DMX Adaptors and Terminators: 3-Pin, 5-Pin and the Plug at the End of the Line

In this guide:3-pin and 5-pin · Adaptors · Terminators · Good practice · Picks · FAQ

DMX is one protocol on two connectors, which is a nuisance that dates back to the standard being written for 5-pin and the industry building cheaper fixtures with 3-pin. Both carry exactly the same data.

That means adaptors are legitimate and useful, unlike most adaptors in this trade. What is not legitimate is using a microphone cable to carry DMX, which is the mistake this guide mostly exists to prevent.

Why there are two connectors

The DMX512 standard specifies a 5-pin XLR. Pins 1, 2 and 3 carry the ground and the data pair. Pins 4 and 5 are a second data pair that the standard reserved and almost nothing ever used.

Manufacturers of budget fixtures saved money by fitting 3-pin XLRs, which carry the same ground and data pair. The result is a market with both, and a lot of rigs running a mixture.

• 5-pin is the standard, and what you will find on most professional fixtures and consoles.
• 3-pin is common on DJ and entry-level fixtures.
• The data is identical, so a straight adaptor between the two is electrically correct.

Using adaptors properly

An adaptor that connects pins 1, 2 and 3 through and leaves 4 and 5 unconnected is exactly right, and that is what a proper DMX adaptor does.

• 5-pin male to 3-pin female takes a standard console output into a 3-pin fixture.
• 3-pin male to 5-pin female does the reverse.
• Keep several of each in the rig. Mixed rigs are normal and the adaptor you lack is the one the hire fixture needs.
• Buy adaptors, not homemade leads with the pins guessed at.

What the terminator does

A DMX line is a transmission line, and an unterminated one reflects the signal at the far end back towards the console, where it collides with the data still arriving. The result is corruption that gets worse as the run gets longer.

A terminator is simply a resistor of about 120 ohms across the data pair, in an XLR shell, plugged into the output of the last fixture in the chain. It absorbs the signal instead of reflecting it.

• One terminator per chain, at the far end, not at the console.
• If the run splits through a splitter, every branch needs its own terminator.
• Symptoms of a missing terminator are intermittent: occasional flicker, fixtures twitching, a rig that behaves differently on a long cable run than a short one.
• Some fixtures and splitters have a termination switch built in. Use it rather than a plug where it exists, and do not do both.

Good practice for a reliable line

• Use proper DMX cable throughout, and label it so it does not get mixed into the audio looms.
• Keep the daisy chain to a sensible length and fixture count. The standard allows 32 devices per run before a splitter.
• Use an opto-splitter rather than passive Y splits. Passive splits are a common cause of unexplained behaviour.
• Terminate the end of every branch.
• Keep a terminator and a pair of adaptors in the toolbox permanently.

The addressing and universe side of the subject is in DMX explained.

Frequently asked questions

Can I use a 3-pin to 5-pin DMX adaptor?

Yes. Both connectors carry the same data on the same three pins, so a straight adaptor is electrically correct and completely normal in a mixed rig.

Do I really need a DMX terminator?

On short runs with a couple of fixtures you will often get away without one. On longer runs, or with more fixtures, an unterminated line causes intermittent flicker and misbehaviour that is very hard to diagnose. A terminator costs almost nothing, so fit one.

Can I use a microphone cable for DMX?

No. It has the wrong impedance and causes reflections. It will sometimes appear to work, which makes it a difficult habit to break, and it is the first thing to rule out when a rig behaves strangely.

Where does the terminator go?

In the DMX output socket of the last fixture in the chain. If a splitter creates several branches, each branch gets its own terminator at its own far end.