I just recorded a quick video of my Kidtunes Keyboard project and wanted to share it with you. This project has been a lot of fun and I recommend it highly. I can’t wait to get an output jack added on so I can run it through an amplifier and see what it’s really capable of.
I’ve been working on a new toy and I wanted to give a quick update on my progress with it. Today I’ve been working on a Kidtunes Electronic Keyboard which I picked up at Value Village. The Kidtunes electric keyboard is made by a Chinese company called Scientific Toys and though I wasn’t able to find an exact year I would assume based on the circuit that it came out in the early 2000s. The keyboard itself is a little odd as it has two octaves (from G to F) but is missing the second F sharp. I guess they assumed kids wouldn’t notice. The toy is monophonic (only one note can be played at a time) but has two distinct voices. There is a sustained organ voice as well as a shorter cleaner piano sound. The Kidtunes keyboard also features a demo mode and a low-high volume control.
One thing struck me as odd on the circuit board of this toy. It looks like, though they have used a black blob IC, they manufactured it separately and then added it onto the board. This has left easy access to the pins of the IC where it was connected to the main board. Though the majority of these solder points are triggers for the keys it still allows a level of access which is rare with modern toys. Additionally all of the components outside the main IC are though hole which allows for fairly easy bending and modification.
The first thing I added to this keyboard was a simple pitch bend. To do this I located the pitch resistor and removed it. On this toy the pitch resistor was located immediately below the IC. The resistor I removed was 220K ohm so I replaced it with a 100K ohm pot and a 150K ohm resistor in series. While playing with the pitch bend I also noticed I could illicit some very interesting glitches by attaching one of the legs of the pitch resistor through a capacitor to the base of a transistor on the far left of the board. I wired this up through a switch and moved on to see what else was available.
The next two bends I found were fairly straight forward point to point connections which I wired through switches. The first (red wires) involved connecting one of the resistors on the board to the trace running across the emitter of the transistor I mentioned in the pitch bend. This bend seems to impact the sustain of the Kidtunes keyboard. By connecting these points all sustain is removed so that the keyboard sounds like an xylophone. The second (yellow wires) connects one of the trigger points to a resistor on the board. When the keyboard is in organ mode this has the effect of holding any note played indefinitely when the switch is turned. Further in demo mode this will cause a note to play repeatedly. This second functionality will be extremely helpful while searching for further bends as I will no longer have to keep pressing keys.
That’s as far as I’ve gotten with this one so far. If I am able to find more I will be sure to provide an update. Also I should have a video of this toy online within the next day or so.
While browsing some circuit bending sites some time ago I found an excellent tutorial over at Circuit-Bent.net for adding a patch bay to a retro Yamaha Keyboard. The tutorial dealt with the PSS-170, 270, 140 and SHS-10 but not having any of these models on hand I wanted to see if I could apply the same technique to the a PSR-6 I recently scooped up on the cheap at a local pawn shop. Finally this past week after the arrival of a big bag of banana plugs from E-bay I decided to give it a try.
– I also came across a very helpful forum post on Electro Music from another circuit bender (user name Dnny) who converted this mod for a PSR-6, It is definitely worth a read if you are attempting this bend.
To understand this bend you have to understand a bit about the inner workings of these keyboards. The PSR-6 (and many others of the era) operates using two primary IC chips. The first of these is the Yamaha XE323B0 CPU chip. This chip is easily identifiable as it will usually be the largest chip on the board and has a huge number of pins (I believe around 60). This CPU chip is the brain of the keyboard. Beside the CPU there is a smaller 18 pin FM synthesizer chip (the YM2413) which is responsible for actually creating the audio signals you hear out of the keyboard.
If you study the back (trace) side of the circuit board you will see there are 8 traces which travel directly from the CPU to the FM synthesizer chip. These 8 traces carry instructions from the CPU to the synthesizer chip and tell it when to make noises, and what noises to create. Further each separate pin carries information on a different aspect of the sound. These 8 traces are what I will be hijacking with this bend.
The first step I took was to cut each of the traces running between the CPU and the FM Synthesizer chip of the PSR-6. This will interrupt the normal flow of data. These circuit boards are very ruggedly made (as opposed to some more modern boards) so you may need to cut across them several times with an Exacto knife. Use a multimeter to confirm there is no connection between the two sides once the traces are cut.
