A-143-4 Quad VCLFO/VCO

click to enlarge

Note: The labelling of the range switches of the front panels of the first module series was reverse. The up position is high (VCO mode), the down position is low (LFO mode)
From the second series the front panel printing is correct (like the above picture)

• four independent VCLFOs/VCOs with triangle core
• frequency range switches: low (bottom position) = LFO mode, high (top position) = VCO mode
• two frequency control CV inputs for each unit
  • CV1 without attenuator (~ 1V/oct)
  • CV2 with attenuator
• manual frequency control
• internal jumpers for the frequency range of the manual frequency controls:
  • jumper not installed: ~ +/- 1 octave range (mainly for VCO applications)
  • jumper installed: ~ +/- 5 octaves range (mainly for VCLFO applications)
• Sync inputs:
  • combined Reset/Direction inputs for unit #1 - #3
  • separate Reset and Direction inputs for unit #4 (normalled sockets, i.e. Reset is connected to Direction if the Direction socket is unused)
  • up/both/down direction switch for unit #4, for technical details concerning the Reset and Direction function please refer to the sketch below
• triangle and rectangle outputs for each unit
• typ. output voltage range -5V ... +5V for both outputs  (i.e. about 10 Vpp, symmetrical with reference to 0 V)
• red/yellow LED displays for the triangle outputs (red = negative output voltage, yellow = positive output voltage)
• common control section with two CV inputs and manual control (these inputs and controls affect the frequency of all four units)
• sum outputs for triangle and rectangle with red/yellow LED displays
• optional ultra-low frequency mode: for this a negative voltage can be applied via a jumper internally to the CV2 input of each unit and the common section (i.e. a negative voltage is normalled to the socket CV2 in question). Then the CV2 attenuator control works as a negative frequeny control (i.e. turning up this control lowers the frequency). Herewith LFO periodes up to about one hour (or even more) are possible.
• optional CV bus access via jumper (i.e. the module can pick up the CV from the A-100 bus, e.g. generated by a Midi/CV or USB/CV interface A-190-x or a bus access module A-185-1/2), if the jumper is installed the bus CV affects all four units as the bus CV is added to the CV generated by the common control section
• typ. frequency range: < 0.001 Hz (~ one hour, LFO mode with ultra-low option) ... 15 kHz (VCO mode with installed frequency range jumpers for the manual frequency controls)
• heat-up time: ~ 15 minutes (required to heat-up the main circuit by the affixed oven)

Important Notes:

The module was planned mainly as a quad VCLFO. But we added a range switch (nothing but a switch for two different capacitors) so that even audio frequencies are possible and the module can be used as VCO with some restrictions too. Because of the closeness of the main circuitry (i.e. four VCO cores within less ~ 1 square millimeter) the oscillators may lock if the frequencies are very close to each other and the VCO frequencies interact marginally. If a high quality quad VCO is required the A-111-4 is recommended as this module has four separate VCO circuits available.
The reset circuitry is optimized for the LFO mode. As it takes some time to discharge the oscillator capacitor the discharge time had to be chosen so that the capacitor is fully discharged in LFO mode. In the high range (where a much smaller capacitor is used) this will cause a zero state duration in the 0.3 ms range if the oscillator is synced (during this time the capacitor is shortened for discharge).
The control scale of the inputs "CV1" is about 1V/octave. To improve the behaviour in the VCO mode a tempco circuit is used to keep the temperature of the exponential converter at a fixed temperature (similar to the tempco option of the DIY SYNTH).. That way the frequency of the VCOs (and even the VCLFOs) is nearly independent from the environment temperature. But the accuracy (1V/octave scale and temperature compensation) is not as precise as for the dedicated VCOs A-110 and A-111-1.

