Month: December 2017

DIY Drum Kit with Circuit Bent Pedal Effects

Sam

I was down in my basement playing with a few of my older projects today and took a quick video to share with you all. In this video I use my 4017 based gate sequencer to control a set of circuit bent Kawasaki drum pads. I took advantage of the stereo output on the Kawasaki drum kit to use a stereo spliter cable to separate the left and right audio channels. I sent the left audio channel directly to my PA system while I ran the right through some circuit bent Danelectro pedals I had laying around. The result Is a clean channel and a distorted/echo channel which I can mix separately on my PA system. If you are interested in learning more about any of the projects used in this video don’t hesitate to visit the following links:

4017 Gate Sequencer
Kawasaki Drum Pad With Triggers
Circuit Bent Danelectro T-Bone Distortion
Circuit Bent Danelectro BLT Slap Echo

Intro to Bipolar Power Supplies

Sam

As you begin to tackle more complex and interesting synthesizer components you may begin to encounter schematics for circuits which require both a positive and a negative power input to operate. As an example Eurorack synth modules use plus and minus 12V power supplies. As a result many DIY synth enthusiasts will also use +\- 12V so that they can interface with their Eurorack Modular set-ups. This is referred to as a bipolar power supply and is necessary for circuits which include operational amplifiers.

Unfortunately this can cause something of a tripping point for electronics or synthesizer beginners. When I first came across this it took me far longer than I like to admit to wrap my head around it. How could a voltage be negative? Do I need special equipment to power these circuits? This confusion was primarily caused by two misconceptions I held at the time:

Voltage is a measurement of force not quantity:
When we think about voltage we tend to think of it as a quantity. We assume that the voltage of a battery is the number of volts which that battery contains. This is perpetuated by the way we refer to voltage ; “This battery is 9V.” This is however not correct. The voltage we refer to with batteries, power supplies and circuits is actually the voltage difference between the positive and negative poles. If you are familiar with the water analogy for describing electricity you may have heard that voltage is the pressure which pushes the electricity through the circuit. If you had a pipe where you applied equal pressure to both ends the water would not move through it. If however you had a pipe where you applied a greater pressure to the water at one end of the pipe, the water would begin moving. Further the force with which the water moves through the pipe would be equivalent to the difference in pressure between the two ends of the pipe. Similarly with a 9V battery the voltage at the positive pole is 9V higher than the voltage at the negative pole which pushes the electricity from the positive pole, through your circuit, to the negative pole.

Consider then if you turned the circuit upside-down. This would mean the same 9V of force was still moving through the circuit. However now it is moving through the circuit in the opposite direction. The 9V of force would now be pulling electricity from the ground connection and pushing it to the power bus. This is what would be referred to as a negative voltage.

Ground is a reference point:
When I started working with electronics I did not have a firm grasp on what exactly ground was. I got used to using the negative pole of a battery as ground and began assuming that it was the lowest pole of the battery or power supply. This understanding served me fine with basic circuits but became a problem as I began working with op-amps and more complex circuitry. The truth of the matter is though that the ground is not an intrinsic point on the power supply and has more to do with the circuit itself than your power supply (That being said some power supplies include circuitry to anchor or shield their ground to make it more stable). The ground ultimately serves as a reference point from which the voltage of the circuit is measured. With some basic components you could set up a ground anywhere between the maximum voltage of your power source and 0V.

Consider the circuit above. The most intuitive way to approach this would be to say that ground is point C. In this case we would measure the voltage difference between B and C to determine that the voltage at point B is 9V. Similarly by measuring the voltage difference between A and C you can determine that the voltage at point A is 18V.

However if you approach the circuit differently you will see very different results. Lets say that we assign point B as ground in the circuit. In this case by measuring the voltage A and B to find that the voltage at point A is 9V. Next we would measure the voltage between C and B and find that the voltage at point C is negative 9V. This means the voltage at point C is 9V less than the voltage at ground (point B). The schematic shown above is the most basic bipolar power supply you can create and is perfect for developing familiarity with these types of circuits.

To make my life easier I soldered this small bipolar power supply together on a scrap of perf board I had on hand. I’ve added two large capacitors (330 uf electrolytic) to provide some decoupling for simple circuits. Additionally I placed leads on the positive, ground and negative traces so I could easily connect this supply to my breadboard.

If you are looking to free yourself from batteries I would strongly suggest looking into MFOs Wall Wart Bipolar Power Supply as an option for moving to a more permanent voltage source (along with the wonderful documentation provided with all of MFOs projects). Alternately if you have a traditional bench power supply there are many projects available to help you create a bipolar supply using the monopolar output these provide.

