Tuesday, December 12, 2017


by Mark King for proworkshop.com

When your recording rig starts to expand you need cables and they need the right connectors on them to give you correct performance. Here we will take a look at the popular connectors used in modern recording and production studios. For detailed information about what signals are flowing through the connectors and cables see this link to Proworkshop Basic Training about Signals and Levels.

The modern phone plug got it's start in the telephone industry, early industrial versions were used by telephone operators to connect one line to another so two telephones could talk to each other.

RULE-ONE: Just because two plugs look like each other and will fit in the same hole does not mean they are compatible.

BAD EXAMPLES: If you plug a high-impedance unbalanced microphone into the output jack of a 150 watt solid-state guitar amplifier you end up with a dead mic and a blown amp. Likewise, if you connect the output of a 100 watt guitar amp to the input of an MXR Distortion stomp-box you end up with a fried stomp box and a blown amp-output transformer. I mention these because I've had both in my repair shops. The plugs fit but the gear did not like it, memorize Rule-One!


Neutrik Tip-Ring-Sleeve 1/4" Male phone plug
TRS means Tip, Ring and Sleeve, this is a description of the physical contact points on the male plug connector (shown above). The Tip, Ring and Sleeve connections are separated by black insulating bands in the photo above. The Sleeve connection is common to the body of the connector and provides shielding to the inner two signal cables.

The TRS 1/4" male phone plug is a three-conductor connector used for two very popular connection types in modern recording studios:

  • Balanced-line level signals, inputs and outputs
  • Unbalanced stereo headphone signals, the plug on the end of your headphone cable

Neither of these signal types are compatible with each other but both utilize the same connector. This means don't plug a TRS headphone amplifier-output into a TRS balanced input on any piece of equipment, likewise don't plug your headphones into a balanced line-output either.

Isolated Tip-Ring-Sleeve 1/4" Female phone jack
The TRS female phone jack is the 3-conductor mate for the TRS male phone plug and it is used for:

  • Balanced line-level signals
  • Unbalanced stereo headphone connections

Neither of these signal types are compatible with each other but both utilize the same connector.

In the above photo the TRS jack is referred to as "isolated" because the sleeve of the connector is plastic which keeps the sleeve isolated from the chassis of the equipment it is mounted in. This can be very important for controlling ground loops.

Panel mounted phone jacks are usually available in both isolated and non-isolated versions. The isolated variant often costs more.

Neutrik Tip-Sleeve 2-conductor 1/4" male phone plug

The TS 1/4" male phone plug is a two conductor connector used for:

  • Guitar-to-amplifier connections (very small instrument-level signals, unbalanced, shielded cable wire)
  • Guitar amplifier-to-speaker connections (large signal size, speaker-level signals, unbalanced, unshielded cable wire)

Another popular Tip-Sleeve type 2-conductor 1/4" Male Phone Plug
Care must be taken to use the correct wire type for the intended application.

Guitar amplifier inputs and outputs use the same connector but the wire is different for each application, one is shielded while the other is not - one uses small electrical conductors while the other uses much larger size conductors.


Non-isolated 1/4" Tip-Sleeve Female Phone Connnector
The Tip-Sleeve 1/4" 2-conductor female phone jack is used for a variety of musical instrument connections. It is usually what you'll find on both the input and the output of modern guitar amplifiers.

This connector is the mate to the 2-conductor TS male phone plug.

In the photo above it is easy to see the tip connection and the sleeve is connected by the overall body of the mating male connector. The jack shown is non-isolated which means the body of the connector or sleeve is in contact with the chassis the connector is mounted in. This means the sleeve connection of the connector is directly connected to the chassis of the equipment it is mounted in.

Many small PA systems use 1/4" female 2-conductor phone jacks for the amplifier output connections which feed signal to the speakers.

Switchcraft A3M Male XLR Cable Connector
The XLR connector was invented by James Cannon who founded Cannon Electric in Los Angeles CA, for this historical reason the connector is sometimes also referred to as a Cannon Connector.

