Doepfer A-147-5 Quad VC LFO Eurorack Module

Module A-147-5 contains four voltage controlled low frequency oscillators (VCLFO) with triangle waveform outputs. All LFOs share a common frequency control. Each of the LFOs 2, 3 features a Delta control which is used to shift the frequency of the LFO in question up or down. With the Delta controls at center positions the frequencies of all LFOs are roughly the same. To control the frequencies by external control voltages four CV inputs are available which follow roughly the 1V/oct standard.

The module has these controls and in/outputs available:

• Control F: manual control of the frequency for all four LFOs
• Control Delta F2, F3 and F4: manual control of the frequency shift up/down for the LFO in question
• Sockets CV 1...4: Frequency control voltage inputs (normalled from top to bottom)
• Sockets with triangle symbol 1...4: triangle outputs
• LEDs: visual displays of the triangle outputs (red = positive, yellow = negative output voltage)

Application examples:

• Generation of four triangle modulation signals with a common frequency control for all LFOs and individual controls for the frequency deviation of each LFO, manually adjustable and controllable by external control voltages
• Generation of modulation signals for polyphonic FM/PWM applications. For this the four CV inputs are connected to the same control voltages which are used to control the frequencies of the corresponding VCOs. That way each LFO follows the frequency of the associated VCO with the possibility to control the frequency of all VCOs (control F) and the frequency deviations (Delta F controls). For the simultaneous modulation depth control the Quad VCA module A-130-4 is recommended.
• Generation of complex modulation signals by summing up the outputs (e.g. by means of a mixer module A-138n / A-138i / A-138j)

Technical notes:

• The level of the triangle outputs is about +/-5V (10Vpp)
• The manually adjustable frequency ranges from about 0.025 Hz (about 40 seconds) to about 50 Hz with the delta controls of LFOs 2, 3 and 4 about center position
• The frequency deviations adjusted by the delta controls are about +/-1:5. Example: with 1 Hz in center position the frequency shift ranges from about 0.2 Hz in position -5 to about 5 Hz in position +5 (1 Hz/5 = 0.2 Hz, 1 Hz*5 = 5 Hz).
• The manual frequency controls and the control voltage inputs have an exponential control behavior
• With external control voltage the max. frequency is about 150 Hz, the minimum frequency
• The scale of the CV inputs is roughly 1V/oct (not adjustable)
• The CV inputs are normalled from top to bottom. Provided that only socket CV1 is patched CV1 controls the frequencies of all four LFOs.
• When each CV input is patched to it's own control voltage each LFO is controlled individually by it's own CV. In this case CV1 controls only the frequency of LFO1.
• Internally the four triangle signals are available at four terminals for internal connections to other modules (e.g. passing through A-130-4 to A-111-4 for polyphonic modulations).
• Internally the four rectangle outputs are available at four terminals (typ level +/-10V or 20Vpp). If required they can be wired to four sockets of a DIY breakout module made by the user, 1k protection resistors are recommended to avoid short circuits. If lower levels are required passive attenuators (voltage dividers) may be used.
• Internally is even an (unbuffered) triangle sum signal available. For this each of the four triangle outputs is simply connected to the sum output terminal via a 47k resistor. This output has high impedance and should be buffered or amplified to avoid level drop when the load changes (e.g. by means of an A-180-3 or A-180-4 or A-183-3).
• By changing the values of the capacitors in the LFO circuits even other frequency ranges are possible (e.g. Quad VCO to form kind of a cloud VCO). Pay attention that the accuracy of the CV input scales is not sufficient for precise 1V/oct VCO applications. The 1V/Oct scales cannot be adjusted and the circuits are not temperature compensated.