Tag Archives: simon allaway

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

My Gold top

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

Original P90 neck pickup and new Gold Foil

Original P90 neck pickup and new Gold Foil

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

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

IMG_2158I’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

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.

telecaster-4-way-wiring

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.

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

Wiring complete!

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

Re-assembled and re-strung

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.

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

0405_Marshall_Amp_630x420Why?

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

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

ZVex Box of Rock – Complete

Build

The build in-progressThe 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

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!

Almost there!

The finished 'Bed Rock'

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.

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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

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

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

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

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

The finished pedal

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

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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

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.

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 guts

The cheesy graphics

The cheesy graphics

 

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TS Overdrive – new enclosure & sound samples

Old enclosure ready for tear-down

Old enclosure ready for tear-down, next to the new one.

Why?

When I built my first Tubescreamer clone (built with a great circuit board from DIY Effects) I was very pleased but left with a few issues that at the time I could not be bothered to fix.

Firstly, the paint finish I used on the enclosure did not turn out very well. I used Rustoleum, and sprayed it on way too thick (because I was impatient…lesson learned). It looked cool, but it didn’t wear well.

Secondly, the DC power connector I originally bought for it turned out to be the wrong size. I only discovered this when I got hold of a power supply, and it didn’t fit. In fact, it was at this point that I tried to use what I thought was an adapter for a smaller power connector. Little did I know that although the adapter fit, it was actually a polarity inverter too; so I blew up 3 JC4558 chips in the process.

So I decided to try an enclosure from Mammoth Electronics, who can provide a painted an drilled enclosure for around $10. Ridiculously cheap.

Wires for the LED "off-board"

Wires for the LED "off-board"

Getting on with it

The rehousing process was very easy; mostly a case of taking the old one apart and carefully assembling it all back into the new enclosure. I did have to redo the LED as the DIY Effects PCB allows you to solder it directly to the board, and let it just stick through the enclosure. I couldn’t do that with the new enclosure and still have it line up with the hole, so I attached wires to the LED and then soldered those to the board. Nice and easy.

The shiny copper on the MOSFET clippers

The shiny copper on the MOSFET clippers

Clipping with MOSFETs

Months ago, after I built my OD2 which uses plain diodes for clipping, I decided to change this OD to use MOSFET clipping. SLW had mentioned it in the excellent PDF file that lays out instructions for building the pedal, and he rated it highly. I was able to purchase the parts easily, and after doing the necessary physical modification (i.e. cutting off most of the mounting lug) the mod was trivial. But what a result in terms of sound! You’ll hopefully hear in the MP3 file below that it has a wonderfully soft clip. It’s as if it has rounded edges. Like an overdriven Marshall, but without the harshness. It does definitely get harsh if you turn the tone all the way up, and responds very well to tone adjustments on the guitar itself. In the clip you’ll hear a variety of pickups and guitar tone control settings (and sadly a lot of repetitive playing).

The setup was:

  • My own build of an AX84 P1 Extreme, with a 6V6 for the output section.
  • Tokai Les Paul with a 1961 Gibson PAF in the neck, and a modern Seymour Duncan JB in the bridge.
  • 2×12 cab with Celestion G12T-75
  • SM57 microphone
  • Recorded in Logic on a Mac. And a touch of reverb in the master output channel.

Click here for the MP3

Almost done

Almost done

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Rehousing a Danelectro Coolcat Vibe

Why bother doing this at all?

Bad knob positioning on the Coolcat Vibe

Bad knob positioning on the Coolcat Vibe. Who thought of that?

Take a look at the picture on the right; that’s the back end of the stock unit. While this device sounds great once you get it dialed in, it’s almost impossible to interact with it while you are playing. While I’ve never thought about it before, it seems that I like to see where my controls are when I’m playing. Perhaps it is akin to driving a car in that even though you might be just cruising along, you still want to be able to glance down and see what speed you are doing. So when you’re tinkering with the vibe’s controls you just can’t see anything because it’s all hidden.

Secondly, the big switch isn’t quite perfect. I’ve become accustomed to the basic switch that every custom builder knows and loves. This one doesn’t seem to switch effectively unless the force you apply is perfectly in line with the axis of travel of the switch.

Thirdly, it’s a really ugly box.

