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RCA. In this case, it usually refers to a line output in the form of a pair of RCA connectors ("tulip")—one for each stereo channel. This output is intended for transmitting line-level audio signals to other system components, such as an audio receiver or active speakers. The RCA connector itself is considered standard for a line interface, and inputs of this type are found in most stationary audio devices.
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XLR. Another type of line output (see "RCA" above), in this case built on XLR connectors. The main advantage of this interface is that it provides balanced connections, allowing cables of significant length to be used without degrading sound quality. Additionally, the connectors themselves provide a tight connection and are equipped with locks for extra reliability. On the other hand, they are noticeably larger than RCA connectors, which is why they are mainly used in professional phono preamps, where these advantages are crucial.
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USB (type B). An output for connecting the phono preamp to computer equipment. The presence of this connector allows for digitizing audio compositions from records and other media (such as tapes and reels) and saving them to computer memory for further processing or transfer to a smartphone/MP3 player, for example.
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Coaxial S/P-DIF. An audio output for transmitting soun
...d in digital format through an RCA jack. Do not confuse this jack with an "ordinary" line RCA—this case uses a single socket and a fundamentally different signal transmission format; a special shielded cable is also recommended. The coaxial interface is functionally similar to the optical one, but differs in having greater sensitivity to interference on one hand, and a stronger and more durable cable on the other.
— Optical. Another type of digital audio output, using optical fiber cables as the name suggests. The main advantage of this connection is complete insensitivity to electromagnetic interference. On the other hand, the cable itself is quite delicate and requires careful handling.
— Headphone. A specialized output for connecting headphones directly to the phono preamp. It usually uses a 3.5 mm mini-Jack or 6.35 mm Jack. Note that direct headphone connections in this context are intended not so much for regular music listening but for special tasks. For instance, a DJ mixing a set or a sound engineer recording music from a record to an external device can continuously monitor the sound being output from the phono preamp using headphones.
— Trigger. A service output that allows the phono preamp to automatically turn on other components of the audio system. When the preamp "wakes up," it sends a control signal through this output, and devices connected with trigger inputs turn on automatically. This eliminates the need to turn on each component separately.
