Mechanical Design Considerations for Pedals

[BlueLdr]

Hey everyone,

As I prepare to build my first pedal, I've had a lot of questions that I've found answers to, like how to make a drill hole template for an enclosure, and what hole sizes to use. The more intimidating part is that I don't know what I don't know.

What are some considerations that are easy to overlook for a beginner? What are some challenges you've encountered that you didn't think about during planning and only realized once you got your hands on and started building?

I also have a handful of specific questions about my own design. I've mocked it all up in Fusion360.

• I plan to have the jacks mounted upside down to make wiring a little easier. I've left ~3mm of clearance from the ceiling of the enclosure. Am I going to run into problems with this approach?
  
  
  



• The sides of the 1590DD enclosure are sloped. What's the best way to be able to drill the holes perpendicular to the face?
  
  


• Due to the clearance under this switch, I've gone with pretty short mounting pegs (4.7mm between the floor of the enclosure and the bottom of the PCB). Apart from trimming the leads short, is there anything I should do to ensure there's no shorting or interference? Is there something I can put under the PCB (besides electrical tape) to be extra safe?
  
  
  
  


• The jacks I've chosen have no metal contact with the enclosure. I know it's preferable (for R.G. at least) to have the input jack ground be the sole connection point to the chassis. But given that I have multiple inputs*, and that there's no metal contact, what's the best way to ground the enclosure? I have a metal-body DC jack there in the mockup, which should do the trick (right?), but I can use a plastic one if that's not the best connection point. (*though only one will be active at a time)

[amptramp]

Pay close attention to the pots you are buying.  I built one unit where I included a separate piece of scrap plastic on the inside to lock into the anti-rotation lugs on each pot.  But with some of the pots, there was barely enough threaded length with the pot going through the plastic plus the outer aluminum structure.  ALWAYS make use of the anti-rotation lugs.  If you use wide knobs, they will hide the anti-rotation lug holes in the structure, so they should be your first choice.  NEVER mount pots on the circuit board or you will crack the solder joints.  DO NOT mount the board by the pots.  Use a lockwasher on the pot and reef it down tight.

This will solve some of the recurring problems we often see - pots that turn beyond the end stops and rip out their wiring and cracked intermittent solder joints.

[GGBB]

Good suggestions from Ron above. However I'm personally not against PCB mounted pots when done properly.

I plan to have the jacks mounted upside down to make wiring a little easier. I've left ~3mm of clearance from the ceiling of the enclosure. Am I going to run into problems with this approach?

Depends on your wiring technique (and soldering neatness). If your wires are coming straight up from the lugs, you may have problems.

The sides of the 1590DD enclosure are sloped. What's the best way to be able to drill the holes perpendicular to the face?

A drill press and a jig to hold the enclosure in the correct position. But you don't need to do this, and you probably don't want to. The jack bodies need to be mounted flush with the enclosure, so their holes should be straight through the side, not angled.

Due to the clearance under this switch, I've gone with pretty short mounting pegs (4.7mm between the floor of the enclosure and the bottom of the PCB). Apart from trimming the leads short, is there anything I should do to ensure there's no shorting or interference? Is there something I can put under the PCB (besides electrical tape) to be extra safe?

A sheet of non conductive material like thin clear plastic used for all kinds of packaging. If you are really worried use something also anti-static. But you don't need to unless you expect your mounts to fail or your circuit board to sag extensively. Or you are running thousands of volts through it. 4.7mm is plenty of room.

The jacks I've chosen have no metal contact with the enclosure. I know it's preferable (for R.G. at least) to have the input jack ground be the sole connection point to the chassis. But given that I have multiple inputs*, and that there's no metal contact, what's the best way to ground the enclosure? I have a metal-body DC jack there in the mockup, which should do the trick (right?), but I can use a plastic one if that's not the best connection point. (*though only one will be active at a time)[/li][/list]

Metal bodied DC jacks usually connect the body to ground which connects to the barrel of the plug. Standard pedal power supplies deliver positive power to the plug barrel. The combination means a dead short of the power supply to ground. This is why you rarely if ever see metal bodied DC jacks in pedals.

