FILTERED COFFEE

Filter effects unit using the popular Korg MS20 filter (+ its VCA & Env.Follower)

Download the USER manual (note this is very early edition - regular updates).

Introduction

This is a versatile filter effects unit whose filter circuits are based on the legendary Korg MS20 monosynthesiser which has a
unique and distinctive sound. The FC has been made to provide a high number of flexible modulation routings to allow many
filter effects to be created.

The FC can produce anything from subtle filter sweeps right up to howling, screaming distorted doings. It can also take
standard acoustic type sounds and make them `analogue' - e.g. play `real' drums through it and get analogue percussion
out the other side.

Two FCs can easily be combined to produce stereo filter effects and auto-panning between speakers. This is easily achieved
by linking the audio source and the LFO signals using the rear jack sockets.

Specification

Rotary Controls: 15
Toggle Switches: 7
Push/Pull Switches: 3
LEDs: 3 - red, yellow, green
Jack Sockets (6.35mm) 14
Size: 1U
Power: 15V AC input, 500mA

Circuits

Envelope Follower
Low Frequency Oscillator x 2
High Pass Filter (12dB/oct)
Low Pass Filter (12dB/oct) - combined with the HPF produces a Band Pass Filter
Voltage Controlled Amplifier
The HPF, LPF, VCA, and Env. Follower are accurate clones of the Korg MS20 synthesiser which has a distinct sound.

Quick Start Guide

This section is intended for those who just want to quickly plug in the unit and get going;

• Ensure the unit is switched off

• Plug you audio input to the rear panel Audio In socket

• Plug the rear panel Audio Out socket to your mixer

• Turn the input level and output volume controls to minimum.

• Set up your mixer levels as appropriate.

• Power up the unit

• Turn the LPF AUDIO IN LEVEL pot to maximum

• Move IN/BYP switch to IN

• Move the VCA switch 2 to THRU

• Turn the VCA CV1/2 LEVEL control to maximum

• Turn the HPF CUTOFF control to minimum

• Turn the LPF CUTOFF control to maximum

• Set the main output level to around 50%

Now, slowly increase the INPUT LEVEL. A signal should start to be heard. The INPUT LEVEL needs to be
adjusted as high as possible without distortion (unless you require distortion as this can be a useful effect).
You will need to balance the OUTPUT VOLUME so you do not overload your mixer.

Now you should be up and running with a fairly un effected signal. Remember, this is an analgoue effect
based on a vary old discrete circuit, so some colouration of even an uneffected sound is possible!

Play around with the other controls for nice filter effects.

Controls In Detail

INPUT LEVEL

This control sets the input level of the signal fed into the Audio In socket. At higher settings it is possible to overload
the input signal for a distorted sound if required.

ENVelope FOLloW LEVEL

This control sets the sensetivity of the Envelope Follower. At higher settings, a larger ENV follower signal will be obtained.

LFO1 SPEED / LFO2 SPEED

There controls set the 2 LFO frequencies.

High Pass Filter

Resonance

This control sets the resonance level. A higher setting increases the intensity of the resonance. At very
high settings it is possible to self-oscillate the filter.

CV1 LEVEL

This control sets the amount the CV source selected via the switch will modulate the HPF cut-off frequency:
The source switch has 3 options LFO1 (up), Off/no signal (centre), PEDAL (down)

LFO1 LFO1 is used as the source

center no signal is routed (no modulation effect)

PEDAL is a CV pedal is being used, this is the source

CV2 LEVEL

This control sets the amount the CV source selected via the switch will modulate the HPF cut-off frequency.
When this switch is pulled out, the CV source is inverted - so the positive signal is flipped over. This is
ideal so you can have, for example, the LPF sweeping up whilst the HPF is sweeping down. The source
switch has 3 options Env (up), Off/no signal (centre), LFO2 (down)

ENV The ENV follower is the source

center no signal is routed (no modulation effect)

LFO2 LFO2 is used as the source

CUTOFF

This control sets the cut-off frequency. As the setting is increased, more and more lower frequencies are filtered out.

