Schulze Modular Synth

Schulze Moog Modular

Overview Back in the mid 1970’s one of the first musicians I listened to who was making electronic music was Klaus Schulze, and I searched out his first 5 LP’s. Klaus bought a second hand Moog IIIP and double sequencer just before Xmas 1975, with a record advance (due to the success of Timewind).

It became the focal point for his live shows, and it was used in many albums for the next 5 years. Klaus moved with his Big Moog into the German countryside after living in Berlin and I started studying electronics at University after building my first synthesizer.

The “Big Moog” was used from the April 1976 tour for many years, until it was retired during the digital 80’s. It re-appeared in the Dark Side of the Moog albums with Peter Namlook in the 1990’s, as Peter had bought it, but after 10 albums he sold it on eBay for £21,000.

I could never afford such a large Moog synthesizer and I have never tried cloning the circuits, unlike ARP and Roland synths of the 1970’s. But I do love the sound it makes, so I can now build one!

Behringer System 55

Behringer System 55 With the release of the Behringer Moog module clones in 2020, it is now possible to recreate a Moog IIIP and build a Schulze setup at around £2,500 rather than £35,000! The System 55 was US$8,085 in 1976 without sequencers, equivalent to £40,000. The IIIP has the original 901 VCO’s, whilst the Behringer has the 921 VCO’s.

At the core of the Moog IIIP are an amazing 10 VCO’s, and one of each of the filters; Fixed, Low Pass and High Pass. It also has 3 VCA’s and envelope generators, and some utility modules. The Moog System 55 is an update on the IIIP with a few changes and modern stable VCO’s. It is an excellent basis for building my Schulze modular, but there are some modules missing which I have recreated;

  • 905 Reverb
  • 984 Quad Matrix Mixer
  • 904C Filter Coupler
  • 993 Trigger Controller

The 984 and 904C modules were dropped from the System 55 by Moog, but they retained the 993 and 905. Behringer also launched the sequencer modules (960,961,962) which means I can build a Schulze Double Sequencer. However all these modules do not fit into one dual row case even if 140HP wide, so I have 2 Mantis 104HP cases and a separate case for the Complement B.

I will re-balance the number of filters with the number of VCO’s in the overall design. I also have a voltage controlled clock divider and a note quantizer, for ratching, and Doepfer make both of these in vintage black which sort of matches the Behringer modules.

Learning Curve The Moog modular, and therefore any clone, takes some different approaches to a modern Euro Rack system, and its important to get familiar with these differences;

  • Gate on is a S-trigger, a short to ground
  • The sequencer modules use familiar V-triggers
  • Control Voltages are +/-6V
  • Audio signals are typically +/-2V
  • A 921 VCO works well as a LFO
  • 921A driver is needed for multiple 921B VCO’s
  • There are separate attenuator modules to control VCF, VCA, VCO input levels
  • There are separate CV input selector modules for the VCF and VCO
  • The Moog has internal busses which the Behringer does not
  • With all this patching in Euro Rack size there isnt much panel space left!
  • Typical Moog systems only have one VC LPF and no S&H

Pre-Patching The original Moog System IIIP had internal “trunk” lines that carried external signals from the rear to the front of the left and center cabinets, into the CP3A modules. They are labelled as Trunk Lines, and are not replicated in the Behringer module. There were no signal busses that spanned the three cabinets, only the 10-pin power cables. Up to 3 external controllers could be connected to the rear of the right hand cabinet, with the Pitch CV and S-Trig signals available to patch from the CP1 module. The System 55 does have inter cabinet busses, as it was not portable.

The Euro Rack standard has no notion of control signals in the 10 pin power connector, and just a single CV and Gate in the 16-pin connector. Behringer System 55 modules do not use a bus concept and only provide external jack sockets, which results in a lot of patch cables. Behringer have included two utility modules; the CP3A-O to control VCO’s and the 992 to control filters, but these require external patching cables to function.

My objective is to reduce the amount of patch cables by implementing internal patching as far as possible, as on the original Moog. The changes are based on 3 new modules:

  • Modified 994 for V-Trig to S-Trig conversion.
  • The 993 Module reduces VCA, Trig Delay Env Gen patch cables.
  • The 904C Module reduces LPF and HPF patch cables.

Summary The Behringer Moog modules are well built and usually aligned and calibrated properly, with only an occasional intervention needed (like VCO Scale). The low cost of each module is attractive but its important to budget for Mixers, Attentuators and Utility modules to augment the core modules, as there are no input level controls. This adds cost, space and patch cables. It is easy to build a 3 VCO synth with LPF and VCA/ADRS’s but that can be done at a lower cost with a Model D.

I suggest building up a bigger modular system with more sound possibilities, with at least 2 banks of VCO’s, use all the filters and add at least one sequencer. It is a bigger investment but it opens up a lot more sound possibilities. My Schulze modular has some custom AMSynths modules added to the Behringer line up, and is currently under construction.

Upgrading The small Euro Rack format with no internal busses and the need for small components means a 5U system is inevitably going to sound better and be easier to use, but at a much higher price point. Behringer use good quality components but there are some upgrades that are worth making, such as replacing the 50KC and 1MA pots (where they are used right at the end of their travel) and using polypropylene matched capacitors in filter circuits.

I have also swapped in expensive multi-turn trimmers (to make adjustment easier). I have not attempted Op Amp upgrades as this may need further circuit changes.

Mods and Extra Modules I have modified some of the Behringer modules and added new ones;

These are explained in the Mods & Modules page.

Klaus add a set of PPG 300 modules in 1976 above the “Big Moog”, including; 2 analog sequencers, 3 VCO’s and various filters and a ring modulator. You can see these modules patched into the “Big Moog” in live concert pictures. He also started using two or three MiniMoogs (for solos) in addition to his ARP white Odyssey, an EMS AKS and an ARP 2600.

My “Big Moog” Setup My Schulze Modular is housed in 3x Doepfer 9U vintage 84HP cabinets; the left cabinet contains the VCO’s and Filters, the middle cabinet the VCA, Env Gens and 984 Mixer and the right cabinet the two 960 Sequencers with 2x 962, a 961, Doepfer Clock Divider and Dual Quantizer). Instead of adding a third bank of 921A/B VCO’s into the middle cabinet I decided to add a Behringer Model D. There is also a replica SCI 700 Programmer and PPG 313 Sequential Switch in the right cabinet, with the 700 controlling the Model D.

The cabinets sit on three oak 1U 19″ rack cases (made in France) which contain: Lexicon PCM60 Reverb, Alesis Quadraverb and a Roland SDE1000 digital delay. An Arturia Key Step is used as the primary keyboard and a Maschine Mikro enables high quality stereo samples to be played. I have a library of Klaus Schulze samples as well as my own.


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