LeSpork Bass Prototype - Winter Time

In the winter time
When all the leaves are brown
And the wind blows so chill

Not very pleased with the Electra Distortion circuit I built to audition for the LeSpork Bass in the early winter, I decided to move on to another circuit.  The small part count and simplicity of the Bazz Fuss intrigued me and so it seemed it might be a good fit.  Substituting a more powerful 2N5089 transistor for the 2N5088 shown in the runoffgroove.com schematic, I put this together and gave it a try.

Although it was quick and easy, the Bazz Fuss had too rough of a tone for my tastes.  At the suggestion of a friend, I moved on to a home-brew incarnation of the Electro-Harmonix Big Muff Pi.  Considered by many as an essential distortion stompbox, variations of the basic BMP circuit have attracted a lot of attention and endorsements over the years.  I started with a typical schematic courtesy of beavisaudio, sourced a variety of parts from some eBay vendors near and far, and made a few substitutions to match my at-hand assortment of semiconductors.

As the folks at beavis and numerous others have documented, there are many ways to modify this basic circuit to suit a variety of tastes, including some better suited for bass guitars.  Due to the numbers of opportunities to make mistakes while bread boarding this circuit, and realizing it would take me a few days to fit all this in to my calendar, I decided to test each of the five stages beavis identified as I built them.

First came a clean preamp.  To be sure I'd have enough room on the bread board, I started at the far left side, using as little space as possible.  I also used a 100k trim pot in place of the "sustain" pot just to get things moving.

A quick sound check verified that things were where they belonged and that I could move on to the first of two identical fuzz stages.

Again, a quick sound check verified that things were working fine.  As expected, there was a loss of volume with this addition, and the germanium diodes introduced a slight, mellow fuzz.  That fuzz was more pronounced yet pleasantly mellow with the addition of the second fuzz stage.

Moving on to the tone stack, I replaced the 100k trim pot sustain control with an audio-taper potentiometer and added a linear-taper potentiometer for the tone control.

After a good night's rest, I added the final stage, including the volume-out control.

With my son's help, I made two quick recordings of this circuit with my iPhone held about two feet from our Crate bass practice amp.  The first one was with the LeSpork Bass straight from the pickup into the BMP.

The second was with my son's Epi LP, with the volume and tone controls both on 10.

My son was very pleased with the sound of his Epi through this basic build, compared to the built-in effects on his amplifier.  So, it looks like a pedal-version build of this is in the near future at These Old Guitars.  I'm not so impressed with the range of the tone control.  I also have some gain and overall volume issues to be addressed.  My goal is to get the same volume and tone levels between the clean and distorted signals with only three knobs on the bass.  Next time, I'll do some tweaking of some of the values.

LeSpork Bass Prototype - Unchained

No, I don't ask for permission
This is my chance to fly
Maybe enough ain't enough for you
But it's my turn to try

While researching the two-band passive tone control circuit I put in this bass guitar, I also came across a few articles on Les Paul Vintage wiring.  In short, the idea is to put the volume control before tone control the way Gibson used to do it on some of their early Les Pauls:

There's plenty written on the subject of "vintage" vs. "modern" wiring on many discussion forum sites, including this one:

and even more on other sites, like this one:

I had two reasons for going with a volume-before-tone wiring scheme on this project.  First is that is how it is done in the P-bass stock wiring

Second was convenience, based on the length of the pickup lead wire and the layout of the controls.  So, here is the diagram I ended up using:

After an hour or so with the soldering iron, I had the jack, pickup, and bridge connected to all of the pots, with two pairs of test clips in place of the capacitors C1 and C2.

 

To make it easier to differentiate between the two tone controls, I used a Fender-type knob for the treble bleed control and a pointer-type knob for the other bass cut control.  After another hour or so, I had the rest of the bass assembled, strung up and tuned, ready for testing.
 

 

With the help of my son, we tried playing with it, mixing and matching the caps: 0.0047, 0.0033 and 0.0022uF in the bass control, and 0.047, 0.033 and 0.022uF in the treble control.  We found the 0.0047 did very little that we could hear in the bass control, noticed some effect with the 0.0033, and more of a tonal range with the 0.0022uF.  We heard lots of tonal range with all three choices in the treble control and found the 0.022uF afforded the most amount of brightness.  There's some interesting interaction between the two controls as well.

 

The guitar amp we played through was likely a limitation to what we can do with this bass.  It will be interesting to hear it through a bass amp, hopefully sometime soon.  My trip to our local Guitar Center and Sam Ash stores in search of a suitable used practice bass amp over the weekend turned up nothing.  We'll see what turns up on Craigslist in my price range.   Now it's time to make her look as good as she sounds.  Next up for this project includes a new color scheme on all of the exposed surfaces, grounding and tidying up all of the wiring in the control cavity, and a custom pick guard. 

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.

Here's a link to a sample of how the bass sounds without and with the circuit.

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.

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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LeSpork Bass Prototype - The Load Out

But when that last guitar's been packed away
You know that I still want to play
So just make sure you got it all set to go
Before you come for my piano

Just when my son got used to having a bass in his room to play, I found some time to get back to this project. The list of things to-do includes:

• final-solder the controls
• replace missing control cavity and truss rod covers
• make and install a custom pickguard
• install a thumb rest
• refinish the body and headstock 
• realign the neck/body/bridge 
• install neck bolt inserts

I took the bass back out to the shed and took a few critical measurements, and put some thought into the best order to handle the to-do list.  The electronics would need to be worked on outside of the cavity, so I desoldered the output jack, pickup leads and bridge ground wire, and pulled out the controls and jack.

I was still undecided on the overall color scheme, including the color and material choice for the missing control cavity cover.  Since I had narrowed my material choices down to wood and plastic, I went ahead and made a control cavity cover from some scrap wood.  The wood cover would certainly come in handy as a template if I were to go with a laminated plastic cover to match the pickguard and truss rod cover.

Before completely tearing down the rest of the bass, I thought it would be best to realign the neck/body/bridge and install a set of neck bolt inserts.  This would ensure that I could properly set the bass action and intonation, as well as to be sure to plug all of the extra holes in the body and neck before doing the refinishing work.  I took a few critical measurements and determined that an adjustment of the bridge towards the lower upper bout by 3/16-inch would realign the strings with both the neck and the pickups as well as to allow me to use the neck-to-body angle as it was.  The neck set angle could still be adjusted by shaping and shimming the neck pocket during setup.

In anticipation of the finish work, I mocked out a headstock modification to make it look more like a Kramer and laid out a Spork shape for the pickguard on the body with some painters tape and markers.  The pickguard would be too close to the pickguard, so I added 'relocate volume control' to the to-do list...

To be sure I would only reset the bridge location once, I thought it would make sense to first lock in the neck-to-body angle by installing the brass neck bolt inserts and stainless steel neck bolts.  So, I drilled out the existing neck bolt holes to the required 1/4-inch diameter and installed the inserts.

Working without a drill press or hole guide, the body/neck bolt holes I made in this bass were out of plumb.  A smart way to increase the size of these holes would have been to use progressively larger drill bits, allowing the drill bit to be guided by the existing hole.  In a rush to get this step done, I overbored the 1/8-inch holes with a 1/4-inch drill bit.  After installing the inserts, I found they did not line up with the holes in the body.  To fix this meant rework in plugging the body and neck holes and redrilling the holes.

 

The upside to this setback was the opportunity to make an adjustment to the neck/body angle.  After a day for the glue to dry, and some work with files, a chisel and some sandpaper, the neck and body were ready for a shim, a new set of bolt holes and proper installation of a new set of inserts.