Sunday, October 11, 2009


i finished this one in august some time.. its a mini keyboard fitted into an old alarm clock i found. all i really remember about this is that i didnt like the first few schematics i came up with so i started over quite a few times. i also remember that i used an old dual audio amp for the filter and the AR generator. i think it was the 4565? yeah the 4565. it gave the AR generator some unexpected shapes but i liked it and kept it. i put a video up in September and it already has 5k hits! thanks to "matrixsynth","make", and others. thanks guys! but yeah, the keyboard is pretty awesome too. check out the schematic and the video demo for more info. heres some crappy pics i just took too.


wow, i have been putting this off for a long time so here we go.
shortly after finishing my "rainbow synth"(mid July) i started on a new keyboard. much like the rainbow synth, i added a frequency divider circuit to the main voice and a vcf with AR generator. the main objective of this project was to use the 4520 chips i've become so fond of to trigger drum sounds, and what better circuit than the notorious hing hon ek001. it all worked out great and i had this keyboard all built in under two weeks. it went surprisingly fast. that may be why i still dont completely understand the schematic. since i finished this project over two months ago, i dont exactly remember all of the details on constructing this keyboard, but i will say that it is truly my favorite. here is a demo video and some really bad pictures i just took. i'll post the schematic soon.

Saturday, July 11, 2009


i just finished this piece a couple of days ago.

the original circuit was from a rather generic toy keyboard from the nineties. all it consists of is a tone generator with i think 3 octaves including sharps. i think it also had some demo songs but i left them out. i took the signal coming from the keyboard, fed it through a comparator, ran it through a frequency divider, ran that through a filter and finally to a little headphone amp. the signal also triggers a one-shot that triggers an attack release generator that modulates the cut off frequency of the filter. sadly though, i built the one shot out of a 555 chip so it does click when the volume levels arent adjusted properly with an external amp. next time i'll use an op-amp or something. the one shot time can be adjusted with the "gate" pot. this kind of works as a sustain. the main vco can be mixed with two sub voices from the frequency divider. with voice one all the way up, it is the only one you can hear. all the way down and its between voice 2 and 3. there is also a 4 step sequencer that is tunable and can be triggered either by an LFO or the main VCO. both of which can be divided by 1, 1/2, 1/4, 1/8, and 1/16 by another frequency divider. the VCO coming to the sequencer divider is actually 1/16 of the main VCO. the one shot can also be triggered with either the LFO or the VCO.

the case was made from an old touch and tell toy that i had in my collection. i added the keys the two big blue holes with all the functions and a big battery compartment. the lettering are dry press decals with lots of clear coat(notice the glaze?). the keys are color coded. this thing was supposed to be an homage to the resistor but the blue is a little too bright.

the lfo speed can be modulated manually too. there is also a resonance pot, envelope depth pot, a fine tuning pot for higher tuning, a coarse pitch bend, and a volume pot. all in all i am pretty happy with this keyboard despite all the grief it was giving me last week. i still have two more of these VCO chips and i think they will be put to similar use.

Monday, June 15, 2009


for the last 3 or 4 weeks i have been liquidating my shop. i have accumulated way too much over the last 3 years that ive lived here. it was a daunting task, but its finally done. its a nice feeling to know exactly what you have and where it is. since my shop had finally been taken care of, my first project would be one that ive been meaning to do for a long time. about a year ago i built a red "novelty synth". its the one with the drum machine and the programmable sequencer.
this keyboard had a few problems that i wanted to fix. i really love the drum circuit in this keyboard and i wanted to do it justice. the 7 step keys that activate each step in the sequence had to be held down continuously for the steps to be triggered. also, the keys themselves were hardly flexible so you had to push down really hard. this eventually caused them to break. i replaced the keys with another set of a similar style but smaller size. i used the remaining space on the keyboard for a small panel. i replace all the momentary tactile switches with latching push switches. push once and the step is on, push again and the step is off. this will make it much easier to adjust the parameters while the sequence is playing. this was all i was going to fix when i started this project, but when i opened it up, i noticed many more things that needed attention. the sequencer was being triggered by the audio output from the lm386 amplifier chip through a chain of signal diodes. the sensitivity switch just bypassed every other one. well its been a year and i can do better than that. i ran the direct output from the drum chip through a comparator and to the sequencer. this makes for much more stable triggering. the output was ridiculous. it was basically a 5k from the lm386 to the speaker and a 5k from the tone generator to the speaker. it was too hot. instead i mixed the signals into the input of the lm386. the drum goes through a 50k to the input of the chip and the tone generator goes through a 50k to the drum 50k. i added a filter to the tone generator with cutoff. i also ran the tone generator through a frequency divider and added a 50k pot to mix between i think 1 an 1/8. it could be mixed better but i think its fine. i also built an attack release generator to modulate the filter. i didnt have enough room for a release pot so i left it closed and just used the attack function. it wasnt until i was finished with this project that i realized i probably could have both on one pot... the A generator is triggered the same way the sequencer is except the trigger goes through the other half of the frequency divider. there is a 3 position switch that will select 1, 1/2, and 1/4 steps. here is the schematic:

here are some before and after shots:




new video

Wednesday, May 13, 2009


this was supposed to be a quick project but i got really sick for a week. after thinking of scrapping the whole project, i soon began to get better and decided to finish it. i am very pleased with the finished product. that is all.

Saturday, April 11, 2009


yeah, i should really think up a better name for this design.any ideas?
first step: gather toys and parts
glitch circuit. this is not the actual toy that i used but it is similar. the glitch comes from shorting the clock speed resistor. the reset is a normally on tactile switch that disconnects the power to the circuit when pressed. the pitchbend is a 10k pot with the outer lugs connected to ground via 10k resistor and to vcc via 27k resistor.

the circuit is too large to fit into the keyboard so i consolidate the circuit and cut it down to a more reasonable size.

the drum circuit is pretty generic. i found two boxes of 12 at an outlet store and bought them all.

this circuit can be found in many different drum toys, but these are much smaller in size making them easier to work with. the pitch bend is the other 10k pot on the joysick with a 15k to ground and a 22k to vcc. the npn transistor on the left used to drive an led. i used this point to trigger the keyboard.

the keyboard is a super cheap toy! the plastic is very thin and sensitive to heat. when hotgluing everything together, i have to keep the plastic cool by blowing it with my airbrush until the glue is cooled. on the other hand, this plastic is extremely easy to cut with an exacto knife. this makes cutting the faceplate section out a breeze.

the circuit in the keyboard is unimpressive. there are no components whatsoever. the circuit loses power when you hit the keys and it sort of detunes the note maybe to get more of a piano envelope or something. there is a demo mode, but i left thos out of the interface. the 8 notes activate by connecting them to vcc. i cut the connection from the vcc to the keys and rerouted them to the drum circuit's LED output. this way the keys will only be triggered if the drums are played. also, the keyboard output is fed to the base of the drum circuit's output transistor. this gets rid of that bad "piano" envelope and the keyboard audio is modulated by the drum sounds making it sound all "8-bit".

in order to use the drum and glitch circuit, i utilize the the unused black keys. for this i have to add a small circuit board.

the 4 switches to the left will activate the drum sounds and, and the one to the right will sound the glitch circuit(carhorn). the 3 drum switches to the left play drum sounds and 3 different rhythms when the rhythm is playing. there is also a 4 position slide switch that will hold the rhythm continuously. the 4th switch to the left is the rhythm start/stop switch.

the joystick is just a run of the mill game controller joystick. i found some little plastic beads and drilled tiny holes into them to replace the big hemispherical caps that were originally on them. i also took the joysticks apart and removed the spring the holds the stick in the middle. this way the stick will stay where ever you leave it.

putting it all together is pretty easy as long as everything is working properly(and you used a 15k not a 51k resistor). after about the 5th time building one of these, it comes together pretty fast. i finished the last of 3 today. from start to finish it took about 2 hours.

since there is not a lot of room in these, i like to keep the wires as short as possible. here are some peeks into the inside of a finished one.

and the finished product

each one of these is slightly different. the one with the blue joystick's audio is mixed differently that the other two, and the one on the bottom has the line out in front of the keyboard(thats because i'm an idiot). to hear these 3 in action, watch this video.


while i was waiting for the paint to dry on my casio pt-100, i threw this together. its basically a new version of the holiday keyboard with the addition of a glitch circuit. watch the video...

