The Fur Face

Taking a Silicon Fuzz Face From Breadboard To Box

© 2010 By Small Bear Electronics LLC

In a previous article, I showed how to set up and tweak performance of a silicon Fuzz Face on a solderless breadboard. The next logical step is to commit to a soldered build on perfboard or printed circuit board and house the effect in a gig-worthy enclosure. I'll show you how to do that in this article. If you bought the breadboarding kit, some of the parts can be re-used if you wish.

Like some of my other designs, this one can be built more "from scratch," or more "paint-by-number" depending on your budget and on how much tooling you feel comfortable doing. You can get to a working pedal starting from an undrilled enclosure and hand-wiring on perfboard (fairly hard, but less $$), or I offer a full kit including an etched and drilled PC board and a drilled enclosure (much easier, but more $$). For those who already have a suitable enclosure, the PC board is available separately. Here is the instruction manual for the kit. I hope to appeal to the widest possible audience by offering many construction alternatives, so I will do the build "from scratch" in this article while noting choices at key points. Also, while this is not meant to be a design manual for stompboxes, I'll anticipate some questions, talk briefly about the process I went through to get to a finished pedal and describe some of the steps in the learning curve.

Breadboard To Box - What Is Involved?

If you followed the breadboard build to its end and tried some mods, you have a working circuit, complete from input to output something like this:

Clearly, a number of elements need to be added to make this into a buildable design for a finished pedal. The most important is bypass switching, to allow the effect to be foot-switched in and out. There are numerous schemes for doing this, and I chose one that's known to work well and uses components that can be found almost anywhere.

DPDT True-Bypass Switching With In-Use LED Driver - How It Works

Here's a bottom view of a typical DPDT footswitch. It has six contacts, and they work as shown in the schem at right. Push/release once and the moving contacts (2 and 5) connect to #3 and #6. Push/release again and they go back. We call this a "latching" or "alternate-action" switch, because the contacts remain in their new position when you release the switch.

Let's add this to the schematic, trace through the connections and see how it works in practice:

As shown, the effect is active. The guitar input goes to the moving contact, pin 2, through stationary contact pin1 to the input of the effect. The output of the effect goes through moving contact pin 5, and it sees the output jack through stationary contact pin 4. OK so far? If you still have the circuit on your breadboard and want to set up the bypass to see/hear it work, by all means do so.

Now visualize the moving contacts switching when you step on the switch. Moving contact pin 2 connects to stationary contact pin 3. There is a wired connection between pin 3 and pin 4, so the guitar connects directly to the output jack. The effect is bypassed. Next look at moving contact pin 5, which now connects to pin 6. Pin 6 leads to an LED driver circuit that we'll add later; the driver circuit turns its associated LED Off when it senses ground at pin 6. Trace back from pin 5, and you'll see that ground is available through one side of the level pot. The driver circuit is designed so that it ignores the resistance of the pot, and the LED is extinguished. When the effect is engaged again, ground is removed from pin 6, and the LED lights up.

Yes, there are other ways to wire a stomp switch, with and without an in-use LED. They will all work, though some may be more suitable than others in a particular design situation. If you want more information, check the Beginner FAQ at diystompboxes.com, or other on-line sources.

Power

While we were on the breadboard, we switched power by disconnecting the battery. That won't work in a pedal, so we have to make some arrangements. And there are several issues:

Most modern pedals accomplish all of this in the same way. External power comes in through a jack like the one in the left-hand pic. This one is designed to be mounted on a circuit board, while others mount on the panel of an enclosure. The typical schematic is shown on the right.

Contact #1 connects to the shell of the power plug, which will be positive in the typical negative-ground pedal design. Contact #3 forms a normally-closed switch with contact #1; it shorts to #1 until a power plug is inserted. Contact #2 is the center pin, which will be ground in this configuration.

Switching the battery off when the guitar is unplugged is done by using a stereo jack for the input. Since the Ring contact of such a jack is shorted to ground through the sleeve of a guitar plug, it provides a cheap and easy way to implement a necessary function. Do take a look at the physical jack and work out for yourself what is happening if you need to. Here's the whole idea in schematic form:

Diode D1 takes care of reverse polarity protection; it will block current flow if the battery or power supply is connected incorrectly. Capacitor C1 is called a "decoupling capacitor." It is added to help the circuit be more stable on a pedal board in which multiple pedals are being driven from one power supply.

