Guitar Fetish “Gold Foil P90 Humbuckers” – in a Les Paul

My Gold top

I’ve owned my Gibson Les Paul Deluxe (made somewhere between ’75 and ’77) since about 1991. It came with P90 pickups, which sound glorious. They’re definitely thinner than your regular humbuckers, but thicker than Fender single-coils. I don’t like mushy tones, so this combination is great for me. The only trouble is, they are really noisy. This is exacerbated by the modern world, which is full of computers (and phones) and Compact Fluorescent bulbs, which all put out a lot of RF interference.

One possible solution was to fit normal humbuckers to my LP, but that would require destructive routing. I chose to go for some P90 sized humbuckers instead…..some of these from Guitar Fetish. They’re the right size, and they’re humbuckers!

Fitting them was relatively easy, just a 20 minute job. The only problem that presented was that the new covers didn’t want to fit inside the old routes, so I tried the old covers and they fit over the new pickups perfectly. So now I have retained the look of the originals.

Some observations:

• These are very quiet P90-like pickups
• The P90 style pole pieces are just for show. These humbuckers have blades inside the coils.
• As you can see from the photos, the gold foil isn’t visible due to my use of the old covers.
• The neck pickup is very loud, whereas the bridge pickup isn’t so much. Time will tell as to whether this is an issue.
• I’ve yet to compare them to my Telecaster, but is suspect these gold foils are louder.
• I need to replace the potentiometers as they’re quite corroded. Time to get some CTS pots, or perhaps splash for an Emerson set.

Original P90 neck pickup

Original P90 neck pickup and new Gold Foil

Gold foil cover doesn’t fit, so here’s the old cover on the new pickup

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Rewiring a Telecaster with a four-way switch

Conventional 3-way switching

I’m willing to be that 99.9999999% of Telecasters are equipped with the conventional 3-way switch that offers up the bridge pickup, the neck and bridge in parallel, and then finally the neck pickup on its own. Time has shown this to be perfectly satisfactory as those 3 different tones have been and continue to be “go to” tones for musicians world-wide. My interest in Telecasters comes from a range of guitarists:

Mark Knopfler

He used one on many tunes like Espresso Love, and even the grotesque Walk Of Life. His Tele tone was always fat and chunky. I don’t know which Tele he used on early tracks, but since late ’79 he used ones built by Schecter back when they really built custom guitars.

George Harrison

He’s famous for his gorgeous rosewood Telecaster, which he used to great effect on “I Want You (She’s So Heavy)”. You can hear him switching between neck and bridge as he plays over verse and chorus, and then the big riff at the end as he grinds through on the bridge pickup.

Joe Walsh

One of my favourite solos ever is the two-player epic that is Hotel California. A fantastic battle between Don Felder on a Les Paul and Joe Walsh on a Tele. You get to hear the difference between the two guitars…the thick bite of the Les Paul, and the sweet glassy edge of the Tele (probably set to both pickups in parallel…the normal middle position).

Conventional 3-way pickup wiring for Telecaster

Why 4?

Over the years I’d always heard that one could get different tones out of a Tele by wiring the middle position so the pickups were in series, rather than in parallel. And that this would give you a “big sound”. That didn’t make much sense at the time, but as I hadn’t ever heard this configuration, I had no reason to doubt it. But I had to try it myself one day.

Recently I spotted a pre-wired kit from Emerson that went for about $65. They do such a lovely job of the wiring I seriously considered getting one. But that’s cheating, so I bought essentially the parts for it from Stewart McDonald so I could build it myself.  Here’s the parts kit. They also sell the ludicrously expensive capacitor that Emerson includes.

The alternate 4-way switch wiring diagram

Pickups

My lovely wife bought me a set of “Vintage Noiseless” Telecaster pickups, made by Fender. That’s just how lovely she is. So this was a perfect time to install those too. I had originally installed a Schaller telecaster pickup in the bridge and a no-name neck pickup. They sounded OK, but in this modern world of computers-as-tape-recorders and compact-fluorescent bulbs, they were very, very noisy. Second only to the P90s in my Goldtop, but that’s another story. A third reason for doing this is that the cheap Japanese 3-way switch I’ve had in it for almost 15 years was failing quite quickly.

So, the wiring wasn’t hard. The only thing that slowed me down was I decided to use the fabric covered wire that came with the StewMac parts kit. I;d never used it before. You’re supposed to cut to length, and then push the fabric back to revel tinned wire. All cool so far, but then the fabric springs back making it a little hard to solder even if you get a good mechanical joint. I’m used to using Teflon covered wire that I strip before soldering. Anyway, it looks cool, so I won’t whine too much. Here’s some photos.

