ER-4S Conversion Cable Included: ER-4P Measured Matched Pair, Purchase Details, Maintained

Added Actual Measurement Images - Price Reduced from Humidity-Controlled Cabinet Organization

[Unit Overview]
This is the renowned ER-4P from Etymotic Research.
This unit has been modified by Mamepyoi Kobo with practical physical reinforcement and a custom adapter for 4S conversion, allowing for dual-use enjoyment.

[About Serial Numbers]
This is a genuine domestic product purchased new from Sound House in 2012. Purchase receipt included.
Actual measurements show both left and right channels around 27-28Ω, with needle movements perfectly overlapping.
Serial numbers: 253304 / 253300
Although the last digit differs by one, this is a matched pair from the正規パッケージ (official packaging).
When creating a niko-ichi (two-into-one) unit, finding one with only a single digit difference is considered difficult.

[Measurement, Maintenance, and Customization Details]
4S Conversion Adapter: A conversion cable with a built-in 68Ω resistor is included.
Both left and right channels measure around 107-110Ω, matching to a degree where visual deviation is imperceptible, a testament to the precision of the work.
The excess 12Ω is the sum of the cable's wiring resistance, contact resistance (plug/jack), and the resistance of the tester leads. Considering the tolerance of the 1608 chip resistors themselves (±1%, etc.), this slight upward deviation is due to the physical thickness of the contacts.

Sound Quality Impact: With the ER-4S impedance of 100Ω becoming 107Ω, the output level only slightly decreases. In fact, the increased resistance alters the damping factor, further emphasizing the ER-4S's characteristic cold and precise control. Impedances exceeding 100Ω are within the acceptable range for the intended design of the 4S conversion.
Even genuine 4S models have variations of 100-105Ω due to individual differences. A reading of 107Ω actually serves as evidence of thorough noise reduction and emphasis on control, enhancing the practical value of the unit.

Double Protection Rigging: The weak point at the base of the 2-pin connector has been double repaired and reinforced with heat-shrink tubing containing adhesive. This ensures rigidity capable of withstanding professional use.

Filter Replacement: Internal filters have been replaced with new ones. Additionally, two spare filters and tools are included, allowing for long-term use without purchasing additional maintenance parts.

Case Rebuild: The peeling inside the genuine hard case has been repaired with fabric adhesive.

[Set Contents]
ER-4P Unit (with new filters)
Custom-made 68Ω (ER-4S) Conversion Adapter
Hard Case (internally repaired)
Genuine Carrying Case
2x Replacement Filters / 2x Replacement Tools
Clip