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Subject: Re: [motm] I just added 5 more outputs to my MOTM 120

From: "Richard Brewster" <pugix@...>
Date: 2003-01-17

I'd be glad to.  I still don't have a decent schematic drawing program.  Most of the schematic programs I've seen come with PC board layout features I don't need.  I've got to find something in this department.
 
The circuits are so simple that I can just describe them.  The pulse outputs are each a simple comparator with the + input of the TL072 op amp coming from a MOTM suboctave output.  I just tapped the +5V pulses off the suboctave pots on the MOTM PC board.  The minus inputs of all the op amps are tied to a voltage divider between +15V and ground, 100K/10K, for about a 1.5V threshold.  The output of each op amp goes through a 3K9/2K2 voltage divider to produce a +/-5V level for the output.  The staircase summer just sums each +5V MOTM pulse wave through a weighted resistor.  The values I used are 25K, 50K, 100K, 200K (by matching up some 1% resistors).  The summer uses a 15K feedback resistor to get output maxed at about -6V.  I wasn't concerned about the absolute value, just that the intervals would be equal.  The other half of the TL072 doing the summing is used to invert the sum back to positive.
 
I have a fairly simple patch up right now (I can hear it in the next room).  A MOTM 390 dual LFO provides the A and B inputs in cross product mode.  I use either mixed output passed through an external scaling attenuator to drive a MOTM 300 and a MOTM 310 VCO patched through a MOTM 440, all on the 1V/Oct inputs so they'll track.  Then I take two of the new pulse outputs (the second and third suboctave work well rhythmically) and drive two envelope generators, each of which modulates the center frequency of the MOTM 440 in different directions.  You would be amazed at the interesting patterns produced by varying the frequencies of the two LFOs.  Now, if I can get going on that recording software!  I still can't make MP3 files of my MOTM.  It'll happen eventually.
 
-Richard
 
 
 
----- Original Message -----
From: Les Mizzell
To: MOTM List
Sent: Thursday, January 16, 2003 8:03 PM
Subject: RE: [motm] I just added 5 more outputs to my MOTM 120

You wouldn't care to share the schemos for that mod, would you?
 
 
 LFO inputs can produce a 16-step sequence for controlling a VCO pitch, all adjustable with the internal mixer.  I used the extra panel space to add five new outputs.