Arcane Knowledge - Module Eurorack SetonixSynth - Free user manual and instructions

USER MANUAL Arcane Knowledge SetonixSynth

Arcane Knowledge Vintage VCA/Overdrive Drive Gain CV Clean Initial Gain Audio In Audio Out SetonixSynch

Arcane Knowledge VCA / Overdrive - User's Manual for Eurorack Copyright 2024 SetonixSynth. All rights reserved.

Hello and thank you for using the Arcane Knowledge VCA / Overdrive for Eurorack modular. We hope you will find it to be a fun and interesting sounding vintage-style processor for your audio signals!

The Arcane Knowledge marries two classic circuits to create what we see as a “utility flavor” module. First up is a discrete transistor core VCA stage similar to those found in very early modular synths: not the cleanest or most precise amplifier, but rather full of harmonic richness and color to bring a little kick to those squeaky clean waveforms.

This VCA may be used on its own or through the switchable Drive circuit, which slaps a high-gain Tube Screamer-style soft clipping overdrive stage on the audio signal. Unlike the Tube Screamer, however, the Arcane Knowledge's drive stage uses different diodes in the forward and reverse position, creating asymmetric clipping with more emphasis of even order harmonics. Using the rear trimmer, this stage can be configured to give the VCA output signal anything from a tasty boost to fully crunched sonic mayhem.

For those looking to liven up their sound, sometimes the old ways are best. Enlighten yourself: it's the Arcane Knowledge!

Technical Specifications:

Width: 10 hp (Intellijel 1U format)

Depth: 35 mm

Peak Current Draw: 15 mA @ +12V, 15mA @ -12V

1. Installing the Arcane Knowledge

The Arcane Knowledge uses a standard 10-pin Eurorack power header which is mounted on the back of the module. When connecting the power cable, make sure that the -12V rail from your case's power supply aligns with that of the module. The stripe on the bottom of the power header and the "-12V" label indicate the location of this rail on the module. The Ancient Scroll has reverse diode protection so plugging it in backwards will probably not destroy the module or case; however, we strongly recommend taking the proper precautions to plug it in correctly before powering up your case.

The 1U format module will fit in any Intellijel-format 1U case. Once your power ribbon cable is connected to the rear of the module, place it in the case and mount it using either two diagonal rack screws or screws in each of the four corner holes.

2. Theory of Operation

The Arcane Knowledge is an audio VCA with Overdrive which is designed to sound nice and impart subtle (or not subtle) distortions (meaning, differences from the original input waveform) which the ear may perceive as more compelling than a totally “clean” waveform, and which will of course provide more material to be filtered, EQ'ed, etc if desired, which we find to be an essential ingredient when recreating the sound of classic analog synthesizers, which are full of life and variation in the sound. Keen listeners or oscilloscope users will notice a slight noise floor from the transistors (especially with the Drive mode engaged) but we believe the interesting sound these circuits provide outweighs a little noise.

With this module, we truly stand on the shoulders of giants. The VCA section is similar to Yusynth's "Simple VCA," a great module in its own right. There is also a very thorough explanation of the circuit in the Erica Synths EDU VCA Manual. The Tube Screamer is one of the most famous fuzz/overdrive effects ever made, and a great explanation of the whole circuit is offered here.

3. Summary of Functions

Initial Gain: Sets the initial gain of the VCA, from fully closed with the knob fully counter-clockwise to roughly Unity gain with the knob fully clockwise.

Gain CV: Controls the gain of the VCA. The voltage present at this input is added or subtracted from that of the Initial Gain to control the overall level of the VCA. Sending positive voltage to this input with the Initial Gain turned up can be used to further overdrive the VCA stage.

Audio In: AC-Coupled Audio input. Audio frequencies which are patched to this input will pass to the VCA stage, while any DC offsets from unipolar voltage sources such as slope generators will be removed.

Drive/Clean: Selects the type of output sent to the Audio Out jack. When Drive is selected, the user will hear the VCA through the onboard Overdrive stage. When Clean is selected, the user will hear the direct "clean" output of the VCA.

Audio Out: Main output of the module, switchable between the direct output of the VCA stage and the output of the Drive circuit. Because the module's signal input is AC-coupled, the output signal will be bi-polar and centered around 0V.

4. Calibration

Patch an Audio signal to the Audio In jack. Turn the front panel's Initial Gain potentiometer to the counter-clockwise or Off position and monitor the Audio Out jack in Clean mode. Adjust the rear trimmer labeled "Initial" until as little audio feedthrough as possible is heard.

Patch a control signal into the Gain CV jack and switch to the Drive setting. Adjust the Drive Amt trimmer for the desired amount of Overdrive, with counter clockwise corresponding to less Drive.

Unpatch both the Audio and CV inputs. Monitor the Audio Out jack in Clean mode using an Oscilloscope or a Digital Multimeter on the Volt-meter setting. Turn the front panel's Initial Gain potentiometer fully clockwise, or all the way up. Adjust the rear Bias trimmer so that you measure as close to 0V as possible.

5. Patch Ideas

"Simple Hi Hat"

Patch a noise source into the Arcane Knowledge's Audio In with the Initial Gain level turned to 0. Patch a voltage-controlled envelope such as the Ancient Scroll into the VCA's Level control input and feed a trigger sequence to the envelope. If your sequencer has a CV output, use it to control the envelope's Decay time in order to produce a variably "open" or "closed" Hat.

"Sidechain Compressor"

Patch an audio signal into the Audio In jack and turn the Initial Gain up to the desired level. Patch your "control" audio, such as a kick drum, into an Envelope Follower, and use an Attenuverter to invert the output from the Envelope Follower before patching this signal to the Arcane Knowledge's Gain CV input. Adjust the response on the Envelope Follower to adjust the response of the ducking behavior.

"Harmonic Exciter"

Switch the output to Drive mode. Patch a basic waveform such as a Triangle, Sine or Square wave into the Audio In and turn the Initial Gain to about halfway, and play around with the sound at different gain levels. Patch the resulting waveform into a filter, resonator, or other effect to give your oscillator a little extra harmonic content.