Harvesting Parts!

Harvesting parts from these old PCBs. I had this need for a A100K pot and Christmas 🎄 has holding up the deliver from Tayda Electronics. So I started digging through my bin of old projects that never made it into a box 📦.

I didn’t my ideal A100K pot, it would have been 16mm with legs, but I did find a couple 12mm pots which might sub. These have a D shaped shaft which makes them harder to fit for knobs.

While not finding what I was looking for was disappointing, I think I may have raided this bin at an earlier date, I did find some surprises. I found at least a half dozen J201 Fets, and a 4049UBE hex inverters. The J201s are great for stomp boxes and hard to get these days.

There was also a few 3PDT switches and a bunch of 1/4” jacks along with a handful of other things. Switches and jacks can always find some use. Personally I prefer the open frame Switchcraft jacks but these plastic ones are a good second choice.

Stomp box enclosures and shielding

I was trying to up the quality of my builds and thought about shielding and noise. Did a little research on the interwebs and came up with a few tips.

First a little background. High gain circuits often run series of gain stages in series. If you have an input stage of x10 followed by an adjustable stage of x10 to x100 you have a minimal gain of x100 to a max gain of x1000. That’s a lot of gain. Anything that gets into your circuit at the input will also be boosted by x100 to x1000! Think of cable crackles, switch pops, scratchy volume pots on your guitar, and more.

Then there’s the noise in the air from electromagnetic interference. It’s not uncommon for pedals to pick up radio transmissions, remember that scene from Spinal Tap? Or the hum of electronic devices like fluorescent lights.

In many ways the enclosure acts as an antenna picking up electromagnetic noise. But it can also be used as a Faraday cage which can be used to protect the circuit inside from electromagnetic interference from the outside. To do this the enclosure must be connected to ground.

if you have open frame jacks like the Switchcraft jacks the sleeve will make contact with the enclosure. This grounds the enclosure for free. If you’re using those jacks with the plastic body you’ll need to run a wire to the enclosure somewhere.

Is it enough to ground the box? Yeah but in the case of painted boxes or boxes with a powder coat the bottom cover may not make an electrical connection to the main body of the enclosure. I used a drill bit to remove the paint from one of the counter sunk screw recesses. This allows the screw to make contact with back cover and main body of the enclosure.

UBE Screamer PCB v1.1

This is the second version of the UBE Screamer board. This version fixes a mistake with the reverse polarity diode. I’m calling this ready for public consumption and will add it to the OSH Park projects pages soon.

The enclosure is grounded through the jacks. The bottom cover though doesn’t make an electrical connection to the main enclosure body due to the powder coat. I used a drill bit to remove the powder coat inside the count sink recess, this allows the screw to make contact with the back cover for full shielding.

Partslist

Capacitors
C1      10n
C2      2n2
C3        470n
C4       100n
C5        1n5
C6        150p
C7         100n
C8       100n
C9        100n
C10       100u
Diodes
D1        1n4148
D2         1n4148
D3         1n5817
D4             LED
IC
IC1      CD4049UBE
Resistors
R1       1M 1M
R2         470k
R3          470k
R4        100k
R5          100k
R6        10k
R7        1m
R8       10k
R9        100k
R10       100k
R11       100k
R12       220k
R13      Rx  (see note)
R14       330
R15         RLED
Pots
TONE   B500k 16MM      
VOL      B100k 16MM    
GAIN    B500k 16MM

Wiring

Build your own! Check out my OSH Park projects page. Or buy this one at my Reverb shop.

Vulcan by Joe Davisson

This is Joe Davisson’s Vulcan overdrive. Starting with a prototype board made at home with the Othermill, then turned this into a board from OSHPARK. Boxed up and is working well. This is an interesting overdrive with a couple unique circuit features.