This is a blue lead-free (ROHS) board. On the back, it says “Rev 3”.
There is one known issues with the PCB.
The decoupling capacitors C6, C7, C21, C22 are connected to each other but not ground. These will not be effective. Required fix: put in link (e.g. snipped resistor leg) between one of the middle holes of the MOTM connector and the immediately adjacent hole of C21 (correction: earlier version had R21 which is wrong.)
Omit capacitors C1, C4 and C5.
Install one only of resistor R30 or R33. Install R30 to mix the bass to the main output. Install R33 instead to mix the bass with the sharkstooth output.
Capacitor choice: Please note that the 1uF DC blocking capacitors C11 and C12 on the two audio outputs should be bipolar (non-polarized) capacitors, such as bipolar (NP) electrolyic capacitors or ceramics. However, the bypass capacitors C2 and C3 should be normal polarized electrolytic capacitors: they can be any value 1uF to 10uF, really. The other smaller capacitors can be any convenient type.
Please note that the correct value for C14 is 22pF. (A draft version of the schematic showed 22nF.)
Knobs choice: the 4HP module is quite cramped if normal knobs are used. I recommend the t18 microknobs (available from Thonk, as use by e.g. Befalco).
Diode D1: use generic 1N4148 (or low dropout germanium diode.)
There is a difference in terminology between the 4HP and 6HP labels. We want to use the terminology “Breadth” rather than “Width” now, to signify it is not a relative amount (like a percentage, like the vanilla PW most VCOs output) but an absolute amount.
Workaround for Swapped Labels of 4HP Panel
The 4HP front panel has an error: the labels for Pulse Out and Sharkstooth Out are swapped.
If you have a 4HP panel with “Out Pulse” at the bottom socket, there is a simple fix for the swapped labels: swap which sockets the final resistors R18 and R19 go to. (If you have already fully populated the board, I recommend removing the ICs to give yourself more room to work.) Remove R18 and R19 if they are installed: they are at the bottom of the board next to the sockets. Install a 1k resistor in standing position between the top hole marked R19 and the neighbouring bottom hole marked R18. Then run a second 1k resistor in lying position between the remaining two holes; make sure you position it so that there will not be any accidental touching or shorts: position the body of the laid-down resistor to be next to the standing-up resistor, to reduce the chances of leads meeting, and try to position the resistor as far away as possible (you may prefer to use heat-shrink insulation tubing.) Reinstall the ICs.
Customizing: Pimp my Blip!
- If you find the modulation input is too weak (and you probably will), change resistor R22 from 47k to 10k.
- If you want a version of Blip! with fewer highs, play with larger values of C4 and C5 to filter the sound a wee bit.
- The +5V line on the power cable is not used by this module, so you may install a 10-pin power socket instead of the shown 16-pin socket, aligned on the red (negative) side.
- If you would prefer the bass to augment the Sharkstooth output rather than the Pulse output, install R33 instead of R30. (This feature is not available in the Rev 2 PCB.) Note that the R33 label is a little above the footprint.
- If you make C14 22nF (or perhaps 47nF) rather than 22pF, the trigger does not have a chance to reset before the next cycle on medium and high notes. This will give a kind of 8ve divider effect on those notes. (We intend to provide a panel labelled Bass for people who want this effect.)
Freak Out! 