Sunday, January 25, 2015

Fender Squier Bullet Strat - Peg

This is your big debut
It's like a dream come true
So, won't you smile for the cam'ra?
I know they're gonna love it, Peg

The guitar in the following picture isn't likely to be featured in a photo with it's name in lights anytime soon, but my son sure enjoys it.  When my son started playing guitar in his middle school jazz band this past fall, we decided it made sense to have a guitar he could leave at school for practices and performances in addition to the Epi LP Junior he plays at home.  Wanting a contoured body and something with a tremolo bar, we started looking online and locally for a used Stratocaster.  We found a few Squier Strats at our local Guitar Center in our price range that were in playable condition.  After trying a few of them, and missing our chance to pick up a sweet Sunburst model, we settled on a gently used Chinese-crafted 2010 White SSS Bullet Strat.

After playing her for a few months, my son mentioned that a couple of the tuning pegs didn't work well.  So, when he brought his Strat home for a new set of strings over winter break, we figured we'd also look into upgrading the tuners with a higher quality set.  Very soon, winter break was over, and that Strat was back at school before we put any more thought into replacing her tuners.

Although I knew little of the finer points of Fender tuning pegs, I knew a few different styles have been used over the years.  Not knowing the history of this Strat, I also wasn't sure if she had all of her original parts.  In efforts to avoid having to overbore peg holes and redrill screw holes, I asked my son to describe what the machines looked like from the rear.  When that proved fruitless, I asked him to identify the the machines by the orientation and number of screws holding down each machine.  The best that I could tell was that a 70s style set should work fine.  The genuine Fender slotted peg set I found on eBay arrived in the mail, just in time for a long stretch of teacher work days and a weekend.  With a few turns of a screwdriver, we figured we'd end up with something that looks like this.

Right away, we noticed a major difference in the screw orientation these two sets of tuners.

After a little more internet research, I confirmed that this difference in attachment screws was typical with Fender tuning peg upgrades.  Since it would result in a higher quality tuner, we decided this still was the way to go.  With any luck, we figured we'd end up with only two extra holes - one at the high E string tuner and one at the low E string tuner.  Instead, it was necessary to redrill holes for more than half of the screws.  Swapping out these tuners also entailed overboring the peg holes from the rear about 3/16" in depth, just to the edges of the grommets, to accommodate the bushing shoulders of the new machine shafts.  The tuner in the next two pictures during fitup is shown with the genuine F-logo stamped cover removed.

After removing the grommets, enlarging one of the holes and replacing a grommet, I was pleased to find that the original grommets would work with the new pegs.  That's a very good thing, since the 70s style grommets have a larger outer diameter and a very different outer profile.  Fun fact, a No. 2 pencil is a great tool for pushing out grommets.

I modified the remaining peg holes the same as the first one.  After making the necessary screw hole modifications, I attached the pegs and reattached the stock string trees with the Bullet's screws.  All but one original screw hole, the one near the high E tuner, is not concealed by the new machine covers.  I plugged it while it was on the work bench, minimizing the imperfection resulting from this upgrade.  Looking at the front of the headstock, the way you can tell the pegs have been upgraded is by the concave surfaces of the peg buttons and the slots in the peg shafts.

Those buttons and slotted shafts sure do make restringing and tuning This Old Guitar quicker and easier!

Monday, January 12, 2015

LeSpork Bass Prototype - Under My Thumb

It's down to me
The way she talks when she's spoken to
Down to me, the change has come,
She's under my thumb

As pop music bands of the 1960s started experimenting with tone and range, the fuzz bass became a familiar sound.  An early popular example is Bill Wyman of the Rolling Stones using it in the song "Under My Thumb" in 1965.

With the basic Electra Distortion circuit built and working, it was down to me to change a few parts to get the synthetic-inspired sound that was in my head, rich with rumbling odd-numbered harmonics.  The initial circuit already had some distortion and gain.  What I wanted to do was to increase the sustain and edginess.  The initial circuit also had less definition with lower notes of the bass.  I also wanted to achieve the distortion effect more evenly throughout the frequency range.