Here is the whole, buildable schem, including all of the support circuitry. The only other thing I added was a 1 Meg resistor from input to ground to reduce "pop" noise from the stomp switch. The LED driver circuit is the variant of the "RAT Bypass" that I have used in other builds.

How Did You Get To The Finished Design??

This is complicated, and teaching it is best left to people who have done it for a living, like R. G. Keen. In his case, he wrote a book about it. But I will not be biting off more than is appropriate by sharing a few basics and suggesting resources for learning more.

Once a design has been made to work on the breadboard, the first considerations for turning it into a pedal are mechanical, and they concern the off-board components and overall size of the circuit board:

The answers to these questions will dictate the size and type of enclosure needed. Since most DIYers will not be making an enclosure, the next step is to pick a standard, off-the-shelf size. While there are other choices of materials, cast aluminum is very durable, and demand has made it inexpensive and widely available.

Based on the answers to the above questions (and a good deal of experience,) I could have chosen to "shrink" this design into something that would fit in a "B-size" (4.39" x 2.36" x 1.03) box. However, I knew that this would be a first-build for many people, and I wanted the box to be roomy enough for a beginner to work in comfortably. I settled on the standard "BB-size" (4.7" x 3.7" x 1.18").

Having picked an enclosure, the next step is to plan where the controls, switches and jacks will go. There is now a lot of on-line help for doing this. Numerous DIY sites, including SBE, of course, offer plans for finished pedals that include downloadable drilling templates for standard enclosure sizes. I didn't have a "stock" set of templates for a three-knob, two jack, one-stomp enclosure when I started the Fur Face, so I drew what I wanted using Jasc Paint Shop. Other people use MS Paint, Corel Draw or Photoshop to get to the same place.

Once the positions of the off-board components have been established, the maximum size of the board that will fit in the enclosure will become clear. At this point, before I plan a board layout, I "mock-up" the mechanical layout in the enclosure, both to be sure that everything will fit and so that I know that components will not bump into each other when the pedal is assembled. I have done this for a couple of standard "shell" designs, which you can find in How-Tos.

Designing The Board

This is the most interesting piece of the job, and absolutely the hardest to learn. When I first returned to building pedals, ten or so years ago, I created some board templates and component outlines using MS Paint and PowerPoint. I made these to work, but ultimately I bit the bullet and and learned to use purpose-designed CAD software. I strongly suggest going this route if you are at all serious about doing your own designs. The learning curve is steep, but very satisfying. A limited-size, but fully-functional, version of EAGLE CAD, which I use, can be downloaded from http://www.cadsoftusa.com. While packages like this are specifically geared to producing printed circuit boards, the layout functions are readily applicable to creating pad-per-hole perfboard designs like the one in this article.

I noted earlier that the size of the board is dictated by the available space in the enclosure and the positions of the off-board parts. Having established all of that, I used the CAD software to draw an actual-size outline of the board. The positions of the controls and the input and output jacks dictate where the input and output on the board will be. From there, designing the layout is an enormous amount of place-and-try to get to something that you want to commit to solder. For a (Very) detailed discussion of good design rules and best practices, check out R. G. Keen's book.

Now that I have given you a look at the functioning of my bearish mind...

Let's Build It!

Here's your first choice: Buy the enclosure pre-drilled, or tool it yourself. Presuming that you are tooling your own, download the template file and print out the templates. The actual size of the JPEG is 1150 x 850 pixels, so you may need to re-size it to those dimensions.

Remove the four screws that secure the lid to the enlosure. With a good, sharp scissor, cut out the template for the top. Attach a couple of pieces of double-sided clear or masking tape to the box, and carefully center the template to the cover. In the same way, attach the templates for sides, being careful to get the holes for the jacks in the correct locations relative to the the switch. The output jack is on the left as you look at the front of the pedal  and input is on the right. Now use a scribe or scratch-awl to put a small dent at the center mark of each of the round holes. We'll get to the cutouts for the DC Jack and the battery drawer later.

