Manufacturer Description:

a-101-6 is a new filter module that uses so-called opto fets to control
the filter frequency. opto fets are very similar to vactrols but use
light depending field effect transistors (fets) instead of light
depending resistors (ldrs). a opto fet is a combination of a light
depending fet and a led (light emitting diode) both put into a small
light-proof case. the advantage compared to vactrols is the much faster
response of opto fets compared to ldrs. this allows much faster
attack/decay times and even fm effects. the disadvantage compared to
vactrols is that the fet behaves as a normal ohm resistor only for small
levels. with higher levels the fet begins to distort. apart from this
the notes mentioned on the vactrol basics page are valid.

module a-101-6 is made of six serial 6db filter stages. each stage can work as lowpass, highpass or one of two allpass types.

the type of filter is chosen by jumpers on the pc board (factory
setting: low pass). the type of filter determined by the jumpers
positions can be marked by means of a water-resistant felt pen at the
front panel. the following document shows the jumper positions for the
four different filter types.

the resonance is controlled by the feedback control up to self
oscillation. by means of a trimming potentiometer the maximal feedback
can be adjusted. high feedback values can be used mainly in the allpass
mode to obtain very extreme self oscillation sounds. even an external
feedback signal can be used instead of the internal feedback connection
(fb in socket).

the mix control is used to pan between the original signal (ccw
position) and the effect signal (cw position). in filter mode (lp/hp)
this control is usually set fully cw. in the allpass modes one obtains
phasing sounds at center position or "pure" allpass sound in fully cw

note: the originally planned version of the module with voltage
controlled switching between the different filter types will be not
realized (see front panel sketch at the left side). because of the many
required voltage controlled switches this version would have been much
more expensive. most of the customers who tried the a-101-6 prototype
suggested to leave out this vc switching feature as it was not that
impressive and instead manufacture the module in a more affordable

it requires 8 te/hp worth of space to fit in a eurorack frame.

Product Specs

Brand New (New)
A-101-6 Opto FET Filter / Phaser
Made In

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Joined Apr 2016
Pomona, CA, United States


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Pomona, CA, United States
Joined: Apr 2016

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Doepfer - A-101-6: Opto FET Filter / Phaser Phase Shifter
+ $5 Shipping