My recommendation is to use at least one 1/4" jack that has a metal bushing. Others like R.G. might recommend against relying on the jack body to enclosure contact for grounding and suggest a dedicated ground wire attached to the enclosure by way of a screw into the metal. Either technique can be done well or poorly. Use a toothed lock washer and a quality solid metal jack and tighten it properly (not over-tighten) and you'll be fine. You'll find that the plastic threaded isolated jacks simply do not torque down as tightly or stand up to minor abuse like jacks being stepping on or kicked - especially so when they are not supported by any other means such as PCB mounting along with other jacks.


One common misstep is trying to emulate the construction techniques used in mass produced pedals (now utilized by many so-called boutique builders), in order to look "professional". Things such as PCB mounting everything including 1/4" jacks and stomp switches, sometimes involving quick connect wiring. Keep in mind that these manufacturing techniques came about to make it quicker and cheaper to build pedals, not to improve their quality and durability.

[ElectricDruid]

I plan to have the jacks mounted upside down to make wiring a little easier. I've left ~3mm of clearance from the ceiling of the enclosure. Am I going to run into problems with this approach?

No. 3mm is loads of clearance. How much voltage do you need to jump a gap that big?!?

The sides of the 1590DD enclosure are sloped. What's the best way to be able to drill the holes perpendicular to the face?

I don't know. I haven't found a way. If the holes are slightly oversized, it doesn't matter and the jacks will move into position when they're tightened down.

More important is to make sure the enclosureis well secured before trying to drill it at all. The common mistake is for the drill to grab the enclosure and suddleny you've got an aluminium box whirling around trying to smash anything in its way. Use good drills (and stepped bits are an excellent choice) and make sure the box *cannot* get loose. After that, who cares about the angle within a few degrees?!?

Due to the clearance under this switch, I've gone with pretty short mounting pegs (4.7mm between the floor of the enclosure and the bottom of the PCB). Apart from trimming the leads short, is there anything I should do to ensure there's no shorting or interference? Is there something I can put under the PCB (besides electrical tape) to be extra safe?

See above. 4.7mm is even more clearance than 3mm, so you're looking at thousands of volts to jump a gap that big.

The jacks I've chosen have no metal contact with the enclosure. I know it's preferable (for R.G. at least) to have the input jack ground be the sole connection point to the chassis. But given that I have multiple inputs*, and that there's no metal contact, what's the best way to ground the enclosure? I have a metal-body DC jack there in the mockup, which should do the trick (right?), but I can use a plastic one if that's not the best connection point. (*though only one will be active at a time)

As others have said, *don't* use a metal body DC jack - the connection it makes with the enclosure is the one you don't want, not the one you do.
Plastic jacks are ok if necessary, but in your situation, you'd be better with good quality metal jacks that you can really tighten. Don't worry about some theoretical ground loop between different jacks and the enclosure. Just connect it all up to ground, it'll be fine. The better the connections, the better - it all forms one massive chunk of "ground", with a resistance that's so low that no-one cares anymore!

I'm also not against PCB mounted pots. Pots on wires coming loose and spinning round and around until the wires break off are a more common failure in my experience. I suppose that's what the anti-rotation tabs are for, but the fact is most people just break them off, me included (but board-mounted pots don't rotate so easily!). If I was building commercially, I'd leave them in for sure, but they seem like a faff otherwise. Bonus points from me for using them if you go that way!

I suppose the final question is "what standard are you wanting to build to?". If we're building for ourselves, maybe it's not a big deal to resolder something if it breaks, or re-tighten jack occasionally. If we're gigging heavily, it's bound to happen right when you don't want it to, so you might want something more reliable. If you're building to sell, or you're hoping this pedal that you're going to give to X famous player is going to make your reputation in Booteek world, then it had better not break down. You can go further or less far along this route of NASA-standard reliability. We don't all have a NASA-standard budget, after all... And it's a pedal, not a moon mission!!

[R.G.]

You're already well ahead of the game by using design software that can show you transparency views. Good on you! Tight mounting in a box is a variation of a 3-D jigsaw puzzle or tetris.

If you use board mounted pots, be very careful what board-to-box distance the pots force on you, and if you also use board mounted switches and/or LEDs, be sure you can get parts that are compatible in heights from pots to switches to LEDs, etc. Also check if your electro caps come in low enough heights to fit with the enforced board-to-mounting distances the pots/etc. require. Sometimes you have to buy premium small-case caps if you're doing a tight fit.