The holes for the potentiometers are 5/16", and the holes for the jacks are 3/8". The hole for the stomp switch is 1/2". If you use standard twist drills, bore a 1/8" pilot hole, enlarge with a ¼" drill, and then use a tapered reamer to slowly bring each hole to its final size.

Many people like to use a step drill (the Irwin Unibit is a popular brand) because it does a quick, clean job of boring any size hole from 1/8" to 1/2".

If necessary, de-burr all of the holes with a small, round file. Remove the templates and tape for the holes you have drilled.

How you make the cutout for the DC power jack will depend on the tools you have. I started by drilling a large round hole that went from edge-to-edge. Then I used a burr in my Dremel tool to create the rough shape (and save a lot of hand filing!) and finished with a small flat file.

The battery drawer, and the cutout for it, are very much optional. It's a nice feature (and wasn't readily-available for DIY pre-Small Bear), but it is a considerable amount of hand-crafting to install, even if you have the proper tools. If you buy the pre-drilled enclosure, the cutout is done for you. If you tool your own enclosure but don’t want to install the battery drawer, you can skip this section and simply add a spring-type battery clip later.

The template is sized for the horizontal-mount battery drawer that I offer as SKU 0614A; other similar types may be usable, but you will have to work out your own mechanicals for them. The most practical tool I have found for doing the cutout is a Dremel handpiece with an abrasive cutoff wheel, which is a standard accessory in most Dremel kits.

Note: Abrasive cutoff wheels are both very useful, and inherently dangerous! In normal use, they throw off particles of metal and abrasive. When they break, and they do, the pieces fly like bullets. You MUST wear eye protection and a dust mask when using them.

Begin by fastening the template to the top using double-sided tape. Using an X-acto or similar knife with a fresh blade, and a steel rule, score all along the outline of the cutout. When done, you can remove the template.

Start making the cutout by using the tool to mark the outline. Then go back and do the definitive cuts. Take your time. It’s normal for the piece to get hot from friction, and you’ll have to change the cutoff wheel at least once. Take care not to let the tool slip. If you are patient, you’ll wind up with a rough cutout. Note: It is far better to have the rough cutout be a little too small rather than too large. If too small, you can trim it later with burrs and/or small files as needed.

The battery drawer has flanges on each end that will snap into place, but they need to be cut down slightly to accommodate the thickness of the enclosure. The cutoff wheel does this very easily. The front and rear sides have ridges that are meant to keep the drawer in position horizontally. I ground down the two in the front and made grooves in the cutout to accommodate the two in the rear.

Press the drawer partly into place and use a Sharpie to mark the positions of the notches. Then grind very carefully with a needle file or Dremel cutter. A little at a time is better, because you want to make room for the ridges without letting the notches show past the outside edge of the drawer on top.

The last two pictures show the result I got. The drawer is in straight, and the cutout does not show. There is some play up and down, but I will be able to cure that with a couple drops of epoxy during final assembly.

At this point, the tooling of the enclosure is finished and it is ready for painting and decorating. There are numerous "recipes" on-line for doing this. If you bought the kit, a decal is included.

Now we'll do a little initial tooling of the circuit board and then "mock-up" the installation to ensure that all of the holes are registered correctly.

In this build, the DC power jack is mounted directly to the circuit board, and slots are needed to accommodate its terminals. The printed circuit board (which will be available soon, either alone or as part of a kit) has the slots machined already.

The photo on the left shows how I marked with a Sharpie the indices where the slots need to be. A #63 drill, preferably in a Dremel handpiece, works well as a router for this job. A standard electric drill can be used if you have a chuck that will hold a wire number drill, or you may want to buy a #65 drill like this one that has a thick shank. Work the drill left and right in index N13 and up-down in index M11. L13 is a little tricky, because the slot needs to be in a horizontal line just below the hole. For that one, insert the drill, route downward just a hair, and then route left-right. The jack should mount such that its forward edge is flush with the forward edge of the board.

Before doing any more work on the board, let's mock up the internal assembly and see how the pieces will fit together.

