designed a very simple one with the option of some slight asymmetrical clipping using a RC4580 op-amp from texas instruments.

The preamp has 3 controls. A gain knob, a master volume knob and a switch which places 2 leds (used as clipping diodes) into the circuit. Below is the schematic i came up with (note that NE5532 and RC4580 are pin for pin compatible and both high performance low noise op-amps). Also the "volume" pot is Audio tapered not linear taper as stated in the schematic.

Without the preamp the output of the pickup is unbearably low.

The bass is now quite usable. I may repaint the body so that you cannot see the crack
but im not sure if I really care that much.