Manufacturer Description:

A-110-4 is a so-called Thru Zero Quadrature VCO. The term "quadrature"
means in this connection that the oscillator outputs sine and cosine
waveforms simultaneously. The term "Thru-Zero" means that even
"negative" frequencies are generated. But this a bit a misleading term
as negative frequencies do not really exist. "Negative" means in this
connection simply that the sine/cosine waves will stop when the linear
control voltage reaches 0V and continue with the opposite direction as
the linear control voltage becomes negative and vice versa.

The module has two control sections: linear and a exponential. The
exponential section consists of the XTune control, the 1V/Oct input and
the XFM input with the corresponding attenuator XFM. The exponential
control voltage is the sum of these three voltages. The linear section
consists of the LFrq control and the LFM input with the corresponding
attenuator LFM. The linear control voltage is the sum of these two
voltages. A dual color LED is used to display the polarity of the linear
control voltage (red = positive, yellow = negative). The pitch of the
sine/cosine outputs is determined by the control voltages of both
sections. The linear section is used to control the pitch in a linear
manner. When the LFrq control (LFrq means Linear Frequency Control) is
fully CW the module works like a normal Quadrature VCO (e.g. like the
A-143-9) and the LED lights red (red = positive). The pitch is then
controlled by the exponential section with the manual Tune control XTune
and the exponential frequency control inputs 1V/Oct and XFM. 1V/Oct is
used to control the pitch by a 1V/Oct CV source (e.g. sequencer or
Midi/USB-to-CV interface). XFM is used to apply an exponential frequency
modulation with adjustable depth (e.g. from an LFO or another VCO). As
the LFrq control is turned counterclockwise starting from the fully CW
position the frequency is lowered in a linear manner until the
sine/cosine waves (nearly) stops at the center position of LFrq
(provided that no LFM signal is present). As the LFrq control is moved
from the center towards the CCW position the wave starts again but into
reverse direction and the LED turns yellow. When the fully CCW position
of LFrq is reached the module works again like a normal Quadrature VCO.
But much more exciting is the usage of the LFM input to modify the
linear control voltage by an external control voltage (typically another
sine VCO like a second A-110-4 - but even normal VCOs can be used).
Linear modulation by another oscillator using the thru zero feature
generates audio spectra than cannot be obtained from an oscillator
without the thru zero function. The reason is that a "normal" VCO will
simply stop as the linear control voltage becomes zero or negative. But a
thru zero VCO will start again with "negative" frequencies as the the
linear control voltage becomes negative.

The main advantage of the A-110-4 compared to other Thru Zero VCOs is
that the design uses a sine/cosine core. The sine/cosine waves are not
derived from other waveforms (e.g. sawtooth or triangle) by means of
waveshaping. Rather the sine and cosine waves are the core of the VCO
which results in very pure waves with a minimum of distortion and

The output level is about 3Vpp. Audio examples and oscilloscope pictures will follow soon.

Important note: Please remove the bus jumper (JP3 "BUS CV") if no CV
transmitter is installed on the same bus (e.g. a Midi/USB-to-CV
interface A-190-x or a bus access module A-185-x). The A-110-4 applies a
small voltage with high impedance (100k) to the CV line of the bus when
the bus CV jumper is installed. This may affect other modules that
pick-up CV from the bus (e.g. other VCOs). As soon as a CV transmitter
is installed on the same bus the high impedance voltage of the A-110-4
is overwritten and no problem occurs !

ConditionBrand New (New)
Brand New items are sold by an authorized dealer or original builder and include all original packaging.Learn more
  • A-110-4 QZVCO Quadrature Thru Zero VCO
Made In
  • Germany
Synth Module Function
  • Oscillator
Horizontal Pitch
  • 8HP
  • 1 Voice
Modular Synth Format
  • Eurorack

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