Friday, April 10, 2009


i finished this one a couple weeks ago. i spent three weeks building it but i was too lazy to even go up stairs to get my camera, so this entry is pretty brief. i found a toy drum at the bins a while back(pre-toy crisis).

i've had a couple of these in the past, but this one was slightly different than the other two. actually the other two are a funny story. back in the earlier days of my bending career, i found one of these for a couple bucks at a thrift store and had big plans for incorporating it with a "yak-back" and some other stuff. i had it all planned out and ready to go, but then i fried it, or so i thought. in order to salvage the project, i shelled out $35 for a new one off ebay. unfortunately the new one wasnt the same. the record function only played back your rhythms as they were recorded. the old one snapped each hit to the step. also, by the time it had shipped to me, i had already lost interest in the project...ok, that wasnt a funny story at all... anyway, i found this one and quickly noticed that the 8 demo rhythms were not as realistic as the first two i had owned. they were pretty much just random sounds and orch. hits. the drum sounds themselves were pretty good though and the retriggerability is great too. i stripped the circuit down to the chip and decided to rehouse it into an old modem box i found.

each drum sound is triggerable via one of six LFOs. because the drum sounds were triggered with pressure sensitive peizos, the LFO frequency can go pretty high without causing any stuttering in the drum sounds with the exception of the kick drum which was triggered with a regular foot switch. for each of the 6 LFO's, there is a 3 position switch. each switch selects either manual(normal)trigger/LFO continuous trigger/LFO manual trigger. below each 3 position switch is a momentary push switch. with the LFO in manual(normal), the sounds will only trigger once per tap. in LFO manual, the momentary switch will enable the LFO only when the button is pushed. in LFO continuous, the button does nothing. to the right of the 6 drum sound buttons are 4 function switches. the two on the left control the tempo and the other two are for record and stop. to the left of the 6 slide pots that control the LFO's frequencies, there is a longer slide pot that is the pitch bend. at the top of the machine is the pitch mod and echo section. from right to left there are a joystick that controls the speed of the pitch bend LFO and the speed of the echo, a three position switch that changes the pitch bend LFO shape from tri to saw to rev. saw, a switch that turns the pitch bend LFO on and off, a switch that turns the echo on and off, and a pot for the number of echos. when the echo times pot is all the way up it feeds back just a little bit and can get out of control if you want it to. in the back there is a power on/off switch, a 1/4" line out, and an RCA mic in jack for the echo. i also left some room back there in case i want to add ports for external devices such as drum pads or a keypad to activate those cheesy demos, and possibly a volume pot for the mic input. the 4 leds in the front indicate from left to right, power on, echo on, pitch lfo on, and the last one blinks with the sounds and also lights up solid when recording. ok, i think thats about it. i kind of wished i had taken pictures of the inside but oh well.

Wednesday, March 18, 2009


i found this keyboard at the bins. it cost about $4 and was covered in filth. despite how dirty it was, the keyboard was in perfect cosmetic condition. i had one of these a long time ago, but i harvested it for parts because it was in such bad condition. from what i had remembered, the pt-100 is pretty limited. there are not a lot of functions on this keyboard. it pretty much just has 8 rhythms, 8 voices, and a very limited accompaniment section. after looking it up on tablehooters , i quickly got work trying out some of his mods. i thought it would be kind of cool to select the rhythms and voices through the keyboard and replace the slide switches with cutoff pots for two separate VCF's. i also replaced the volume switch with a volume pot.

