AM8012 ARP2600P VCF

AM8012 Module

Overview  This is a 4-pole 24dB low-pass filter constructed around a traditional “Moog” transistor ladder. It is temperature compensated and has a wide cutoff range between 0 – 35kHz. It appeared in early ARP 2600 synthesizers in 1971, and it is a refinement of the ARP 1006 filter in the 2500 Modular synthesizer.

The AM8012 has been re-engineered to improve on 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. The module captures the sound of the ARP version of the traditional transistor ladder.

EuroRack Module:   16HP wide
User Manual:             AM8012 User Manual V2

AM8012 PCB

Description  This 16 HP wide module has at its heart a traditional transistor ladder, with a dual FET based Differential Amplifier, with the whole core surrounded by buffer amps to interface to modular standards. The transistor ladder uses matched transistor arrays at the top and bottom, as well as for the exponential generator. This means we don’t need to hand match transistors!

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 lowest jack socket marked Out is the audio signal output of the filter and it is typically connected to a VCA. The Frequency 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 FINE slide potentiometer enables small change in cutoff frequency and is used when adjusting the frequency of the filter when it is self oscillating. The Q 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 KYBD slide potentiometer varies the amount by which the keyboard note voltage on the Doepfer bus varies the cutoff frequency of the filter, from zero to maximum. This enables the note value you play to determine cut-off.

Module Availability  The AM8012 was launched at the end of 2012 and has been through a series of manufacturing runs. The Mark 2 version has a revised exponential generator circuit and dual matched Linear Systems transistor pairs.

2024 Update In 2024 a 14HP Eurorack version was released with Q compensation, external Q CV and resonance ping (from the 1047). More details are here.


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