555 Based Drone Synthesizer With LFOs

Sam

Today I have an update to the 555 Based Drone Synthesizer which I posted last week. I was having a lot of fun with my Drone synth but wanted to expand on it to get a bit more variation from the sound. To do this I added a set of LFOs to modulate the frequency of the drone oscillators.

To accomplish this I built a second set of three 555 based oscillators. These new oscillators are identical to the ones in the drone synthesizer except for a change to the capacitor between pin 2 and ground. By increasing this capacitor from 0.01uf to 1uf I was able to lower the frequency of the square wave they produce. This makes them perfect for use as LFOs.

I then connected the output (pin 3) of each of these new oscillators to the control voltage input (pin 5) of the corresponding oscillator in the drone synthesizer through a 1K resistor. An additional modification that can be made to this circuit to provide further control would be to replace this 1K resistor with a 10K or 50K ohm potentiometer which would allow you to modify the amount which the LFO modulates the oscillator in the drone synth.

In this experiment I have used LFOs but you could easily control the drone synth in other ways as well by providing a control voltage to pin 5. I am interested to see how this set-up would react to a control from a sequencer or keyboard and may try this in the future.

Simple 555 Based Drone Synth

Sam

Today I have another very simple breadboard project based around the 555 timer. I’ve built three 555 astable oscillators similar to what I used in my 555 Serial Oscillator Project. This time however instead of connecting the oscillators in series I have run their square wave outputs through a simple mixer onto a single audio channel. This is known as a drone synthesizer.

As you can see from the schematic this drone synth is a fairly straightforward build. If you are familiar with 555 oscillators you probably recognize the layout of the 555 chips as a basic astable oscillator almost directly out of the 555’s datasheet. Once the three oscillators were created I added a 1K ohm resistor to the output of each (pin 3) and connected these outputs together. Once the three outputs are connected you can run this through a large capacitor (I used 330 uf) and out through your output jack. It is also possible to connect this circuit directly to a speaker though the audio level may be a bit low without amplification.

Once you’ve built this circuit you can begin experimenting with it. Pin 5 on the 555 chip can be used as a control voltage input so you could easily add a method of control voltage to this circuit. The easiest way to do this would be to build three more 555 oscillators and connect their outputs to pin 5 of the 555 chips in your drone synth. These will function as basic LFOs and modulate the frequency of the drone’s oscillators. You could also experiment with other voltage controls like a sequencer or keyboard. You could also replace one or more of the potentiometers with things like photo-resistors or body contacts to make the project even more interesting.

Lastly I wanted to mention that this drone synth is not limited to three oscillators. You can add as many 555 oscillators as you want in parallel to make an even deeper and stranger sound. If you’re interested in seeing the extreme of this a YouTube user by the name of Look Mum No Computer recently built a 100 Oscillator Drone that is definitely worth checking out.

Atari Punk Console – Adding LFOs

Sam

Today I wanted to show you guys something new I’ve been playing with on the breadboard. Essentially what I have here is a twist on a classic project. I’ve taken an Atari Punk Console (Stepped Tone Generator) and added two 555 timer based oscillators as LFOs to add more depth and interest to the sounds produced.

This modification is built on one simple characteristic of the 555 timer (and by extension the 556 which consists of two 555 timers). This is the control voltage pin which allows you to use an external voltage source to modify the chips performance. On a traditional 555 timer the control voltage input is located on pin 5 while on the 556 you would use pins 3 and 11 as I have here. By connecting the outputs of two 555 oscillators to these pins on the 556 we are able to use them to modify the frequency of the stepped tone generator.

You may notice in the video I play mostly with the left LFO knob. This is because in my experimentation I was able to illicit much more noticeable effects from the first oscillator connected to pin 3 of the Atari Punk Console. The second oscillator (connected to pin 11) only seemed to have a pronounced effect at fairly high frequencies. For this reason you may want to try switching the 500K pot on the second oscillator for something smaller like a 100K or 50K. Another option to increase the frequency range is to change out the 3.3uf capacitor for a 0.1uf cap.

Another thing you can do with this circuit to gain further control is to add a potentiometer to control the modulation of the LFOs on the Atari Punk Console. To accomplish this you can add a potentiometer in place of the 10K resistor at the output of the LFO oscillators. A 50K pot would likely work best for this.

Finally if you enjoyed this project I did build an Atari Punk Console back in the early days of this site with jacks for control voltage inputs. Feel free to have a look if you are interested.