Steve Turner

Eurorack Trunking Modules

Large Eurorack systems can be very difficult to use and may stunt creativity when sitting down with a swelling ocean of ready to patch modules as your blank canvas.  You might run a few tentative patch cables, then suddenly you're trying to navigate a chaotic web of creativity killing tentacles.  I solved this issue by installing a combination of trunking modules to tame what could have been a very difficult to use system.  

The 18u 168HP system in operation.

Terminology within this article

• Case / Boat: I will use these terms interchangeably, they refer to a physical enclosure that hosts Eurorack mounting and power resources in a single air flow domain.  Each case (or boat) is physically separated from the others, but may be used collectively to build a Eurorack system.  The term ‘Boat’ is used by ELBY Designs who's products I use extensively.
   
• Eurorack System: a collection of cases or boats which host Eurorack modules and are used together within a single Eurorack domain.  These may be situated in a single area, or multiple areas, but are nearly always in a single room.  
   
• Intra-case Trunk: source and destination trunking modules are located within the same physical case or boat.  Cabling between intra-case trunking modules may be over the top of the modules, but is more commonly patched beneath the modules within the case.
   
• Inter-case Trunk: source and destination trunking modules are installed in separate cases.  Cabling between inter-case trunking modules is nearly always over the top (OTT) of the modules, unless your case allows for inter-case cabling (e.g. it has holes or routing mechanisms that allow connectivity between cases).  
   
• Caveat: in reality, there is nothing stopping you using two inter-case trunking modules in a single case, or hacking together a way to use two intra-case trunking modules in multiple cases.  So, the definition of the module is implied by the intention of design, and also the way the user deploys it in their system.  
   
• Source and Destination: define patch signal routing facilitated by trunk modules.  Note that trunking modules are bi-directional and are not reliant on being deployed as source or destination utilities.  Signals can go either way.  Source and Destination will be subjective based upon the patch being executed. 

Please make sure at the very least you understand INTER and INTRA case terminology.  The same terminology is used in data networking which might be familiar to some of you.  

My system overview

Below is a summary of my main Eurorack modular system.  Getting some insight into my setup will help you understanding the choices I have made with regards to trunking modules, and hopefully help you make good choices for yourself.  

• My system is 1,008 HP in total.  It was built using three 168HP ELBY Design Boats.  
• The Studio Master solution by ELBY Designs provides shoulders and bracing for the 3 Boats as one system.
• Each boat is on a concave angle which provides an excellent ergonomic arrangement.  
• I can easily remove and take the lower boat elsewhere.  
• Using the above definitions, this is a single Eurorack system, with three cases/boats.  
• Case design means that inter-case trunking modules are required to patch over the top.
• There is plenty of room in the cases for intra-case trunking cabling to be run underneath the modules. 

A quick note about ELBY Designs cases

ELBY Designs offer their Eurorack case products as modular segments of 42hp each for the boat structures.  This means you can build 6U boats of varying sizes and install power as needed.  I grew my system from 126HP/12U up to 168HP/18U over a 2 year period.  Available sizes in the ELBY range are multiples of 42HP (so 84, 126 and 168HP) and other options with a 20HP skin that allows 62 and 146HP.  

My inter and intra-trunk module solution

Below is a Modular Grid screen shot demonstrating my inter-case trunking in green, and intra-case trunking in orange.  

Modular Grid image with inter and intra-trunk modules and connectivity.  

Solution elements

To solve the chaos of a large system I deployed:

• 4 pairs of BEEP BOOP Telecoms RJ45 inter-case trunking modules 
  • Two pairs of Telecoms RJ45 modules are installed on the left and right shoulders of the upper and lower cases.  None are installed in the middle case. 
  • Telecoms RJ45 source and destination modules are connected vertically between cases.
  • CAT6 Ethernet cables running over the top (OTT) of system between the two cases. 
  • The Telecoms RJ45 provide 6 in/output jacks per module.
  • Powered from case power boards (10 pin)
  • Supplied with a 3 metre ethernet cable.
  • I went to the local electronics shop and bought 50cm variants to keep cable runs shorter.  
• 9 individual ELBY Designs CGS793 intra-case trunking modules 
  • Three CGS793 modules installed per case.  
  • One on the far left, the second somewhere around the middle, and the third towards the right.
  • The second and third CGS793s are installed in alternate 3U positions (upper and lower)
  • Connected under the faceplates via 16 pin ribbon cables, taped into place with electrical tape.
  • Each CGS793 has two connector points on the back of the PCB.  
  • The connectors allow CGS93s to be daisy chained so that signal from trunk 1 is sent to trunks 2 and 3. 
  • Ribbon cable connects to power bus to provide 0v connection for screening purposes.  
  • You can use it without the ribbon to the bus board, but doing so improves signal isolation from noisy modules.  
  • ELBY Designs recommend separating digital/logic signals through a separate trunk from CV. 
• ELBY CGS793 and CGS93 modules