Next up comes the really fiddly part. I soldered lengths of wires to each pin on the CPU and each pin on the FM synthesizer. I used yellow wire on the CPU and blue for the synthesizer so that they were easily identifiable. It is very important at this point to keep the pairs of corresponding wires together. I used pieces of painters tape to temporarily attach the pairs of yellow and blue wires together and numbered them in order from 1 to 8.
Once I had drilled and mounted the components for the patch bay I was ready for wiring. I soldered the blue and yellow wires to the middle and lower lugs of a row of switches. I then ran wire from these switches to two rows of banana jacks. All of the CPU connections I ran to the top row of jacks and all the synthesizer connections to the bottom row of jacks.
From here I closed up the keyboard and powered it up. To my delight it worked great. When the switches are all in the up position the data lines are connected and the keyboard works the same as it did without any modification. However when you flip the switches or connect any of the red jacks to any of the black jacks… things get weird.
When you are getting started with this patch bay it can be a little intimidating. It will crash and it will spew loud garbled noise, don’t be discouraged. You will also find strange, new and truly bizarre noises you never knew the PSR-6 had in it. A good way to get your feet wet is to choose any instrument on the keyboard. flip down the second switch and then change to a different instrument. The turned switch will stop some of the information regarding the new instrument from reaching the FM synthesizer and you will be left with a strange hybrid of the two voices.
The more I play with this keyboard the more fun I have. Slowly I’m beginning to understand what each data line controls and I’ve been able to create more and more interesting patches. One surprising thing I’ve found is not all but many of the patches are repeatable allowing you a level of control over the noise I didn’t expect. This makes the device quite viable for live performance.
Now that I’ve gotten my feet wet with this bend I’m incredibly interested in taking it a step further. I’ve seen other circuit benders set up LED’s associated with each data line allowing you to see the data traveling through each connection. This seems like it would be extremely helpful in developing your understanding of what each connection controls. I’m also going to do some tests injecting a square wave oscillation into the data points to see what kind of results this elicits. Finally I’d also be interested to try running the data through an inverter or other logic gates. If I have success with these tests I will create a second post detailing what I’ve found.
While completing my first set of mods on my Yamaha PSS-30 I noticed that the internal amplifier driving the mini keyboard was a 386D amplifier chip. This chip has an identical pin out and seemingly identical function to the popular LM386 which gave me some ideas for possible bends I could try. If I was able to apply some common modifications or adjustments which work with the LM386 in amplifier applications like the LM386 guitar amp I may be able to further expand the versatility of the instrument.
The first modification deals with the gain of the amplifier. If you’ve worked with LM386s in the past you may already know that the gain of the amplifier is set using pins 1 and 8 of the chip. Essentially by placing a resistor (usually 1 ohm – 10K ohm) and a capacitor (typically 10 uf) between these two pins you can set the gain. The higher the resistance of the resistor, the lower the gain. Upon inspection of the circuit I could see this is exactly how this 386D chip was set up. Pin 1 is connected through a 10 uf capacitor, which connects to a 1.1K ohm resistor (immediately to the left of the chip) And then to pin 8 of the chip. In order to replace this system with a variable gain control I removed the 1.1K resistor and replaced it with a 5K ohm potentiometer. By reducing the resistance you can get a slightly crunchier and more distorted sound, and by raising the resistance you can get a cleaner more polished sound. Note the gain level will influence the volume of the output so you will need to compensate for this either at the volume control added in Part 1 or at your mixer/amplifier.
While I was under the circuit board attaching the leads for the gain pot I also connected a few more wires for use with my second mod. I connected the first wire (yellow) to pin 1 (gain control pin) and two blue wires to pin 5 (output). These will be used for the second modification I had in mind. This is a slightly less used LM386 circuit modification but still one which is fairly well documented. By sending a signal from the output pin (5) through a small capacitor and resistor to the gain control pin (1) you can create a bass boost effect. To accomplish this I attached the first blue wire to a switch on my panel. I then ran it through a 0.1 uf capacitor and a 10K ohm resistor. I attached the yellow wire to the other side of the resistor completing the circuit. Now by flipping the switch you connect the bass boost circuit.
