The Pickin’ On channel is filled to the brim with great acoustic bluegrass interpretations of some of the best songs around. From Nirvana, to The Guess Who, to Lynyrd Skynard, they’ve done it all!

Check out one of my faves:

The post Pickin’ On Series appeared first on Jacob N Calvert.

PCB and Parts are here!

The printed boards from OSHPARK arrived recently and so did the components. Below is a list of the components I selected for this board.

Prototype PCB from OSHPARK

Check out the images of the PCB OSHPARK made for me.

Prototype PCB

Some Corrections

I started to build the pedal circuit and realized I did not need 100mF caps everywhere. I re-simulated the circuit with 100uF caps, and it works just fine. I started with a huge cap value just as a placeholder and never updated the schematic.

Prototype One

For the first build, I soldered the components on and just left fly wires hanging off. I did this so I could pump signals into it and test the circuit response. See the prototype one below.

Prototype One

I didn’t save my oscilloscope captures.. I will remember next time! The good news is that from 20Hz to 8kHz there was a good solid amplification with minimal change of the input signal. Driving the input harder resulted in soft-clipping, but it was very minimal and still showed a solid gain performance. As predicted in the previous post, there was an amplification of around 2-3x the input signal, resulting in a noticeable volume increase.

Prototype Two

The second prototype is the “final product.” I stuck the circuits + inputs/outputs in the enclosure I purchased. It made for a nice looking product at the end of the day.

I am very happy with the results! It works and sounds great!

Restrospective

So, the question must be asked, did I complete my stated list from the previous post? The list is below as a reminder.

1. Take an AC signal around 300mV pk-pk and boost it by some multiple
   1. Check! It takes an input signal and boosts it by 2-3x
2. The boosted signal should not be muddled or distorted/clipped in any way
   1. Aside from the soft clipping when driving the input stage hard, yes!
3. The output signal should model the input signal, with the only difference being the amplitude
   1. Check!
4. It should run on +9V (either a battery or a standard guitar pedal wall-wart)
   1. Check!
5. It should have an adjustable output gain
   1. Check!
6. It should have a bypass capability
   1. Check!
7. It should not load the input source too much
   1. Check! Simulation showed less than 10mA sink.
8. It should have enough power to drive the output easily
   1. Check! It drives my amp input just fine!

In retrospect, I completed my requirements. But no retrospective is complete without some lessons learned and a demo!

Lessons Learned

1. I need to think about power input filtering on my next design. My 1Spot brand wall wart induces a high pitch whistle into the output stage that a 9V battery does not. It does this on every pedal I own, so this may be more of a power supply issue, but it might be solved with some input filtering. The whistle is barely noticeable, but in a very quiet room, I hear it.
2. More time needs to be spent on laying out the physical interface. I just sort of hacked this one together, but a more complex project could have been difficult.
3. Use quieter switches. I bought cheap DPDT switches, and they’re pretty loud engaging/disengaging. Listen for them on the demo.

Demos

Clean Boost Example

This example shows the clean boost aspect of the pedal. It simply boosts the volume of the signal.

Overdrive Boost

This example shows the pedal driving an amp harder into overdrive and getting a nice crunchy result.

Wrap-Up

All in all, I had a great time building this pedal, and I’ll continue making more pedals in the future! Stay tuned for the next project!

Thanks for reading!

The post Build Your Own: Clean Boost Guitar Pedal Part 2 appeared first on Jacob N Calvert.

In this series, I will detail how I have built my own clean boost guitar pedal. I will detail the schematic, what parts are chosen, the circuit stages, and how they operate, as well as following through to the finished product.

The Beginning

A clean boost guitar pedal should accomplish a few things:

1. Take an AC signal around 300mV pk-pk and boost it by some multiple
2. The boosted signal should not be muddled or distorted/clipped in any way
3. The output signal should model the input signal, with the only difference being the amplitude
4. It should run on +9V (either a battery or a standard guitar pedal wall-wart)
5. It should have an adjustable output gain
6. It should have a bypass capability
7. It should not load the input source too much
8. It should have enough power to drive the output easily

So what’s a clean boost pedal for anyway? Think about driving your amp a little hotter going into a lead part, or maybe you just need a little extra volume. With an adjustable clean boost, you can get that perfect amount of pre-gain for any sound you want.

