MidiALF/CV board

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).

MidiALFCV_naked_(small)

Features

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)
  • Velocity
  • CC1/2
  • LFO1/2
  • 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.

DIY Resources

Schematics: alf_cv#1 alf_cv#2 (v0.3)

Schematics: alf_cv#1 alf_cv#2 (v0.4)

MidiALF_CV

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.

Tuning procedure

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:

  1. connect note CV output to your 1/V per octave VCO input
  2. connect MIDI OUT to a reference synthesizer MIDI IN
  3. click encoder under C4 and tune your VCO frequency controls so that VCO pitch matches reference synthesizer pitch
  4. rotate EncB to make C3 visible
  5. rotate step encoder under C3 tuning output CV so that VCO pitch matches reference synthesizer pitch
  6. press step switches on notes between C3 and C4 to interpolate their tuning, manually tweaking each note tuning after interpolation if necessary
  7. 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.

Ordering

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).

Shipping:

  • Continental USA — $5
  • Canada – $10
  • Europe, Asia and Australia – $15

Building MidiALF/CV

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. 

MidiALF_DC2DC

The bare pcb de-greased with isopropyl alcohol:

balfcv#01

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:

balfcv#02

Add 8 x 100K 0.1% resistors:

balfcv#03

Add miscellaneous resistors:

  • 2 x 10K
  • 1 x 750
  • 1 x 560

balfcv#04

Add 16 x 100n capacitors. For v0.4 add 4 x 47p capacitors.

balfcv#05

Add 6 x 1n4004 diodes:

balfcv#06

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

balfcv#07

Add 2 x ferrite beads:

balfcv#08

Add voltage regulators:

  • 1 x 78L12
  • 1 x 79L12
  • 2 x LM317LZ

balfcv#09

Add 4 x 10u tantalum capacitors:

balfcv#10

Add 2 x 100u 16V electrolytic capacitors:

balfcv#11

Add 6 x 2 female connector header. You can use more common 5×2 connector since rightmost two pins are not used.

balfcv#12

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.

balfcv#13

Add 2 x stereo and 4 x mono connectors. The board layout supports both 3.5mm and 1/4″ parts.

balfcv#14

Add 2K trim pot:

balfcv#15

Finished MidiALF/CV extension board:

balfcv#16

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.

Powering MidiALF/CV from your modular system.

Leave out all components outside the two pink rectangles, install ferrite beads L1, L2 and C20,C24 only. Add jumpers in place of D1, D2 to provide power to the MidiALF main board. This routes positive power rail from your modular to power input on the MidiALF main board where it gets converted down to 5V by switching voltage regulator.
If you’ll feel that your modular’s positive power rail became noisier (MidiALF’s LCD and MCU may spill some noise in there), installing C17,C21 100n ceramic caps and C19,C23 tantalum 10u 25V may help.
ModularPower
 D1 and D2 on the PCB:
MidiALFCV_D1D2
Have fun!

72 thoughts on “MidiALF/CV board

  1. Pingback: MidiALF/CV info, schematics and docs published | MidiSizer

  2. Hi Peter, are these boards ready (midi to cv)? If so, I’d like to order one, please send invoice when ready (shipping to Australia)

  3. Hi Pete, you say the power supply should be 16VAC, but i think it has to be 16VDC because the DC-DC converter handles DC only? also, it seems a much higher voltage is possible, up to 24V?
    can you confirm?

  4. ok, i bought this 16VAC PSU and exchanged the 7805 regulator for the murata one, plus deinstalled the MIDI in/out LED’s plus their resistors – then i plugged it in, but MidiALF doesn’t boot anymore :-/ the screen is full of blocks, all led’s are on and the atmega gets very hot… i re-checked all the voltages on the board at the points given in the MidiALF construction guide and there is 5V everywhere as recommended. i tested with and without CV board connected.
    any idea what might have gone wrong?

    • This does not sound good. I’d remove all ICs and check for shorts. If none found, insert Atmega, make sure it is oriented correctly. If it’s still hot, it might be fried.

      • I had exactly the same problem as Gerhard, and found that this can be resolved by either going for a somewhat higher voltage PSU (18VAC, say), or increasing the value of C3 (to 1000 uF, for example).

  5. Hi Pete. If I power the MidiAlf/ CV-board from my modular PSU (+12v/ -12V), will the MidiAlf mainboard be powered as well? Or do I have to power it seperately? I have changed the power reg 7805 on the mainboard to the switching one.

  6. Hi Peter,
    I can’t find the 5V regulator (part number : OKI-78SR-5/1.5-W36H-C), but I can buy a LM1084 (Vin up to 25V, 5v output , 5A). I think it could be a good replacement. Do you think I can use it ?
    MidiAlf finished ( Killer sequencer, I love it), now working on the cv board
    Thank you

  7. Hello Pete,
    I’ve finished the Midialf+cv , it had worked for ten minutes and after a big mistake (of me) , certainly a shortcut, no more cv, no more gates…(midi works correctly)
    I’m trying to test the cv/gate pcb, but honestly I have really no idea, no signal at the input of the 2 opamps (LF412)…wich component could be the most sensitive to a shorcut ?
    thank you in advance
    Fabien

    • It really depends on where the short happened. What did you short ?

      Start probing DACs MOSI and SCK signals, there should be some pulses there, check VREF, it should be +5V, check DAC outputs.

  8. Hello, just finished my MidiAlf and cv-board, about to do some testing before I put it in an enclosure. So far I`ve come up with to problems; the SEL-led doesn`t light up when I push it, only when I turn power on, then it acts as it`s supposed to. Second, I have no output from gate one, the rest seems to be working fine. Any suggestions?

    • SEL LED — MidiALF firmware does not use it at this time, so it is only lit during power up sequence.

