AM8075SE Athena VCF

Arp 4075 Filter replica

This module is a replica of the ARP 4075 24dB low pass filter in the ARP Odyssey Mk3, and the 4072 VCF used in later models of the ARP 2600. It also has a single pole High Pass filter connected in series after the low pass filter, just like the ARP Odyssey.

This Special Edition (SE) has been re-engineerd to improve and simplfy the original design, with upgraded high quality internal components such as matched transistor arrays, and precision capacitors.

The external design replicates the "look and feel" of the ARP Odyssey Mk1 with slide potentiometers and coloured caps. Athena is the Greek Goddess of inspiration and skill, and this filter captures the essence and sound of the ARP Odyssey Mk3.

This 16 HP wide module has at its heart the LM3900 Norton Amplifier chip which delivers the distinctive "smooth" 4-pole low pass filter, with a clean low distortion output that will easily oscillate at higher resonance settings. The filter response at high resonance remains faithful to the original with a slight loss of bass at higher resonance settings. The high pass filter in the original ARP Odyssey is rather a nasty affair based on a CA3080 OTA chip, so I have replaced it with an improved 6bD design based on the higher quality BA6110 OTA chip. No noise now!
The two uppermost jack sockets INA and INB are for connecting audio signals into the input side of the filter, these signals are mixed together. The level of each audio signal can be varied from nil to maximum using the front panel slide potentiometers InA and InB. The middle jack sockets CV1, CV2 and CV3 are for connecting modulation control voltages into the filter. These signals vary the cut off frequency of the filter, with the front panel slide potentiometers adjusting the amount of modulation, except for CV3 which is directly connected to the VCF. The lowest jack socket marked Out is the audio signal output of the filter and it is typically connected to a VCA.

The VCF Cutoff slide potentiometer varies the cut off frequency of the low pass filter. At the minimum setting the filter will cut off all frequencies with no audio output and at the maximum setting the filter will pass all frequencies.

The VCF Resonance slide potentiometer adjusts the resonant peak of the filter from a minimum setting of no resonance, through subtle resonance enhancement to a maximum setting when the filter will break into self oscillation. The HPF Cutoff slide potentiometer varies the cutoff frequency of the high pass filter

http://www.amsynths.co.uk/products/filters/am8075se-athena-vcf/