ZXY-3012 Permalloy Audio Isolation Transformer, DIP Through-Hole, Sealed 31.0 mm Metal Case, Five Turns Ratios from 1:1 to 12:1

1. Product Name

ZXY-3012 is the product marking. JT-DB-EPC is the drawing model identifier printed above it on the case label, and ZXYAUDIO and ZXYL are the two brand marks used in images and datasheets. This device is a Permalloy audio isolation transformer in a sealed cylindrical metal case, 31.0 mm in diameter and 22.0 mm high, with six through-hole pins at the bottom arranged in two rows and no mounting flange. It is mounted to a circuit board or socket via its pins.

The label is the only location where the device states its own specifications, so it deserves a close read. The label carries the brand, the word TRANSFORMERS, the drawing model JT-DB-EPC, the marking ZXY-3012, and around the edge of the case a line reading Frequency Response: 20Hz - 20kHz and Ratio: 1.1 - 12:1. Note the punctuation in that last number: the same line uses a decimal point in 1.1 and a colon in 12:1, while every other document in the set gives the range starting at 1:1. The range is understood here as 1:1 to 12:1, and the printed label is reported as-is without correction.

2. Product Function

Its function is the same as every isolation transformer: two pieces of equipment share a common mains earth, the shield of the cable between them completes a loop, and current in that loop superimposes a hum on the signal at mains frequency and its harmonics. Inserting a transformer in the path breaks that loop because the signal transfers by induction and no copper conductor touches another. It also blocks DC, which is why this kind of device protects a following stage from bias faults or phantom power applied to the output, and why the product description lists it as a characteristic rather than a claim.

The Permalloy core is the key to that structure. Permeability determines how much inductance a given number of turns produces, and inductance determines whether the primary winding shorts the signal at low frequencies, so a high-permeability alloy can work at 20 Hz with fewer turns and a smaller core than silicon steel ever could. The price is saturation: the nickel-iron alloy reaches its flux limit earlier than steel, which is why the device is rated by maximum input level at 20 Hz and 1% distortion rather than by a power rating. This is a line-level component and the specification sheet should be read that way.

3. Five Turns Ratios

This is the part of the product that has to be settled first. The five windings share one case and one set of six pins; what differs between them is the ratio, the DC resistance of each winding, the level the core can take at 20 Hz, and how flat the response is. Higher step-down ratios put more turns on the primary winding, which raises its resistance and raises the voltage the core can handle before saturation, so the level column improves from one end of the table to the other while primary resistance climbs with it.

These levels are worth converting because the decibel values hide how far apart the variants are. The 1.5:1 version accepts +2 dBu at 20 Hz, about 0.98 Vrms: that is a low-level device that cannot take much line output at the bottom of the band. The 12:1 version accepts +21.5 dBu, about 9.2 Vrms, an entirely different class of headroom. Both conversions are arithmetic from the definition of dBu and are given here as derived values.

This family is not a multiplier series. The ratios are 1:1, 1.5:1, 3.5:1, 8:1, and 12:1, whose squares give impedance steps of 1, 2.25, 12.25, 64, and 144, so this is not the 2, 4, 8 ladder of a catalog line. These ratios look tailored to specific equipment rather than a standard series, and that is worth asking about: the answer usually tells you which design each model was originally made for.

4. Core, Case, and Pins

The case is a drawn metal can with a green printed label on the front and a crimped rim at the bottom where the can meets the base. Because the can is metal and sealed, the electrostatic shield is the case itself: no separate shield pin is needed, only that the can be tied to chassis or to whatever reference the layout requires. That is the real difference between this device and a molded-case transformer with a shield terminal, and it is why the mounting surface matters as much as the winding.

Six pins emerge from the base in two rows, with 1 and 4 on one side and 8, 6, 7, and 5 on the other, at 3.8 mm spacing within a row and 19.0 mm between rows. That row spacing is wider than any standard DIP grid, so this device needs its own pad layout or a dedicated socket, not a generic DIP position. There is also a plain round hole in the center of the base, drawn but never dimensioned or named on any drawing; round holes on sealed cans like this are usually fill or vent ports for potting and should not be used as a locating feature without confirmation.

5. Electrical Specifications

Every electrical parameter in this product is stated on the controlled datasheet at 25 degrees Celsius, which is a better starting point than most parts in this class. The conditions are consistent: the same 20 Hz to 20 kHz band, the same 1250 V dielectric test at 1 mA for one minute, and the same 2% ratio tolerance. What varies is frequency response and level, and both vary with the ratio, which is why they belong in the ratio table rather than in a single-line specification.