Preparations

I knew I would have to replace a few parts here and there. Here’s what I bought:

  • Potentiometers. I saw from this post that I needed 2 x B50k pots and 1 x C 50k pot. I found 16mm Alphas at Mammoth Electronics, who I had been wanting to try since a recommendation from Shawn over at DIY Effects.
  • DC power connector. The existing one is square and I don’t have an square drill bits.
  • 1/4″ jacks. The existing ones are probably crappy PCB mounted ones.
  • An enclosure. You can get a painted and drilled enclosure from Mammoth for $10. At that price why would I ever do this myself? When I tried it for my first ever pedal build it was messy, time-consuming and ultimately I was not pleased with the results.

Coolcat Vibe - in pieces ready for rehousing

Coolcat Vibe - in pieces ready for rehousing

Disassembly

This part was easy as I could use normal tools, so it only took five minutes. It’s a shame really; this enclosure is really well made, and would probably stand up to a considerable amount of abuse. If only they had located the knobs in a useful place (and it didn’t look like a clam).

The coolest part was finding a ‘real’ 3PDT switch underneath all that cast zinc. It fit the pre-drilled hole in the new enclosure and it seemed I would not have to bother removing the small PCB that it was soldered onto.

Still functioning, sans enclosure.

Still functioning, sans enclosure.

At all stages in disassembly/assemblyI wanted to make sure I didn’t break anything, so I made the effort to plugin and power up the device.

Mounting inside new enclosure

Mounting inside new enclosure

Assembly

The first task was to isolate the power supply jack, and the input/output jacks. You can see that the jacks are PCB mounted, and there are thin shield wires going between this PCB and the switch PCB. I chose to use those wires, and simply solder them to the appropriate replacement parts. At this point I was able to mount the switch and the new signal jacks into the new enclosure, and test once more. So far, so good; I haven’t broken it yet.

One by one the pots get replaced 'off board'

One by one the pots get replaced 'off board'

The next stage was to replace the pots. I had a feeling this was going to be painful, and I was not wrong. Over recent months I’ve replaced many a component in my amplifiers, and other pedals, but I’ve never dealt with PCB mounted potentiometers. What a terrible, terrible nightmare. I fully understand that they are designed this way so that untrained monkeys can assemble the boards, and then they slap some molten solder underneath and its done. After all, I did buy this device for $40 online,so you can imagine that its out-of-factory price is probably closer to $5. But it makes repairs very hard indeed. I managed to cook one leg of the first pot, which meant the PCB trace lifted from the board. Nothing that super-glue couldn’t fix though. My technique of removal was using a solder-sucker. It wasn’t very efficient as the suckers nozzle is quite larger compared to these component legs, and it was hard to keep the sucker ‘focussed’ on the leg AND hold the soldering iron in place. I was more careful with the other 2, so they went more smoothly. And when I say ‘more careful’, I mean I desoldered as much as I could with the sucker and some wick, and then mechanically pulled the pots off the board while trying to keep their solder molten. I know, I know.

The tabs that hold the LDR/Bulb enclosure in place.

The tabs that hold the LDR/Bulb enclosure in place.

Potentially the most treacherous part was rewiring the LED. To get to the soldered legs I had to take off the little metal box that enclosed up the light bulb and LDRs (light dependent resistors). Here’s a great article all about the inner workings of a classic Univibe.

The bulb and LDRs in action!

The bulb and LDRs in action!

You can see in the picture to the left, that there are three metal tabs surrounding the blue LED. All I had to do was gently bend those perpendicular to the board, and the box came right off revealing the bulb. Of course I couldn’t resist powering it up again, just to see the bulb working. In the picture you can see that there are two solder points above the bulb; these are for the LED indicator. Once again I had to carefully de-solder these, so as not to de-laminate the traces. I then attached wires, and connected a bright blue LED in its place.

Enclosure finished

Once I’d mounted the LED in it’s little bezel, I was basically done. I had to make sure I put the metal bulb enclosure back in place, of course, but all that was left was to tighten up any mounting nuts, and close up the box. Here’s a shot of the newly rehoused Coolcat Vibe next to my also-recently-rehoused DIY Effects OD (fantastic Tubescreamer clone).

The finished item...so far

The finished item...so far

An idea

I suddenly had an idea to make this rehouse a little more interesting. In other words, I looked at my vibe and the DIY Effects OD, which I had also rehoused (the green one, duh), and thought they looked somewhat plain. I’m basically proficient with publishing/layout-tools, so I thought I would try and create a decal for the top of the units. I took some basic measurements, and setup grids and guidelines, and just kind of went for it. Sadly I cannot find my decal paper (must buy some more), but I did do a basic printout onto photo paper. This is a work in progress, so updates to follow when I do finally buy some decal paper. The real one would not have the yellow background obviously. I can turn that layer off when I print so that it’ll be transparent, but you get the idea.