the two VCF pots had to be modified. the 100k slide pots i have are really slow to slide. this is because there is this thick grease in there that slowed them down and makes them smoother. i wanted these pots to be quick so i opened them up and wiped out all of the grease. the fast action makes for better filter modulation in my opinion. originally i had planned on adding an AR generator to modulate the filter, but i soon found that this keyboard is very stingy with its mA's. this was a real problem when it came to finding a good source on the board for the VCF's and the DCO for the pitch bend. eventually i had to resort to replacing the weird power switch with a normal power on/off switch. the pt-100 has a dpdt switch for the power, but it could be replaced with momentary on and off switches because power is still going to the board even when its off. i thought this was kind of pointless so i wired the on switches together and turned the slide switch in to a power on/off switch. this way the VCF and DCO are sure to not drain the batteries while the power is off. i had the DCO running from a 5v point at the amplifier section, but it was starving the CPU for some reason so i threw in a 7805 and a decoupling capacitor at the 7.5v source, and it fixed the problem. the pitch bend is just under two octaves.
anyone who has ever circuit bent a casio pt-100 knows that there are some great distortions to be found when shorting the R/C mixer section. for my mods i added 3 thumb wheel pots. the top one distorts and de-syncronizes the PCM of whatever voice you are on. with the combination of the variable amount of the bend, the pitch bend, 6 voice polyphony, the VCF, and 12 voices, this keyboard can make some pretty interesting waveforms. the sound kind of remind me of some of the better bends found on a CASIO SK-1. the middle thumb wheel pot controls the gain of the chord section. this one can get pretty nuts too. when turned all the way up, it makes a wall of distortion that can then be filtered by the VCF. the third thumb wheel controls the gain of the bass chord. this makes the bass chord sound much richer and analog with the VCF. the bass is mixed with half of the drum section, so it shares the same filter and distortion mods as the bass. the chord and bass also share the same VCF, but there is a 3 position switch to change between bass/bass&chord/chord. the other half of the drum section which consists of the bass drum and toms bypasses any filtering and goes straight to the amp unless you turn it off via the little black switch in the middle of the keyboard. when the bass drums are off, the rest of the accompaniment gets a little bit louder even when the drums aren't playing. this kind of doubles as a volume limiter for the accompaniment section say if you want the lead to be a bit louder than the chord. the other 3 position switches are for selecting rhythms and voices on the keyboard. in the center position the keys will act like normal keyboard keys, but in the up or down positions, you can select 12 rhythms and 12 voices. this is an upgrade from the previous 8 rhythms and 8 voices that were selectable through the slide switches. thanks again to tablehooters for the idea.
alright, what am i forgetting? the pt-100 also includes a chord on/off switch, a rhythm stat/stop switch, tempo up/down switches, a demo button, and an added 1/4" line out. during this project i developed a greater sense of respect for people who circuit bend vintage casios and yamahas. i almost forgot how frustrating it is to not know what the hell anything is without a service manual. it will probably be a long time before i circuit bend a vintage keyboard again. this one took over two weeks to debug. i've had to reopen and re close this thing more time than i can recall. during all the debugging, the paint job acquired a few scratches and scuffs too. oh well, i guess thats just part of it.

i am planning on selling this keyboard on eventually. if you are interested, just look up circuit bent on ebay in the coming week.

Tuesday, February 24, 2009


well its been a long week. after spending about 14 hours putting all the circuitry together on friday, i took a 3 day break for my day job. it was quite the wait. i thought that if the circuits all went to plan, i would have a new keyboard by friday night, but naturally some things didnt work. in a nutshell, the filter/amplifier module was wrong(i still dont understand why), i drew up the keyboard's schematic wrong in some places(three times), and some of the lfo mods that i didnt breadboard first didnt work at all. i put in a few hours before and after work over the weekend, but it wasn't until today that i wrapped this project up. i rebuilt the amplifier/vcf module and fixed the errors i had made with the schematic. i put it all on bread board before i built the module again. it was exactly the same as the first one. i still dont understand why the first one didnt work. the second lfo that was supposed to modulate the pitch bend didnt go deep enough and raised the minimum pitch too much to have a coarse and fine pitch bend. instead i sent the square output to the vcf so now you can modulate it with either ramp or/and square. i also got rid of the feedback function and used the pot to cap the depth of the square vcf mod. there was some bad buzzing coming from this keyboard. i knew it was there the whole time. thats just the price you pay when combining toys and single supply vcf's, but when i put it back together it was much louder. i went back in and found that the filter/amp section needed to be further away from the keypad. i had to UNGLUE it! i hate ungluing! i pulled it away and wrapped it in electrical tape(not sure if that does anything) and now the sound is as faint if not more so than when i prototyped the circuit. there are still some things i have to fix though. the lfo pots that trigger the cowbell and bass drum also control the vcf modulation. the switches that turn the triggers on and off are supposed to be right next to their respective knobs, but for some reason the switch for the bass drum is next to the cowbell pot and viceversa. also the square signal that is modulating the vcf is a little too strong. you can hear an annoying click when you turn the speed up. i also need to fix the 1/4" line out. it sounded kind of squirly when i hooked it up to my computer. i'm sure its an easy fix. here are some pictures of the assembly.

the video is pretty uninformative because my camera ran out of batteries and space. i hope its audible.