Here are the noiseless pickups sat waiting for me to begin removal of the old pickups.

Wiring complete! You can see the ludicrously overspecced 200 volts capacitor, from Emerson.

Re-assembled and re-strung

Sound demo

The only thing left to do was to plug it in and see what it sounds like. Here’s a quick recording of me noodling around in Em, and switching between each position. This is plugged straight into my AX84 single-ended tube amp, set to be somewhat crunchy, into my 2×12 cab with celestions. Recorded with an SM57 right into a Mac.

I begin on the bridge pickup. The switch to neck and bridge (parallel) is at 1:49, the switch to neck alone is at 2:43, then to neck and bridge (series) at 4:14.

Building a “static wah” pedal on veroboard

What is a wah pedal?

A normal “wah pedal” is a device that you drive with your foot. When you waggle it back and forth it makes your guitar sound like a human literally going “wah wah”. It was built (possibly by accident) to emulate the way a trumpet player might use a hand-held mute, but it doesn’t really sound much like that on a guitar. It is definitely its own sound. To understand the ‘traditional’ circuit here’s just about the best explanation ever written about them. Indeed, within weeks of the first useful device appearing on the market, Eric Clapton was using it on the Cream track “Tales of Brave Ulysses” to great effect. Then it became de riguer, and the likes of Hendrix, Beck and even George Harrison took it to great heights themselves. And for us amateurs, a pedal board is not complete without one. I currently have a Boss V-Wah, which does a passable simulation of a standard Cry Baby wah, as well as others.

Jimi doing the wah thing

What is a “static” wah pedal?

Sometimes when you’re playing with a wah pedal you end up leaving it turned on without your foot on the pedal. And sometimes it will even sound good. Legend has it that Mark Knopfler played the Money For Nothing intro using a wah pedal left in a certain fortuitous position. After reading various interviews about those mythical sessions, it’s not so clear. It seems the tone was achieved accidentally with some unorthodox positioning of the mics, which implies their locations created odd phase relationships, which in turn may have sounded as if someone used a notch filter (kind of like a wah). But then this one talks about Knopfler himself describing the concept of a static wah. I read a third interview once (can’t find it now) that supports both. i.e. the studio recording was the accidental mic positioning, whereas when MK tried to recreate the tone elsewhere he tried using a wah pedal (in a static position). Either way, I want to build a static wah for a second, and perhaps more important reason: Robin Trower uses a static wah for solos. Here’s Mike Fuller, from Fulltone:

11 years ago I made a couple of fixed wah wah effects I called the Wahfull®… they were simply the guts from a wah wah stuffed inside a box with a knob so you could find that perfect Mid-Boost sound every time you kicked it on. Nice effect, sold a few, moved on. Last year Robin Trower called me and said he was doing some gigs with Jack Bruce and asked “Would it be possible to have a wah wah in a regular box so that one could get that “fixed wah” sound by clicking on the pedal?” So I made one up and he’s been using it ever since.

Here it is in all its glory on Trower’s stage rig:

Trower’s rig – including the Wahfull

* Note how Trower doesn’t use a power supply, or even a pedal board. Rock ‘n’ Roll!

Bringing it to fruition

So, all I had to do was find a decent circuit, and make the damned thing. I didn’t have to worry about buying either a broken wah or buying a new empty enclosure as this will fit in a standard pedal enclosure, such as the 125B I had laying around. I found a circuit on Sabrotone’s site: Here are the useful features over and above a normal wah circuit:

• A ‘gain’ control to add a bit of grit/boost. I am a big fan of using a booster to give you a bit of “ooomph” when entering a solo.
• a ‘Q’ control to change the width of the notch. This offers flexibility for little cost.
• A ‘volume’ control to help match levels, especially when you’ve cranked the Gain a bit.
• A multi-position rotary switch to adjust the main filter’s capacitor. Again, flexibility is good if it doesn’t degrade tone.

The mods are such that it still retains its bog-standard Vox circuit, but it becomes a little more useful for modern times.

The layout

The Sabrotone “WahWithMods” layout

Almost there

I forgot to drill the hole for the capacitor switch. Doh!

The finished article

Demo

Here’s a demo clip. It’s with the usual setup: my Tokai Les Paul, the one with the 1961 hum bucker in the neck. It’s going into the static wah, then my Box of Rock clone. Then into my AX84 amp, into a 2×12 cab.

I start off with the clean signal, then I turn on the way. Then I turn off the wah, and turn on the Box of Rock for a second. Then the wah goes back on. Each time the wah goes on I begin with the frequency knob anti-clockwise and work my way around to maximum. This is the same as ricking a wah pedal from back to front. You can hear that happening especially in the overdriven section.

