Saturday, 29 July 2017

Testing my PCBs easily

A while back I designed my own EAGLE CAD part for the interconnect between the 3PDT PCB and effect PCB a while back to make it easy to link up my boards.

My custom part. IN GROUND V+ OUT

To test my finished PCBs I would solder 4 leads on and wire the completed board into my test rig. I had a bit of a brain wave today and thought up of a device that could clamp over the pad that would be permanently wired to my test rig. I had a bit of a look around in my junk boxes and found a bulldog clip. The custom part I made has a 2.54mm spacing between pads which is the same as vero board. 
Pin header, Vero scraps and a bulldog clip
I glued the bits of vero to the inside of the bulldog clip with some loctite 401. Soldered the pin header at the end of one of the vero strips. Drilled 2mm holes on the other vero strip. Soldered some tails onto it and it's ready to go.
Finished clamp
Mouth open
Clamped onto the PCB
Clamped on to the PCB

So the clamp works pretty well. By using big grunty solder blobs on the pin header they make good contact with the pads. They took some adjusting to get right. I've checked this with a multimeter on the resistance scale and got readings between 0.2Ω and 0.4Ω on all 4 points back to spots on the PCB. Will test it out with an amp when I get a chance. The beauty of this thing is it will work on all my PCBs that I get made up so I can test quickly before boxing up.

Thursday, 20 July 2017

BOSS HM-2 Mod. Make it work on a 9v Power Supply

I recently scored one of the legendary BOSS HM-2 MIT beasts. I got in in an auction on eBay saying it was faulty. The description was along the lines of "works with a battery but not a power supply". I thought hey I know what that is!!

Boss have this ridiculous thing where they made you buy only BOSS power supplies back in the day. They called it ACA. Essentially they set up the pedal to work from a 12v supply by adding a resistor and a diode in series with the supply.
HM-2 Schematic

Here is a close up of the section that I need to do the mod.

I want to keep this as close to original as possible So instead of removing D1 and R2 and putting a link in I will just put a solder blob across wire 4 and wire 5

With the solder blob in place the mighty HM-2 will now run from a 9v supply perfectly. This mod can be applied to any BOSS ACA style pedal. If you are going to do this mod make sure that you confirm the correct components and wires.

Wednesday, 12 July 2017

Changing Potentiometer Shafts/Wafers

As a busy hobby pedal builder (300+ builds to my name) I buy a lot of pots.
My bulk pot storage
My everyday pot storage

I buy most of my pots from Tayda Electronics. They are alpha pots which are pretty good. I've ad no issues with them in the 6 years I've been building. They are well constructed and come with a handy little dust seal. The only issue I have from time to time is getting the right value with the style of shaft. I was building a Hot Cake clone and it called for a C50K pot (anti-log) I had some but they had spline and split shafts on them. I wanted to have a round shaft so I could put MXR style fluted knobs on them.
I need the round smooth shaft on the C50K

I set up my phone and recorded a short video of me swapping the shafts over. If you don't like loud angry music turn the volume down. I don't do any talking in it ( I have a terrible radio voice).

It's very simple with the right tools. I use an arbor press but it can be done in a vice too. I don't actually have a vice but I find it easier in a vice than the press.

  • Remove the back by lifting the tabs with a pair of pliers or any other tool will do.
  • Place the pot upside down on the press into a sleeve so the shaft can move freely. I use a discarded linear bearing off my 3D printer but anything can be used.
  • Using something skinny press down on the centre of the shaft. In the video I used the closest thing I could find which was a little phillips screwdriver, again anything smaller than the small shaft is fine. It wont go all the way down and out, the rest I pull apart by hand. This also helps make sure I don't drop/loose any bits.
  • Swap the wafers (the flat bit with the carbon track on it) over onto the shaft that is desired and grab a plastic wiper wheel.
  • This is the tricky bit. It takes a bit of practice and I've broken plenty of wiper wheels trying. You have to hold the pot and wiper and line up the small shaft on the pot to the wiper wheel. They are shaped like two D's back to back. Press it a little bit and check it. If it's no good re-position it and try again. If it's good make sure the wafer is lined up on the little locating pins and then press it all the way home.
  • Spin the pot so the stopper lump on the wiper wheel is at the top and fit the back back onto the pot. 
  • Repeat for the other pot.....if you want to. I have a big box of pot bits that I haven't put back together

That's pretty much it. I plan to design and build a jig to make this easier at some stage. For now this works for me.