X-Series MKII Backend Filter

24dB/octave VCF/VCA with envelopes

Think of Macbeth's Backend Filter as a classic subtractive analog synth without the oscillator section. It consists of an audio mixer, a low-pass filter with four different outputs, two envelopes and a VCA. Except for one IC, the module is completely discrete, which guarantees vintage sound

New features to the predecessor:

-use of very high-quality parts throughout the signal path. Significant improvement in the choice of capacitors.

-In addition to the 16-pin Doepfer standard connector for the power supply, the rarely used CV bus has now been used. On the Backend Filter not only the CV busses but also the gate connector was installed. Both can be switched on or off discretely at the back of the unit(s).

-Throughout the Backend Filter, a mixture of selected 'passive' components and precision-matched transistors provides a particularly warm filtered sound.

-The jack sockets have been redesigned. In the original X-Series, Ken Macbeth used the same type of 'box jack' that many others use. Ken began to question the reliability of this type of plug - and now with the MK2 versions about to be launched, he felt it was important to upgrade the jacks to a higher quality type. As far as plugging is concerned, they will have a much longer life, which in turn will increase reliability."

From the product information sheet:
The MACBETH X-SERIES MKII BACKEND FILTER is a dedication to quality and authenticity. Discrete circuit design using premium components, including selected bipolar transistors and audio-optimized capacitors, ensures a purist approach to analog sound.

At the heart of the Backend Filter is a 24dB/octave low-pass filter, capable of self-oscillation and equipped with four distinct response outputs. These outputs are accessible pre-VCA, offering rich tonal shaping options for any patch. The filter tracks pitch via the TRACKING CV input, enabling seamless integration into melodic patches. A dedicated envelope generator drives filter modulation, with control over modulation intensity via the VCF EG/CV parameter.

The audio inputs on the Backend Filter are highly sensitive, contributing to its signature vintage character. These inputs can introduce subtle warmth or push signals into a pleasing saturation, perfect for adding depth to your sounds. Attenuators ensure precise control, allowing to maintain clean signals or explore driven, harmonic textures.

Complementing the filter are two voltage-controlled amplifiers (VCAs), each with distinct roles. The primary VCA delivers standard amplification with the potential for pleasant, analog overdrive when handling hot signals. The secondary VCA is ideally suited for velocity-like dynamic control or creative amplitude shaping.

The two envelope generators are dedicated to the VCF cutoff frequency and the primary VCA. The envelope generators also have output jacks for external patching. The VCF envelope features an additional inverted output.