AM991 Fixed Filters

OVERVIEW This is recreation of the Moog 991 Fixed Filter module from 1968, an accurate reproduction of the original schematics. A passive design that requires no power.

The module contains a pair of fixed filters (single pole -6dB Low Pass and High Pass) and an attenuator. There are five filter positions for each filter and the extra attenuator is really useful.

It is a nice alternative to the 923 module, as the 991 fixed positions require no dialing in of values.

DESCRIPTION There are five different value polypropylene capacitors in each filter with a 6-way rotary switch selecting each capacitor in turn, with a final bypass position at step 6.

The cutoff frequency of both filters are the same;

• 16Hz, 41Hz,159Hz, 482Hz, 1591Hz

There is also a fixed attenuator with a high quality Alpha control potentiometer. The module is designed to complement the Behringer System 55 Modular System, with a black anodised aluminium 8HP panel with 2 rotary switches and one potentiometer.

CONNECTIONS There are six 3.5 mm jack sockets on the base of the black anodised aluminium front panel:

• High Pass Filter: Audio Input and Output
• Low Pass Filter: Audio Input and Output
• Attentuator: Audio Input and Output

The module comes with a set of mounting screws and washers (M3 black).

2024 MODEL The front panel has been upgraded with an improved black finish, and the correct silver graphics and silver edge strips. The price has been reduced by a massive 50% to £59!

MODULE STATUS: PRODUCTION