The CV and Gate-trigger connectors on FatMan are outputs only. The exponential pitch cv (doubles or halves for octave spaced key presses up or down on the keyboard) from the MIDItoCV conversion is output on the Pitch CV connector. As an aside, this is the same type of pitch cv used by the older PAiA 4720 and 2720 linear-response VCOs and FatMan can work as a MIDItoCV converter for these older modulars. FatMan's MIDItoCV converter uses the note-message velocity data for the Velocity CV output. The Gate-trigger output is derived from one of the IC1 uC port lines used to operate/monitor the VCA ADSR. It is active for the duration of a key pressed condition as signaled by the MIDI source.
It isn't too difficult to change FatMan so an external pitch cv is substituted for the on-board one. The MIDItoCV conversion results in a pitch cv ranging from 0-7v dc from IC12:A pin 1 (manual fig. 5a) which goes to the Glide section around IC10:A (manual fig. 5b). The printed-circuit layout has a wiring point for the CV and a trace running over to the pitch cv output connector. The wire carries the cv up to the VCF Pitch (cv amount) control and the Glide control R32. This is a good spot to open the circuit and substitute the external pitch cv. An added connector and switch could be used to input and select internal or external cv, or, a closed-circuit phone connector can be used to automatically select the external source when a plug is inserted. I've included some notes for this at the end of this message. Note too, this same sort of thing can be done on the Velocity CV and this is a way the VCA can be opened/closed in lieu of a gate-trigger to it's associated ADSR envelope generator--send the Gate in as the external velocity cv. Advancing the VCA Velocity (cv amount) control will open the vca to let the VCO and VCF sound through to the output.
Adding an external gate input is a little more involved because the VCA ADSR envelope begins with the gate being active, but it is the gate deactivating AND a signal back to the uC that the envelope has peaked that results in the condition which allows the envelope to enter its release phase and end. So, in addition to adding the external gate input, some extra circuitry is needed to mimic the function of the uController gating the adsr. I've attached a pdf with the schematic for the circuit. A DIP IC experimenters board like RS model 276-150 makes it easier to construct the circuit.
Sincerely, Scott Lee
Corey hall wrote:
> Hello Scott, I was planning to hook up a Voice of Saturn sequencer to my Fatman and was curious about how to proceed. The Sequencer has a CV out, Clock out, and Trigger out and I need some help figuring out where to hook these up to. Should I run it through the Trigger or CV of the 555 on the Fatman? Any help or suggestions are deeply appreciated.
> Thank you for your time, Corey
Adding external pitch or velocity cv inputs to the FatMan.
Closed Circuit (c.c.) Phone jacks, 1/8" or 1/4", can be used to both
interrupt the normal cv circuit and substitute an external cv. The cc jacks work to
switch the cv from the internal source to an external source whenever a plug is
inserted. In addition to the normal Tip and Sleeve, these also have a Shunt
(or Switch) contact and terminal. This contact normally rests against the Tip
contact but when a plug is inserted, it pushes the Tip contact away from the
Shunt contact opening the Tip-Shunt circuit.
Using this type of connector to implement external cv input function on the
FatMan eliminates the need for an Internal/External switch in addition to the
added input connector.
The FatMan CV source to destination (pitch cv to VCO, or, velocity cv to
VCFand/orVCA) circuit is opened by disconnecting board to panel wiring. The
circuit is completed again by reconnecting it to the Shunt terminal of a cc jack
and adding a wire from the Tip terminal of this cc jack to the original
The FatMan Pitch CV originates at circuit board wiring point (AI) and goes to
panel control R71-3, the VCF pitch_cv_amount ((and from there on to R32, the
Glide control over another wire) and then back down to the board and then back
up to the Pitch control before going to the VCOs). This is where the new
external_pitch_cv_input c.c. jack is to be wired. Disconnect the wire from AI at
the R71-3 terminal and reconnect it to the shunt terminal and add a new
length of wire from the tip terminal to R71-3 where AI had connected. The sleeve
terminal of this c.c. jack connects over to a nearby circuit ground/common
point (ie R71-1) using a new length of wire.
The FatMan Velocity CV originates at circuit board wiring point (AJ) and goes
to panel control R69-3, the VCF velocity_cv_amount (and from there on to
R104, the VCA velocity_cv_amount control over another wire). This is where the
new external_velocity_cv_input c.c. jack is to be wired. Disconnect the wire
from AJ at the R69-3 terminal and reconnect it to the shunt terminal and add a
new length of wire from the tip terminal to R69-3 where AJ had connected. The
sleeve terminal of this c.c. jack connects over to a nearby circuit
ground/common point (ie R69-1) using a new length of wire.
The panel controls for the Velocity in the VCF and VCA sections and the Glide
and Pitch in the VCO and VCF sections affect the external cv input to these
added connectors. The normal FatMan cvs range from 0-7v and the external cvs
should be kept within this range. The original cvs have no effect when the
external cv inputs are connected. To get an external gate input requires a
modification involving the addition of a new IC and some extra associated
Scott Lee 9/23/04
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