This is a "semi-manufacturable" design, meaning that some components that are usually external are mounted directly to the board to reduce wiring and assembly time. The design will accommodate board-mountable potentiometers like the one on the left, or you can use regular solder-terminal types like the ones that come with breadboard kit. But if you do the latter, bend the solder terminals upward parallel to the body and solder an inch or so of bare, solid #24 or #22 wire to each terminal as shown. Also, using a diagonal cutter, break off the anti-rotation tab on the side of each pot, as this build does not use them.

The pic on the right shows the setup. If you are using solder term pots, a 4-40 screw goes in each mounting hole; if you use board-mountable pots, screws are only required on the edge in front of the pots. Add two compression lockwashers before screwing on each stud; this will shim the board to exactly the correct height. Slip the mocked-up board into the enclosure and finger-tighten the hardware on the pots. The lower pic shows how things should look.

If this much is OK, take apart the mock-up and we'll secure the studs to the enclosure. Place the board on the floor of the box, flush with the front wall, using the location of the power jack as a guide to its horizontal position. Use a scribe or scratch awl to mark the position of each hole.

Now re-assemble the mock-up and prepare the enclosure and the board. Scrub the marked locations on the enclosure floor with #220 grit sandpaper and clean up with acetone. Scrub the studs using a Q-tip wetted with acetone. Mix a small volume of quick-setting epoxy cement, and apply a small bead to each location in the enclosure. Carefully, set the mock-up in place as you did earlier. Give the adhesive a couple of hours to cure before proceeding.

When the adhesive has hardened thoroughly, remove the screws. Mix another batch of epoxy and add more around the sides of each stud.

Assembling The Board

If you have built an effect on perfboard, like the Tweak-O, you will be familiar with this method of construction. If this is your first build, you may want to look at that article and possibly practice making connections on a scrap piece of material before you commit to this board.

Following are a layout drawing, a parts list and a photo of the top of the board.

I suggest starting by soldering all of the components in place, paying very close attention to getting them in the locations shown in the drawing and the photo.

As you make solder connections, mark them off on the layout drawing using a highlighter and then test continuity to make sure that the joint is solid and that it actually goes to where it should.

Here are a few notes about what I did at certain indices that might be helpful:

Once you have done all of the wiring, you can mount the LED. Notice that the connections to the LED run outside the pad-per-hole pattern. This was a design choice that I made so that I could spread out the components sufficiently for easy wiring, but it means that you have to bore two holes for the leads. Use a #63 drill, and center the holes in the silkscreened numbers12 and 13 as shown in the left-hand pic.

Now we'll get the LED positioned on the board and lined up with its hole in the enclosure.

Keep in mind that you are now at a delicate stage, because you have put a lot of work into finishing the case. Slips, falls and mistakes with tools can ruin the finish and cost you a lot of grief, so stay focused and work patiently. Set yourself up with a towel or soft cloth on your bench to protect the face of the enclosure while you work.

I chose not to use a bezel for the LED; if you want one, this is the time to add it. Enlarge the hole as necessary with a reamer. Slip the LED into its holes on the board. Set the board in place in the enclosure and screw it down enough to make it stable. Push the LED into its hole in the case and clip its leads, leaving about 1/8" above the component side of the board.

Disassemble. Slide a small piece of spaghetti insulation onto each lead of the LED and insert it in the holes again. You will know when the length of the insulation is right by the 1/8" of bare lead sticking up from the component side.

Take the LED out and put right-angle bends in the leads. Pay attention to polarity, and solder in place. The flatted side of the LED connects to the lead from R13. Set the board in place in the enclosure once more to make sure that the height and position of the LED are OK. Then secure the leads going to the LED with a few drops of clear, quick-setting epoxy.

Before mounting the potentiometers, solder at H3 the lead for the input to the board. I suggest this because the location is underneath the can of R5. Then secure the shims at the corners of the board using a drop of epoxy cement. A toothpick makes a good tool for positioning them one on top of the other and centering.

