ZXY-2622 75:75/300/600 Ohm Audio Isolation Transformer, Shielded Chassis-Mount Line Transformer with Tapped Secondary

1. Product Name

The ZXY-2622 is a shielded, chassis-mount audio isolation transformer with a 75-ohm primary and a tapped secondary, providing 75, 300, and 600 ohms. The housing label reads ZXY AUDIO, TRANSFORMERS, 75:75/300/600, and ZXY-2622. Behind it is customer drawing G2525, revision A/0, dated November 6, 2025, which also provides the manufacturer's own part name as ZXY2600-75:75/300/600. Three identifiers describe the same component: marking, drawing number, and internal part name. Reference any one of them; the other two should be understood.

The twelve pins are arranged in two rows of six, with a row spacing of 35.5 mm, and two mounting ears spaced 59 mm apart for fixing screws. This combination makes it a chassis-mount part rather than a board-level one: the mounting ears bear the mechanical load, the pins carry signals, and the housing can be bolted to a metal panel, but unless pin 5 is connected to the panel, the windings are not connected to it. Photos show it secured with screws to an amplifier's internal circuit board and point-to-point wired in a tube chassis, which is precisely the purpose of the mounting ears.

2. Function Description

Two devices connected to the same mains supply are linked via their safety grounds, and the cable shield between them forms a closed loop. Current in this loop appears as hum at the mains frequency and its harmonics in the signal, and it cannot be eliminated by internal shielding because the loop lies outside the devices. The transformer breaks the loop: the signal is transferred inductively, and the ground path no longer exists. When levels must remain unchanged, a 1:1 winding is used, so the receiving end sees the same impedance as before. This same break also prevents digital noise from propagating between a converter and an amplifier sharing a common ground.

75 ohms is not an audio convention like 600 ohms; it is the standard impedance for unbalanced broadcast and installed AV wiring, matching values used for video and 75-ohm digital audio. Thus, a transformer with a 75-ohm primary sits at the edge of that domain. The model's flexibility lies on the other side: the secondary is not a single winding but has taps, allowing the same unit to match a 75-ohm source to 300 or 600-ohm inputs without adding a second part number to inventory.

3. Tapped Secondary Winding

These three ratios are not three separate windings but taps on the same winding, with pin 8 as the common: 8-9 is 1:1, 8-10 is 1:2, and 8-11 is 1:3. Since the ratios land exactly on 1, 2, and 3 within 0.5%, the three sections between taps must have equal turns, so the turns from 8 to 9, 9 to 10, and 10 to 11 are each the same as the primary winding. This is important for wiring: the taps are electrically uniform, not trimmed for specific loads.

Selecting a higher tap does not preserve the level. Impedance matching through the transformer is a step change in turns ratio, so the 1:2 tap raises the voltage by about 6 dB, and the 1:3 tap by about 9.5 dB, while the load impedance viewed by the source is divided by the square of the turns ratio. If the receiving stage has its own gain, the difference is absorbed there; if not, the tap choice changes both the operating level and the match.

4. Construction and Shielding

The housing is a dark gray molded shell with a recessed top for the rating label, a stepped shoulder at the front, and mounting ears drawn as part of the same molding. The shield has two separate pins: pin 4 is named the shield, and pin 5 is named the metal housing, so they can be connected at one point or brought out separately. Whether the metal housing connects to the panel is a wiring decision, not a mechanical one, because the mounting ears are molded as part of the shell. In chassis construction, the usual arrangement is pin 5 to the panel, and at the point of the loop break, the shield is connected to the end with the lowest hum measurement, but the drawing does not specify either.

5. Electrical Specifications

The electrical page of G2525 is short, and each line is a measured characteristic rather than a marketing claim. Impedance is referenced at 75 ohms on the three taps, tolerance ±10%; turns ratio tolerance ±0.5%; response in the audio band referenced to 2 Vrms; distortion measured at a single frequency and level; and the dielectric test is 1000 V AC between windings for one minute. This is a workable set of small-signal parameters. What it omits is any information about the windings themselves, and for a line transformer, these omissions are what a designer notices first.

Two of these need careful reading. The response line on the drawing is marked with a reference of 2 Vrms and parenthetically ±1 dB, then the result is ±0.4 dB, so 1 dB belongs to the reference condition and 0.4 dB is the product value; the description mixes both without separating them. The distortion line gives +4 dB but does not state the reference, and +4 dBu differs from +4 dBV by 2.2 dB, so the test level is either about 1.23 Vrms or 1.58 Vrms.

6. Mechanical Dimensions

The outline drawing is dimensioned in four views, which is more than most parts of this kind provide. Front and side views give the envelope, the bottom view gives the pin row and mounting ear locations, and the top view gives the space occupied by the label. Everything needed to lay out a panel is provided, except one value where the mounting ear detail does not agree with the overall.

The 35.5 mm is the distance between the two pin rows, and the 59 mm is the distance between the two mounting ear holes; they are not two substitute values for the same measurement. The 6 mm is the offset from the edge of the molding to the first pin in the row, which is the dimension needed for package layout when placing solder pad areas.

7. Application

The intended use is a 75-ohm line that must reach a device at a different ground potential, or a 75-ohm source driving a 300 or 600-ohm input. Broadcast and installed AV racks are the obvious applications: 75-ohm patch runs between rooms, monitor feeds that hum when patched, and mixing console outputs entering a 600-ohm house system. The same part also addresses the old studio problem of 600-ohm lines picking up noise along long cables, because the break at the transformer eliminates the loop, and the 1:1 tap keeps the level unchanged.

Test and measurement is another natural fit. An isolated branch in bench instruments prevents ground loops from injecting line-frequency current into signal leads, and the three taps make one stock part usable for both a 75-ohm instrument output and a 600-ohm monitor input. Discrete construction uses it the same way: the second scene shows it fixed to a tube preamp chassis, where the metal housing and separate shield pin allow it to sit near the transformer powering the rectifier without mutual interference.

8. Ordering and Marking

Purchase to drawing G2525 (rev A/0, dated November 6, 2025), whose revision record has only one entry, the initial issue on that date. The drawing states that measured data is available on request, which is how to get response curves, distortion sweeps, and dielectric test records rather than relying on claims on a page. Alternate lead lengths, tap combinations, and mounting methods are available on request, so a different tap set is a custom product on a new drawing, not a variant of this one.

The housing prints the ZXY AUDIO name, the ratio 75:75/300/600, and the model ZXY-2622. The description states that the housing markings include CCC, CE, RoHS, and UL compliance marks. In the provided images, all four marks appear together only in the composite product photo, arranged on a white strip above the transformer; the close-up of the molded housing shows a green label without marks. This is a presentation difference rather than a claim difference, but buyers needing marks on the part should confirm where each mark is printed and request the certificate numbers behind the four marks.