Building a PT2399 based delay pedal

The populated board, close-up

My friend at DIYEffects was kind enough to send me a PCB he had constructed for a delay pedal. His is based on a PT2399, which is a very popular (and extremely cheap) integrated circuit that will take an audio signal and produce an echo of up to 500-600 milliseconds. It does all this in 44k of digital memory. That’s nothing at all. Oh and they cost about $2 at the time of writing. Seems too good to be true?

Maybe. There are compromises of course. Mainly in what amounts to fidelity of the repeating signal. With only 44k of memory there’s no way this will be a sparklingly clean 16bit/44 kHz digital delay that you might expect from Lexicon. As is fairly typical in the world of guitar effects, it turns out nobody actually wants a crystal clear delayed signal. If you ever get to try it out you’ll find that the repeats tend to drown out the dry signal as a hi fidelity ‘wet’ signal will have all the same frequencies as the dry signal so it kind of stomps all over it. The ‘low fidelity’ wet signal of the 2399 has somewhat muted high frequencies, so it sits under the dry signal quite nicely.

Problems!

The biggest issue I had with this circuit was that it would only work intermittently. In fact, it worked perfectly on first power-up, and I was able to play it for an hour or so with no issues. But when I came back to it this year ( I had populated the board and got it running a couple of years ago) and fired it up, there were no echoes. None at all.

I always blame power first, so I did some measurements to ensure that the op-amp had some power, and the 2399 chip itself had things in the right place. It looked like the 5v regulator wasn’t quite doing what it should, so I replaced that and made sure the pinouts were going to the right sockets. This helped as now I had a steady 4.8v at pin 1 (Vcc) of the 2399.

Still no echoes though. I read a post (here) that talked about “latching problems”:

First, I’ve had the PT2399 ‘lock up’ on me two or three times now.  When this happens the circuit passes signal but you get no delay.  The regulator inside also gets hot (and could cut out I guess).  The effect can come back to life with the same PT2399 after disconnecting it from the power supply for a spell.

This sounds exactly like the issue I’m having. So this post lead to one from Merlin himself:

Some devices appear to latch up or fail to function properly if digital ground (pin 4) is left unconnected. This pin should usually be connected to analog ground (pin 3).

So I made a simple jumper from some scrap bits of stranded copper wire, and soldered it across pin 3 and 4. Problem solved.

A real effects pedal power-supply

Why?

Over my playing years (more than 30 now) I’ve owned many effects pedals, spent a ton on 9V batteries and even tried many different power supply devices. I had one of those VisualSound “1-Spot” daisy chain things, which worked quite well. And recently I was given a Furman SPB-8 which appears to be the mother of all pedal boards. If you’ve been to this site before you know I’ve built an amp, and a whole slew of different pedals. All of these things I mention have one thing in common: there’s a lot of attention paid to converting alternating current from the wall outlet into direct current to power the circuit.

How?

After looking at many different power supply circuits, I realised they looked very simple, but I did not know the first thing about why each component was there and what they did.

My cousin Mike was in need of a power supply for his pedal board that could handle anything that he threw at it (i.e. multiple voltages and a useful current handling capability). Naturally there are products one can buy, such as the Voodoo PedalPower or the MXR Brick, but these can be quite expensive. And lets face it, I wanted to build one, so I could find out how they work.

What?

So, what does this thing need to do? Basically the following is desirable:

• Provide a steady 9 volts.
• Do not introduce noise into the circuit.
• Handle at least ten pedals’ loads, which might approach 1 Amp.
• Be small enough to fit under Mike’s pedal board.

Transform, rectify, smooth and load

From my work with tube amps and reading everything I could find in print or online, it became clear that, at a fundamental level, there are only a few discrete steps to accomplish:

1. Transform the outlet supply from 115V to something closer to the desired voltage.
2. Use a rectifier to convert the AC supply to a DC supply.
3. Use filters to smooth out the now rippling DC.
4. Load the circuit with whatever you wish to actually provide power. Whatever that is, it require voltage, will draw current and therefore has resistance.

A transformer is easy to get hold of. Even Radio Shack sells a 9V AC ‘wall wart’ that will handle 1 amp. A rectifier is easy too; just a bunch of diodes arranged in a certain way.

The filtering though was a mystery. How do you know what values to use? After gathering quite a few different circuits it seemed everyone was using different values, so who had it right?

The idea is this: use the characteristics of a capacitor to ‘fill in the gaps’ of a rippling DC supply. Remember, we rectified AC, which gave us rippling DC. That ripple will be at a frequency that can be heard by us humans, so we need to reduce that ripple to be inaudible.