The Design

The design of the clean boost started with the above design considerations in mind.  The circuit needed to have a few key components to satisfy my requirements. First, the circuit needed to have a pre-filtering stage that would prevent loading the input signal too much. There would also need to be a boost stage, and lastly an output stage to provide the output specs I wanted. I came up with the following circuit to accomplish this.

Schematic

Build Your Own Boost

The circuit is comprised of very few components, and is made up of four stages.

Input Stage

Input Stage

The input stage does a few things for the boost pedal. Notice the power supply section. The diode provides a little circuit protect from reverse biasing the circuit. Next notice the capacitor C1 feeding into the the pull-up-down resistor network. This section of the circuit provides the input AC signal with a DC offset of 1/2 the supply voltage. This allows us to use GND for the negative reference of the op-amp and the supply voltage as the positive reference.

Pre-Boost Stage

Pre-Boost Stage

The pre-boost stage is comprised of the op-amp, and a capacitor. This section of the circuit serves to satisfy the no-load requirement from the input source, as the op-amp is in a voltage follower configuration. Since the input signal to the op-amp is between GND and the supply voltage, with AC perturbations from the input stage, the output will follow that exactly. The capacitor at the end of this stage serves to block the DC component of op-amp output, and only pass the AC component on to the power stage.

Power Stage

Power Stage

The power stage does what its name implies. It provides the power for the boosted signal. The input from the op-amp perturbs the NPN BJT, and because the resistor network surrounding it has the BJT in its active region, the output taken on the collector is boosted. One thing to note at this stage, the output is inverted from the input signal. The signal amplitude has been boosted by several times. This is the essence of our clean boost pedal. Also note that the output signal has a large DC offset which is not what we want for the output.

Output Stage

Output Stage

This final stage serves to take the DC component out of our signal (C3) and to attenuate the signal. I have chosen to represent a potentiometer with two series resistors. When we move the wiper of the potentiometer, R7 and R8 will adjust to give us a variably attenuated output signal.

Simulation of the Circuit

To see how the circuit might perform, I used LTSpice to simulate the circuit under various circumstances.

I simulated the input signal to be a sine wave at 880Hz  with an amplitude of 150mV. The power supply was set to 9V. Basing my simulation on a B50k and going in 5% steps, I obtained the following data.

Example of Simulation Data

The Implementation

I knew I’d want to have a PCB printed for this project, just to make things really clean. I drew up the schematic (with a few logical modifications) in EagleCAD and laid out the board.

Schematic Capture

Schematic Capture

Notice there are a couple of key differences. I have added 0.1″ pitch terminals for the the signal in/out, 9V in, and two 3×1 0.1″ pitch terminals for a boost select and bypass select. Also, there are two op-amp; one is in use and the other is in a strange configuration. The series of op-amp I have elected to use has two amplifiers in the package. To keep the unused one from injecting noise, I put it in a known configuration so it will not be noisy in the circuit.

Boost select is where the potentiometer will wire into the circuit. Bypass select will allow me to put a SPDT switch in and connect common to the pole number 2. In position 1, the pedal will be engaged, in position 2, it will be fully true-bypassed.

Layout

The Layout

The layout is based on the size of a Hammond 1590G project box. The 3-terminal part for the footswitch is located at the bottom of the board, while the 3-terminal part for the boost select is located at the middle-top area. The signal in is on the top right of the board, and signal out is on the top left. Power (9V) in is in the center of the top.

PCB Spin

I use OSHPARK for all my prototype PCBs because they’re quick, good quality, and have free shipping. Here’s what OSHPARK says the final product should look like:

OSHPARK Render

Next Steps

Next, I need to order the PCBs, order my parts, and wait! I will make another post when the parts and PCBs come in, and show how it turns out. I ‘ll also include and audio test.

Thanks for reading!!

The post Build Your Own: Clean Boost Guitar Pedal appeared first on Jacob N Calvert.

A New Spec

These days the MIDI spec can be be found implemented on tons of hardware, from synthesizer boxes and keyboards, to guitar amplifiers with built-in General MIDI support. Recently, the MIDI Manufacturers Association (MMA) ratified a new extension to the MIDI spec called MIDI Capabilities Inquiry or MIDI-CI. This new extension allows MIDI-CI compatible devices to communicate about Profile Configuration, Property Exchange, and Protocol Negotiation. Additionally, this new functionality will not trample on simple MIDI 1.0 devices on the bus. So what does this addition bring to the table?