Re: grounding to the metal box
- there exist ring terminals with internal teeth, and with inner diameters of 3/8" and 1/2". One of these under a pot shaft or jack bushing will bite into the metal box even if the bushing is non-metallic. Only one connection to the box is preferred for shielding reasons, but in something as small as a pedal you usually get away with more than one. Do not use the box as a conductor for power supply ground or currents.

Beware of multiple mounting planes. If you have through-box parts firmly mounted to a PCB, you may or may not be able to insert the fully populated PCB into the pre-drilled box if the through-box parts mount on multiple faces. Your pictures seem to say you want to mount parts to four of the six faces of the box. It's really unlikely that you can do this with all board mounted parts unless the box holes for these part are all slots, not holes so you can slide the PCB in by moving only in one direction. It requires extreme precision and modelling, as well as a few trial-and-error loops to get parts to mount to more than one plane. Unless some of the fits are deliberately sloppy, you'll get jamming on assembly. It's bad form to enforce using a soldering iron to assemble/disassemble the stuff in the box.

Even if you can get a two- or three-plane fitment to work, only one plane can be used as the master fixing plane. Parts on a PCB that are then bolted/screwed to the box on more than one plane stress the solder joints so they eventually fail. Two planes is much worse.

You're probably going to have to use flying leads on most of the jacks and such. Be sure there is room for the wires to trail around the PCB to get to where they're going.

[BlueLdr]

As others have said, *don't* use a metal body DC jack - the connection it makes with the enclosure is the one you don't want, not the one you do.

Noted.

I suppose the final question is "what standard are you wanting to build to?". If we're building for ourselves, maybe it's not a big deal to resolder something if it breaks, or re-tighten jack occasionally. If we're gigging heavily, it's bound to happen right when you don't want it to, so you might want something more reliable. If you're building to sell, or you're hoping this pedal that you're going to give to X famous player is going to make your reputation in Booteek world, then it had better not break down. You can go further or less far along this route of NASA-standard reliability. We don't all have a NASA-standard budget, after all... And it's a pedal, not a moon mission!!

Well, I'm just building for myself and not gigging. So for practicality, I should be building to a relatively low standard. But I'm a perfectionist to a fault, so...

Beware of multiple mounting planes. If you have through-box parts firmly mounted to a PCB, you may or may not be able to insert the fully populated PCB into the pre-drilled box if the through-box parts mount on multiple faces. Your pictures seem to say you want to mount parts to four of the six faces of the box.

Yeah, I eliminated the idea of board-mounted jacks/controls pretty early on for exactly that reason, so everything's chassis-mounted. Other factors were the sloped sides of the enclosure, and the fact that I couldn't find the switches/pot I needed with enough thread/pin length to work out with all the other clearances.

[davent]

Pay close attention to the pots you are buying.  I built one unit where I included a separate piece of scrap plastic on the inside to lock into the anti-rotation lugs on each pot.  But with some of the pots, there was barely enough threaded length with the pot going through the plastic plus the outer aluminum structure.  ALWAYS make use of the anti-rotation lugs.  If you use wide knobs, they will hide the anti-rotation lug holes in the structure, so they should be your first choice.  NEVER mount pots on the circuit board or you will crack the solder joints.  DO NOT mount the board by the pots.  Use a lockwasher on the pot and reef it down tight.

This will solve some of the recurring problems we often see - pots that turn beyond the end stops and rip out their wiring and cracked intermittent solder joints.

At least with Hammond diecast enclosures you don't have to drill through the top face of the enclosure to create a straight sided divot that will engage the anti-rotation lug of the pot.

You do have to file the lug shorter, it's a very soft metal, and if you're using a drillpress it's simple to set the stop on the drill advance so the drill bit doesn't break through the top surface of the enclosure.

[PRR]

....The more intimidating part is that I don't know what I don't know.

Analysis paralysis.

What happens if you are wrong? Unlike rocket science, nobody is likely to die. If you short-out a $35 power supply, you will be sad, but your next of kin will never know. These may not be "cheap" lessons but the scent of smoke stays in the mind forever. (Even virtual financial "smoke" lingers.)

3mm or ~1/8 inch won't arc. BUT we have all seen solder joints with 1/8" wire-stubs or solder-tits. As long as you and all your repair techs (even you, late nite dark stage) remember the need for non-interference, all can be well. (Also on that type jack you can flatten the lugs with a thumb.)

