A-101-2 is a vactrol based combination of Low Pass filter (LP) and VCA and was inspired by the Buchla module 292.

The term "Low Pass Gate" was created by Don Buchla and stands for a module that can be switched between low pass and VCA. The control (manually and via external CV) is responsible for frequency in the low pass mode and for loudness in the VCA mode. Additionally a combined mode LP+VCA is available. In this mode the sound becomes more dull as the loudness decreases. In contrast to the Buchla design the A-101-2 offers attenuators for both CV and audio input, a manual resonance control and two gate inputs to control the function of the module in addition to the manual toggle switch.

In principle the A-101-2 is a 12 dB low pass filter that can be switched to VCA or a combination of Low Pass and VCA. The controlling elements for frequency (LP mode) resp. amplitude (VCA mode) are so-called vactrols. Vactrols are known for their smooth sound behaviour. Because of the vactrol circuit the audio signal is not fully attenuated in the VCA mode at the minimum setting of the F/A control. The Frequency (in the LP mode) resp. the Amplitude (in the VCA mode) is controlled manually (F/A) and by the 2 control inputs CV1 (without attenuator) and CV2 (with attenuator). The audio input is equipped with an attenuator to enable distortion too (above ~ position 5 distortion is obtained with standard A-100 audio levels, e.g. VCO).

The resonance function "colors" to the sound and is adjustable all the way up to self-oscillation. Resonance and consequently self-oscillation may vary with the filter frequency because of vactrol tolerances. Due to the circuit the resonance has a little bit an influence on the audio level (increasing resonance = increasing audio level). To obtain the original Buchla sound the resonance control simply has to be set fully counterclockwise. The function of the module is controlled by a manual switch. The left and right positions of the switch correspond to LP resp. VCA mode. In the middle position one obtains the combination of Low Pass and VCA. In this position it is also possible to control the function of the module by the two Gate inputs G1 and G2. The table printed at the front panel shows the connection between the gate levels (L = low, H = high) and the module function.

Merk:

Doepfer

Type:

Filter

Nummer:

A-101-2

Diepte:

50mm

Breedte:

8HP

Power:

20mA @ +12V, 20mA @ -12V

Module A-130-2 is composed of two identical voltage controlled amplifiers (VCA). Each VCA has a manual gain control (also named Initial Gain) and a control voltage input with attenuator. The character of the control scale can be switched to linear or exponential. All inputs and outputs are DC coupled. Consequently the VCAs can be used to process both audio and control voltages (e.g. for voltage control of the level of LFO or envelope signals). The signal input has no attenuator available but is capable to process up to 16Vpp signals (i.e. -8V...+8V) without distortion. For the processing of higher levels an external attenuator (e.g. A-183-1) is recommended.
The amplification range is 0...1. Even with a higher external control voltage the amplification remains at 1 (kind of "amplification clipping" at 1). 

Controls (for each of both units):

• Gain: manual gain control (Initial Gain) in the range 0...1
• CV: attenuator for the CV input
• lin/exp: switches the VCA characteristic to linear or exponential, in center position the VCA is off (mute function)

Inputs and outputs  (for each of both units):

• CV: control voltage input, min. +5V required for max. amplification (1) with CV control fully CW and Gain fully CCW
• In: signal input, max. 16Vpp (+8V...-8V) without distortion
• Out: signal output

A-130-2 is the slim version of module A-132-3 and offers essentially the same features. But the distances between the controls are smaller and rubberized small-sized knobs are used. In return the front panel has 4 HP only which is half the width of the A-132-3. The module is primarily planned for applications where only limited space is available.

Merk:

Doepfer

Type:

VCA

Nummer:

A-130-2

Diepte:

50mm

Breedte:

4HP

Power:

30mA @ +12V, 30mA @ -12V

Module A-131 provides voltage-controlled amplification. For audio signals, you would normally use the exponential VCA (A-131), and for control voltages, the linear VCA (A-130). It doesn't always have to be that way, though. The amount of amplification the VCAs provide is determined by the voltage at the CV input, and the position of the gain control, which sets the overall gain in the system. The VCA has two audio inputs, each with an attenuator. They are amplified by an amount determined by the combination of the gain and the two CV controls.

Merk:

Doepfer

Type:

VCA

Nummer:

A-131

Diepte:

45mm

Breedte:

8HP

Power:

20mA @ +12V, 10mA @ -12V

Module A-132-3 is composed of two identical voltage controlled amplifiers (VCA).

Each VCA has a manual gain control and a control voltage input with attenuator. The character of the control scale can be switched to linear or exponential. All inputs and outputs are DC coupled. Consequently the VCAs can be used to process both audio and control voltages.

The input has no attenuator available but is capable to process up to 16Vss signals (i.e. -8V...+8V) without distortion.