Though the bass boost is audible I am not overwhelmingly impressed with it. It is far from the thumping low end I was hoping for. This may be a limitation of the device itself but I feel like further experimentation is needed. I will be going back in to experiment with some other cap/resistor values and other circuit options to see if I can get a better effect. I will report back here if I find better results.
The second blue wire I connected through a resistor to an LED and tucked it behind the circuit board. Because I used a transparent panel this creates a cool back lit effect and since it is powered from the amplifier output it pulses along with whatever is being played on the keyboard.
That about raps it up for the PSS-30 for the time being. I really love the small form factor of this device and would love for it to make it’s way into my regular instrument lineup. In spite of this circuit being a bit limited as far as bend points and options, I still had a lot of fun and got to try out some interesting new things on the circuit. I’m going to keep this device in the back of my mind as I work on other projects and hopefully I can return to it down the road with some new ideas to further mangle it’s square wave outputs. That’s all for tonight but thanks for reading and happy soldering!
The thrift store gods smiled on me again this past week. During one of my usual trip to my local charity shop I found a Yamaha PSS-30 marked at 5 dollars. Not only was this tiny keyboard still in the box, it looked like it had barely been played since it’s manufacture back in 1987. I happily scooped it up and brought it home to investigate.
Now after looking inside this keyboard and spending some time online I found unfortunately the PSS-30 may not be the holy grail I had hoped it would be. Many of the Yamaha Keyboards of this era (along with many of the infamous Casio SA keyboards) contain two primary chips. The first is a synthesizer chip (usually an FM synthesizer) and second a CPU which monitors the inputs and digitally controls the synthesizer. This allowed some extremely interesting bending by cutting or crossing the data lines to modify the signal reaching the synthesizer chip.
Unfortunately the PSS-30 in an effort to cut costs and save space is built to run on only one IC chip. This means the single YM2410 chip monitors the inputs and generates the audio signal internally leaving us unable to access the data flow. That being said I still wanted to have some fun with this very cool vintage keyboard.
I wanted to start this project as I do most of my builds, By adding a line out. It was also fairly important to me to add an analog volume pot along the line out. The reason for this was simple, This keyboard uses a basic digital volume control which is extremely loud and distorted on the maximum setting. Unfortunately whenever the device is powered off and back on the digital register for the volume setting resets and it returns to this obnoxiously loud setting. With the addition of an analog volume pot I can set the volume where I want it and leave it there without having to worry about it resetting.
To add the line out I cut the speaker lines. I wired the positive speaker line to the top pin of a 100K potentiometer and the ground to the bottom pin. From here I connected the tip tab of a 1/4 inch jack to the middle pin of the pot and the ground from the jack to the bottom pin. This functions as a simple voltage divider and allows you to adjust the amount of the signal which reaches the jack.
Since the keyboard itself is so small, In order to create room for the controls I had to remove the speaker altogether. Initially I attempted to drill holes for my components into the slatted plastic speaker cover but things quickly got messy and it became obvious that wasn’t going to work. Instead I used my trusty rotary tool to cut out a rectangle where the speaker had been and covered it with a square of plastic I cut from an old DVD case. This will be my control panel for the time being. Once I have the device working how I’d like it I will likely replace this plastic panel with acrylic or steel to give it a more professional look.
Additionally as something of an experiment I built a small two knob tone control circuit into the line out. This is a circuit I picked up from an excellent article over at Nuts and Volts (Fig 12). The circuit essentially functions as an adjustable low pass and high pass filter. Since the circuit itself is passive I did experience some attenuation but not enough to become an issue. Since this keyboard uses only square wave audio the capacity of these filters is somewhat limited. You can make some adjustment to the sound but if you limit either end too far the sound will become very flat and tin-y.
I also noticed that the PSS-30 uses an LM386 as an amplifier meaning that I can try some common LM386 amplifier mods on the circuit as well. I will be posting again shortly to let you know how they went but in the interim thanks for your time and happy soldering!
