Audio connectors
6.3mm connectors
6.35mm (or 6.3mm) connectors are often called phone connectors, phone plugs or phone jacks, and the connector originated in telephone exchange patch bays, from which the name comes. Today, phone connectors are mainly used in various types of musical equipment, e.g. in electric guitars, synthesizers, mixing consoles, amplifiers, etc. Another common area of use is as a headphone connector, mainly in professional or Hi-Fi equipment. Low-end vocal microphones also commonly have a hard-wired telephone plug.
The outer diameter of the connector is 6.35mm, a 1/4”, and they are often called quarter inch jacks / plugs.
Phone connectors are available in two versions, mono, or stereo. The mono version (2-pole) is often called TS (Tip, Sleeve), while the three-pole (stereo) is called TRS (Tip, Ring, Sleeve). 1/4” TRRS connectors have never been used. As with other miniature phone jacks, the sleeve is always used for ground, and is normally connected to the plug housing (unless plastic or insulated). The tip is used for signal, and in balanced uses, tip is normally hot (+), with ring being cold (-). For headphones, tip is the left channel and ring has the right channel. Other than for headphones, 6.35mm connectors are normally not used for stereo signals, unlike 3.5mm connectors.
Illustration of TS and TRS on a 6.3mm phone plug.
3.5mm connectors
3.5mm connectors are commonly called “mini jack” connectors (somewhat confusingly, this wording is even used for the plugs, which aren't called ”mini plugs”, nor ”mini phone connectors”). The type is indeed miniaturised, a space-saving version of the larger phone connector (6.35mm). The outer diameter is 3.5mm. The size is often called 1/8", although that “conversion” isn’t really correct (1/8 inch is 3.175mm).
Mini-jack connectors are mainly used in headphone jacks on computers, mobile phones, media players and so on. They are also used for other audio signals with line level, for example, on system cameras or in modular synthesizers such as Eurorack and similar equipment with limited space. 3.5mm connectors are also used for smaller condenser microphones, for example in portable recording equipment. In these cases, stereo connectors are often used, with one conductor for the microphone's signal, and one conductor for phantom power to the microphone.
Illustration of TS, TRS and TRRS connectors.
3.5mm connectors are available with two, three or four poles. One of the conductors is always used for ground, and it is always the one furthest back on the plug. It is known as the sleeve, or S for short. The sleeve is also connected to the connector housing (unless plastic). The other contacts are known as tip (T) and ring (R), the latter of which there may be one or two of. The naming of plugs follows the same convention as for phone plugs, with the addition of TRRS for four-pole connectors.
Mini jack connectors are cheap and available in many forms with different features, and ready-made cables in several different lengths are easy to come by. Thus, they can be a good choice even also for non-audio electronics, and they have indeed been used for low-quality (composite) video and DC power supplies.
2.5mm connectors
The 2.5mm connector is fairly uncommon, and has been mainly used in portable equipment where space is limited. 2.5mm can also be a good choice when one wants to minimise the risk of a user inserting 3.5mm plugs and potentially damaging other equipment, i.e. in environments where 3.5mm plugs are already in use. The connector is sometimes referred to as “sub-mini tele”.
2.5mm plugs and sockets are available with either two, three or four conductors. The different types are often called TS, TRS and TRRS, where the letters stand for Tip, Ring and Sleeve. The number of letters in the abbreviation is a quick way of knowing how many poles a connector has.
Two-pole commonly called mono, and three-pole ones stereo.
As the name suggests, the outer diameter is 2.5mm, i.e. close to 1/10" (2.54mm).
2.5mm connectors are found in voice recorders (dictaphones) and older mobile phones among other places. They have also been used in some DSLR and mirrorless cameras for transmitting audio, or for connecting a simple remote control of the shutter. The connector type has also been used for low voltage DC power supplies.
DIN connectors
The DIN connector standard was developed in the 1950s in West Germany by the Deutsches Institut für Normung. The connector comes in many different versions, and has been used for everything from audio and video to computer peripherals and for supplying DC power. The popularity of the DIN connector has declined over the years, but some models are still used in contemporary equipment, and the older models are of course still needed for repairs and for connect to older equipment.
One common area of use is for MIDI communication (a digital interface for controlling synthesizers and other music equipment), where the 5-pin DIN connector with a 180° angle is used.
The degrees-angle is a common source of confusion and irritation with DIN connectors; some (not all) DIN connectors have multiple physical designs for the same pin number. There are, for instance, three distinct 5-pin DIN connectors, which are completely incompatible. They are identified and labelled by the number of degrees the angle between the outermost contacts creates, e.g. on a 180-degree DIN connector they opposite each other on a semicircle.
The example below shows two different 8-pin DIN connectors. It's not easy to tell them apart straight away, but the difference is usually visible when comparing with a photo.
A two-pin DIN connector of a different design is also available, you will find them in the speaker connectors category, as they have mainly been used for this purpose.
Two 8-pole din connectors with different contact angles
There also exists a two-pin DIN connector, which is a different type of connector. They are commonly used as speaker connectors.
Microphone connectors (GX16 and GX12)
The GX-16 connector was developed as a Japanese alternative to the German DIN connector, and is (much like DIN) available with many different pin numbers (2 to 8 pins). The number 16 stands for the diameter, 16mm; or 12mm on the slightly smaller GX12 connectors which have come later. One somewhat unusual feature is that the male connector (plug - with mating pins) is normally chassis mounted, while the female (jack, with sockets) are on the cables.
One common usage is for microphones for amateur radio transmitters, and the connectors are often just called microphone connectors. The XLR connector is more frequently used for microphones, but in the audio industry, and both types are referred to as microphone connectors. Note that the types are not at all compatible.
The connectors all come with threaded locking fasteners and are robust; they can usually also handle relatively high voltages and current. Therefore, they are also used in avionics, marine electronics and for DC power supplies, not least ones with two or more supply voltages, where common two-pole DC barrel connectors won't work.
The connector itself is standardized, and – unlike DIN connectors – doesn't have different physical configurations for the same pin number. However, pinouts are completely unstandardised, and different manufacturers often have wildly incompatible configurations, even for the same connector and use case.