The accepted modern industry moniker of XLR is now applied to models from several brands like Switchcraft and Neutrik with standardized shapes and sizes which allows interconnections between brands.

The most common use for the 3-pin male XLR is balanced microphone connections although it can also be used for balanced line-level connections and even speaker connections.

Pin #1 = Ground or Common
Pin #2 = positive
Pin #3 = negative
Switchcraft D3M Panel Mount XLR Male Connector
Up until the late 1980's there was still confusion about whether pin 2 or 3 is positive in balanced circuit wiring.

Finally the audio industry came together and everyone signed off on an industry standard of pin #2 = positive, pin #3 = negative. This meant that professional audio equipment could be connected using industry standard wiring instead of custom wiring according to each piece of equipment and each manufacturer.

Switchcraft A3F Female XLR Cable Connector

The 3-conductor female XLR connector is commonly used for:

  • Low-impedance balanced microphone connections (shielded, small signal level)
  • Balanced line-level audio connections (shielded, line-level signals)
Notice that both of the above applications require shielded cable.

Both of these signal levels will work with cabling that has conductors as small as 26-gauge (that's very small wire). 

22-gauge is common in professional and commercial installation applications and for longer wire runs. 24-gauge is common in low priced budget cabling and multi-pair cable.

Modern usage on audio equipment:
  • Male 3-pin XLR is typically used for balanced audio output
  • Female 3-pin XLR is typically used for balanced audio input

Switchcraft D3F Panel Mount XLR Connector, typically a balanced input connection

XLR Panel mount connectors are used for microphone-level and line-level balanced audio signals.

Sometimes 3-pin XLR connectors are used for flexible gooseneck lights on mixing consoles, it's important to know what the function of a jack is before you plug something into it. Remember Rule-One!

On mixing consoles and signal processors (on the hardware itself):

  • XLR male is usually used for an output connection
  • XLR female is usually used for low impedance microphone and balanced line inputs

Two Male RCA / Phono Connectors

The RCA / Phono connector is a two-conductor, unbalanced part and may be used for analog audio and video or digital signals like S/PDIF (Sony / Philips, Digital Interface Format).

It is referred to as an RCA connector because the RCA Victor company created it as a way to disconnect the phonograph connection in 1930 and 1940 entertainment equipment. Even today, you'll still find this connector used for turntable connections on modern recording and sound equipment.

Years later the connector was used more frequently for other analog signals and it became an inexpensive way of interconnecting hi-fi consumer entertainment equipment.
Two Female RCA / Phono Connectors

RULE OF THUMB: When you find RCA / Phono connectors on a piece of equipment it usually infers lower signal-level on these connection points.

EXAMPLE USAGE: The Soundcraft mixer in our studio uses all line-level, balanced 1/4" connections rated for 0-dBu line-level signals. The two stereo tape return inputs in the master section are fed by a pair of RCA / Phono connections on the rear of the console, these are rated at .3 volts which is about half the signal size of all the other line inputs. This lower signal level is typical of consumer recording equipment that adhered to the -10 dBv standard (popular Fostex and Tascam consumer or prosumer recorders).


  • On hardware like amplifiers and video equipment RCA Phono connectors are usually female
  • On cables RCA Phono connectors are usually male on both ends
  • Sometimes an RCA Phono cable may have a male on one end and a female on the other end, this is usually an adaptor or an extension cable.
  • RCA Phono cables almost always use shielded type of wire


Cell phones and portable music players have popularized the use of miniature phone plug connectors that look just like their full size counterparts.
1/8" TRS non-isolated open-back female jack
1/8" to 1/4" adaptor

TRS 1/8" Connector
The 1/8" inch TRS female jack has become popular as a headphone connector. It is used just like the 1/4" TRS to carry left and right audio with a common ground between the two channels.
Side view of 1/8" TRS open back female jack, note Tip and Ring contacts

Most professional audio equipment still features 1/4" connection points for headphones but it is becoming increasingly common to find 1/8" headphone outputs on equipment as well.

