MidiALF/CV extension board is mounted at the bottom of the MidiALF main board using 8 x 7/8 stand offs. You can choose to build it with 1/4″ or 3.5mm jacks. It could be powered by MidiALF main board (which in this case needs to be powered by 16VAC adapter) or your modular system (+-12 or +-15V via optional Eurorack 5×2 or MOTM MTA-156 connector).
4 CV outputs: 1/4″ or 3.5mm jacks, range 0 to +10V or -5 to 5V .
Each CV output can be set to:
- Note (1V/Oct with per note tuning)
- After touch
- Pitch bend
4 Gate outputs: 2 x 1/4″ stereo jacks (Gate1/3 and 2/4) or 4 x 3.5mm jacks, normal or inverted.
Gate level is set by on-board trim pot ( +4.5 to +11.5V).
Strobe pulse width is configurable from 1 to 5 ms.
Each Gate output can be set to:
- Gate (on while key is down)
- Strobe (pulse on key down)
- Clock (pulse 24 PPQN)
- Start (on while sequencer is running)
- Seq (pulse on sequence start)
- LFO1/2 (pulse on period start)
Large hacking area with ground and positive/negative power rails.
Bill of Materials (vo.3)
Bill of Materials (v0.4)
Eagle files: alf_cv_v04
CV/Gate configuration page
-CV1| CV2| CV3| CV4|| Gt1|-Gt2| Gt3| Gt4 note|velo| cc1| cc2||gate|strb|lfo1|lfo2
This page is shown when rotating EncA in page selection mode.
Step encoders select CV/Gate mode: note/velo, gate, strob, etc.
Step encoder click toggles CV range (0 to +10V or -5V to +5V) or inverts Gate output.
Note CV tuning page
C4 | C#4| D4 | D#4|| E4 | F4 | F#4| G4 -23| -21| -19| -17|| -15| -13| -11| -8
This page is shown when Tune command is selected on the Command page.
EncA shifts all notes tuning up or down 1 step (or 10 steps if SEL is held down).
EncA click resets all notes tuning to zero (with confirmation).
EncB selects visible note range, hold down SEL to shift by an octave.
EncB click saves current tuning and cancels note sound.
Step Encoders change note tuning by 1 step (or 10 steps if SEL is held down).
Step Encoders click sends the clicked note to both MIDI and CV outputs.
Step switch resets note tuning to zero or, if it’s already at zero, interpolates the note tuning.
Per note tuning covers entire CV range, so you can use it to change note CV output to whatever requirement your VCO has.
Note tuning interpolation speeds up the process significantly by estimating the note tuning value using the non zero tuning values to the left and to the right. Here’s the typical procedure:
- connect note CV output to your 1/V per octave VCO input
- connect MIDI OUT to a reference synthesizer MIDI IN
- click encoder under C4 and tune your VCO frequency controls so that VCO pitch matches reference synthesizer pitch
- rotate EncB to make C3 visible
- rotate step encoder under C3 tuning output CV so that VCO pitch matches reference synthesizer pitch
- press step switches on notes between C3 and C4 to interpolate their tuning, manually tweaking each note tuning after interpolation if necessary
- Repeat steps (5) and (6) for all octaves you want to cover.
Note that if note CV output has been tuned before, but sounds out of tune the next day, you may want to try rotating EncA shifting all notes tuning up or down first to bring C4 in tune.
To order MidiALF/CV extension board, please send an email to pete at kvitek c o m specifying how many PCBs you need and a country where to ship them, and I’ll send you PayPal invoice.
MidiALF/CV board $30 (please note that you’ll need MidiALF main board to use this extension board).
- Continental USA — $5
- Canada – $10
- Europe, Asia and Australia – $15
If you have soldered LM7805 on your main MidiALF board, you’ll need to replace it with switching DC to DC converter: RECOM R-785.0-0.5 part . Unless you have a re-work station or a good desoldering tool, I recommend cutting the legs of 7805 and then desoldering them one by one. It is not worth risking MidiALF PCB pads attempting to save 50 cent component. When all three legs are removed you can clean the pads with a solder wick and solder in 3 pin header to make it easier to install DC to DC converter. You will also need to replace C3 with 220uF electrolytic capacitor with 25V rating, mounting it sidewise because there is not enough room to mount vertically: the connectors on the CV board leave very little space in the sandwich.
The bare pcb de-greased with isopropyl alcohol:
Add 10 x 220 ohm resistors (v0.3). For v0.4 add 2 x 220 ohm resistors on the left and 8 x 1K resistors next to 4504N and LF412:
Add 8 x 100K 0.1% resistors:
Add miscellaneous resistors:
- 2 x 10K
- 1 x 750
- 1 x 560
Add 16 x 100n capacitors. For v0.4 add 4 x 47p capacitors.
Add 6 x 1n4004 diodes:
Add IC sockets. Note that the notch should be pointed to the left.
- 1 x 18 pin DIP
- 5 x 16 pin DIP
- 2 x 14 pin DIP
- 3 x 8 pin DIP
Add 2 x ferrite beads:
Add voltage regulators:
- 1 x 78L12
- 1 x 79L12
- 2 x LM317LZ
Add 4 x 10u tantalum capacitors:
Add 2 x 100u 16V electrolytic capacitors:
Add 6 x 2 female connector header. You can use more common 5×2 connector since rightmost two pins are not used.
Add 2 x 560u 25V electrolytic capacitors. These should not be higher than 20mm if you’re using standard 7/8″ stand offs to sandwich the boards.
Add 2 x stereo and 4 x mono connectors. The board layout supports both 3.5mm and 1/4″ parts.
Add 2K trim pot:
Finished MidiALF/CV extension board:
Connect MidiALF/CV extension board to the main board using 2×5 extension headers.
Use trim pot to set desired gate level. If you don’t have oscilloscope to check the voltage you may set sequence note lengths to be longer than sequence step and measure gate output with regular voltmeter.