Midi to CV unit for Mini Synth

[RockRaver]

Hi fellas. Anyone here use the MidiBox CV unit (www.uCApps.de) as a Midi to CV unit? I want to play my Midi Keyboard Controller (M-Audio Keystation 88ES) with the Mini Synth (that I plan on building as soon i'm done with the Sub Commander unit which I just ordered parts for). I am also incorporating the Guitar Trigger into the unit as well so I can play either my guitar or my keyboard thru the Mini Synth.

[sneakthief]

Yeah, I built one 7 years ago and it's the heart of my system.

It's rock-solid and works great!

Scroll down on this page to see the write-up I did when I made it:

http://sneak-thief.com/modular/

[RockRaver]

Hi sneakthief. I forgot to ask you, what version board did you use with your MidiBox CV unit? Was it the AOUT, AOUT_LC or the AOUT_NG?

I was gonna go with the AOUT but, the MAX525 is expensive so, everyone is suggesting the NG version. The LC seems like the least favourable one on the Midibox site.

Also, being i'm only using this to interface only one Midi Keyboard Controller, it seems like overkill to use something that gives me 8 CV out's. Is there a way to only use one CV Out and Gate Out with any of these boards? Or, will they just be wasted. Not that I mind really.

Lastly, I realize now that I don't need a bankstick either, as I don't see how i'd be able to create any presets with the Mini Synth anyway.

Basically, my only concern is to add a Midi In and Midi Thru to the Mini Synth, along with the Guitar Trigger, and that's all.

Any thoughts?

[sneakthief]

The MIDIbox AOUT LC is exactly what you need!

That's the whole point of the AOUT LC: you can select a 12-bit output paired with a 4-bit output (or a pair of 8-bit outputs).

The 12-bit output is perfectly accurate enough to drive a VCO over its entire octave range, whereas in 8-bit mode, you would get tuning inconsistencies with some notes due to the lower DAC resolution.

I have the MAX525 version which I got as a f*r*e*e* s*a*m*p*l*e* from Microchip

I do recommend the bankstick however because the menory chip is cheap and there are many interesting settings available in the MIDIbox CV software. Keep in mind you also get a configurable/dividable Clock output, a start-stop output, 2 gate outputs, CV slew (portamento generator), mono/legato mode, transposition and various other options.

Having presets lets you quickly and easily recall all these aforementioned parameters.

[RockRaver]

Thanks for the reply. So..., you're saying I should go with the LC version, huh? I thought that chip wasn't up to snuff for what I was looking to implement? It'd be cheaper I know but, i'm just worried about the quality of the chip.

Also, when you say that the 12-bit resolution is good enough for the whole octave range of a VCO, you're not talking about musical octaves, correct? You're talking about octaves as it relates to voltage, correct? How do the two relate? Sorry if that's a dumb question but, it's been a while since I read up on Synth electronics.

Lastly, can you let me know if I got the following right (if i'm only using one keyboard controller):
1) Keyboard into Midi In port (on the MidiBox Core unit)
2) Core unit connects internally to the MIdiBox Midi to CV Unit
3) CV Out1 (of the MidiBox CV) into the OSC-1 CV port on the Mini Synth

I guess as long as I can achieve 12-bit resolution with the one CV port, that's all I need to worry about, correct? I won't need the Gate Out (which the LC doesn't provide) for my needs, correct? Also, the Mini Synth has two CV In's (OSC-1 CV and OSC-2 CV). Will I be losing something if i'm only using the OSC-1 CV input only? Wouldn't I want to use both CV ports simultaneously?

let me know you're thoughts and, thanks again for your help.

[sneakthief]

12-bit DAC resolution is a 12-bit DAC resolution, regardless if it uses an expensive MAX525 chip or a R2R resistor ladder (using matched resistors of course).

12-bits means that there are 4096 different voltage levels that can be selected.

In a musical 1V/Octave scale, you don't need 4096 different voltages, but you need them to be exactly as close to each semitone as possible. so when the DAC needs to put out 4V, you get 4V and not 4.1V for example.

Having more voltages means you can get closer to the perfect voltage for each note in a scale.

You can split the CV outputs from the main CV out of the AOUT LC to drive both VCO 1 and 2 at the same time.

Or you can make a switch on the AOUT LC to switch between 12 & 4 bit mode to 8 & 8 bit mode. You can drive both VCO's separately in dual 8-bit mode but the notes won't necessarily be tuned as well. Could sound very nice!

Correct, the gate outputs come from the core module.

Don't forget to use the midi clock output too! It can trigger gates and other things.