Merk:

Doepfer

Type:

VCA

Nummer:

A-132-3

Diepte:

50mm

Breedte:

8HP

Power:

30mA @ +12V, 30mA @ -12V

A-134 is a voltage controlled universal panning and/or crossfader module. If the module is used a voltage controlled Panning device one audio signal is panned to two different outputs. If the module is used a voltage controlled Crossfader two audio signals are mixed to one common output. The module enables even compositions of both functions. The module contains two linear high quality VCAs (made with CEM3381). VCA2 works in the opposite direction of VCA1 i.e. the more VCA1's loudness increases the more VCA2's loudness decreases. The panning or crossfading is adjusted with a control knob (manual control) and by two external control voltages, one equipped with an attenuator. Suitable control voltage sources are e.g. LFOs, envelope signals, random, Theremin or a voltage coming from an MIDI-to-CV-Interface. The panning/crossfading is displayed with 2 LEDs. A-134 has an audio input with attenuator for each VCA. If the audio input of VCA2 is not used the audio input of VCA1 is connected with audio in of VCA 2, i.e. the sockets are "normalled". The module has three audio outputs: Left Output (VCA1), Right Output ( VCA2) and Mix. For Panning applications the outputs Left Out and Right Out are used. If the module is used as as Crossfader the Mix Output functions as output. Module A-134 enables voltage controlled stereophonic panning effects (one audio signal distributed to two outputs), crossfading effects (two audio inputs mixed to one audio output with voltage controlled loudness proportion) and combinations of both effects.

Merk:

Doepfer

Type:

Insert, Panner, Crossfader

Nummer:

A-134-1

Diepte:

40mm

Breedte:

8HP

Power:

40mA @ +12V, 20mA @ -12V

A-135-3 is a  is a voltage controlled stereo mixer with four inputs. Behind a front panel with 8 HP only eight linear VCAs (voltage controlled amplifiers) and the mixer based on the VCAs are available.

Controls, Inputs and Functions of each input:

• Level (manual control of the VCA amplification), small rubberized knob (L1...L4)
• Control voltage input with associated attenuator (CV 1...4), for the full VCA control range about 0...+5V control voltage are required (attenuator fully clockwise), for higher control voltages the attenuator is used, the attenuators are without knobs, just plastic shafts with white marker
• Signal Input left/right (InL 1...4 / InR 1...4) 
• The signal inputs are not equipped with an attenuator. But the VCAs can process all signals up to 15Vpp / -7.5...+7.5V without clipping. In case of higher levels an external attenuator is required (e.g. A-183-1).

The sum of the left and right signals appear at the sockets Out L and Out R. The maximal amplification is  about 0.5 to avoid clipping at the mixer outputs (otherwise the outputs may distort with 15Vpp signals at each signal input and full amplifications). If another maximal amplification (e.g. 1) is required two resistors have to be replaced. 
All inputs and outputs are DC coupled. Consequently the module can be used to process both audio and control voltages.

Additional technical specification for each VCA (based on the specifications of the VCA circuits CEM3360/AS3360 used in the module):

• Crosstalk between two channels: better than - 80dB
• Signal attenuation at 0V CV: better than -80dB
• Total harmonic distortion: typ. 1%
• Control voltage feedthrough: max. 15mV

Merk:

Doepfer

Type:

Mixer

Nummer:

A-135-3

Diepte:

45mm

Breedte:

8HP

Power:

40mA @ +12V, 40mA @ -12V

Module A-138j is a four channel mixer with an additional polarity/mute switch for each input. In the upper position of the corresponding switch the inverted signal is used. In the center position the input in question is turned off (mute) and in the lower position the "normal" (i.e. non-inverted) signal is used. The inverting of signals is used especially for control voltage signals (e.g. LFO, ADSR). But even for corellated audio signals this feature is useful. For example for feedback applications or the mixing of original and processed signals (e.g. original and filtered signal to obtain new filter types).
Channel 1 features in addition an Offset function: provided that no plug is inserted into socket Input 1 control Lev.1 generates an adjustable DC voltage (positive or negative depending upon the position of the polarity switch).
On top of that the module is equipped with two types of single outputs and a dual mix output.  All inputs and outputs are DC coupled. Consequently the VCAs can be used to mix both audio and control voltages.
Each input is  - apart from the polarity/mute switch - equipped with a linear attenuator. The amplification range is 0....1.
The single outputs offer the attenuated and possibly inverted/muted signal of the channel in question. Two version of single outputs are available:

• Single Output A: If a plug is inserted into the single output "A" socket the channel in question is removed from the sum signal.
• Single Output B: If a plug is inserted into the single output "B" socket the channel in question is not removed from the sum signal. This type of single outputs is available only for the channels 1 and 2.

Based on this flexible structure each channel can be used also individually as attenuator or inverter (i.e. without mixer function). 

The output is twice available (two sockets, hard-wired like a multiple).

The distances between the controls and sockets are smaller as for the standard A-100 modules and rubberized small-sized knobs are used. In return the front panel has 6 HP width only. The module is primarily planned for applications where only limited space is available.

Merk:

Doepfer

Type:

Mixer, Inverter, Offset

Nummer:

A-138j

Diepte:

40mm

Breedte:

6HP

Power:

20mA @ +12V, 20mA @ -12V