MATATRON!!!

My old buddy Matt Wright contacted me recently and asked if he could buy my FUNKY GLITCH BUDDY. I don't know why, but it is hard for me to sell things to good friends... Do you give them a discount?.. Or just give it away?.. Either way, I didn't want to give up my funky buddy just yet, so instead, I would build him something unique as a friendly gift. Matt is a master guitar tech/luthier, so I wanted to make him something guitar shaped that he could hang in his shop and maybe be a conversation piece. 

I have been holding on to this "Music Maker" guitar for years, and I was actually about to get rid of it. I grabbed it from the pile and devised a plan for the circuit and hardware arrangement. The original circuitry in the guitar probably could have worked, but it was a little slow to respond to key-presses, so I decided to go with another toy organ COB circuit from an old Hal Leonard Piano Fun keyboard. A lot of early 90's toy keyboards can actually be pretty useful as the base for a synthesizer. They usually have gate outputs that trigger volume envelopes on key-presses. A little reverse engineering, and you have a square wave VCO with a keyboard input and a gate out. 

I thought it would be cool to use the square wave VCO to clock an LFSR noise generator circuit. I have been experimenting with LFSR's a lot lately... The only problem with this idea, is that the LFSR patterns are so long, the pitches of the VCO end up being too low for my liking, so I fed the square wave VCO to CD4046 frequency multiplier. I found that the CD4046 can cover almost 7 octaves, and since I didn't want to be stuck with just one, I added a CD4512 data selector chip to set the one of seven octaves. I also wasn't content with just one LFSR pattern length, so I selected my favorite 8 of a certain combination of taps, and fed them to another CD4512. I wanted to be able to shift through the pattern lengths and octaves smoothly, so I programmed a micro-controller to be a dual 3-bit flash ADC with code from robstave/ArdinoComponentSketches. The octave and LFSR shifting are the heart of this design, and they sounded really crazy and fun on their own, but I wanted a little more control, so I threw in a diode based Lunetta style VCA, as well as a PWM filter for the main voice. For modulation, I put in two looping AR generators; one for the VCA and one for modulating the PWM or the pitch of the keyboard. I modified the VCA envelope generator so that it could be switched from Attack/Decay, to Attack/Release in "SUST" mode(see faceplate).

Once everything was bread-boarded, working, and documented, I thought it might be nice to use the design in other builds. I was also thinking it would be a lot easier to have some nice new PCB's made instead of the painstaking task of engraving a PCB on my CNC, so I opened up KiCad and did it the easy way. I think I was overcharged, but you won't hear me complaining because I only spent about $20, and 10 perfect circuit boards were on my doorstep in just one week! I really don't think anything can bring me more joy than circuit boards in the mail.

Anyway, while I was waiting for the PCB's to arrive, I prepped the body of the guitar. I made all of my hardware selections and designed a faceplate. Without an accurate method for measuring the dimensions of the guitar toy, it was difficult to determine a good perimeter for the faceplate. In the end, I ended up just taking a picture of the guitar and tracing it. I cut the shape out of paper on my laser cutter and adjusted the drawing as needed. Surprisingly, I got a pretty good shape on the third try. I cut out the faceplate and painted it blue. I use acrylic airbrush paint because it doesn't react with the plastic, but it can scratch easily, so I usually always cut out a piece of dust cloth to match the shape of the faceplate and protect the paint from the hardware that is mounted to the underside.

Well, I'm sure I haven't covered everything, but this one is pretty straight forward. Hopefully my future self will be able decipher the details in ten years time ;)

     

EHX 16 SECOND DELAY MOD

A friend of a friend contacted me in the summer of 2020 to have his EHX 16 Second Delay reissue modified. I had done some pedal mods for him in the past, so I was willing to give it a go, even though I was pretty bogged down with remodeling projects in my house. I was happy to be in my shop again and working with something other than drywall.. I didn't end up finishing the mod until the winter of 2021, but the owner didn't seem to mind the wait. Thanks Joe!

I can't remember what exactly he originally asked for, but I think he complained that the sound was too digital and he wanted to be able to switch the feedback on and off. Those were easy enough things to address, but I also came up with a bunch of other mods that I thought would compliment the pedal, and he agreed. So I spent some late hours of the nights that I wasn't too sleepy to mod this crazy beast.