Electric tape under pressure may hold for months but WILL eventually yield to long sharp pressure. When you wrap house wiring electric splices they are not supposed to press sharp points. (Formerly we double-wrapped house wiring splices with 'friction' tape but vinyl is enough better than the old rubber electric tape that this is unknown today.)

Plastic from detergent, bleach, etc jugs, or heavy bubble-packs, or salad-trays, will probably outlive you even under some point-pressure. WASH: chlorine is hell on metals.

Foam plastic works today and DOES decay all too soon. I had a recent run of rotted foam, some of it also electrical insulation. Save that for your 90-day warranty products. Cardboard too. (Corrugated plastic may last a lifetime but is too expensive for one-off unless you steal real-estate signs.)

[Toy Sun]

True about all of those insulation materials. Been burned (not literally) by vinyl electrical tape, which eventually by be punctured by a sharp wire/joint. I've had a lot of success the last few years with bits of an old bike inner tube. I just cut what I need off with a scissors and cram it in-between potential (ouch, bad pun) contact points.

I agree on paralysis by analysis. You have to build + learn, build + learn, etc... Only when a design is finally finished and out of the workshop and into the field will you really find out what works and doesn't. So.. take a backup if you take your homemade pedals out on a gig, at least to start. That's my 2c.

[Phend]

To manufacture Holes,  tools need to be used. Yes at some expense.
Small bench top drill press with at least 3/8 inch chuck. 100$
Plus a vise, you CAN'T hold your enclosure by hand, or you might have only one hand left to use.
And these..





As far as templates,  can you make and print a 2d layout from you 3d model?
That being needed if holes are required to be accurate between themselves.
Else, another tool, a good scale. To use that you need a nice square block to put up against the bottom edge.
(Because of the draft on the enclosure walls) of course the dimensions to a hole must come from that edge.
This is just one way, sans laser to make marks for you.
BUT remember,  safety first, drilling sheet metal IS dangerous.

[GibsonGM]

Yup. It's a good idea to clamp down any metal you're drilling and have a piece of scrap wood beneath it (Tom described the scene...whirling metal pieces slamming you in the hands, and if sharp, uh oh).  You'll usually only do this once, and after the stitches come out, you'll WANT to take the time to clamp them down   
You have been warned. 

[teemuk]

Also, if it is a one-off build, or just a prototype for several following builds, I would wait that all the components are at hand before doing any drilling or even drawing any templates. Because, due to Murphy's law, the critical physical measures of those components are surely going to be different than what your layout editor says or what you will think they are.

Pots and jacks can have myriad of different thread diameters, lug sizes and distances, etc. Murphy will make sure that the one for which you drill the holes is different than what the postman delivers. Same with capacitors and maybe to some extent with even DIL sockets. Been there myself. 

Also, make sure that everything fits, and that everything can still be assembled once it fits. Mr. Murphy will surely rear his ugly head here too: Everything looks cool in the layout editor, but then, in practice, you notice that (then) too obvious detail why the plan actually doesn't work. So, lay out the design in real life once you have all the parts, then do the fine tweaks to the design, templates, and etc. If you by chance do happen to nail it in a single lucky shot without further adjustments then that day is the good one to also hand out a lottery coupon. That I have never experienced myself. 

[Phend]

As others have said, *don't* use a metal body DC jack - the connection it makes with the enclosure is the one you don't want, not the one you do.
Plastic jacks are ok if necessary, but in your situation, you'd be better with good quality metal jacks that you can really tighten.

Ok, confusion here.
What kind of metal dc jack has a center negative?
Or is it plastic / metal combo?

[GGBB]

As others have said, *don't* use a metal body DC jack - the connection it makes with the enclosure is the one you don't want, not the one you do.
Plastic jacks are ok if necessary, but in your situation, you'd be better with good quality metal jacks that you can really tighten.

Ok, confusion here.
What kind of metal dc jack has a center negative?
Or is it plastic / metal combo?

I think line 2 is about 1/4" jacks not DC jacks.

Otherwise, I suppose it's technically possible to built a medal bodied DC jack that can be used as center pin negative which means the body is not connected at all, but I'm not aware of any in actual existence.