Profile Configuration

The new Profile Configuration aspect of MIDI-CI will allow complex controller mappings to be communicated to devices via profiles. This simplifies large control surface setups so that they are simpler and quicker to implement.

Property Exchange

The Property Exchange (PE) feature brings together the worlds of metadata and music data. This element allows the storage and retrieval of “product name, configuration settings, controller names, controller values, patch names and other meta data, etc“. This has many, many uses in the future.

Protocol Negotiation

This feature is the most straightforward  addition to the MIDI spec. Protocol Negotiation makes it possible so that newer generation controllers and devices can take advantage of newer features (more channels, increased resolutions, etc.), while not trampling on devices that only implement the base MIDI 1.0 spec. This opens the door for greater flexibility in the number and types of MIDI devices that can be networked down the road.

MIDI is still super cool!

All in all, the MIDI spec is still cool, useful, and very much alive. Even though we have ubiquitous 1GbE, ubiquitous 10GbE right around the corner, high-speed USB everywhere, and tons of other bus technologies, MIDI still has its niche (and I’m really happy about that).

Check our the MIDI.org article for more information about MIDI-CI.

The post New MIDI protocol extension paves way for “significant expansion” appeared first on Jacob N Calvert.

How’s it made?

The guts

This project has the following components:

• 1 wooden cigar box from a hobby shop ($7)
• 1 clone Arduino Mega from Amazon ($9)
• 4 faders and 8 pots from digikey ($18)
• 1 1602A LCD from Amazon ($8)
• 1 rotary knob with pushbutton from Amazon ($3)
• 4 LEDs in different colors (freeee – I have a bunch already)
• 1 SPDT switch from Amazon ($1)
• 1 hot glue gun and hot glue sticks from hobby shop ($15)

Manufacturing

I first drew out a few templates on graph paper of what I wanted the end product to look like. Then I took each variation and taped it to the box’s top and tried to visualize using it in that form factor. Once I had decided on the way it was to be laid out, I went to the shop.
I taped over (with clear tape) where I would cut and drill so the layout template wouldn’t tear off, then I used a drill press to put holes in the right places and the jigsaw to my the slots and the LCD hole.

The Assembly

The first parts I put in were the faders. I used Gorilla Glue to tack them in position, and I let them cure for about 2 days. Then I put in all the other pots, switches, and hot-glued the LCD in place. Finally I put in the LEDs and hot-glued them in place.

Here’s a picture before all the hardware was in:

MIDI Control Surface w/ Some Components

I used solid core wire and high quality solder to build the wiring harness. The last step in assembly was to cut a slot for the USB cable go through the side of the box and wire up the microcontroller.

The uC

I used the Arduino Mega form factor, but did not use the IDE. The code I used was AVR-libc based and was an extension of the littleKernel project I had been working on. I eventually added the optiboot bootloader so I didn’t need to pull the Mega from the box to update the code. I’ll get around to putting the code up eventually (probably).

What does it do?

Here, a feature list makes sense:

• MIDI TX and RX lights
• Power good light
• Debug light (always good to have)
• Reset switch
• 12 control surfaces which can be independently mapped to different MIDI channels and Change Control numbers
• LCD and scroll knob user interface for setting up the aforementioned options
• A settings Save and Recall function using the uC EEPROM
• A settings Dump and Load function using the serial interface

All in all, this was a really fun project. Perhaps I’ll put up a demo of me using it with a DAW…
Anyhow, here are the pics of the final product and an early prototype for reference! Thanks for reading!

The post Presenting…. The MIDI Control Surface (Rev. A) appeared first on Jacob N Calvert.

Introducing littleKernel

As the name implies, it is a little kernel. I’ve built this little multitasking kernel for a project I’ve got in mind down the road. For now though, I’m going to learn as much as I can about multitasking while improving my own littleKernel project.

The project down the road

I love to make music. Whether it be from a physical instrument, digital instrument, or a combination — I love doing it. I’ve built the hardware for a 12 channel MIDI control surface. I built a 4 channel prototype earlier this year, but wanted to do a bigger, more multi-functional version of that. I’ll post pics later on, but this project is the primary reason for home-rolling a multitasking kernel for a microcontroller.
Until next time…

The post I’ve been busy working, but I’ve started a side project appeared first on Jacob N Calvert.

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