These little 1/8" connectors are difficult to solder due to very tight tolerances and close quarters of the contacts.

The most common use for the 1/8" connection in a modern recording studio is headphones.

Other popular uses of the 1/8" connection is headphone and microphone connections in cell phones, there are several standards using the same connector which makes things very confusing.
Apple added another "ring" to the tiny TRS plug to create the TRRS connector
1/8" TRRS connector, these are quite difficult to solder reliably
The TRRS is not common in modern recording situations and it is not used on professional recording equipment.


In 1991 Alesis came out with the ADAT digital tape recorder which recorded eight tracks of digital audio on to S-VHS video tape cartridges. These decks had a rather expensive Elco multi-pin connector on the rear, this was a standard, high-reliability connector in professional studios, used to make multiple connections through a single plug.
Elco EDAC multipin connector for Adat connection

This one plug connection allowed all eight balanced inputs and all eight balanced outputs to be connected by a single connection on the rear of the recorder.

The balanced wiring for the ADAT Elco connection is shown above.
Typical Elco 16-channel connecting cable
Making Elco cables was not a fun process for the home studio owner. A special crimping tool is used to crimp the connection contacts to the ends of the wires, then using an insertion tool each pin is installed into the multi-pin body. If you accidentally install one contact wrong then you need the corresponding "de-insertion" tool to remove the pin.

The Elco style connector is not suitable for nightly connection and disconnection, the gold contacts are soft and easily bent if the connector is not carefully lined-up.

These connectors have quickly faded from regular use in modern studios.

Tascam specification D-Sub to Eight Balanced TRS Male Plugs
A year after the ADAT hit the market Tascam came out with their own multi-track digital recording system which used 8mm video tape instead of S-VHS tape. Instead of using the expensive 16-channel Elco connector Tascam repurposed the inexpensive 25-pin D-Sub connector (borrowed from the computer industry) into an audio connector which could plug in all eight inputs with a single connector. A second D-Sub provided all eight outputs on a single connector.

Third party cable manufacturers quickly jumped on the D-25 audio bandwagon and a new pro-audio standard connection was born. Today you find this type of connection used on a wide variety of pro-audio equipment.

Many audio professionals viewed the D-25 as an inferior connection when it first was used on the Tascam recorders but over the next 20 years it became an industry standard and is now found on everything from ProTools interfaces to Neve mixers.

Numerous cable companies offer eight-channel audio connection cables which utilize the D-25.
D-25 to D-25 Connection Cable for Audio

The Tascam D-Sub connection became a new industry standard for making multiple audio connections with a single plug. The connector is capable of handling 25-conductors but only 24 are used for analog audio connections.
Tascam D-Sub Wiring Diagram
The D-Sub connector gets its nickname from the D shape of the connector body. These were popular computer interface connections for printers in the early days of PC computing.

When used for eight channels of audio each balanced connection uses a ground, a plus (or hot) and a minus (or cold) signal connection.
D-Sub-25 to XLR Male Cable

Soldering these 25-pin D-Sub connectors with balanced audio cables is not a fun project. The shielded-pairs of balanced wire must be very small in diameter to fit inside the connector body.
Note the metal D-Sub connector, this one is repairable if necessary
The advantage of D-Sub-8 cables is that equipment requires fewer individual connectors on the rear panel. This can result in fewer connection errors because there are fewer individual connections to be made. The use of D-Subs also allows more connections in a smaller footprint.

The disadvantage of the D-Sub-8 can be poor mating between different and less expensive brands. Some D-Sub connectors don't fit as tightly as you might like. D-25 connectors are also difficult to repair because of the tight density of connections inside the plug body. Molded D-25 connectors are not repairable at all, although you can cut them off the end of the cable and replace the connector with a metal component connector.


There are many other connections found in modern recording situations but the ones covered here are the most common and the ones you'll find most often used for audio connections.

In future articles we'll examine audio adaptors and other types of connectors for DC, AC and computer networking. We'll also look at the confusing American Wire Gauge system and present some guidelines for choosing wire size.

Good music to you!