how to amp AOUT voltage on CORE32 SEQ V4

[robotfunk]

Hi all,

after years of procrastinating planning, I finally started to build my Midibox SEQ V4, starting with the CORE32 board.

First of all let me compliment Thorsten and SmashTV, the step by step build / test instructions are very helpful so far and the PCB oozes quality. I just got MIOS studio talking to the core, w00t!

Now my question, I'm planning to use this mainly to control my Eurorack modular synth and I was aiming to use CV rather than MIDI if possible. Now in the build document I read that the CORE32 can't deliver more than 3.3V to AOUT, I swear I see this for the first time, although in hindsight, it's rather obvious that you can't output more than goes in.. Now ideally I'd like to multiply this voltage by 3 to arrive at nearly 10V which seems to be the most common analog standard for pitch CV. I think I'm gonna need at least 5V for the gates/triggers as well.

How to go about this? I'm figuring some opamps and an external +/- power supply, after reading http://www.acroname.com/robotics/info/articles/interface/interface.html .

Now most circuits I've seen with opamps are really attenuators rather than real amplifiers, so I'm wondering if anyone else has an idea how to go about this. Since my modular already has a +/- 12V power supply, perhaps I could build a 'breakout euro module' that is housed inside the modular, not sure if noise is going to be an issue though.

Any hints would be much appreciated,

Jilt

[TK.]

Hi Jilt,

welcome back! I remember that our last conversation was in 2001! :)

There is a big problem with the "internal DAC" channels of STM32: the output is located at the same pins which are used for SD Card accesses, and there is no alternative pin mapping. Therefore unfortunately these channels cannot be supported by the MBSEQ V4 application.

If this restriction wouldn't exist, you could amplify the outputs with the same OP Amp circuit as used by the MBHP_AOUT_LC module: http://www.ucapps.de/mbhp_aout_lc.html

So, you will need one of the MBHP_AOUT* modules. AOUT_NG is the most preferable solution, AOUT_LC the cheapest, and the original AOUT if you don't like SMD soldering (but it's more expensive)

Gate/Trigger pins at J5 can be shifted to 5V with a 74HC541 buffer IC, see this datasheet:

http://www.standardics.nxp.com/products/hc/datasheet/74hc541.74hct541.pdf

Pin 1 and 19: OE# connected to ground

Pin 10: to ground as well

Pin 20: to 5V

Pin 2..9 are the inputs

Pin 11..18 are the outputs

Best Regards, Thorsten.

[robotfunk]

Hi Thorsten, thanks for your quick reply! you seem to have elephant memory ;)

Even though my soldering has improved a lot in the last 10 years, I'm still uncertain I'll manage to solder SMT, so I think I'll spend a bit more and go for the original AOUT.

One step at a time though, gonna finish the core first, thanks again.

Jilt

[vcfool]

Now my question, I'm planning to use this mainly to control my Eurorack modular synth and I was aiming to use CV rather than MIDI if possible. Now in the build document I read that the CORE32 can't deliver more than 3.3V to AOUT, I swear I see this for the first time, although in hindsight, it's rather obvious that you can't output more than goes in.. Now ideally I'd like to multiply this voltage by 3 to arrive at nearly 10V which seems to be the most common analog standard for pitch CV. I think I'm gonna need at least 5V for the gates/triggers as well.

From the SEQ V4, the CV outputs on my AOUT_NG are delivering up to +10V. That's using a +/-12V PSU. And unipolar mode.

IMHO that's more than enough for driving Eurorack gear. Normally voltages on there are 10V peak-to-peak, so +/-5V.

10V are spanning 10 octaves (!!!) for Pitch. Usually 5V is more than enough.

from Doepfer's site:

http://www.doepfer.de/a100_man/a100t_e.htm

Audio Signals are produced by the sound source Modules (such as VCO or NOISE), and lie in the range from -5 V to +5 V (10 VSS).

...

Control voltages, as produced by modulation sources like the LFO and ADSR, are from -2.5 V to +2.5 V (5 VSS) for the LFO, and from 0 V to +8 V for the ADSR.

Trigger or Gate Signals, which start a process or function, are typically from 0 V to 5 V, with the trigger occurring as the leading edge of the waveform shoots up from 0 V to 5 V.

I think I'm gonna need at least 5V for the gates/triggers as well.

Gates on the Core32 (J5) are indeed +3.3V. For now I am using external modules to boost the gates when needed. If you need more than +5V (as I do) you can also use the +12V from the AOUT_NG PSU.

BTW don't let the SMD in the AOUT_NG put you off. This was my first SMD soldering and was easy enough... GM5 has been a little harder :)

Good luck!