Low Pass Filter

Resonance

This control sets the resonance level. A higher setting increases the intensity of the resonance. At very high
settings it is possible to self-oscillate the filter.

CV1 LEVEL

This control sets the amount the the CV sources selected via the switch will modulate

the HPF cut-off frequency. When this switch is pulled out, the CV source is inverted - so the positive signal is
flipped over. This is ideal so you can have, for example, the LPF sweeping up whilst the HPF is sweeping down.
The source switch has 3 options LFO1 (up), Off/no signal (centre), PEDAL (down)

LFO1 LFO1 is used as the source

center no signal is routed (no modulation effect)

PEDAL is a CV pedal is being used, this is the source

CV2 LEVEL

This control sets the amount the CV source selected via the switch will modulate the HPF cut-off frequency.
When this switch is pulled out, the CV source is inverted - so the positive signal is flipped over. This is ideal
so you can have, for example, the LPF sweeping up whilst the HPF is sweeping down. The source switch has
3 options ENV (up), Off/no signal (centre), LFO2 (down)

ENV The ENV follower is the source

center no signal is routed (no modulation effect)

LFO2 LFO2 is used as the source

CUTOFF

This control sets the cut-off frequency. As the setting is increased, more and more higher frequencies are filtered out.

AUDIO IN LEVEL

This control sets the audio in level to the LPF (following the output of the HPF). This control must not be at zero
to hear some effect. In normal use leave it at maximum. Use it to adjust the audio in level when using the LPF
Audio In socket on the rear panel.

VCA

Bypass Switch

The filter effects can be switch in (IN) or out (BYPassed). This allows you to compare the unprocessed input signal and the final
processed signal for comparison.

IN (switch up)
The effect is switch in. The signal at the output socket is the processed signal.
BYP (switch down)

The input signal is directly routed to the output signal and the filters have no effect. The processor is literally bypassed.
To hear any effect of the filters/VCA the switch must be at the IN position.

CV1/2 LEVEL

This control sets the amount the CV1/2 sources selected via the switches will modulate the VCA level.
The CV1 source switch has 3 options ENV (up), Off/no signal (centre), LFO1 (down)

ENV The ENV follower is the source
center no signal is routed (no modulation effect)
THRU The VCA is held open at a level near full volume
The CV2 source switch has 3 options LFO2 (up), Off/no signal (centre), inverted LFO2 (down)

LFO2 LFO2 is used as the source
center no signal is routed (no modulation effect)
-LFO2 LFO2 is inverted and used as the source

To hear any processed signal at the output socket, the VCA must be active by applying CV. The CV 1/2 LEVEL control must be used in conjunction with the CV source switched.

OUTPUT VOLUME

This control sets the final main output level.

Rear Panel Connectors

Connectors as view from the rear, right to left. The Filtered Coffee provides un-unusually high number of connection sockets,
more commonly associated with modular synthesisers. The maximum amount of connectivity, space allowing, has been
supplied for maximum flexibility.

POWER IN

This unit requires a 15 volt AC signal (not DC!). 500mA minimum. Although the unit requires AC, the type of plug required is called a ‘2.1mm DC plug’.
All jack sockets are 6.35mm mono, except the Pedal Input socket which is a stereo type.

SIGNAL IN
Plug your audio in here. The input will take guitar and line level signals without the need for pre-amp'ing.

SIGnal IN THRU
This is a direct copy of the input signal, which is made availbe to be fed through to other Filtered Coffee’s or other processors. Note the signal is unbuffered.

ENVelope OUT
The envelope follower CV signal is available here.

PEDAL IN
Plug the optional CV pedal in here. There are notes later if you wish to source your own pedal.

PEDAL CV OUT
The Pedal signal is turned into a useable CV and is available here. The range is 0 to 12V.

