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Quick Start Guide

904B VOLTAGE CONTROLLED 

HIGH PASS FILTER  

Legendary Analog High Pass VCF 

Module for Eurorack

Controls 

(1) 

FIXED CONTROL VOLTAGE

 – Also referred to as “cutoff 

frequency”, this knob manually determines the frequency 

below which frequencies are attenuated. The resulting 

frequency will depend on this knob’s setting as well as 

voltage received from the control inputs. 

(2) 

FREQUENCY RANGE

 – Select between Low (4 Hz to 20 

kHz) or High (10 Hz to 50 kHz) to set the frequency band in 

which the fixed control voltage operates. 

(3) 

SIGNAL INPUT

 – Connect the incoming signal via 3.5 mm 

TS cable. 

(4) 

SIGNAL OUTPUT

 – Send the processed signal to another 

module via 3.5 mm TS cable.

(5) 

CONTROL INPUTS

 – Connect control voltage signals from 

other modules to affect the cutoff frequency. The sum of 

the voltage received doubles the frequency cutoff point 

for each 1 V increase. 

Power Connection

The module comes with the required power cable for connecting 

to a standard Eurorack power supply system. Follow these 

steps to connect power to the m   odule. It is easier to make 

these connections before the module has been mounted into 

a rack case. 
1. 

Turn the power supply or rack case power off and 

disconnect the power cable. 

2. 

Insert the 16-pin connector on the power cable into the 

socket on the power supply or rack case. The connector has 

a tab that will align with the gap in the socket, so it cannot 

be inserted incorrectly. If the power supply does not have 

a keyed socket, be sure to orient pin 1 (-12 V) with the red 

stripe on the cable.

3. 

Insert the 10-pin connector into the socket on the back of 

the module. The connector has a tab that will align with the 

socket for correct orientation. 

4. 

After both ends of the power cable have been securely 

attached, you may mount the module in a case and turn on 

the power supply.

Installation

The necessary screws are included with the module for mounting 

in a Eurorack case. Connect the power cable before mounting. 
Depending on the rack case, there may be a series of fixed holes 

spaced 2 HP apart along the length of the case, or a track that 

allows individual threaded plates to slide along the length 

of the case. The free-moving threaded plates allow precise 

positioning of the module, but each plate should be positioned in 

the approximate relation to the mounting holes in your module 

before attaching the screws. 
Hold the module against the Eurorack rails so that each of the 

mounting holes are aligned with a threaded rail or threaded 

plate. Attach the screws part way to start, which will allow 

small adjustments to the positioning while you get them all 

aligned. After the final position has been established, tighten the 

screws down. 

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