Here’s a graphic showing a number of things. Firstly, this is a time-series showing voltage over time for the circuit at the top of the bitmap. Its a simple circuit showing an AC source going through a rectifier. Then the AC signal flows across C1, a capacitor. This graphic is to explain how to calculate the value of C1, and the influence it will have on the green waveform, which is the rippling DC source (post-rectification).

Ripple smoothing calculation

So imagine it like this:

1) The rippling DC source voltage rises to reach about 32 volts. During this time C1 is charging.

2) as the DC source starts to come back down, C1 starts to discharge. This serves to “fill the gap” between the ripples.

The chart is showing, with the different coloured lines, the influence of different values of C1 on the rippling DC.

Here’s a great article on this subject.

A more modern approach.

It seems to me that it is rather than painstaking to install a network of capacitors to perfectly smooth out the rippling DC. Also, transformers are far from perfect, so under load they sag, in terms of voltage. Even if you got all your calculations right, under load it will behave differently.

It is far easier, but not necessarily more efficient (in terms of trees and polar bears), to use a voltage regulator. The 78XX series works very well. You give it more voltage than you require, say 12V, and it does the work to provide you with an almost entirely ripple-free steady 9V. Any excess voltage is ‘given up’ as heat. This is why you might need a heat-sink (and why dolphins and rainbows are destroyed). Here’s a typical circuit using regulators:

A typical regulated power supply for guitar pedals

The end result

I came up with a simple circuit that used part of the above circuit to provide 9V and 18V for about 10 pedals. My initial circuit was flawed in that I’d ordered the wrong voltage regulators. They could only handle 100mA. Once we’d connected up all of Mike’s pedals, it would literally cut out. I even connected each one individually to my bench supply so I could measure each ones current draw.

Investigation showed that the regulator was extremely hot, so it became clear that the thermal protection was being tripped. I replaced the 7809V regulators with higher current handling ones and all was well.

Here’s some photographs of that build:

A very simple decal makes the enclosure look quite spiffy, I think.

The circuit mounted inside, with all the DC connectors

The final schematic

And the final schematic, with values underneath:

• D1 – 1N5401
• C1 – 470uF
• C8 – 0.1uF
• D2 – 1N4148
• IC1 – L7809CP
• C3 – 10uF
• R1 – 100R 1Watt
• C2 – 100uF

 

Building a “Tremulus Lune” on vero-board

One of my favourite pieces of music, let alone guitar playing, is by Ry Cooder. A track called “Feelin’ Bad Blues”. This video is an excerpt from the film Crossroads where the tune was used to great effect. For me it is the epitome of blues guitar. Sad, slow and gritty. And that thick tremolo (probably from an old Fender amp, not a Pignose) is the icing on the cake.

So that’s what this post is all about; making a pedal to give me that tremolo effect. It didn’t take long to find the defacto standard tremolo pedal; the Tremulus Lune.

Layout

Layout

Research showed that I could buy a kit, or even a pre-made one, but where’s the fun in that? I went for the layout from Guitar FX Layouts (seen here).

The novelty with this circuit for me was it used a component called a Light Dependent Resistor (LRD). Essentially one part of the circuit is a Low Frequency Oscillator (LFO), controllable with various potentiometers. The ‘low frequency’ part refers to the fact that it is creating a sine-wave in the range of 3-10hz (I haven’t actually measured it). This wave is used to drive a normal op-amp, thus varying amplitude over time, which is in fact the definition of “tremolo”. One difficulty was getting hold of the correct LDRs.  They needed to have the range 5k/500k. It was easy to get hold of all kinds of LDRs, even from Radio Shack, but I had to trawl through Ebay to find the right ones. I have a bag of 20 now.

The build

The finished board

This isn’t my first veroboard build, so the build/assembly went quite quickly, in a pleasant way, and I had it operational on my prototype rig within a couple of hours. It sounded amazing! It truly is a versatile tremolo; you really don’t need anything more complex than this.

The device has three LEDs. One for the usual on/off indicator; another one to couple the LFO with the op-amp (by pointing the LED at the LDR, kind of like a vibe pedal does) and a third one to show the speed of the LFO externally. I decided to use the nice fresnel lens LED holders I bought a while ago. I just think they look really cool. The picture below shows them in their full glory, although the red LEDs look somewhat pink. To fit them I needed to get a 17/64ths drill bit. I have hundreds of drill bits, but not that one. So, a trip to Ace Hardware for that.