This document explains the functions of the 17 jumpers: A143_4_jumper.pdf

Technical details concerning the Reset and Direction function:

The reset of a triangle based LFO or VCO consists usually of two functions:

• Discharge of the capacitor that is used to generate the oscillation (i.e. set the output voltage to 0V)
• Pushing the LFO into the right direction. Usually an LFO starts from zero with it's positive slope after a Reset. Without this second function the LFO would randomly start with positive or negative slope (exactly: it would keep the direction that was present while the Reset has been carried out)

For unit #4 all types of sync are available:

• Separate Reset and Direction function (separate, normalled input sockets for Reset and Direction)
• Direction switch up/both/down
  • In the up position only a direction change to rising slope is possible (triggered by the rising edge of the direction signal)
  • In the down position only a direction change to falling slope is possible (triggered by the falling edge of the direction signal)
  • In the both position both direction changes are possible (the positive edge of the direction signal causes a change to the rising slope, the negative edge of the direction signal causes a change to the falling slope)
  • the direction signal causes only an effect if the slope is not yet in the direction in question (e.g. the rising edge of the direction signal has no effect if the LFO signal is already in the rising stage)

A-143-4 Quad VCLFO/VCO
"History"

• four independent VCLFOs/VCOs with triangle core
• two frequency control CV inputs for each unit: CV1 without attenuator (~ 1V/oct), CV2 with attenuator
• manual frequency control
• triangle and rectangle outputs for each unit
• common control section with two CV inputs and manual control (these inputs and controls affect the frequency of all four units)
• sum outputs for triangle and rectangle

Additional features of the second version:

• frequency range switches
• LED displays (useful only for LFO range)

Additional features of the third version:

• additional Sync input with combined Reset / Direction input sockets for unit #1 and #2
• Reset socket for unit #3 with switch to use the Reset signal optionally for Direction too
• Separate Reset and Direction sockets for unit #4

Technical details concerning the Reset and Direction function:

The reset of a triangle based LFO or VCO consists usually of two functions:

• 1. Discharge of the capacitor that is used to generate the oscillation
• 2. Pushing the LFO into the right direction. Usually an LFO starts from zero with it's positive slope after a Reset. Without this second function the LFO would randomly start with positive or negative slope.

In the third version of the A-143-4 these two functions are processed in different ways for the four sub-units:

• For the units #1 and #2 an internal jumper is available that can be used to connect the Reset and Direction function as usual. If this jumper is removed only the Reset is carried out (i.e. the capacitor is discharged and the LFO starts with zero Volt). But the Direction after the Reset is defined by the slope of the LFO signal just before the Reset occured. If the LFO had a rising slope during the Reset occurrence it starts from zero with a rising slope, if the LFO had a falling slope it starts with a falling slope.
• For unit #3 a switch is available that can be used to connect Reset and Direction. If the switch is closed the unit behaves like the units #1 and #2 with installed jumpers. If the switch is open unit #3 behaves like the units #1 and #2 with removed jumpers.
• For unit #4 two different sockets for Reset and Direction are available. This means that different signals can be used to trigger the Reset and the Direction function. The sockets are normalled, i.e. unit #4 behaves like the units #1 and #2 provided that the Direction socket is not used.
• It would be possible to manufacture the module in another version with separate input sockets for Reset and Direction for all four units. But this would increase the width of the front panel again by 2 HP (and increase the price a bit).

For the fourth and probably final version these changes have been made:

• different front panel layout:
  • units 1...3 are identical (one socket for Reset/Direction, internal jumper to interrupt the connection Reset-Direction, internal pin header to add all the features of unit 4 to the units 1...3)
  • separate Reset and Direction sockets for unit 4 (Direction socket is normalled to Reset, i.e. if no jack plug is inserted into the Direction socket Reset and Direction are connected)
  • Direction switch (up / both / down) for unit 4, with this switch one can select if the direction signal may change the triangle output into both directions (rising edge of the direction signal enforces rising direction, falling edge enforces falling direction) or only one of both directions (up or down)
• optional ultra-low frequency range: for this a negative voltage can be applied via a jumper internally to the common input control socket with attenuator (i.e. a negative voltage is normalled to the socket). Then the attenuator control works as a negative frequeny control (i.e. turning up this control lowers the frequency). Herewith LFO periodes up to ~ one hour (and even more) are possible.
• CV bus access via jumper (i.e. the module can pick up the CV from the A-100 bus, e.g. generated by a Midi/CV or USB/CV interface A-190-x or a bus access module A-185-1/2).