Project 6 - Valve Caster | F1
Having already built a few transistor-based circuits, I decided it was time to try something new. The Valve Caster was designed in 2007 by Japanese builder Matsumin. His original goal was to make a simple 9-volt tube booster that anyone could easily build. What sets this device apart from other boost pedals is that it uses a vacuum tube instead of a transistor to generate overdrive distortion while boosting the signal.
The moment I saw photos of this pedal I knew I had to build one; and since it was designed to be an easy build, I assumed this project would be a breeze... It seems I was wrong.
Choosing the Schematic:
Searching online you'll discover several variations of this pedal, each one slightly different from the next. When trying to decide which schematic to follow I thought I would save some time and chose a wiring diagram that already had the strip board layout completed.
I made the foolish assumption that this layout was correct and didn't bother testing the circuit on a breadboard - this was a huge mistake.
The wiring diagram turned out to be wrong. Had I actually tested it first on a breadboard I would have discovered this, saving myself from weeks of frustration. I guess some lessons can only be learned the hard way.
LED's:
The first thing everyone notices about this pedal is the illuminated vacuum tube. This was done by adding a 5mm LED just below the tube socket.
Initially, I wired it so the LED was activated only when the pedal was engaged; but I really liked the ominous red glow, and rewired it to be On whenever my pedal board is powered.
Now that the LED was now always lit, it was difficult to tell when the pedal was engaged; so I added a 3mm indicator LED just above the foot switch.... problem solved!
Power Supply and Vacuum Tubes:
All the guitar pedals I've build have been powered with a 9-volt centre-negative adapter.
When searching online for schematics to build the Valve Caster I noticed some versions were powered with 12-volts and decided to give it a try.... The sound difference is truly incredible!
Turns out, most vacuum tubes function better when powered by higher voltages, resulting in more headroom and better distortion. For anyone interested in building a Valve Caster, 12-volts is the way to go.
Another great feature of the Valve Caster design is that you can switch out the vacuum tube with virtually any other vacuum tube, so long as it has 9-Pins.
So far, I have tried a 12AU7, 12AT7, and what is probably the most common vacuum tube, a 12AX7.
I didn't like the 12AX7 and found it to be rather flat.
The 12AT7 was really nice, but had a bit too much distortion.
The 12AU7, which I ended up choosing, gives the Valve Caster just the right amount of warm, tingly distortion that's not quite as "heavy" as the 12AT7. This one sounded the best to my ears.
Graphics:
I knew early on that I wanted to include the image of a Formula 1 race car because the U-bolt, which helps protect the tube from being accidentally kicked, reminded me of the roll cage or engine intake commonly found on these cars.
Etching:
Although it is difficult to see in the photos, the graphics have been etched into the enclosure. If you've read my previous post (Etching Aluminum with Ferric Chloride) then you already know that I've been experimenting with chemical etching.
Truth be told, I actually etched this pedal before fully understanding the etching process and was still using photo paper to transfer the image.
Photo paper is virtually impossible to remove (once it's been ironed) without lifting some of the toner. This created small holes in the toner that allowed the Ferric Chloride to eat away at areas that were suppose to be covered. This resulted in some pitting, that can be seen on the top surface of the enclosure, and the rough looking lines on the image itself.
Sanding and Polishing:
Once the etching was complete I applied some black spray paint and left it to dry overnight. The following day I sanded the entire enclosure with 600, 1000, 1500, 2000, and 3000 grit wet/dry sandpaper, then polished it with Mother's Aluminum Polish.
Because the etching didn't go as deep as it should have (again due to my lack experience with the etching process), some of the black spray paint was removed during the sanding process and needed to be touched up with a small paint brush.
Quick Tip: I've since discovered that 600, 1000, 3000 grit and Mother's Aluminum Polish looks just a good; so, you can skip the 1500 and 2000 grit.
Here's how the enclosure looked after sanding, before I touched up the paint and polished it...
Technical Issues:
In addition to the etching problems, there were also some technical issues that needed to fixed.
After completing the build, I quickly noticed I forgot to add the power supply filtering and reverse polarity protection circuit that I've been including in my pedals.
This circuit uses a 100ohm resistor, 100uF electrolytic capacitor and 0.1uF non-polar capacitor to filter out any noise that might come from power lines or the use of a low-quality power adapter.
The circuit also includes a 1N4002 diode that helps protects against the accidental use of a centre-positive power supply (like you often find with Germanium fuzz pedals).
Both centre-positive and centre-negative adapters look identical, so it's easy to mistake one for the other. The only way to know for sure is to check the adapter for one of these two symbols...
Now that the power supply filtering and polarity protection circuit was added, I tested the pedal and realized that the Gain and Tone controls didn't seem to work. I thought it might be defective pots and went ahead and replaced them; but this didn't fix the problem. Not sure what to do, I decided to move on.
The next, and by far worst problem I encounter was a very loud "pop" every time I activated the foot switch.
Searching online I discovered that several pedal builders recommend adding a large value "pull down" resistor right before the input capacitor. This will supposedly send any stored current to ground before it can be discharged into the signal path when activating the switch.
I added a 1M resistor, but this didn't resolve the issue.
I then read that popping could be caused by the indicator LED. So, I followed the article’s instruction and added a 4.7k resistor and 10uF capacitor right before the LED resistor... This also didn't resolve the issue.
Having made several alterations to this pedal I was now left with a rather unattractive wiring mess (as you can see in the photo below). Since I was still able to use the pedal without the Tone and Gain controls, I decided to leave it and work on another pedal.
A few weeks passed and I found myself obsessing over my failed attempts at completing this project. Other pedal builders didn't seem to have trouble the Valve Caster, so there was no other information online that would shed some light on the issues I was having. So, I did the only thing I could and began cutting out the wires. It was time to start over.
This time I chose a schematic posted by bevaisaudio.com - a trusted source of information for pedal builders like myself. I also test the circuit on a breadboard to make sure there were no surprises before wiring everything into the enclosure.
The schematic was accurate and everything worked as it should; so, I was finally able to complete the project. Now I have a fully functional Valve Caster that looks great and sounds great too. I'm even happy with new wiring; which is a lot cleaner than my earlier failed attempt. There does seem to be a small issue with the B50K Gain pot (it's sounds a bit scratchy), but I can live it... for now.
For my next project, I've designed a component switching device that allows me to switch between different resistors, capacitors or diodes when building circuits on a breadboard.
Until then, keep building.
M
