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Doepfer A-101-2 LPG | Vactrol Low Pass Gate | NOT FULLY FUNCTIONAL

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  • Regular price $ 90.00


The top two CV inputs on this module are not working, and the LED is not responding to knob turns, meaning there is no activity in the vactrol. 

A-101-2 is a combination of low-pass filter (LP) and VCA. It is based on the idea of ​​the Buchla module 292. The term "Low Pass Gate" was introduced by Don Buchla and refers to a module that can be switched between low-pass filter and VCA, with the module control (manual or CV) in the first Case for the frequency, in the second case is responsible for the volume. In addition, there is a combined LP + VCA mode in which the frequency and the volume change simultaneously: the quieter the signal is, the duller it gets. 
In contrast to the Buchla design, the A-101-2 module also has attenuators for both the externally supplied control voltage and the audio input signal. In addition, the module has a manually adjustable resonance(to self-oscillation) and two gate inputs to control the function - in addition to the manual switch - via external gate signals. 
In principle, the A-101-2 is a 12dB low pass that can also be switched to VCA or a combination of low pass and VCA. The controlling elements for the filter frequency (in LP mode) or for the volume (in VCA mode) are so-called Vactrols . These components are known for their "soft" sound, which is due to the fact that they are linear elements that do not cause distortion. For more on Vactrols, visit the Vactrol Fundamentals page . Due to the Vactrol circuit, the signal in VCA mode is not completely suppressed even with minimal control voltage!
The frequency (in LP mode) or the amplitude (in VCA mode) can be controlled manually (F / A) and via 2 external control voltages CV1 (without attenuator) and CV2 (with attenuator). 
The audio input is also equipped with an attenuator. The audio input of the module is very sensitive, so that, for example, from the controller position 5 with the use of standard A-100 audio signals (eg VCO A-110) targeted distortions can be generated by clipping the power supply limits. 
The Resonance function adds color to the sound by raising the frequencies at the filter point. The resonance can be up to the natural vibration Due to the Vactrol tolerances, the natural vibration may not be available evenly over the entire frequency range. The resonance setting has an influence on the output amplitude. This increases slightly at higher resonance values. However, this behavior is also found in many other filters. The resonance function was not available in the Buchla module. In order to preserve the sound performance of the Buchla module, the resonance control must be turned all the way to the left.
The function of the module is set with a toggle switch. The left and right positions correspond to the lowpass and VCA modes, respectively. In the middle position the low pass / VCA combination is selected. In this switch position, the module function can also be controlled externally by means of two external gate signals G1 and G2. A small table, which is printed on the front panel, shows the relationship between the gate signals and the module function (L = gate level "low", H = gate level "high").