Tags: Phaser module

Notes: The Polaris is a 4-stage cascaded OTA filter designed by David Dixon. It builds on the lineage of the Dr. Octature and Atlantis filters, but with a totally revised core and resonance control. Along with dedicated LP, HP and BP outputs it features a configurable MULTI output capable of an unprecedented 27 different filter modes.

With drive turned down the Polaris is capable of buttery smooth filtering, and the cutoff control range has been fine-tuned for playability. With the drive dialled up and the new asymmetric multi distortion circuit engaged it creates a more aggressive sound. Not content to be just a filter, the Polaris's AP phaser mode combined with frequency modulation can be used to achieve a phaser effect.

With so much versatility in a modest size, the Polaris is an ideal filter for a starter system and an excellent addition to the tonal palette of a larger modular.

Notes: Module A-101-8 is a 8-stage phase shifter which uses light-sensitive resistors (LDR) and is a replica of the Compact Phasing A manufactured by the company Schulte in the seventies. The actual phasing circuit is identical to the historic model. Only the illumination control of the LDRs is different: the A-101-8 uses LEDs to illuminate the LDRs, the historic model used incandescent miniature lamps. And the A-101-8 has no built-in LFO but can be controlled by any external control voltage source (e.g. LFO, ADSR, random, Theremin, ribbon controller, sequencer, midi). The phasing offset (i.e. the base value for the phase shifting) and the modulation depth of the external control signal can be adjusted separately. The Compact Phasing A had no offset control but only a depth control for the built-in LFO. Feedback and mixing ratio of the output signal are set by two controls. The audio input is equipped with an attenuator. The module has two audio outputs available (same as the historic model) and a visual display of the phase shifting.

The module has these controls and in/outputs available:

Control Man. : manual control of the phase shift offset (base value)

Control CV: attenuator for the signal applied to the CV socket

Control Feedb.: Feedback or Resonance (similar function as filter resonance/feedback/emphasis)

Control Mix: sets the mixing ratio between original and phase shift signal appearing at output 1

fully CCW: only the modified input signal appears at output 1 (see note below *)

center: a mixture between the modified input signal and the phase shift signal appears at output 1, that's the standard position for the classical phasing effect

fully CW: the pure phase shifted signal appears at output 1 (e.g. for vibrato effects)

Control Input Level: attenuator for signal applied to the In socket

Socket In: audio input

Socket CV: control voltage input

Socket Out 1: audio output 1 (mix signal)

Socket Out 2: audio output 2 (modified input signal)

LED: visual control of the phase shift

The module has some peculiarities (same as the historic model):

The input signal is processed at first by a pre-stage which outputs a "modified" input signal (*). This signal is not processed by the phase shift stages but is affected by the feedback setting. Only when feedback is set to zero this signal is identical to the input signal. Otherwise it contains feedback components.

This signal is output on socket Out 2.

When both output sockets Out 1 and Out 2 are used as stereo channels one obtains a spatial stereo sound effect.

The same signals is also used for the CCW position of the mix control. With mix control fully CCW the unmodified signal appears only if the feedback control is set to zero. Otherwise it contains feedback components.

The historic model had two audio inputs: one 5-pin DIN socket and a 1/4" jack socket. The DIN socket was intended for high-level line signals. When the 1/4" jack socket was used the amplification of the pre-stage increased by about 100. The 1/4" jack socket was intended for low level signals (e.g. electric guitars or microphones). For this feature the A-101-8 has an internal jumper that can be used to increase the amplification. As long as the module is used within the A-100 system usually the lower amplification is used to avoid distortion.

The 8 photo resistors and LEDs are assembled within an small lighproof box. In addition the pc boards are made of lighproof black material to avoid interfering light from other modules or the bus board.

Dimensions
4 HP
45 mm deep

Current Draw
30 mA +12V
30 mA -12V

Notes: 'Vintage' black panel version of Doepfer's updated frequency shifter module, offering weird and wonderful effects by shifting all frequencies by a fixed amount. Unique sound, not to be confused with pitch shifting.

Supplier's Notes:
Module A-126-2 is a fully analog frequency shifter for audio signals. A frequency shifter is an audio processing unit that shifts each frequency of the incoming audio signal by the same frequency. If the shifting frequency is e.g. 200Hz an incoming audio frequency of 1000 Hz becomes 1200 Hz, 2000Hz becomes 2200 Hz, 3000 Hz becomes 3200 Hz and so on. Pay attention that this is different from pitch shifting where all frequencies are shifted proportional (e.g. 1000>1200Hz, 2000>2400Hz, 3000>3600Hz) !
The frequency range of the internal quadrature VCO is about 8 octaves (about 20Hz ... 5kHz). If required an external quadrature VCO can be used.