A mock-up of the decal

A mock-up of the decal

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What does an AX84 P1 eXtreme sound like?

From the posts in this blog you might know already that my first (and only, so far) amplifier build was a P1 eXtreme, which is a design from the AX84 ‘movement’. It has these characteristics:

  • Single-ended, i.e. Class A output stage, using a single pentode.
  • A two-stage triode-based preamp. My build is using a single JJ Electronic ECC83S (12AX7).
  • A simple tone stack sitting in between the two triode stages.
  • Capable of using multiple 8-pin tube types. My build is using a JJ Electronic 6V6 pentode.

Since I built it I’ve been playing it as much as possible, trying to get to know it’s sound and feel. The only decent amp I’ve ever owned prior to this was a Marshall 2204 50 watt head, which in itself is lovely, but it is way too loud for good tone to be had at home. This was the major reason why I built the P1 eX in the first place. But the question I am most asked is “what does it sound like?”. So this post is to present some recordings I did this weekend.

P1-eX with Tokai Les Paul copy

P1-eX with Tokai Les Paul copy, my 2×12 cab with the SM57 placed scientifically ‘in front’

Setup

I have a very crude recording setup at home. My ‘office’ is an 8’x10′ room with wood panels and a reasonably high ceiling, which is terrible for recording. But these didn’t come out too badly I suppose. Here’s the setup:

  • Apple iMac with built in audio input.
  • Nicely cheap Behringer mixer acting as mic preamp.
  • Shure SM57 placed ‘somewhere in front’ of the guitar speaker.
  • A custom build (I made it myself) 2×12 cabinet largely modeled on the THD design, with Celestion G12T-75 speakers I got off eBay years ago for $50.

The ‘made-up-as-I-went-along plan’

I decided to start with the master volume up full, and the preamp gain down low. Then I’d play a bit, crank the preamp gain a bit, play a bit…you get it. The idea being that one could hear the entire range of the amp from quite to full-on cranked. I also wanted to show the difference between the typical Les Paul type guitar and the typical Strat type guitar.

Recording One – Les Paul

About 5 years ago my wife bought me a fantastic Tokai Les Paul. It’s a pretty damned good copy of someones notion of what a ’59 sun burst would be like. I love it. It plays like butter. (Towards the end listen for my apology to my wife…apparently a cranked P1 was enough to completely freak-out the dog). Pickups-wise I started with the neck and made my way through both pickups on and then the bridge only. As is fairly typical when and amp is cranked you end up with a good tone on the bridge, but then you get mush when you switch to the neck.

Click the orange/white play button for the audio clip: 

I was standing about 4 feet away from the amp which was the sweet spot where feedback was easy to control….right up until it was dimed. You can hear at the end (if you last that long) where she just wanted to squeal whenever I stopped playing. So it must be said, this amp is great just below ‘full-on’. The recording doesn’t do justice to the feeling of being in the same room as this amp, but we’ve all been there, right?

Recording Two – Steinberger

This recording is with my Steinberger. It has the so called ‘7’ configuration of pickups, which means an 89 in the neck position, an SA in the middle and an 89 in the bridge. The 89s have the ability to turn off a coil and pretend to be SA pickups. This means I use this for strat-like tones rather than Les Paul tones. So this recording starts off with the neck pickup in single coil mode. In fact I never use humbucker mode on this recording at all.

Click the orange/white play button for the audio clip:

While I like the tone of a strat-type guitar with this amp, I am still so very biased towards Les Pauls. i.e. if Eric Clapton calls me right now and said “I need another guitarist tonight” I’d take my Les Paul.

Recording Three – Les Paul + a lame tune

This is a simple jam track that I made with my son Dylan. He was noodling around on the keyboard and created this lovely haunting chord pattern. I then ruined it by putting drums and bass on it. Anyway, the ‘solo’ guitar is the Tokai in the middle position, with the neck volume backed off a bit, and the P1 preamp gain at about 80% and the master volume at about 30%. Same recording setup otherwise, in fact the picture above was taken right after I recorded this.

