The Modules of the Vintage ARP 2500

Rolf So., 29.05.2022 - 05:51

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ARP 2500 modules Music of the Krell Voltage Modular

The Modules of the Vintage ARP 2500 – Part 12

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“A Whiff of Krell” or “ARP2500 and Voltage Modular go Krell”

Today´s patch is inspired by what is usually called “Krell Music”. A bit of background information about”Krell Music” may come in handy here. It was the year 1956, when the film “Forbidden Planet” went to the cinemas.

ARP 2500 vintage synth forbidden Planet Krell Music

It was one of these “vintage” black-and-white science fiction films with cardboard space ships and rockets looking like big cigars, but there were some, well philosophical ideas concerning civilisations and societies in the plot, that made the film more fascinating than a lot of others of the same category. There were talks about an vanished but extremely developed ancient civilisation called “the Krell”. The Krell had a very special kind of music, as the whole soundtrack of the film was very special to say the least. The composer couple Bebe and Louis Barron invented even their own electronic circuits to make audible, what was in their composer brains. And when they published the whole soundtrack as an LP a lot later in 1976 the modular synthesis communities in the whole world ventured their own tries on Krell music.

Todd Barton is generally called the “father of modern Krell music”, as he firstly published AND explained the basics of Krell patches. So, let´s try something similar with the modules of the ARP 2500 in Voltage Modular.

I have called this patch (and this article) a “whiff” (only a whiff) of Krell, because the envelopes of the ARP 2500 don´t have CV controllable envelope stages, and we would need to CV modulate at least the rise (attack) and the fall (decay) stage of the envelopes, which would have to loop (what´s impossible either with the vintage ARP 2500 modules). But we are able to create something, that comes quite near to “Krell music”. Let´s do so. If you want to look at and listen to the patch and the music at first, just click the following link, where I have uploaded the result of what I´m going to explain step by step now:

The patch contains the following modules:

3 oscillator modules 1004-T, two of which serve as LFOs

1 sample & hold module 1036

1 multimode filter module 1047

1 modamp module 1005

1 reverb module 1025

11 patch cables

VCO 1 (the upper left one) and VCO 2 (the upper right one) are switched to “LOW” mode, VCO 1 is running at 0.5 Hz, and VCO 2 at 2 Hz.

The sine wave output of VCO 1 modulates the DRY/WET mix of the left reverb in the dual reverb module 1025, and the triangle wave output of VCO 1 modulates the GAIN of the amplifier in the modamp module.

ARP 2500 vintage synth Voltage Modular Krell Patch

But this triangle wave of VCO 1 modulates the rate of VCO 2 as well (let me repeat it: both VCOs work as LFOs here in this patch).

ARP 2500 vintage synth patch Krell Music Voltage Modular

The triangle wave of VCO 2 modulates the cut-off frequency / centre frequency of the filter module, and the square wave of VCO 2 triggers the sample & hold module.

ARP 2500 vintage synth Krell patch Voltage Modular

The sample & hold module modulates the pitch of VCO 3 (ha! Something that makes sound at last). The mixed output of VCO 3 is fed by the square wave and the saw wave. This mixture of waves is patched into one of the audio inputs of the Multimode Filter / Resonator Module 1047.

ARP 2500 vintage synth Voltage Modular Krell Music

The patch uses two of the Filter´s outputs: the low-pass filter and the notch filter. The output of the low-pass filter is directly sent to the right reverb unit of the Dual Reverberator Module 1025 (remember: only the left of the two reverb units is modulated by VCO 1, which generates one of the nice stereo effects). The notch filter output is patched into one of the Audio inputs of the modamp module (remember: the Gain of the VCA is modulated by VCO 1).

ARP 2500 vintage synth Music of the Krell Voltage Modular

In other words, the amplitude of the notch filter´s output undergoes the modulation by VCO 1, but the amplitude of the low-pass filter´s output doesn´t. Both are patched into different reverb units, each of which is patched to a different stereo channel – that´s the second aspect of the mentioned stereo effects.

There is a bit of resonance adjusted (about 12%), and the centre frequency of the notch filter is different from the cut-off frequency by one half – please see the second article in this series about the Multimode Filter / Resonator Module 1047 if you have forgotten the meaning of this. The links to the articles are below.)