Fresnel lenses

The enclosure

This one’s got 5 knobs, so I had to use a 1590BB and I chose to go for a vertical orientation. As for a design I went for the whole Crossroads theme. I combined the lyrics to the famous song, and depicted the actual crossroads by using highway signs. As far as the decal goes, I wanted it to wrap over the sides as I thought it would look cool. I printed it on transparent ink jet decal paper this time as the enclosure is bright white.

Drilling the enclosure

The decal

Demo Recording

So I finished the assembly and got it all plugged into my usual rig, and recorded a swift demo. As I mentioned earlier, the reason I wanted to build this was for that archetypical blues tone. So here’s my own sloppy rendition of that kind of sound:

Click here for MP3

The setup was: Tokai Les Paul, neck pickup (a humbucker from a 1961 ES-335); my AX84 P1 Extreme into a 2×12″ speaker cab, with Celestions; my Box of Rock clone for some grit, and the Tremulus Lune of course. The reverb came from Logic, and was a ‘small church’ kind of setting.

The finished pedal

Building a Z.Vex Box of Rock on vero-board

Why?

As most guitarists will admit, we’re always looking for a better sound. Some look for new and perhaps innovative sounds. Others, such as myself, want to sound like the players we admire. One classic tone I had never really toyed with is the sound one gets when you crank a JTM45 Marshall. In my opinion it is in my Top 5 sounds. The likes of Clapton, Hendrix, Young (Angus), and many others, started their careers with it. There’s no need for me to recount the origins of the circuit as that’s well documented.

So, you might ask “why not just buy a JTM45?”. Well, one in good condition from the 60’s might set you back 5-10 thousand <local currency units>. A new one, such as those available at Ceriatone go for about $1000….a ‘real’ Marshall? more like $1800.

How

One solution is to approximate the tone in a pedal. And yes, I’ve built way too many overdrive/distortion pedals already, but not one like this. The approach here is to cascade two or more gain stages to ape the design of the JTM45. This has been done may times in plenty of pedals, but a popular one is the Z.Vex Box of Rock. I first heard of this device when it was mentioned by Davy Knowles, who is an excellent blues guitarist. Searching briefly online and I found that the design of the pedal built upon the Super Hard On booster; one of which I built last year. This struck me as a great way to go as I understood that circuit.

Schematic

ZVex Box of Rock schematic

Even if you can’t read schematics, you can probably see a pattern repeating itself. There are 4 BS170 transistors arranged as gain stages. They’re chained together and setup in such a way to simulate the characteristics of a tube amplifier. There’s a 4th one (at the bottom right of the schematic) which is the boost section. That will have its own footswitch, so it can be turned on when you “need a bit more”.

I went for a slightly different EQ section. As it stands the BoR just has a simple Muff-style filter. As in, a low-pass filter and a high-pass filter ‘mixed’ together by the tone knob. There’s a great variant that adds a ‘mid scoop’ control, as specified beautifully here by AMZ. It was simple enough that I decided to add it myself.

Layout

I got the veroboard layout from my usual place: Guitar FX Layouts. This guy always does a great job, and is always around to help or explain things. Fantastic!

ZVex Box of Rock – Complete

Build

The build started off ok, but proved tricky. I quickly realised that I’d done something very wrong as it just sounded very odd. I remembered experiences from previous builds and went back with a fresh printout of the layout, and ticked off each cut, link and solder spot, and made sure the component values were correct. It turned out I had got some cuts in the wrong place. Literally as simple as that. I was careful to use sockets for the BS170s; this meant I was able to leave them out until the last minute so as to not expose them to static shock risk.

Enclosure

Spray and bake – the black paint hardening under the lights

I went for some custom graphics again. As is typical I couldn’t really think of anything particularly innovative, and ended up calling it “Bed Rock”. This stands to mean two things: 1) This tone is the bed-rock of modern music 2) You can get that tone at low volumes so you can ‘rock’ in your ‘bedroom’. I know, cheesy.

Most of all I wanted to created something with a splash of colour. So many pedals look so very boring. I did the usual flow of finishing the enclosure with enamel based spray paint. This time it was a cheap can of black from Ace Hardware. I was actually going to try something new and bake the enclosure in a toaster oven, but I realised that I was already doing a kind of slow bake with my work-lights. And as I wasn’t in a hurry, I stuck to my usual routine.

For the decal itself, I used a combo of Photoshop and Illustrator to create an image. It was printed on my trusty HP Office ink-jet printer, onto white-backed decal paper; purchased from Small Bear Electronics.

One pleasant discovery was that you can get high-quality fonts for free at sites like FontSpace. Here’s the one I used for the main wording, All Ages.

Almost there!