The potentiometers mount similarly to the LED. Start by inserting R5 into position on board. Set the board in place, and install the potentiometer nut and washer finger-tight to secure it temporarily. Put right-angle bends in the leads to set their length. Disassemble. Solder the leads to the connections on the board and clip the excess on top. If you are using board-mount pots you will need to cut away a small part of the terminals at B23 and B25 in order to avoid a short with the lead that passes in column 24. Can be done with a needle file, but a Dremel burr makes it much easier. Similar tooling is needed for the Fuzz pot at index B3 and B5. Also, it is OK to remove with your soldering iron any unused "in-between" pads that would cause pot terminals to short. The lower pic shows this as well as the tooling of the terminals.

Install the other two pots similarly. The outside contacts (cw and ccw) of the tone pot R8 are soldered to their contacts on the board. Its center contact is wired on the component side to the cw contact of the level pot R11. The center contact of the level pot is the output from the board, and it will be wired to the stomp switch during final assembly. Solder a lead there, and another at index M22 for the LED control. Add a lead for the board ground at L1.

Enlarge the holes at L10, M10 and L15 by routing with a #63 drill to make them just large enough to pass the leads for the battery snap and the lead for the center pin of the power jack. Solder these in place. Install the transistors that you want to use for Q1 and Q2 and the appropriate resistor for R6.The board is finished.

Setup and Initial Testing

Before doing the final wiring and assembly, do this basic test to see if the on-board wiring is correct. Set the board in place in the enclosure. Install the input and output jacks, and install the hardware for those and the potentiometers finger-tight. Now make these connections:

Connect your guitar and an amplifier and connect a battery. The LED should light. If it does not, you probably have a problem in the driver circuit. The LED should extinguish if you touch the control lead to ground. Try out the controls. If it sounds like a Fuzz Face, good job! Before you continue, connect a power supply and make sure that everything still works with/without a battery.

Troubleshooting

Unlike most builders, you have probably breadboarded the circuit, so you know that you had something working before committed to solder. Unfur-tunately, small mistakes have a way of creeping in during soldering and assembly. Time to break out the multimeter and figure out where the problems are. Here are the measured transistor voltages in the build you see here:

  Collector Base Emitter
Q1 1.56 .65 0
Q2 4.93 1.56 .93

YMMV depending on transistor gains, but any serious differences are a sure indication that something is not right. Keep in mind that hand-wired boards are by nature more subject than printed circuit boards to problems with continuity and and shorts. Check everything against the layout and the pics. This being essentially a Fuzz Face, their are gazillions out there who have built it and can help you debug a build. The Forum at diystompboxes.com is an amazing resource for this.

Final Assembly

If the board works, un-tack the temporary wiring and screw down the board. Mount the stomp switch. Make a permanent connection to the sleeve of the output jack. Run this to the sleeve of the input jack, add the lead from board ground and solder. Wiring the switch contacts invariably confuses a lot of people, so let’s do it “by the numbers”:

 

 

 

 

 

 

 

 

Now connect up your gear again and give the pedal a thorough test. Sound Hendrix-y enough for ya?

CONGRATULATIONS!

Tighten up the hardware and add knobs. If you did not install the battery door, you will want to add a spring clip holder; if you did, add a couple of beads of epoxy cement along its edges inside the the case so that it can't wander. Install rubber feet.

Now for the final question that you were wondering if I would ever address:

Can I Use Germanium Devices?

Sure, with a couple of caveats. First, I purposely did this design with cheap, readily available NPN silicon devices so that anyone could build it and it would play gracefully on a board with other negative-ground pedals. No separate power supply is required. NPN germanium is available, but a pair that hits reasonable gain buckets and is not too leaky may cost you as much as all of the rest of the parts combined. It's not a conspiracy; for historical reasons, good quality NPN germanium is relatively scarce. See my stock list if you are interested. If you troll E-Bay, get some assurance from the seller that you will be able to return unsoldered devices that are hissy or excessively leaky.

The other thing I would suggest is using socket-pin material for all four bias resistors. Germanium varies so much in gain and leakage, and is so temperature-sensitive, that you may need more control than just adjusting one resistor will give you.

I hope you enjoy your new noise-toy. Comments and questions welcome at smallbearelec@ix.netcom.com.