Saturday, 2 May 2015

Stompbox guitar tuner stolen idea

If you've ever seen a live band at the local pub (or bar) there's one song you've probably heard more than any other. It's an instrumental, and it goes "dum, dum, dum..... der, der, der...... der, der, ding, ding, ding, ding, ding".

Of course, it's the tune-up song, that just about every guitarist plays when they get up on stage. If you're lucky, you get to hear it once, at the start of the gig. If you're unlucky, they play it three or four songs in (and you've just endured the most atrocious fifteen minutes of out-of-tune string-twanging).

It's a pretty short song (if released as a 7" single, it'd probably have a run time of 0:21 or something) but it's tedious and noisy for everyone who has the misfortune to listen to it.

In a live environment, unplugging guitars from amps set to "moderately loud" can mean lots of popping, crackling and buzzing, as cables are removed, left lying around and generally abused. As a general rule of thumb, once you're plugged in and audible, it's best to try to stay plugged in (and use the guitar body volume to reduce any unwanted noise between songs).

Which means that plug-in tuners have lost out in the fashion stakes, for the cheap, vibration detecting, sit-on-the-headstock-and-detect-the-note-frequency type tuners - especially in a live environment. Which means, that as you tune your guitar, and watch the display at the end of the head, waiting for the note to appear in tune in the little window, everyone else has to listen to "twang, twang, twang" at performance volume; often as many as six times (each string needs to be plucked at least once, even if it's in tune, just to see that it is!)

A little while back, Tom - (the dude in all the videos from the previous stompbox workshop at BuildBrighton) - had an ingeniously simple idea. He took a cheap, plug-in tuner and turned it into a stompbox.

The point? Well, with the footswitch in the "default" position, it acts as a true bypass - simply sending the incoming signal to the output jack (and on to the amp). But when activated, not only can you direct the input signal to the onboard tuner input - you can also short the "output" signal to ground - ensuring that your audience hears nothing, while you're busy playing the open-string-tune-up song.

A plug-in guitar tuner costs about £3 on eBay, so it's no big expense, even it is goes wrong! We weren't not sure if our (cheap Chinese) guitar tuner was exactly the same as the one Tom had, so we had a quick look inside

This particular model had a mic (so it could pick up sound from an acoustic guitar, and be used for tuning non-electric instruments too) a battery compartment, an input jack and a circuit board.

Tom's design was so simple, we just had to rip it off - use it for our own project. He basically just clipped the heads off the LEDs on the circuit board, connected a couple of wires, and attached them to some LEDs that were mounted into the stompbox enclosure.

We ditched the microphone - we'll be taking the signal from the guitar out and it'll probably be a bit noisy for the tiny little mic to be reliable anyway. To make things easier, we soldered wires onto each of our LEDs before arranging them inside the stompbox enclosure. Then the hotglue gun came out and sneezed all over the place, inside the box.

It may look horrible inside, but once the box is done, it'll only need to be opened up once every now and again, to change the 2xAAA batteries that power the circuit board. By running the power lead from the batteries through one set of contacts on the footswitch, the batteries will be physically disconnected from the entire circuit when not in use.

A combination of poor drilling and sloppy application of hot glue means a couple of the LEDs don't sit perfectly true, but they're good enough for the effect we're after!

There's a tangled mess of wires by the time each of the nine LEDs has two (overly long) wires running to them, plus all the wiring between the circuit board and the push button. But eventually we crammed everything inside the little box.

(Before committing to screwing the base on the underside, we tested the pedal. Here you can see we're playing the G string - fnar, fnar - and our pedal is telling us that we're perfectly in tune)

The final pedal, ready for a nice sticker labelling the LEDs.
In our design, the top LED is always on, while the pedal is active (yes, we forget that since the top and bottom strings are both E we only actually needed five, not six, LEDs for the different strings, so found a purpose for this "extra" LED). Because power from the battery is also routed through the pedal, when it is off, the battery is physically disconnected from the rest of the circuit (rather than using the rather leaky soft-on button) so this should help reduce battery drain when the pedal is not in use. So, when the tuner is activated, we'll make this top LED light up (so you can see at a glance whether your guitar output is going to the amp or not).

The final pedal, with all the guts stuffed away inside.

Like our earlier fuzz face stompbox, this was a nice, easy, no-more-than-a-couple-of-hours project, but we've actually got something quite useful from it.

There's no real need for a full write-up and circuit diagram - it was more of a "hack" than a "build". All we've really done is just take existing LEDs, soldered on some wires, and connected up alternative LEDs on the face of the box. For anyone interested, here's how we wired up the footswitch.

The layout for drilling the stompbox enclosure is below.
(the drawing also includes the drilling layout for the earlier, as-yet-incomplete Fuzz Factory pedal, and some ideas for a sequencer wah pedal we're playing about with)