AM1044 24dB Low Pass Filter

12 HP|AM1044 24dB Low Pass FIlter|User Manual (PDF)|ModularGrid|You Tube

OVERVIEW This 12HP wide AM1044 is a re-issue and expansion of the original AM8044 from 2013, using the CoolAudio V2044A chip and some design ideas from the SSI2144 datasheet. The V2044A delivers a fantastic sounding transistor ladder filter, which we have added some amazing Q compensation to.

 
DESCRIPTION The V2044A is a re-imagined SSM2044 chip which found its way into the various Korg synths like the Mono Poly in the 1980's. In 2013 I issued the AM8044 based around this chip, but its was a low volume run due to its scarcity. Fast forward 13 years and the V2044A chip is easy to source, plus some ideas in the SSI2144 datasheet about how to add Q compensation.

The  V2044A chip creates a 24dB cascading ladder filter, with an extra OTA circuit providing Q compensation, which ensures no loss of bass response when Q is driven into self oscillation. The Q circuit also has a Q CV input (with an attenuator) for achieving variable feedback from a CV input. The self oscillation goes down to below 20Hz.

The module has a two way LED circuit which has a green LED to show normal signal levels and a red LED to show boosted levels. Subtle amber LEDs continuously light up the CV potentiometers.

 CONTROLS

• • Three audio inputs (INA, INB, INC), with the first two having a volume control
  • Four CV inputs to the VCF (CV1, CV2. CV3, CV4), three with a level potentiometer
  • Large control knob for filter CUTOFF
  • Q is controlled via a dedicated RESONANCE potentiometer
  • Q CV input and level control
  • Two way switch (Q COMP) selects whether Q compensation is on or off
  • ARP 2500 style control knobs

CONNECTIONS There are nine 3.5 mm jack sockets on the anodised aluminium front panel:

• • IN 1, 2 & 3 - audio signal inputs with individual level control
  • CV 1, 2, 3 & 4 - 1V/octave control voltage inputs for filter cutoff
  • QCV - control signal for adjusting resonance
  • OUTPUT - audio signal output

  
The module comes with a set of M3 mounting screws and washers, and a standard 10 to 16-way Doepfer power cable.

 
MODULE STATUS: IN PRODUCTION