The module is equipped with these controls, inputs and outputs:

Frequ. 1: first manual control of the shifting frequency (factory setting: coarse, range about 20Hz - 5 kHz)

Frequ. 2: second manual control of the shifting frequency (factory setting: fine)

by means of internal jumpers the sensitivity of Frequ.1 and 2 can be swapped (i.e. Frequ.1 = fine and Frequ.2 = coarse)

the relation between coarse and fine control is about 25:1 (corresponding to about 8 octaves to 1/3 octave)

FCV In (socket) and FCV (small control without knob): control voltage input with attenuator for the external voltage control of the shifting frequency

Mix: manual control of the up/down shift panning unit, fully CCW = down shift, fully CW = up shift, in between a mixture of down and up

Mix CV In (socket) and Mix CV (small control without knob): control voltage input with attenuator for the mixing unit for external voltage control of the up/down mixing

Audio In (socket), Level (small control without knob) and Overload (LED): audio input with attenuator, typ. audio in level = 1Vpp, the level control has to be adjusted so that the overload LED just begins to light up a bit, when the LED is fully on clipping/distortion occurs, when the LED is permanently off the input level is too low and the signal-to-noise ratio increases

Audio Out (socket): audio output of the frequency shifter

Squelch (small control without knob): controls the squelch function: fully CCW (Env.) the output VCA is controlled by the envelope signal, which is derived from the audio input signal, fully CW (open) the output VCA is permanently open (no squelch function), in between the squelch intensity can be adjusted

Quadrature VCO Outputs (sockets Sin and Cos): outputs of the internal quadrature oscillator, about 12Vpp level (+6V/-6V)

Ext. Inputs Sin and Cos (sockets): required when an external quadrature VCO (e.g. A-143-9 with a wider frequency range or A-110-4 with thru zero feature or A-110-6 with different waveforms) is used instead of the internal quadrature VCO, the levels of the external VCO should be about 10Vpp (8...10Vpp are OK) and the signals have to be symmetrical around zero Volts, the sockets are normalled to the internal quadrature VCO (i.e. the sockets are equipped with switching contacts that interrupt the internal connection as soon as a plug inserted)

VCA ext. CV (socket): used when an external control voltage (e.g. from an envelope generator) should be used to control the output VCA instead of the internal squelch unit, the socket is normalled to the output of the squelch control (i.e. the socket is equipped with a switching contact that interrupts the internal squelch connection as soon as a plug inserted). From about +8V external control voltage the VCA is fully open.

Internal terminals (pin headers, e.g. for a DIY breakout module):

envelope follower output

dome filter output 1

dome filter output 2

ring modulator 1 output

ring modulator 2 output

Up shift output

Down shift output

Notes: A-101-6 is a new filter module that uses so-called opto FET's to control the filter frequency. Opto FET's are very similar to Vactrols, but use light dependent field effect transistors (FET's) instead of light dependent resistors (LDR's). An opto FET is a combination of a light-dependent FET and an LED, both put into a small light-proof case. The advantage, compared to vactrols, is a much faster response of opto FET's compared to LDR's - this allows much faster attack/decay times and even FM effects.

The variable resistors corresponds to the opto FET. The brightness of the Opto FET LED's, and consequently the filter frequency, can be adjusted manually (Frequ. control) and controlled by means of an external control voltage (CV) with attenuator. The LED at the front panel reflects the LED brightness inside the opto FET's.

The type of filter is chosen by jumpers on the PC board (factory setting: low pass). The type of filter determined by the jumpers positions can be marked by means of a water-resistant felt pen at the front panel.

The resonance is controlled by the Feedback control up to self-oscillation. By means of a trimming potentiometer the maximal feedback can be adjusted. High feedback values can be used mainly in the all-pass mode to obtain very extreme self-oscillation sounds. Even an external feedback signal can be used instead of the internal feedback connection (FB In socket). Whenever the filter type is changed by means of the jumpers the trimming potentiometer for the maximal feedback has to be re-adjusted.

The Mix control is used to pan between the original signal (CCW position) and the effect signal (CW position). In filter mode (LP/HP) this control is usually set fully CW. In the all-pass modes one obtains phasing sounds at centre position or "pure" all-pass sound in fully CW position.