A Workout in circuit bending

I hacked a toy keyboard which i got from buddies to really make it produce new, awesome sounds. Pictures, schematics along with a video with demo-music below.

A Workout in circuit bending the second

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This project was produced on 06/13/2018 and last updated 5 several weeks ago.


I acquired a classic, cheap (and most likely toys-R-us store brand) toy keyboard free of charge. It’s 2-tone polyphonic even though it struggles with discovering two keys pressed at the very same time, which disqualifies it as being helpful instrument. I needed to compromise inside a headphone jack, however made the decision to complete more serious modifications.

Within the situation is nearly empty, with one PCB housing all active components and a few more PCBs the buttons and keys. The seem generator is attached to the volume-slider and after that, to some LM386 that drives the only real speaker.

I didn’t buy anything with this hack and used junk which i had laying around. Look into the schematics and descriptions below for that hacks. Observe that I didn’t draw in the earth line to anything within the schematics.

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Workout in circuit bending the schematics

A simple hack: adding a change to switch between speaker and headphone jack (I didn’t possess a switching headphone jack) and leading the output in the LM386 via a 500Ohm-pot as master-volume control.

Toy-keyboards will often have a resistor somewhere that defines the pitch (tone height). It may be discovered by shorting out random resistors around the circuit board having a 10-20KOhm resistor and checking if the tone changes. My keyboard were built with a 100KOhm pitch resistor that we substituted for a 500KOhm pot. A 50K resistor in row along with a 500KOhm resistor parallel towards the pot make certain the total resistance varies between 50K and 250K after i spin the knob. I’m able to tune the laptop keyboard one octave lower and something octave up.

Both effects may be used individually or chained together, see schematics. The output in the keyboard’s signal generator goes (following the original volume slider) in to the reverb-amp after which in to the overdrive amp.

A stereo headphone amp circuit obtained from an under-a-DELL-monitor speaker is wired in a manner that the creation of one funnel adopts the input from the other. The gain-pot is backward and forward amps, the vol-pot following the second amp. I additionally altered the input-capacitors from the amps to bigger ones (1uF) to obtain more bass. Two amps consecutively create a relatively good noise, and so i added a minimal-pass filter following the second amp. The filter includes a capacitor to ground following a resistor and will get eliminate the noise.

Two loudspeakers obtained from these DELL-speaker are affixed to a wood ruler. The membranes from the loudspeakers are affixed to along side it of the metal spring, that is put under tension. The spring is wound from old post of various thickness which i’ve soldered together. One speaker vibrates the spring and yet another speaker functions as microphone to consider the vibrations.

A TDA2022-based amp from cheap multimedia loudspeakers can be used to power the reverb. One funnel drives the speaker, another funnel amplifies the input in the speaker that functions as microphone. The signal in the keyboard goes using a 50% current divider in to the amp that drives the spring. The gain-pot is really a 500Ohm pot that sits between your microphone-speaker and also the second amp, the amount-pot adjusts the output-level following the amplification. The amp includes a bad mix-signal shielding, therefore the output is definitely a combination between your signal which comes with the spring and also the original signal. Additionally, it has a tendency to distort and extremely oscillate once the containers are positioned excessive.

The recording having a musical demonstration is embedded above.