LFO1 OUT
The LFO1 CV signal is available here.

LFO2 OUT
The LFO2 CV signal is available here.

HPF CV IN
The HPF cut-off can be controlled via an external CV using this socket. Range is -12 to +12V.

HPF SIGnal OUT
The signal filtered by the HPF is available here, before is is further filtered by the LPF.

LPF SIGnal IN
If you wish to feed a signal through the LPF/VCA only, bypassing the HPF, use this socket.

LPF CV IN
The LPF cut-off can be controlled via an external CV using this socket. Range is -12 to +12V.

VCA SIGnal IN
If you wish to feed a signal through the VCA only, bypassing both filters, use this socket.

VCA CV IN
The VCA level can be controlled via an external CV using this socket. Range is -12 to +12V.

SIGNAL OUT
The processed signal is available here. (Unprocessed if the Bypass switch is set to BYP.

Optional CV Pedal Control

Introduction

The FC features a CV pedal input. A special kind of variable level foot pedal can be used to produce a variable CV.
The CV range is 0 to 12V. The signal can be routed to various modulation destinations via the front panel switches.
The pedal is ideal for hands free control, i.e. guitarists!

Use

Connect the CV pedal to CV PEDAL IN on the rear panel. As the pedal is push forwards, the voltage will increase.
The optional pedal is made of very durable plastic and will suit most musicians. However, we have yet to see whether
it will withstand unreasonalbe stomping from heavy metal guitarists!

Any CV pedal that is terminated with a stereo 6.35mm jack plug, and with the correct internal wiring can be used.
The stereo 6.35mm pedal jack plug must have the potentiometer wiper on the tip.

Description of Sections

ENV FOLW (Envelope Follower)

An envelope follower is a circuit that takes an audio input signal, and produces an output control voltage that represents
the amplitude of the audio input. This would generally be used so that a VCA level could be controlled by the audio input level.
It can also be used to control the filter cut-off. The CV LEVEL control will set how sensetive the follower is to the input level.
The follower LED will indicate when it reacts to a signal.

LFO

A Low Frequency Oscillator is a circuit that produces a repeating waveform. The unit has 2 independent LFO's each outputing
a triangle waveform voltage. The signal can be used to sweep the filters up and down., or to add tremelo to the output level.

VCA

The Voltage Controlled Amplifier is a device that controls the level or volume of a signal via a voltage. This way the output level
of the unit can be varied with a LFO or cv pedal. If the VCA is not modulated by any CV, or it is not switched to THRU, no signal
will be heard as the volume will be zero.

HPF

The High Pass Filter is a circuit that can will only let high frequencies through it. It filters out the lower frequencies. The point
at which the lower frequencies are filtered is set by the cut-off frequency. The roll-off is 12db/oct.

LPF

The Low Pass Filter is a circuit that can will only let low frequencies through it. It filters out the higher frequencies. The point
at which the higher frequencies are filtered is set by the cut-off frequency. The roll-off is 12db/oct.

Together, the LPF and HPF can be combined to be a Band Pass Filter (BPF). This means a band of frequencies are passed
through, filtering out the lower and higher frequencies, passed the cut-off points set by the two CUTOFF controls.

Certain combined settings of the LPF and HPF may result in no output signal. This is because we have not restricted the
ranges of the two filters, so it is possibly to filter out all the signal. The controls are unrestricted to allow maximum flexibility.

Note

The Filtered Coffee (and SY02) is as close a clone of the MS20 filter as is possible without digital modelling. It uses the
same circuit design. It uses all the same components, except for 2. 1 of which will not affect the sound, the other has been
superceeded by a part that is essentially the same. In all other respects they are the same.

Not all MS20s sounds the same, and for the same reasons not all Filtered Coffees or SY02s will sound identical to each other
or the MS20. Reasons could be trimmer setting variations, component tolerances, but these are the consequences of buying
analogue! The FC and SY02 do sound like MS20 filters.