I started tweaking the gain by bypassing the 680-ohm resistor between the emitter and ground.  This gave too much gain, so I put it back in.  I moved on to tweaking the distortion by changing the diodes.  Of all the combinations of IN4818, IN4001 and IN914 I tried, I settled on a mixed pair of an IN914 with an IN4001.  This pair gave a consistent amount of distortion over the frequency range of this bass as well as the middle-of-the-road fuzziness I had in mind.  Moving back to the gain, I tried a more-powerful 2N5089 transistor.  It also had too much gain so I switched back to the 2N3904 plus the 680-ohm resistor.  Swapping out the input cap with other values I had on hand made little difference in tone, so I'm sticking with the original one, for now.  So, other than using a different pair of diodes, what I have at the moment is the circuit as originally designed.

Next time, I'll add in the volume and passive tone controls, and check for any interactions between them with the effects part of the circuit going in to This Old Guitar.

Thursday, January 8, 2015

LeSpork Bass Prototype - Make A Circuit With Me

A sweet romance is not for me
I need electricity
If you wanna make me flip
Hit me with a micro chip

It’s not unusual for guitarists to know a little about electronics.  I fall into the category of knowing just enough to be dangerous when it comes to electronics.  Over the years, I have learned my limitations, and generally stay away from tinkering with anything that has more than an amp of alternating current, or anything that would be considered high-voltage DC.  The end of the patch cord I’m working on has low enough voltage and current to make it almost impossible to do any damage to an instrument, an amplifier or myself.  So, with the encouragement, advice and parts-box resources of my long-time friend, electrical engineer and fellow guitar enthusiast BJ, plus a few more inexpensive electronics bits and pieces, I am adding an on-board effects circuit to This Old Guitar.

My first attempt was a simple, passive, hard-clipping diode fuzz circuit.  The idea is that the diodes, one wired with anode shunted to ground and the other wired with cathode shunted to ground, cut away the peaks of the signal.  This changes a clean-sounding sine wave into a fuzzy-sounding wave that approximates a square wave.  The sound is similar to an overdriven amplifier.

The wiring is simple.  I wired a pair of IN4001 silicon diodes and a single pole switch between the pickup and output jack leads.

The downside to this circuit is that you need a healthy amount of impedance in the pickups for the diodes to clip the signal.  As I found out, the single-wound pickup in this bass does not generate enough of a signal to make it work.  So, it was time to move up to an amplifier circuit.

As this is my first time building a circuit in many years, I kept away from micro chips.  I wanted to go with something that was well documented, has one transistor and a minimal number of components.  After considering numerous options, I decided on the classic Electra Distortion circuit.

At the heart of the circuit is a simple one-transistor amplifier.  This little circuit has been used successfully by many audio professionals as well as amateurs like myself with numerous variations and modifications as far back as the 1960s.  In the 1970s, a distortion circuit was offered as a plug-in module by Electra Guitars, allowing guitarists to customize their own on-board guitar effects.  In more recent years, variations of this circuit have been made available under many names by a variety of boutique pedal manufacturers in the form of an external stompbox.  A DIY stompbox version with demo and a tutorial has also appeared in the October 2014 issue of Premier Guitar in an article written by Joe Gore.  With so much already written and documented on this circuit, I've focused this blog entry to a few aspects of my own build.

I started by building the stand-alone circuit on a breadboard.

While waiting for one of the fixed resistors I bought to arrive, I improvised by using a 100k trim pot dialed in to the appropriate 47k value.

After double checking the layout, I moved things into the house to do a proper sound check on the circuit with an instrument and an amplifier.  My only blunder so far was a soldered lead on the output jack.  After a little troubleshooting, the Electra Distortion circuit worked as expected.  Success!

Next up, I'll do some tweaking with the semiconductor types and values to customize the sound for my LeSpork Bass.

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