Click the orange/white play button for the audio clip:

I love this tone. It’s what I always end up dialing up on any amp and the P1 gets me this tone at very low volume. That was the whole point right? 🙂

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Tubescreamer transistor substitution

As part of the Tubscreamer clone project, I ordered parts from Mouser based on the list provided by the DIY Effects build documents.  They listed the MPSA18 as the transistor of choice, but at the time of my order Mouser had none, and I substituted a PN2222ATF. But, I realised much later that I didn’t have even the slightest clue as to whether this was a good thing.

From the Geofex site, there are some recommendations on choosing components:

6. Transistors: When in doubt, use a 2N5088. Or a 2N3904 – or a 2N4401 – or a BC549 – or… find cheap, available NPN and PNP devices that you can get easily and use them.

From a Tonepad customer on a forum:

Tonepad site indicates using a 2N3904. This is certainly acceptable, but you may have a little more oomph on the output with a 2N5089 or an MPSA18. 2N3904 are fine units for a lot of purposes, but in this case not so much. You’ll likely be more satisfied with MPSA18 or 2N5088/5089. Stock TS9s come with 2SC1815 transistors which tend to be higher hfe than 3904s, though not quite as high as the A18s or 508Xs.

So it’s all quite ambiguous as these all come across as “opinions” rather than an objective assessment. Time to learn something about transistors, as right now all I know is:

  • They’re all black plastic things on 3 legs
  • See previous point.

Now of course I know that tubes aren’t readily substitutable without knowing more about the application. You can’t blindly replace a 12AX7 with a 12AT7, even though they’re both 9-pin glass bottles, without knowing that the AX has a gain of 100 but the AT is more like 20. Searching around for answers led me to a document that has been plagiarised all over the inter-tubes:

Understanding the transistor data will definitely helps you to find the right and correct part number for substitution.

So, comparing the various parameter’s ratings as written in the “official” Fairchild PDF documents linked above, I see that the PN2222A is actually a pretty good fit for the MPSA18 in terms of VCEO, VCBO, IC etc. But when I look at HFE, the DC current gain, I see:

  • MPSA18  (VCE = 5.0 V, IC = 1.0 mA ) = Min 500
  • PN2222A (VCE = 10V, IC = 1.0mA) = Min 50

This seems to be off by an order of magnitude (even if you adjust for the current difference), almost like the 12AX7/12AT7 tube swap I hinted at before. So it seems the PN2222 is NOT a good fit. I’m going to ask a very knowledgeable friend about this to confirm my guesstimate.

Until I find a good answer, RadioShack has 2N3904 and 2N4401 transistors on their website, so I’m going to wander over to their store at lunchtime and buy a few of each.

UPDATE: RadioShack has little packets of 15 “assorted transistors” for about $2.50. Guess what’s in there? 2N4401, 2N2222 and 2N3904. So I bought a pack each of NPN and PNP. On the back of the pack it describes the NPN types as:

  • Typical HFE: 200
  • VCE 30V
  • IC 800mA
  • Power dissipation: 1.8W
  • …designed for high-speed, medium-power switching and general-purpose applications.

UPDATE AGAIN: Here’s the post with all the details of the final build.

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Boss DS-1 – The Keeley Modification

Boss DS-1

Boss DS-1, innocently waiting to be torn apart. The controls in this configuration sound terrible, by the way.

This weekend I finally got to play more with my new tube amp, and that included plugging in my Boss DS-1. I have to admit, it was somewhat disappointing:

  • It won’t do “clean boost” or even “slightly dirty boost”, which means its not so hot at driving a tube amp cleanly.
  • The tone control is close to useless. It has a really narrow usable range at about 8 o’clock on the dial. Anything above sounds fizzy and thin, anything below sounds muddy.
  • When you get it in the sweet spot though, it does sound good for lead tones.

So I thought I’d look around for modification ideas. I’d read about plenty of them, but never with a mind to actually performing them myself. I’d read about the Analogman modded DS-1, which apparently gets good reviews from Steve Vai (among others), whom I admire.

Also there’s the Robert Keeley modifications (a review). Now remember I am lazy and new to this, so it’s not like I’m going to analyise the circuits myself and come up with anything just yet, so I searched around for practical guides to these modifications, and found this Instructable on doing the Keeley Mod which seemed nice and easy.

The next step is to get the parts lined up, so I used the Instructable documentation to create a project on the Mouser web site. Try this link to my Keeley DS-1 mod “project” which is just a parts list really, but it makes ordering easy. Anyway, parts are on their way, so I’ll post more when I actually perform the mod 🙂

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