After getting my feet wet with my Danelectro T-Bone Distortion Pedal I wanted to keep up the momentum. My next victim would be my Danelectro BLT Slap Echo mini pedal. Like the T-bone the Danelectro BLT Slap Echo pedal is an extremely low cost and relatively simple pedal which makes it a perfect candidate for circuit bending.
The BLT Slap Echo consists of two circuit boards. The lower board (brown) is dedicated to driving the inputs and operating the foot switch. This lower board is identical to the one found on the T-Bone Pedal. Because it is not involved in effects creation I will be ignoring it while circuit bending.
The upper green board is where the magic happens. The upper board is driven by a PT2399S Digital Delay Analog Echo chip which is where I found the majority of the bend points. The second smaller IC is a simple TL072 op-amp which I largely ignored. One thing you will notice about these Danelectro mini pedals which makes them extremely pleasant to work with is that there are unused solder points throughout the circuit which can be easily connected to to create bends.
After probing the circuit board and some experimentation I settled on the points shown above. I soldered leads to each of these points using different colors to distinguish the different bends. Once the soldering was completed I also applied some glue to each solder point to hold the wires in place. This glue will keep the wires from tearing off the (admittedly weakly constructed) solder board and also prevent them moving around and touching other points.
From here I ran the wires out through the hole in the pedal case I had drilled and through the lid of the container I would use to house the switches. This container will likely be a temporary housing as it lacks the durability you need in a pedal. Down the road when I have the materials available I will create a post where I rehouse both the T-Bone pedal and the BLT Slap Echo into their own custom pedal boxes.
The first bend here is made by connecting the green and blue wires. This produces something of an infinite echo. rather than the echo decaying over time as it normally would it will continue until the bend is disconnected.
Next I used an on – off – on switch to connect the blue wire to either of the yellow wires. This bend creates a crunchy distorted echo effect. One of the yellow wires will give you a more treble base distortion, and the other will give you a more bass distortion. I have not tried it yet but I would be interested to know what happens if you wire the blue to the wiper on a potentiometer with the yellow on either side. You may be able to tune the pitch of the distortion this way. I expect I will attempt this when I rehouse the pedal.
Third I connected the red wires together. This is probably my favorite bend on this pedal. It is more subtly then some of the others but creates a really satisfying slow reverb effect that I really love.
The final bend was to connect the black and green wires. during testing this created a nice white noise effect behind the pedal output. Unfortunately though now that I have wired everything up it does not appear to be working. I’m not sure if I mixed up the solder points or if something came disconnected while I was closing up the circuit, but I will do some troubleshooting and provide an update if I can get it working again.
From there all that’s left is to box everything back up and get playing with it. I will be creating a video within the next few days to demonstrate the bends on both my T-Bone Distortion Pedal and this BLT Slap Echo pedal. Overall I’ve found these Danelectro pedals to be really rewarding and great way to initiate myself into the world of guitar pedal bending. Hope you all enjoyed and have a great week.
It’s been a few weeks since my desktop amplifier kicked the bucket and being a bit shy on money at the moment I decided to take a slightly more creative approach to replacing it. What I had on hand was an admittedly oversized Sanyo Boombox from the 90s. Stereos and boomboxes of this vintage are fairly plentiful (and cheap) these days as people are more and more abandoning them for sleeker, smaller and newer models. And this plentiful availability makes them fantastic for experimentation. Today I’ll be adding an input for using it as an amplifier for use with a guitar or other sound devices.
The front panel of these stereos can be removed by taking out a number of screws from the back. You will usually need a fairly long screwdriver as many of the screws are very deep set. One nice thing which Sanyo does (as well as a number of other manufacturers) is mark the screws for the front panel with small arrows to let you know which must be removed.
As I began to pull this guy apart I began getting excited. Internally I found a number of complex boards built entirely of through hole circuitry (perfect for modding and circuit bending). The above image is the amplifier board, The chip in center is the main amplifier chip (A 222003 chip). Also there were a number of very interesting mechanical features. Today my stated goal is simply to add an input jack but I will be returning to this board to see what else I can force from it.
