Bringing Guitar Synthesis To The Microcontroller

If you’re working with audio in an embedded environment, the best option for years now has been the Teensy 3 microcontroller board. This choice has mostly been due to its incredible power and audio libraries, but until now we really haven’t seen a stompbox-style interface that used the Teensy to its fullest extent. Now we have, in [Wolkstein]’s GitSynth, everything you could want in a synthesizer that processes the signals from an electric guitar.

The core of this build is a Teensy 3, and all the audio goodies that come with that. Also included is a USB MIDI and audio interface, smartly both attached to a panel-mount USB-B connector on the back of the stompbox. Other controls include a single mono in jack for guitars and synths, two mono out jacks for stereo-ish output, a bunch of footswitches for bypass, tap tempo, preset selection, a jack for an expression pedal, and some buttons to move around the LCD user interface.

While putting a powerful microcontroller in a stomp box for is a project we’ve seen many times, this project really shines with the MIDI GUI that’s built for a device with a real display and a mouse. [Wolkstein] built a PyQt-based app for this synth, and it’s a plethora of buttons and sliders that looks similar enough to a real synthesizer. There’s enough configurability here for anyone.

You can check out the demo video (in German, but auto-translate subtitles exist) below.

Thanks [Mynaru] for the tip!

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Only Mechanical Relays Will Do for Automated Hi-Fi Audio Source Switching

If you are a devotee of audiophile-quality analogue hi-fi, switching between sources simply can not be done through a solid-state device. Only physical switches will do because they come without the risk of extra noise or distortion that their silicon equivalents might bring.

That is the philosophy that lies behind [Skrodahl]’s relay-based audio switching board, which boasts 5 high-quality relays each handling a stereo input, with their control passed either to a rotary switch or to an ESP32 module. The ground connections on audio and switching sides are isolated from each other to avoid transient noise finding its way to the speakers.

You might think that an audio switching board is a very simple device indeed and thus not worthy of Hackaday’s attention, but it’s surprisingly easy to make a mess of a module like this one and they have put in some effort to avoid the pitfalls. The metal-can version of the switching transistors seems a little overkill, but fancy audio is a funny business.

If the ESP isn’t your bag, we’ve brought you another relay based audio switcher in the past that used an Atmel chip.

Learn About Waveforms Interactively

We’ll be honest: If you are a regular Hackaday reader, you probably won’t learn much new information about waveforms from this website. However, the presentation is a great example of using React on a webpage and — who knows — you might just pick up something interesting. At the very least, it’ll be a great resource the next time you try to help someone starting out.

The animated waveform is cool enough. It is also interesting that it changes based on where you are in the text. The really interesting part though is that you can press the M key to unmute your audio and hear what the wave sounds like. You can also use adjustments to control the frequency and amplitude of the wave.

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Making A Headphone Amp Perform New Tricks

Hands up if you’ve had the misfortune to work in an office with a fondness for following the latest fads. Paperless office, how long did that last? Or moving from physical telephones to a flaky VOIP application on your Windows computer, that’s sure to be a resounding success! We’ve all been there at some point, haven’t we?

[Joshua Wise] found himself in that unenviable situation of the VOIP app move, and since he is a habitual headphone music listener the prospect of wearing his company-supplied headset was not appealing. His solution was to take his HeadRoom BitHead amplifier and plumb into it a microphone channel, and though he went through quite some work to reach that point the quality of his final work is very high.

He was in luck with the headphone amplifier, because the USB audio codec turns out to have an unused audio-in function as well as some HID input lines. His headset has a set of buttons as well as the microphone, which switch in and out a set of resistors to indicate which of them is pressed. Some work with a microcontroller to detect this resulted in a working interface, which he put along with the microphone circuitry on a beautifully done piece of protoboard.

Most constructors would have been happy at this point, but not [Joshua]. He proceeded to design a PCB to fit into the space around the headset socket, to contain the circuitry and better fit within the case. The result is an exceptionally high quality piece of work which he admits consumed a huge amount of resources but for which we applaud him.

So [Joshua] has a cool headset. But is it solar powered?

Chest of Drawers Stores Audio Memories

Some people collect stamps, some collect barbed wire, and some people even collect little bits of silicon and plastic. But the charmingly named [videoschmideo] collects memories, mostly of his travels around the world with his wife. Trinkets and treasures are easy to keep track of, but he found that storing the audio clips he collects a bit more challenging. Until he built this audio memory chest, that is.

Granted, you might not be a collector of something as intangible as audio files, and even if you are, it seems like Google Drive or Dropbox might be the more sensible place to store them. But the sensible way isn’t always the best way, and we really like this idea. Starting with what looks like an old card catalog file — hands up if you’ve ever greedily eyed a defunct card catalog in a library and wondered if it would fit in your shop for parts storage — [videoschmideo] outfitted 16 drawers with sensors to detect when they’re opened. Two of the drawers were replaced by speaker grilles, and an SD card stores all the audio files. When a drawer is opened, a random clip from that memory is played while you look through the seashells, postcards, and what-have-yous. Extra points for using an old-school typewriter for the drawer labels, and for using old card catalog cards for the playlists.

This is a simple idea, but a powerful one, and we really like the execution here. This one manages to simultaneously put us in the mood for some world travel and a trip to a real library.

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The Best Stereo Valve Amp In The World

There are few greater follies in the world of electronics than that of an electronic engineering student who has just discovered the world of hi-fi audio. I was once that electronic engineering student and here follows a tale of one of my follies. One that incidentally taught me a lot about my craft, and I am thankful to say at least did not cost me much money.

Construction more suited to 1962 than 1992.
Construction more suited to 1962 than 1992.

It must have been some time in the winter of 1991/92, and being immersed in student radio and sound-and-light I was party to an intense hi-fi arms race among the similarly afflicted. Some of my friends had rich parents or jobs on the side and could thus afford shiny amplifiers and the like, but I had neither of those and an elderly Mini to support. My only option therefore was to get creative and build my own. And since the ultimate object of audio desire a quarter century ago was a valve (tube) amp, that was what I decided to tackle.

Nowadays, building a valve amp is a surprisingly straightforward process, as there are many online suppliers who will sell you a kit of parts from the other side of the world. Transformer manufacturers produce readily available products for your HT supply and your audio output matching, so to a certain extent your choice of amp is simply a case of picking your preferred circuit and assembling it. Back then however the world of electronics had extricated itself from the world of valves a couple of decades earlier, so getting your hands on the components was something of a challenge. I cut out the power supply by using a scrap Dymar Electronics instrument enclosure which had built-in HT and heater rails ready to go, but the choice of transformers and high-voltage capacitors was something of a challenge.

Pulling the amplifier out of storage in 2017, I’m going in blind. I remember roughly what I did, but the details have been obscured by decades of other concerns. So in an odd meeting with my barely-adult self, it’s time to take a look at what I made. Where did I get it right, and just how badly did I get it wrong?

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