[ElectricDruid]

As others have said, *don't* use a metal body DC jack - the connection it makes with the enclosure is the one you don't want, not the one you do.
Plastic jacks are ok if necessary, but in your situation, you'd be better with good quality metal jacks that you can really tighten.

Ok, confusion here.
What kind of metal dc jack has a center negative?
Or is it plastic / metal combo?

I think line 2 is about 1/4" jacks not DC jacks.

Otherwise, I suppose it's technically possible to built a medal bodied DC jack that can be used as center pin negative which means the body is not connected at all, but I'm not aware of any in actual existence.

Yes, sorry, that's my fault. Line 2 *was* referring to the audio jacks. In my own defence, OP/BlueLDR was talking about DC jacks and audio jacks in the same paragraph that I was replying to, so it all got a bit mixed up.

The point is that you need to ground the enclosure somehow. Since the DC jack is going to be centre-negative, using a metal DC jack *won't* work, but using a metal audio jack where the sleeve is grounded *will work*. OP had plastic bodied jacks on their original 3D mock-up, and I was suggesting that's not the best idea. Better to reverse it, use a plastic DC jack and metal audio jacks.

[aion]

The best thing you can do is buy or borrow a flagship pedal from JHS, Wampler and EQD and open it up and see how they do things. Those three are the closest intersection of DIY and small/medium manufacturing. You won't get many practical ideas from bigger companies like Boss/Ibanez since they are on a whole different level that doesn't really scale downward, but those three in particular are great to learn from.

Pay close attention to the pots you are buying.  I built one unit where I included a separate piece of scrap plastic on the inside to lock into the anti-rotation lugs on each pot.  But with some of the pots, there was barely enough threaded length with the pot going through the plastic plus the outer aluminum structure.  ALWAYS make use of the anti-rotation lugs.  If you use wide knobs, they will hide the anti-rotation lug holes in the structure, so they should be your first choice.  NEVER mount pots on the circuit board or you will crack the solder joints.  DO NOT mount the board by the pots.  Use a lockwasher on the pot and reef it down tight.

This will solve some of the recurring problems we often see - pots that turn beyond the end stops and rip out their wiring and cracked intermittent solder joints.

With much respect to Ron, I strongly disagree with all of this - at least framing it in absolute never/always terms. I've been designing and building pedals for over a decade and I do none of these things and have never had a single failure due to them. To reference JHS/Wampler/EQD again, all of them use PCB-mounted pots and none of them use the anti-rotation lugs. They've been doing it the same way for many years. These types of practices can cause issues in sloppy builds, but with good engineering (drilling, PCB layout, component placement, matched mounting heights) they are not risk factors and so are not inherently bad practice.

[PRR]

> with good engineering (drilling, PCB layout, component placement, matched mounting heights) they are not risk factors and so are not inherently bad practice.

But isn't this thread for people who do NOT yet have "good engineering" mastered?

I do like the idea to open a medium-production pedal "and see how they do things". You can learn a lot by looking. And for this purpose an older or damaged pedal is as good as any.

[GGBB]

I do like the idea to open a medium-production pedal "and see how they do things". You can learn a lot by looking. And for this purpose an older or damaged pedal is as good as any.

Everyone should do this! But we should never assume that how they do things is good - because the vast majority of times that is mainly concerned with cost reduction - quality is secondary. Why they do things that way is equally - if not more - important. Don't take a monkey-see monkey-do approach to designing your pedals.

[Phend]

Tried plastic barrel jacks (stereo and mono) once. Will stick to using these instead.



Plus on the plastic DC jack, I used locktite (or similar) blue thread lock. You can't use it on plastic so I just put a drop between the nut and housing.

[Mark Hammer]

Missing from much of this discussion are the ergonomic considerations.

Is the location of any footswitch likely to be comfortable or does it assume any sort of awkward angle for your foot?

If there is more than one footswitch, can they each be stepped on without accidentally stepping on both?  If there is a good reason for being able to step on more than one at a time, can that be easily done?

Is there a reasonable distance between any place you plan to stick your foot and any toggles or pots?

If there is any critical illumination on the pedal (e.g., status LED, rate indicator LED), is it easily visible?  That includes where it is located, but also brightness and colour contrast against the chassis.

Does the location of any jacks - power, in/out, expression - permit comfortable and tidy placement among other pedals?