The finished ‘Bed Rock’

Demo

I think it came out well. With a Les Paul, it’s ridiculously easy to get that classic AC/DC rhythm tone with everything at 12 o’clock, and with the boost section kicked in you’ve got just that little bit more sustain available for a solo. Even a Strat sounds good. On mild gain settings it really makes single-coils come alive. I ought to do a recording of that too, I suppose. Here’s a demo file of the device.

My setup is the same as usual: Steinberger GM-7SA plugged into an AX84 tube amp, running clean into a 2×12 open-backed cab, with Celestion G12-75T speakers, miced by a Shure SM57 being recorded by an Apple Mac.

AC128 Germanium FuzzFace – with ‘Fuller Mods’ – from DIY Effects

Over the last few weeks I’ve had the privilege to assist SLW over at DIY Effects on a new PCB offering. It’s a FuzzFace circuit that has many great features:

• A nice quiet power supply section that offers positive and negative ground. You simply place a jumper where you need it to be. Firstly this means you can use NPN and PNP depending on your set of transistors. Secondly with the recommended transistor sockets, (and the jumper sockets I added) you can switch between silicon/germanium or NPN/PNP in about 30 seconds. (See the ‘B’, ‘V’ and ‘A’ holes on the partially assembled picture below).
• It has options for a couple of caps that can help reduce hum and soften the distortion a little. These are part of the Fuller Mods.
• It has options for the other Fuller Mods; namely the ‘Less ‘ and ‘More’ pots. ‘Less’ or what I decided to call ‘Load’ (even though SLW nor I can decide on what to call it) acts upon the input. The ‘More’ control plays with the voltage on the top of the second transistor, which in effect changes the bias. This will tweak the waveform distortion characteristics. In fact, SLW prefers to call this control “Bias”, because that’s exactly what it is. More on this later.
• The PCB features a spot for an optional trimmer to aid in deciding where the ‘Bias’ pot ‘centers’. More on this later.
• The PCB has been designed to use DIY Effects ‘stmp’ switch and ribbon combo. This makes the wiring of the off-board stomp 3PDT switch a 30 second job. We’ve all spent much longer than that cutting and stripping 9 wires to wire one up normally, so this is a godsend.
• The other time-consuming (and error-prone) part of wiring a stomp box is the potentiometers. The DIY Effects fuzz PCB has holes setup so that you can use PCB style Alpha pots instead of the regular lug type. Again this significantly speeds up the assembly of the board. And it gives you a very sturdy board support within the enclosure, so no need for dodgy nylon supports anymore. Of course if you want to use wires, you still can.
• The PCB is designed to fit neatly into a 125B sized enclosure.

Partial assembly showing the new pot mounting holes and the power jumpers

Choices to make

There’s no shortage of voodoo going around about the FuzzFace circuit; mostly surrounding which transistors to use. Some say that germanium is the only way to go, but it seems that’s more an artifact of the times rather than through any real objective truth. Jimi Hendrix was using germanium FF boxes because that’s all there was at the time (probably). The likes of Eric Johnson (or any modern hipster indie guitarist playing a Mosrite) is probably using a silicon transistor based FF. The reason being, germanium transistors are unstable depending on temperature, and they vary widely in terms of gain and leakage from one to the next. The industry switched to silicon precisely to combat this problem. So this is yet another case of a manufacturer using whatever they had on had at the time, not because of some kind of mojo.

Standard silicon fuzz on the prototype board

Despite all this superstition, which normally sends me running, I went for a pair of AC128 germanium transistors from Mammoth Electronics. A pair of germanium transistors can cost anywhere between $10 and $50 depending on how much you’re prepared to be fooled; either way they’re orders of magnitude more expensive than their silicon counterparts. So choice one: AC128 transistors. This means I must use positive ground when I wire everything up. Make a note.

I also chose to try all the Fuller Mods. This was mostly because I hadn’t ever used a Fuzz-face before, so was eager to try it in all it’s ancient and modern glory. As a nod toward what might be called the mediocre standard circuit, I did initially build a completely standard silicon fuzz. This proved encouraging, so I ploughed on. Geofex has a fantastic discussion on The Technology of the Fuzzface (including the Fuller Mods).

Decals

This is often the most stressful, but ultimately satisfying part. I was able to designing something with much greater confidence this time as I started with a drilling guide supplied by DIY Effects. It was PDF form, and layed out accurate to the millimeter. This meant not only did I have a perfect basis for my design itself, but I could design it over the spots for the holes that I would then use for a drilling guide. Adobe Illustrator was my software of choice. Inkscape wasn’t working out as you cannot zero the ruler arbitrarily, which irritated me to no end.

