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16 Step Sequencer Gate & trigger Levels

Posted: Thu Mar 16, 2017 9:34 am
by sixbyseven
Hi There, I am having some issues getting other synths to trigger off the MFOS 16 step sequencer. Does anyone know what the voltage level and the signal length is for the trigger out?

I am getting 12V at the gate, and it works fine, CV also works correctly but I am having a dickens of a time trying to capture the trigger signal on the scope.

I have even set the sequencer to maximum clock rate, to provide a really fast pulse for the probe. I can see the blips on the screen that corresponds to the clock rate (so there is a signal), but the max voltage I am seeing is only 124 mV and I thought it should be somewhere around 10V to 12V

In the schematic, both gate and trigger come from the same source, but they use U6 a bit differently before the output.

I am wondering if the signal is just too short in duration, and wonder if C13, the 0.001microfarad cap is the reason.

Anyone else have this ?

Thank you.

Posted: Sat Jul 08, 2017 4:39 pm
by eljay
To lengthen the Trigger pulse make the following changes on the Analog Sequencer Digital Board : Change C13 from 0.001uF to 0.01uF and R28 from 100K to 470K. This gives a theoretical trigger length of 4.7ms, I measured consistent 4ms trigger lengths on my scope after making the changes. This now works perfectly as a trigger source with my Oakley modular.

Posted: Wed Sep 05, 2018 7:58 am
by eljay
I've also used Ray's guidance from the MFOS website in the article "Interfacing your Synth with MFOS gear" to reduce the Trigger and Gate output voltage levels.

Under the heading 'Limiting MFOS Gate and Trigger levels' is a simple to implement resistor and diode modification to make on the output sockets, I used the recommended 3k resistor and a 5.1V Zener diode on each of the trigger and gate output sockets to achieve a measured 4.7v output level. This works and is now consistent with the voltage levels on my Oakley modular.

Further on in the same article in the box headed 'Boosting low voltage Gate/Trigger Voltage to drive MFOS gear' is a small circuit that I put on a piece of veroboard to boost my Oakley output gate level so that it can trigger the sequencer using the Ext Start socket.