A Guitar From an Old Tin Box

omar-mos

[Atdiy and Whisker], collectively known as  [The Tymkrs] have been busy honing their luthier skills. They’ve created a 10 part YouTube series about the construction of their new cigar box guitar. Instead of a cigar box though, they’ve substituted a 1920’s tin cigarette box. The Omar Cigarette company gave “Project Omar” it’s name. Like [Tymkrs] previous guitar, Omar is a three string affair. The neck was cut from Black Palm, which really shined when polished with a mixture of orange oil and beeswax. They also threw in a couple of new tricks on this build. Omar is an electric guitar, with a pickup custom wound  by [Bob Harrison]. Omar also has frets, which creates a whole new set of complications. Frets are generally installed by cutting slits in the guitar neck with a fret saw. Rather than buy a new tool, [Tymkrs] created a simple jig for their mini table saw. The jig held the guitar neck perpendicular with the saw blade. This made quick work of the many fret slits to be cut. Installed frets must also be dressed and leveled, which is a time-consuming process. 

The tin cigarette box also created a new set of problems. The thin tin proved to be a bit on the weak side when the strings were tightened down. A bit too much pressure on the box while playing would cause notes to bend, much like the tremolo or whammy bar on a standard electric guitar. [Tymkrs] were able to counteract this by adding bracing inside, and a couple of black palm braces to the back of the box.

Hum was also a problem. When [Tymkrs] first plugged in, they found they had more 60Hz mains hum than signal from their strings. Omar uses a classic single coil guitar pickup. Single coils will pick up noise from any magnetic field, including the field created by the studio electrical system. A humbucking pickup uses two coils to counteract this effect. Humbuckers also have a slightly different tone than single coils. [Tymkrs] wanted to stick with their single coil tone, so they counteracted the hum by raising the pickup closer to the strings. Higher pickups receive more signal from the strings, so this is basically a free signal to noise ratio improvement. They also grounded the entire tin box, along with Omar’s metal tail stock. The final build sounds great, as evidenced by the jam session toward the end of Video 10.

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Circuit Bent Toy Keyboard is MIDI Controlled

tymkrsKeyboard
The [Tymkrs] crew has come up with a pretty neat circuit bent toy keyboard hack. It’s been a while since we’ve seen a good circuit bending hack. This project started as a way to demo the [Tymkrs] “MIDI In Me” kit. A cheap toy keyboard was sacrificed for its sound generator board. Like many cheap mass-produced toys, this board is based upon a COB (chip on board) package. The silicon die of the main ASIC is placed directly on the PCB and bonded out to pads. A round epoxy blob keeps everything protected.

The [Tymkrs] found a number of the chip’s pads were unused in their keyboard. The inputs appeared to trigger drums, possibly for use in a different toy. These inputs, coupled with the ‘demo song’ buttons turned out to be the basis of this hack. MIDI input is sent to a Parallax Propeller. The prop runs a program that will set its I/O pins based upon MIDI Note On/Off commands. The I/O pins then drive transistors which inject signals into the button inputs of the keyboard.

The [Tymkrs] even went so far as to use a voltage divider on the main clock circuit of the keyboard. Changing the main clock causes a sort of pitch bend effect often heard with circuit bent toys. As with the buttons, a MIDI signal commands the prop to enable or disable oscillator signal injection. A potentiometer is used to tweak the oscillator frequency.

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