The original plan was to create an analog signal path from the output of the pedal to the input with highpass and lowpass filters, but unfortunately there was just too much aliasing noise feeding back and being amplified, so I had to scrap that plan. I kept the filters, just created an alternative analog output to give the pedal a warmer sound. At least I think that's what I did... To be honest, at the time I am writing this, I am having trouble deciphering my notes and schematics, and my Kicad files are a mess from a catastrophic version change... I do not have a video to reference and the pedal got shipped home over a year ago, so I am just trying to recall from memory. I am pretty sure that the filters do NOT feed back into the delay though.

All of the controls on the pedal are 3.6 volt CV inputs so I added mod switches for most of them to be modulated by either a guitar audio triggered envelope generator or an external CV/pedal. The slope of each can be inverted independently. I drew up a pretty useful manual, so I will defer to that... 

I found a pretty cool local seller of high quality toggle switches. I love the stubby little ones!

Well, I guess I'll keep this short since I cant recall too much about building this. I will say though that this pedal is powerhouse of drone! If you see one, get it! It is always a treat to occasionally mod or repair rare things that I was never aware existed. I only wish i had recorded it before sending it back.

FUNKY GLITCH BUDDY-REVISED

While cleaning shop, I came across an old friend. I built this little keyboard monster back in 2013. The FUNKY GLITCH BUDDY was an interesting concept, but it suffered from some pretty challenging design flaws that I had always wanted to fix, but never had the time. For one, the keyboard would draw so much current due to the fact that the keys were all infrared proximity sensors. There were a lot of 7400 series chips and opto-isolators in the design too, so overall this thing was pretty inefficient and noisy. Two of the voices were 8-bit LFSR noise generators which didn't particularly sound like noise. The third oscillator was a basic two transistor oscillator that I ripped out of a cheap organ toy, and had died some time ago. At the time of this build, I had just started using my CNC to engrave and cut my own circuit boards. This was my first project using the CNC, and the design and orientation was pretty sloppy. Everything was jammed together, and I never even took the time to draw out my schematics, so finding and fixing problems years later was difficult to do. Instead I thought it would be quicker and more fun to just completely redesign the circuit.

The concept for the new version would pretty much stay the same, but there would be three LFSR noise generators instead of just two, and the pattern select keys would just cycle through the patterns rather than shifting through patterns depending on how far down the key was pressed. I replaced all of the 7400 series chips with their 4000 series counterparts, and got rid of any opto-isolators and unnecessary reference voltage trimmers. I used OTA VCA's. Unfortunately I hadn't yet discovered the Lunetta style diode VCA' at this point, which would have been perfect for this application... Oh well. Since the pattern select switches were sequential, I had three extra switches to make use of. The original design could only shift through 8 patterns with the variable-press keys, so I had "SHIFT" switches for each pattern to access the other 8 available patterns. Now that I didn't need the shift switches, I used them to set different taps for the LFSR noise generators. I have found that when it comes to LFSR noise, there are certain bit lengths that sound better than others, and they are not always the longest. Shifting the taps is a nice feature but can be problematic sometimes, because shifting the inputs can sometimes cause the LFSR to lose its "SEED"... Without going too far into LFSR's, I'll just say it was a little troublesome towards the end but I was able to create stable LFSR's with a little trial and error. I found that the more finicky tap combinations preferred CD4014 to CD4021 chips, which I don't fully understand why, but whatever, they work.. 

I had to get creative with some limitations to the interface, too, since there was no "freq" or "lfo" hardware for the voice that had been the toy organ oscillator. The pitch and LFO of the third(red) voice is shared with the second(blue), and the "amt" control is an attenu-verter, so the third voice can not be totally attenuated with the VCA. However, one of the 16 patterns is 0000000000000000, so it is possible to mute the voice that way.

The new circuitry was pretty easy to design and prototype on breadboard. I tend to use my CNC less and less these days since ordering PCB's from china is so affordable and easy. It seemed fitting that I design and cut all of my circuit boards with my CNC for this project since it was the first ever project I used the CNC for. Designing circuit boards this way is pretty challenging and frustrating sometimes, but it is gratifying when it comes out. 

The FUNKY GLITCH BUDDY is now finally up to my liking and it is pretty fun to play.