The design in Illustrator

Assembly

Initially I made a huge mistake in ordering a 1590B enclosure instead of the correct 125B size. This mean I went ahead and drilled the holes and even sprayed the enclosure a lurid gold metallic. When I came to test the layout by offering up the board it didn’t fit…at all. But that’s OK. I will use the gold enclosure for an eventual silicon fuzz. 5 minutes on the Mammoth site and I had ordered the correct enclosure with a lovely Tiger Red sparkle finish.

The ill-fated gold enclosure next to the assembled Fuzz circuit

NOTE: It’s hard to see from the above picture, but there are only 4 wires coming off this finished board; signal in/out, 9V in and ground. With the new ‘stmp’ board and SLW’s choice of potentiometer, this is all you have to then wire into the enclosure. It’s magical!

Biasing and Temperature

As mentioned in the preamble, the fully featured PCB has a Bias control, and a trimmer. The Bias control is able to swing the bias on Q2 across an approximate range of 3 volts.

The typical FF circuit is setup to have -4.5v (measured at point ‘T’ on the PCB). The Bias knob allows you to swing that up to as much as -5.0v. The trimmer will allow you to decide the start of this range of adjustment.

While tinkering with these two controls I happened upon a characteristic of germanium transistors. i.e. they are sensitive to temperature. Now after reading plenty of articles about FF circuits I knew this, but I didn’t really understand what it meant. I had imagined that it meant their “performance” in a circuit might be thrown off by say 50%; much like the way most reasonably priced passive components have tolerances. What I wasn’t expecting was what I observed first hand. When I was tweaking the trimmer to adjust the range of the bias I had the unit on its back with the bottom plate off, and my left hand held the red multimeter probe on lug T. My right hand held the screwdriver placed on the trimmer. My multimeter sat behind the unit so I was forced to lean in close to see it. When I started to make the adjustment the first time, the bias voltage leaped up to about -6.5v!!

This caused me to replace R2 with different values, but that made no difference. And indeed I was getting what amounted to random bias ranges with each change. At this point I became frustrated and stopped for a while. When tempers cooled I came back to it, and measured the bias again…it had dropped back to around -5v and I could move it back towards -4.5v with the trimmer. But then as I did just that it started to rise again. I checked for the seating of the transistors in their little sockets, but they seemed firm. Then it hit me…temperature! I placed a finger on top of the transistors and sure enough, the voltage went nuts. It was being affected by me breathing on it while I was making adjustments.

So at this point I returned the circuit to standard values, set the bias for -4.5v (with the ability to go up to -5.0v using the bias knob) and called it a day. A very instructive waste of time 🙂

The finished article

Once the decal had dried, and the clear coats had been sprayed, I waited 3-4 hours for the paint to dry. The last couple of pedals I finished myself I had used Krylon clear coat. It works well, but it sprays on very, very thick, and literally takes weeks to dry sufficiently. Until that point it is prone to finger prints and other such handling artifacts. For the Fuzz I tried Rustoleum clear gloss. It sprayed on about the same as the Krylon, although it was less forgiving and I had to be careful to keep it “wet” but not by too much. Also, due to my impatience I was spraying in high humidity, so it tended to go on cloudy (moisture in the air), but cleared soon after. But anyway, all turned out well, so here’s the finished pedal:

The finished pedal

A quick demo MP3 file of the DIY Effects Fuzz Circuit:

Prototype reverb pedal using the Accutronics/Belton BTDR-2H module

As a follow-on to my previous post about building a breadboard prototyping rig, here’s some information about my first attempt at a circuit.

The schematic

I found a schematic within the application note for the module itself, on this page but it did not include schematics for the power supply circuitry. I’m still so new to op-amps that I wasn’t about to make things up on the fly. I then stumbled upon this schematic on freestompboxes.org. Here’s the post, but you need to register to see it. Here’s the drawing I studied:

Box_of_Hall_Schematic_V1-1

So if you break it down into discreet sections, it’s actually rather simple:

Power supply

In many respects the power supply section was the eye-opener for me on this project. I’ve worked with tube amp supplies before, but never one designed for not only op-amps, but with provision for a ‘module’. So what you see at the top of the drawing is exactly that; 9V coming in from the wart/battery, a little bit of filtering, R1 and R2 dividing the voltage, to get 4.5V for op-amp bias, and the 7805 regulator to give the reverb module 5V. The voltage from the divider goes into one of the opamps to be regulated.

Shawn over at DIY Effects very patiently helped me understand the ins and outs of op-amp power, which was very useful. I had read a lab paper that has some great exercises for exploring op-amp behavior: here, which insisted that op-amps must be powered appropriately, regardless of whether the schematic indicates this. I’m used to tube amp schematics omitting the heater wires (they’re always there, so why bother?) so it became clear with Shawns help that this was true, and that I had simply missed the part of the schematic where pins 4 and 11 are connected to the TL074 quad-opamp. Duh!

