Multiples are another one of those unglamorous utility modules that you should probably spend more money on than you were expecting

As we’ve said before, when you’re configuring your modular synth, it’s easy to leave out the all-important utility modules that will help glue a patch together as well as open more creative options. We recently discussed ideas you should explore when choosing a utility mixer; in this note, we’re going to focus on multiples (“mults” for short), including when you need the different types that are out there.

Why Do I Need a Mult?

Black Market Modular Monomults

Black Market Monomults in the thick of a complex patch

Sometimes, you need to send a signal to more than one place. The most obvious example is the pitch control voltage from your keyboard, sequencer, or MIDI interface: you often want it to go to more than one oscillator, and maybe the filter or other modules that you want to respond differently based on the note being played. This is also true for the note gate/trigger or a clock pulse: You may want to trigger more than one envelope generator, perhaps reset an LFO (low frequency oscillator), and maybe send it to a clock divider or other logic module. And there are a lot of other signals you may want to send to multiple places, such as the output from those LFOs and envelope generators. With Eurorack in particular being a small format to begin with, it’s not common for a module to have multiple outputs to cover you, so you need to find a way to split the signal yourself.

What’s the Difference Between Mults? They Sound Pretty Simple…

In broad terms, there are three ways to split a signal:

Intellijel HUBs at work

Intellijel HUBs at work

•     Passive Mults, which are essentially a bunch of jacks wired together with no circuitry in between them. You plug your source into one of the jacks, and take copies of it out from the other jacks. This is the cheapest solution, requiring no power to work. However, if something nasty is happening on one of the outputs – such as a short circuit – it would be felt by the input as well as by all of the other outputs. Some circuits are internally buffered in a way to reduce interactions with the modules they’re connected to; others are more sensitive, meaning connecting to more than one output could change the voltage or even waveshape that the input was trying to send.

There are numerous inexpensive passive multiple modules available; they can be as cheap as $10 for a 1U-high tile with one set of mults and run from $25 to just over $50 for a normal 3U-high module, often with more than one set of mults. They’re also easy to wire up yourself; you just need a blank panel, a drill, some jacks, a little bit of wire, and beginner soldering skills.

TipTop Stackable and Erthenvar IV cables

TipTop Stackable and Erthenvar IV cables

There are a few trick patch cables available that split the signal, such as TipTop Stackables and Erthenvar IV cables. IV cables with an extra jack in the middle typically cost 75 cents more than an equivalent Erthenvar cable ($2.00 versus $2.75 for a 30 cm/1 foot cable); TipTop Stackables have extra jacks on each end cost $8.75 each regardless of length up to 5’. Some prefer splitters that you plug your cables into, such as the five-way Black Market Monomult for $7.99, or the four-way gold-plated Intellijel HUB for $10 that comes with an optional magnet to stick in place.

•     Buffered Mults, which copy the voltage from an input jack to an output jack. Since there is circuitry between the input and output and they do draw power, these are sometimes referred to as “active” multiples. With these, what’s happening on the output does not affect what’s happening on the input – and by extension, the other copies of the input are left alone as well.

A selection of buffered mults in the 1U "tile" format

A selection of buffered mults in the 1U “tile” format

These are most often implemented as a small patch panel with an input and several outputs. There are often more than one multiple in a module, and the input of the one is often cascaded to the next in line unless something else is plugged into its input. That means a module with a pair of 1-into-3 multiples can also act as a single 1-into-6 multiple; the Malekko Performance Buffered Mult distinguishes itself with a switch on the front panel for this function. 1U tiles can go as cheap as $20 for the Erthenvar or Pulp Logic; 3U modules range from $50 to $150 – so very roughly twice or the price of a passive mult module.

Circuit Abbey Hydra

•     Logic Mults, which are specialized binary versions of buffered mults, as it too buffers each output from the input as well as any other outputs. With these, you send a signal into a circuit that measures its level. If the input is below a certain reference, send out 0 volts. If it’s above a certain reference, send out a “full level” signal – usually +5 volts. A good example is the Circuit Abbey Hydra ($80 assembled or available as a kit) that is designed to replicate clock signals; other logic-based modules can often also work as gate or trigger mults.

Can I Get Away With Just Using Passive Mults?

Passive mults are cheaper than active buffered mults, so of course there’s a desire to use them whenever possible. Some synthesists use only passive mults – until something goes wrong; then they swap in an active one.

If you want to take a more scientific approach, in general you can usually get away with splitting any one signal into two, but it will depend on the modules involved – some have better internal buffering than others. The signals least sensitive to the use of passive mults would be your modulation sources, such as envelopes and LFOs: With these, the precise voltage is usually less important than the overall voltage swings its shape. You can also probably get by most of the time with splitting a clock, trigger, or even audio signal into two or three cables using passive mults.

You never want to use a passive mult to mix two signals together. Yes, with good module design, sometimes you can get away with it – but you’re asking for trouble.

When Do I Need to Use a Buffered Mult?

The flippant answer would be “whenever you can’t get away with using a passive one.” More scientifically, most often you want to use a buffered mult for any signal that controls tuning and pitch. Splitting a signal passively can reduce its level, which can result in a drop in pitch and poor tracking or intonation.

(That said, a poorly-designed buffered mult that does not exactly copy the input voltage to the output can induce intonation problems, leaving you worse off than you started! For the technically-minded, Allan Hall of AJH Synth shared that there is potential for trouble if the manufacturer added an extra resister between he output of the opamp and the output jack. The purpose of this is to limit the current through the opamp should the output be shorted to ground, which is normally good, but the result could be a change in overall resistance at the input to a VCO, causing it to detune.)

Lesser known is that if you try to drive too many clock or gate inputs using passive splitters, you could start to distort the shape of the trigger or gate to the point where some of the destinations may start misfiring. Some users indeed report their systems exhibit “tighter timing” when they use buffered or logic mults for their clock and gate signals. To correct this, you could use a logic mult such as the Hydra in place of an any-voltage buffered mult.

Odd circuits may require you to use a buffered mult even when feeding just one input to one output. For example, patch cables that have LEDs embedded (like those from UTOPb) pull their power from the signal, which can reduce its strength or change its shape on the way to the destination. As UTOPb points out on their web site, using a buffered mult in front of a LED patch cable of these can help clean up some of these problems.

Okay – I Need Some Buffered Mults. Who Makes Them?

I created a rack on ModularGrid that includes a selection of buffered mults available today:

A selection of buffered mults (and more!) on ModularGrid.net

A selection of buffered mults (and more!) on ModularGrid.net

The top row contains simple buffered mults that reproduce the full range of voltages accurately. The middle row contains 1U “tile” format buffered mults.

The bottom row contains some examples of modules that contain buffered mults, plus do more. Many of them contain both unity mixers and signal splitters in the same module. Others include inverters, attenuators, and even line level boosters (such as the AniModule Line_Amp).

Just remember to include some mults when planning out your system, and make at least one of them a buffered mult.