      Gate1: chances are you have connectivity problem (cold joint or a short) on a connection from IC12 pin 2 to Gate1 out.

      • Thank you for helping out, I had a bad wire, changed it, and now it’s up and running! Great fun and an excellent machine!

  9. Hi Pete – would a midialf with CV board work as a live MIDI to CV converter for live incoming signals from the MIDI in port?

  10. Pete, if I want to power this from modular power, is there any harm in installing the components ” outside of the pink rectangles? I bought all the parts anyway, may as well install them in case I want to power the device from the 2.1mm jack sometime, assuming there’s no technical reason why I shouldn’t.

    …obviously, the D1, D2 diodes have to be replaced with jumpers to use modular power…

  11. Hello Peter, I received yesterday the PCB, well packed, quickly soldered, I just miss a few components before testing it with my Midialf. Just to make sure everything is OK : you mention to solder 6 x 1N4004 but the Mouser SKU of your BOM is 1N4001s, that I ordered. Is this OK ?

  12. OK thanks, my expansion board is soldered and mounted, but now the midi-in LED is not lighting up anymore, and firmware upgrade from my 0.92 is stuck before the midi in LED steadily lit. Any ideas ?

  13. I used Elektron C6 and did set this interval to 250 ms. When launched the job, I waited like 2 minutes, and nothing happened, neither on the leds side, which scares me on the hardware side.

  14. I juste tested again, I simply didn’t have selected the midi in & out ports on C6, now it’s ok, the 0.94 cv .syx was totally sent after a few minutes, but when I restart, midialf doesn’t boot anymore, the screen is full of blocks, all led’s are on, and I can’t reset the device. Since I plugged the expansion board, midi-in led never works, and when I send midi data to midialf, strangely midi out led blinks instead of its neighbour. Even the Midialf alone, without CV board, has the same behaviour.

    • MIDI IN and OUT LEDs are not functional when CV board is connected — their ports are used to communicate with the expansion board. You may want to temporarily disconnect CV board and reload the firmware sysex watching the LEDs behavior.

  15. OK cool, I managed indeed to upgrade midialf with expansion board disconnected, and now it can send via gate & CV. But my LEDs still seem buggy. Is it normal that, even when sequence is stopped, midi out led is always on, and midi in is always off, sequence playing or not ?

  16. Hi Peter,
    after a long time i managed to finish the CV board v3.
    I removed the MIDI LEDs and the resistors for those, swapped the 7805 for the recommended OKI regulator, swapped the capacitors and fired up the board with my old power supply, all fine so far but very underpowered. After reading that it is now necessary to use a 16V AC power supply i bought one, plugged in and everything was lit and the CV Alf stopped working. Now i am a bit lost about where to look what may be the issue here as the built looks ok…

    • I’d temporarily disconnect CV board, remove all the ICs from the main board, and make sure that the +5V voltage on the main board is correct. Then i’ll insert main board IC’s back and check if it works, Then remove all the ICs from the CV board, connecto it and verify +12 -12V voltages, etc.

  17. Ok, removed chips and get a clean 21,8 V on every point on the mainboard when the 16 V AC PS is plugged in. Looks like Mouser sent me a defective converter or a wrong part, cannot determine this as i never have used this type before. And at least the ATMega has met his ancestors. I tried to hook up my USBASP programmer and this stated that no device is answering…now i can only guess what else has been fried. A bit frustrating as it took nearly 5 months to get the converter from Mouser. And i measured the AC output of the PS with nice 17,8 V…this sucks.

    • Oh… i’m really sorry to hear that. I will update build instructions to suggest people to remove ICs and test VCC after PSU re-work.

      Fried ICs are easy to replace. I’d be more worried about LCD — if it’s fried, i’d recommend cutting off its connector and then desoldering its pins one by one.

  18. I used an oldschool crystal LCD and it looks like its still alive, if not than it is a good excuse to put in a new one…i still wonder if the 17,8 V of the AC powersupply have fried to converter first.

  19. Ok, here we go: clean 4,92 V on the VCC rail and on the mainboard, 11,8v on the power rail of th CV board. This looks better…now to the bad news: ATMega is absolutely dead and the LCD shows only backlight. So now my question: is the LCD driven by the ATMega and this is normal or should i prepare myself for the worst and replace the LCD too ?

    • LCD is certainly driven by the ATMega, and if the latter is fried, the LCD wont show characters. However, LCD controller could also be fried. One way to test it is to turn LCD Trim all the way in one or the other direction. If at some point you see one like of box characters, the LCD controller may be still functioning: LCD controller fills up the top row with boxes if it receives no communication from host CPU.

      If you have to replace LCD and you don’t have a decent re-work station or solder sucker tool, i’d recommend cutting the LCD board next to the connector, then cutting the connector and removing connector header pins one by one.

  20. As i had an ATMega for another project lying around, i managed to replace it and flashed the firmware. Sequencer and LEDs are running, as far as i can tell, because well the display shows nothing but backlight and here and there some boxes, but however i turn the trimmer it doesn’t really change or work. A quick measure of the connectors shows that it should…well it’s time to pick up my Dremel and cut this bitch out. I guess now its time for some patience while desoldering it.

  21. Hi, I’m selling my MidiAlf, with CV expansion board, all mounted, and with a DIY plexi/wood box. It’s in France currently. Anyone interested ?

  22. Is it possible to use the MidiAlf as a sequencer and a Midi to CV interface at the same time? So that e. g. two gates/cv-outs would be used to play a sequence and the other two gate/cv-pairs would translate a seperate incoming midi signal ? Thanks.

  23. hello Pete!! here i am again ..! i want to order another midialf cv v.04 kit plus an ic preprogramed. send me the invoice to my mail. i will send you some pictures of my work soon.. greatings from argentina!!

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