How to Properly Connect the DB-25 Jack on Your Audio Device

How to Properly Connect the DB-25 Jack on Your Audio Device

Many times, people look at the jacks on the back of a device to figure out what cables they will need. While this is not really the best way to figure things out, most of the time it will get results. If you see an RCA jack and ask for an “RCA cable”, you’ll probably find a suitable cable (though there are different types of cables that use the RCA connector). But if you don’t get a little more information, you’ll most likely run into trouble when you see a DB-25 jack on the back of your audio device.

DB-25, or D-sub, connectors were originally created for computer applications. The audio industry adopted the DB-25 as a way of getting multiple channels in and out of devices while taking up minimal space. In this regard, the DB-25 connector works great. However, the use of this connector is problematic because there is not one universally accepted way of wiring it. In fact, there are three widely used wiring conventions when it comes to DB-25 in the audio world.

Some devices use D-sub connectors as a way of inputting or outputting eight channels of balanced analog audio. Each balanced channel requires three pins—one for the positive signal, one for the negative, and one for the shield—and each channel is grouped in a triangle pattern by taking two pins from one row and one pin from the other. Eight channels require 24 pins and pin 13 is simply not used. The Hosa DTM-800 series balanced snake is wired this way. It connects to the DB-25 output and breaks out to eight XLR male connectors. The Precision 8 mic preamp by True Systems uses a DB-25 connector to output all eight channels. This makes it possible to run a single cable with eight channels to an audio interface or mixer.

Professional audio devices can also use one DB-25 connector for eight channels In & Out (I/O) using the AES3, or AES/EBU, format. This digital audio format enables devices to send two channels of audio along one balanced audio line. This is where it really gets fun, as there are two standards for AES/EBU multi-channel I/O—and manufacturers choose which one to use.

The first is known as the Tascam wiring standard. The Tascam wiring standard is the same as the analog standard at the DB-25 connector end. The wire, however, must be different, as it is not passing analog sound. The AES3 specification requires 110-ohm balanced cabling for AES/EBU signals. Unlike analog snakes, AES/EBU snakes carry two digital channels on each balanced line. This means through one DB-25 snake, the device can send eight channels and receive eight channels simultaneously. If you are using a digital snake that breaks out to XLR connectors, it will have four male and four female XLR connectors instead of four like connectors on the analog snakes. Avid and Universal Audio are two companies using the Tascam standard. Avid’s ProTools HD I/O uses AES/EBU via a DB-25 jack.

Companies such as Apogee and Mackie, among others, have adopted the Yamaha wiring standard for their AES/EBU I/O. The wire is the same as that used for the Tascam digital snakes but the pin configuration is much different. In this case, the ground wires are on one side of the connector, while the other side gets the conductors. The Lynx Aurora 16 AD/DA converter uses AES/EBU with the Yamaha standard.

Note that if you are connecting two digital devices, you must make sure to use the correct pinout for each. If one of your devices uses the Tascam standard for its AES/EBU I/O and the other uses the Yamaha standard, you can still use them together. You must, however, use a snake with the Tascam pinout on one end and the Yamaha pinout on the other. Analog to digital is not as simple. You cannot use a DB25 snake to interconnect AES/EBU and analog signals. This would require a separate interface, which is a topic for another discussion.

The next time you turn to the back of your device for cable answers, remember the connector type is not everything—especially with DB-25. Your first question should be whether you’re looking at an analog or digital connection. If it’s digital, the next step is to figure out the wiring standard the device uses. Taking these steps will decrease headaches down the road and ensure you purchase the right DB-25 snake the first time.

- Jose

Y Cable Vs. Stereo Breakout Cable

The Y cable earned its name from the way it looks. There is a single connector on one end with a cable that splits, either as a zip cable or with a small box that conceals the split, and finishes with two connectors at the other end. A stereo breakout meets this same visual description and yet does not perform the same way as the typical Y cable. Let’s take a look at the difference between the two.

What is a Y Cable?

The function of a Y cable is to duplicate a single audio signal into 2 identical audio signals. The two signals can be connected to two new destination devices. A Y cable can also be used to change the connector type to avoid using a Y cable plus connector adapters in the same chain.

A Y cable is used when there is one signal that must go to two different places. For example, when you have one 1/4-inch TRS headphone output and you want two people to listen to the same thing on their own headphones with 3.5 mm connectors. The quickest solution to this problem would be a Y cable with a single 1/4-inch TRS male to dual 3.5 mm TRS female jacks. Each of the two headphones will get exactly the same signal. The cable is wired so each contact on the single end connects to the equivalent contact of each connector on the dual end. Be advised that a traditional Y cable is designed specifically to split a signal. Using a Y cable to combine two signals is not recommended because you have no control over the way the signal is combined.

What is a Stereo Breakout Cable?

As opposed to a Y cable that duplicates a single input, a stereo breakout cable will take a single connector stereo output from a device and separate the left and right signals into their own connector. Much like a Y cable, the connectors at the two ends of the stereo breakout cable can vary to eliminate the need for adapters.

A common situation requiring a stereo breakout is playing music from an iPod® through an audio mixer with 1/4-inch TS inputs. The solution is a 3.5 mm TRS to dual 1/4-inch TS stereo breakout cable. You connect the 3.5 mm end to the iPod and on the other end you’ll have the left signal (tip of the connector) on one of the 1/4-inch connectors and the right signal (ring of the connector) on the other, allowing you to connect each to its own input on the mixer. When used properly, a stereo breakout can be used in either direction. You could use the same breakout from the previous example to take the left and right outputs of a mixer and connect them to a laptop equipped with a 3.5 mm stereo input.

TRS vs TS Cable

Before making a purchase, it’s important to know what type of inputs and outputs you need. TRS stands for Tip, Ring, Sleeve. These cables are known as balanced, or stereo. They can either carry a single balanced signal or separate left and right signals in a single cable. TS stands for Tip, Sleeve. These are unbalanced, or mono cables and only carry one signal. While most modern equipment will have TRS inputs and outputs, there’s still lots of equipment that may require separate left and right inputs, which requires splitting that TRS into two TS connections.

It’s important to know what you need to accomplish in order to select the right cable. Hopefully this has shed some light on these common audio problem solvers so that you can always make the right choice. Check out Hosa’s Y Cable and stereo breakout selection to find your perfect cable.

- Jose