In order to add the input jack there are three wires you will need to solder onto the board. The first is a ground wire which can be connected to any ground point in the stereo. I wired mine from pin 5 (ground) of the 222003 amplifier chip. Next up you will need to locate the left and right signal inputs. I initially planned on sending these into the amplifier chip as well but after some testing I found I got a much better signal sending them into the volume control board as shown above. To locate these points I built a small 555 buzzer circuit on my breadboard. I attached the ground from the stereo and touched the output to various points on the circuit.
NOTE : I strongly recommend powering the stereo using batteries when you are feeling around for these points. If you choose to do so with the stereo plugged into the wall I take no responsibility. Mains voltage can kill. Be aware of the location of the transformer and stay far away from it.
Once I had located the speaker left and right inputs I attached lengths of wire to them. I connected these two wires to either side of a 100K (If you need to get more volume try a 50K or 10K pot) pot which will allow you to pan the signal between the two speakers. If you are not interested in having pan you could easily replace this pot with two static resistors. Then I connected the center pin to the tip of a 1/4 inch jack. In retrospect you may want to add resistors on either side of the pot to buffer the signal as it gets quite loud if you go to either end of the pot. I expect about 10K would work perfectly. If you are interested in adding a separate volume control or switch just add them in line in between the pot and jack.
From here you can drill and mount the pot and jack. Put the stereo back together and you are all set. You’ve just converted your tired old Boombox into a perfectly functional amplifier. I’ve had great results using this stereo with my guitar, circuit bent devices and my synth modules. The sound is actually quite clean. The stereo also has a 4 band equalizer and a bass booster which give you a fair bit of control of the sound.
Hope you guys enjoy this project, have a great weekend!
The latest toy to come across my work bench was a Little Tykes Pop Tunes Keyboard. This toy stood out to me at the thrift store for a few reasons. First and most obvious is the awesome LED ring located between the power knob and speakers. Further it had some weight to it and appeared to be solidly constructed which gave me some hope for what may be found inside. Finally the song samples made it stand out from a lot of other toy keyboards I had played with. Rather than ear shattering renditions of “Old MacDonald” or “Mary Had a Little Lamb” the pop tunes keyboard featured recognizable (if a bit outdated) popular music (“ABC” by the Jackson 5 for example).
Upon opening it up I found a fairly simple SMD circuit board with a black blob IC. There were quite a few transistors and resistors though a large quantity of them seemed to be associated with the LED functionality. Still there was plenty to play with so I set to it.
The first step (as with all my toys) was to set up a kill switch and line out for the toy. For the kill switch I simply cut the battery positive wire and placed a switch on it. As far as the line out I cut the speaker positive wire and ran it through a toggle on – on switch. The other side of the on – on switch I ran through a 1K resistor and into the tip of a 1/4 inch jack. I then placed a 10K ohm resistor between the tip and ground and ran a wire from the ground back to the ground point on the speaker. I recommend experimenting with different resistor values to get the volume level you require as it can vary from device to device and also depending on where you are sending the signal.
Next up I set up a pitch bend on my Pop Tunes Keyboard. First off a big thank you to alienmeatsack who made a great post about this toy on Electro-Music.com and led me to this bend. This pitch bend is slightly different than the ones I’ve used in the past as it makes use of three points on the board rather than replacing a single resistor. For this bend I used R1 as the pitch base and soldered it to the center pin of a potentiometer. I then connected the outer pins of the potenetiometer to R07 and R011 which shift the pitch up and down respectively. The toy will crash if you shift to far to either side so you may want to buffer the pot with resistors on the outside pins. I found around 4K to 5K worked fairly well for this but there is no substitute for experimentation.
I was blown away by the low end bass when the pitch was shifted down on this device. The quality of the rumbling drones you can produce are just incredible for a toy like this.
Alienmeatsack also talked about getting good results from a voltage starve on this device so I may try that out. And I’ve found a few glitchy areas on the board which I would like to investigate. I should be back to update you on my progress soon.
NOTE : Shortly after writing this post I was experimenting on this board trying to force a loop when one of the resistors cooked itself… There was a little puff of smoke and many tears. I will come back to this toy and see if I can replace the resistor and get it running again but it may be on it’s way to toy heaven. This problem was not caused by the pitch bend which seems to be very stable and produced excellent results but if you are exploring the board be careful as some of the resistors appear to have a very low tolerance.
