Doepfer A-147-2 Eurorack Voltage Controlled LFO Module

The Doepfer A-147-2 Eurorack Voltage Controlled LFO Module is the successor to the VCLFO A-147 , but offers much more options than its predecessor. Essentially, the module consists of the following three subunits:

• VCLFO: Voltage Controlled Low Frequency Oscillator (LFO)
• VCA: voltage controlled amplifier (VCA), switchable to polarizer/ring modulator
• VC delay unit: voltage-controlled, linear delay envelope (with only one parameter: delay or attack) for delayed LFO use with voltage control

LFO

The voltage-controlled LFO has the waveforms triangle, sine, sawtooth and square and is additionally equipped with a reset/sync input. The LFO outputs sine/triangle and rectangle are displayed with two-color LEDs. The sawtooth output of the LFO is displayed with a monochrome LED. The output levels for triangle, sine and rectangle are around -4 - +4 V. The output level for sawtooth is approximately 0 - + 8 V.

The function of the CV control for the external control input can be switched between Attenuator and Polarizer ("CV Mode" switch). In polarizer mode, the control voltage applied to the "LFO CV" jack to the left of the center of the CV control negatively affects the LFO frequency, to the right of the center position as a normal attenuator.

The frequency range of the LFO without external CV is about 0.005 Hz (about 3 minutes per period) up to about 200 Hz (with external CV up to about 1 kHz). In addition, a so-called ultra-low mode is possible (similar to the A-143-4). For this purpose, a jumper can be set on the circuit board, which supplies the "LFO CV" socket via the switch contact a fixed voltage. In polarizer mode, the CV control adjusts extremely low frequencies (up to an hour or more). To do this, the jumper ex works on the pin header JP7 ("Dummy") must be transferred to the pin header JP6. JP6 is behind the CV controller. JP7 itself has no function and serves only to "park" the jumper.

VCA

This is a VCA with linear control voltage characteristic that can be switched between "real" VCA (Voltage Controlled Attenuator) and Voltage Controlled Polarizer using the "VCA Mode" switch. In "real" VCA mode gain +1 is achieved at approximately + 5V control voltage. In polarizer mode, the gain ranges from about -0.5 (ie inverted at about half level) at 0 V control voltage to about +0.5 (ie non-inverted at about half level) at about +5 V control voltage. At approximately + 2.5 V control voltage, the CV signal in polarizer mode is suppressed.

The VCA of the A-147-2 has the three sockets "In" (signal input), "Out" (signal output) and "CV" (control input). The triangle output of the LFO is connected via the switching contact of the socket "VCA In" to the signal input of the VCA. If another LFO waveform (or other external signal) is to be edited with the VCA, this can be done by patching the relevant signal to the VCA In "VCA In" input. The VCA can also be used independently of the LFO and delay unit for other functions than stand-alone, linear VCA, polarizer or ring modulator. In this case, the 3 sockets of the VCA (In, Out, CV) should be patched accordingly. The VCA can also be used as a waveshaper for the LFO signals.

Attack/Delay

The third unit in the module is a simple, linear envelope generator with only the Attack parameter. After every delay reset, this unit generates a linearly increasing voltage starting at 0 V, the slope of which can be voltage-controlled manually with the delay controller and additionally via the "Delay CV" socket. The waveform of the delay output voltage is linearly increasing, the control characteristic is exponential. The output voltage of the delay unit is represented by a single-color, green LEDs and is available at the "Delay Out" socket.

The Delay control sweeps - without external "Delay CV" - a range of about 5ms (right stop) to 2 minutes (left stop). With the help of an external control voltage this range can be extended. With increasing CV, the delay time shortens! The delay output voltage is in the range of approximately 0 - +5 V. The rising edge of the gate, clock or trigger signal applied to the "Delay Reset" socket resets the delay voltage to zero.

The output signal "Delay Out" is connected via the switching contact of the "VCA CV" socket to the control input of the VCA and thus controls the level of the triangle signal, if no other interconnection is made.

If the "Delay Reset" uses the gate signal of a USB/MIDI interface, you can create the function of a "transient vibrato" or "transient tremolo" by switching the VCA output to the frequency control input of a VCO or VCFs, or the control input of VCA connects.

however, the delay unit may - as well as the VCA - be used completely independently of other tasks in the a-100, for example as a voltage controlled wave shaper or for other functions in which a linear rising signal with a voltage-controlled Steepness is needed.

Specifications:

• Output level triangle, sine and rectangle: approximately -4 - +4 V (zero-symmetric)
• Output level Sawtooth: approximately 0 - +8 V (purely positive)
• Frequency range without external CV: approximately 0.005 Hz (approximately 3 minutes) - 200 Hz
• Frequency range in ultra-low mode or external CV: approximately 1 hour period ... approximately 1 kHz
• Trigger signal for LFO-Reset/Delay Reset: Rectangle with min. approximately 6 Vss (AC coupled, therefore, the voltage difference is crucial, 0 V/+6 V works as well as -3 V/+3 V), if you reset the gate output of one of the MIDI interfaces A-190-x to control LFO or If you want to use Delay Reset, the interface may have to be set to high gate level, a (steep edge) rectangular signal must be used for triggering, a "soft" signal such as the output of an envelope generator or the triangle signal of an LFO are not suitable.
• VCA control voltage/gain: 0 - +5 V for gain 0 - +1 (in VCA mode), 0 - +5 V for gain -0.5 - +0.5 (in Polarizer-Mode)
• Delay range: about 5ms - about 2 minutes