Also, most articles focussed on theory talk about bipolar power supplies providing + and – voltage for the opamp, and then a virtual ground in between for bias. This didn’t make much sense until I realized the schematic here provides +9V from the main source, 4.5V for bias, and zero V ground. In relative terms this is identical. Here’s a good article on ‘virtual ground circuits‘.

Anyway, that top section of the schematic was my starting point, so I made reasonably fast work of getting it all working on the breadboard. I was able to measure 9V on the main rails, 4.5V on VB (meaning Voltage for Bias, we supposed) and 5V at VA (for the module. All cool so far.

The rest

The next day I just continued by working my way from left to right on the schematic, wiring up components and crossing them off the printed schematic. Again, through building tube amps I learned to mark progress as I went along; it really helps me as I have a terrible short-term memory.

The challenge at this point was to translate the schematic to a breadboard layout, which I had not done before (other than the 555 LED blinker project from ‘Electronics for Dummies’). I have no magical insight here, I was just lucky I think as this circuit doesn’t sprawl across the board; it’s very simple.

Mistakes were made, absolutely. When I first fired it up I got no sound, but this just meant I got to debug it. I went back with my multimeter and checked power. It was clear that something was wrong as I was getting about 7V for VB, which should’ve been half of the main 9V rail (due to those two 10k resistors between the rails acting as a divider). This led me to check all the connections surrounding the opamp, and I soon found that I had screwed up just two wires, and forgotten to ground the opamp at all. By this point I had a guitar and amp connected, so when I powered it up for the 3rd time, I knew I had a signal. And sure enough it works!!!

Bread-board chaos

UPDATE! I managed to get this circuit onto veroboard, using the ‘Box of Hall’ layout that’s floating around online.:

The circuit on veroboard.

Here’s a recording of the unit, with a clean sound to start of course:

UPDATE! July 29th The reverb pedal now has an enclosure…

The guts

The cheesy graphics

 

Breadboards and prototyping pedals

As time goes on I become more and more addicted to futzing with pedals, which is a good thing I suppose. But it is tempting to just keep building kits without really knowing whats going on in there. I’ve made attempts to tweak the pedals I’ve built from DIY Effects but only to the extent of messing with clipping diodes. And to be honest they sound great already, so there isn’t much to be done. What I really want is to go back to basics and learn how different parts of the circuit work and also how they interact with others.

So I needed a way to, for example, build a simple transistor gain stage (like the SHO I did before) and perhaps chain it with another one, to see what happens. Or build a generic fuzz and then play with bias values or different transistors. You get the idea. All this is harder to do if you are constantly soldering/desoldering components, so it’s time for breadboards 🙂

This project is nothing magical, just some parts assembly, but it was a lot of fun. I based my version on the Beavis Audio board that you could once buy in kit form. Here’s the link to the Beavis site, and a photo of mine:

The prototyping board in its first incarnation.

What’s going on?

Power comes in from a small bench supply I have (not shown) via a standard 2.1mm socket on the back of the breakout box. That goes into the 10k pot, which lets you simulate crappy batteries. ALso not visible are the two 1/4′ jacks that serve as guitar in and effect out signals. You can clearly see the 3PDT stomp switch and the smaller toggle. All these connections are present on the connection block which I bolted to the side.

I also added a board on the back with some handy holes drilled in it. These will hold whatever pots and/or switches the circuit might need. Shawn from DIY Effects had done this, and it looked like a great idea, so I stole it 🙂 Here’s his blog entry showing a massively complex circuit on his protoboard. One day I’ll get to this stage!

What’s next?

• Build a reverb circuit, probably the ‘Box of Hall’ circuit featuring the BTDR-2H reverb module. It should be very simple.
• Build a generic fuzz-face and then progressively mod the crap out of it to see how it works.
• Try some cascading gain stages (based on the Z.Vex SHO) to see what following the tube amp topology achieves.
• Arduino!!! (this is a potential can of worms that will end with a switchable rack system…mark my words)

UPDATE! Here’s the Box of Hall circuit on veroboard. I still used the breadboard rig to hook up to power and I/O. And with great joy I realized that my little Marshall practice amp (if you can even call it that) clips onto the the back quite nicely 🙂

The circuit on overboard, connected to my huge Marshall stack.

UPDATE 2: I did a prototype of the classic Fuzz Face. Not much to see, but it’s proof that the breadboard has made it very very easy for me to experiment with different circuits.

Silicon Fuzz-face!