A few weeks ago during one of my usual thrift store exploration I picked up a Kawasaki I-Soundz drum kit. Even before doing any bending I started having a great time with this toy. It has a large and varied vocabulary of samples and surprisingly high quality stereo audio driven by an internal TDA 2822 operational amplifier. I was also pleased to find that rather than the tactile buttons I’ve seen on many toy drum pads the Kawasaki kit is driven by piezo disks similar to higher end drum synthesizers. Unfortunately the device does not offer any polyphony but given the price point I did not expect it.
The drum pads also contain a number of interesting on board rhythm samples. Unfortunately these samples only play for about 30 seconds before stopping (regardless of whether you are playing the kit). Since I was looking for something I could use to set up repeating rhythms while I played other devices this left me with a need. I wanted to set up external triggers for the drum sounds. By using these external triggers in conjunction with my recently completed 4017 gate sequencer I could turn the Kawasaki drum pads into an 8 step drum machine and unlock a world of new rhythms.
The first step whenever you are setting up external triggers on any toy is to create a ground share point. This can be done by simply adding a banana jack or binding post and connecting it to any ground point on the circuit. If you are using grounded connections from your trigger source (such as 1/4 inch, 3.5 mm or RCA cable) then you can simply connect the ground point to the ground on your trigger input jacks rather than having a separate plug.
Because (in it’s normal operation) this toy is triggered by piezo disks most of our work is already done for us. When the pads are hit the piezo disk creates a trigger pulse. This pulse is sent to the base of an internal transistor (highlighted above), which switches the circuit on momentarily and causes it to play the sample associated with the drum pad hit. All we need to do to set up external triggers is send our external signal to the base of these transistors to switch them the same way the triggers from the piezo do.
One thing I am admittedly not incredibly comfortable with is soldering onto SMD (surface mount) circuits. That being said this is something that I feel I need to improve and develop my comfort with. Surface mount technology becomes more prolific and through hole circuitry becomes rarer and rarer each day. Further developing my comfort with SMD will open up near endless possibilities of new circuits I can work with. For this reason I have made it a goal not to shy away from these circuits. I will take the necessary care but am determined to become as familiar and comfortable with them as I am with more traditional components.
Where possible I soldered my leads to resistors adjacent to the internal transistors as there was less risk of damaging these components.
To solder I held my soldering iron to tinned wires to heat them up prior to touching the board. Once the solder on the tinned wire was liquified I lowered the wire and soldering iron to the soldering point together. I raised the soldering iron from the board almost immediately after touching the two down and held the wire in place until the solder solidified. The key here is to spend as little time as possible with the soldering iron on the board. The components are significantly smaller and the solder connections are significantly weaker than traditional through hole circuitry. This means any excess heat on the board can damage components or loosen their solder connection knocking them out of place.
Since my solder points were weaker and the circuit was so crowded I also added a small amount of hot glue to each connection. This gives each connection added strength and also insulates the wire from the other components to ensure it doesn’t touch any other solder points.
For reference the solder points I used for the triggers were on R10, R13, R8, Q3, R2 and R4.
Finally connect the wires from the trigger points to the trigger inputs of your choice. I was short on plugs so I have used bolts but you can easily use banana, 1/4 inch, 3.5 mm, RCA or any other type of input you have on hand.
Now that I have the external triggers set up on this drum pad I will be going back into the circuit and completing some more traditional circuit bending. I will be adding a pitch bend and hopefully will be able to find some other interesting bends and effects to give me an even wider range of sounds to use.
Hey guy’s I just created and uploaded a quick video to show off my progress on the Vtech Alphabet Apple. Unfortunately I was having some issues with my portable amplifier so I ran it through the internal speakers but this should still give a good idea of what the bends I’ve completed so far can do. The demo starts off a bit slow but picks up after 1:20 or so. I also get into a really interesting glitch near the end of the video using the voltage starve.
If you want to have a look back at any of the previous posts they can be found here :
VTech Apple Part 1 – Kill Switch and Line Out
Vtech Apple Part 2 – Exploration and Pitch Adjustment
Vtech Apple Part 3 – Voltage Starve
Vtech Apple Part 4 – Body Contacts
Vtech Apple Part 5 – 555 Trigger Oscillator