To avoid confusion looking at photos of my Eurorack system, I am going to point out that I have a mix of CGS793 (current) and the CGS93 (older) products.  For simplicity I will refer only to the CGS793 product name.  Both are functionally similar for the purposes of this article, however you should look for the CGS793 as the older CGS93 is no longer available.  

Deployment examples

I use a CGS793 and dual Beep Boop Telecoms in the bottom left of my case near my Vector Sequencer.  

Telecom RJ45 (two) CGS93 (left position) in the lower case

Intra-case trunking example

• The above photo shows the Five12 Vector Jack Expander Mk2 with all 8 trigger outputs patched to a CGS793.
• Two more CGS793s are installed within the same case and located right next to my sampling and drum modules.  
• I can easily route trigger outputs from the Vector Mk2 Expander to either the Rossum Assimil8or or the Tubbutec 6m0d6 - or to any other module near by the CGS793s.  
• The following photo shows the 2x CGS793 modules installed next to the destination modules. 

CGS93 (lower case lower middle position) connected to a Rossum Assimil8or

CGS93 (lower case, upper right position) connected to a Tubbutec 6m0d6

Inter-case trunking example 1

• The Beep Boop Telecoms RJ45 modules are on the left shoulder of the lower case (see two photos above).
• They are connected via RJ45 to the receiving modules in the upper case.  
• Six patching cables are permanently set from my Vector Mk2 sequencer
• These six inputs routing two sets of pitch, gate and velocity to the Telecoms RJ45 in the upper case.
• I leave the second Telecoms RJ45 free for any ad-hoc routing from four additional pitch, gate and velocity sets available on the Vector Mk2

Inter-case trunking example 2

• I have two sets of Telecoms RJ45 modules installed on the right shoulders of the upper and lower cases.
• I use these to route outputs from the end of my voice signal chain (VCO, Envelope, Filter, VCA, Effects) 
• An RJ45 cable connects the Telecoms RJ45 in the upper case to a destination Telecoms RJ45 in the lower case.
• The destination Telecoms RJ45 presents the signal chain output to my After Later Audio Bartender Mixer inputs.

Telecom RJ45 (two) and CGS93 (upper case, lower left position)

Multiple Hops

Once you have deployed your inter and intra-case trunking modules you can send CV through multiple routes.  With good quality trunking modules you can do this and not experience pitch CV degradation resulting in really bad outcomes.  For example:

• I can send a pitch CV from my Vector Mk2 to the Telecoms RJ45 in the lower case.
• This is routed via RJ45 over the top to the Telecoms RJ45 in the upper case. 
• I can then patch the Telecoms RJ45 output to a CGS793 input.
• The signal is routed via ribbon cable underneath the module faceplates.
• The signal presents at the destination CGS793 output.
• I can patch it to a CV input of a nearby oscillator. 

Other options

There are many other trunking module options and even some which can be operated as inter or intra-trunk utilities.  The main thing you want to keep in mind is they should be powered so as not to degrade pitch or other CV signals, and should not introduce noise or crossover of signals into your system between inputs.  The modules I have used and named have given me no problems under extensive and demanding use.  Trunking modules also work great in small systems, especially when routing multiple trigger sources from a sequencer to a sampler or percussion type module or set of modules.  

Fear of a Jazz Planet…

Prior to installing the trunking solution, this 18U system was more than a little intimidating.  What had once been a smaller and easier to use system became a sprawling and chaotic mess of long patching cables that made it hard to work and maintain creativity.  It was especially hard to hand modulate knobs and faders on the fly for fear of knocking out a patch cable.  

Many people fear large Eurorack systems in the same way they fear jazz.  But just like fear of jazz, careful consideration of the shapes an patterns leads to beautiful harmony. So, if  you relate to this feeling in a growing  system trunking modules in your system can go a long way to helping you feel in control again.