【Professional Spec】SONY MDR-CD900ST

This is a modified MDR-CD900ST, newly purchased, with improvements made to address weak bass, enhance left-right balance, increase resolution, enable re-cabling, and make it foldable.

The modifications include all the services offered on the Umbrella Company website.

Specifically:
- Cable converted from 3-core to 4-core: By making it 4-core up to the point of plugging into equipment, common impedance is reduced to the absolute minimum.
- Air release port drilling (pinhole).
- Optimized driver unit angles for left and right.
- Installation of a dummy cable inside the right unit.
- Left and right Perfect Symmetry Mod.
- Driver unit tuning.

These are the tune-up services proposed by the Umbrella Company.

In addition to these:
- Re-cabling.
- Installation of a dummy terminal and wiring in the right unit to equalize left-right balance. (The headphone side uses ground-separated wiring).

*Note: Re-cabling involves adding a plug inside the unit, creating a significant difference in internal space between left and right. Therefore, to achieve left-right balance with re-cabling, it is essential to install a similar dummy in the right unit. However, modifications that go this far are rare.

- Foldable design: MDR-7506 parts are not available individually, so they were repurposed from a relatively good condition used item. The headband has been replaced, making it more convenient for carrying.
- Left and right crossover wires upgraded to OYAIDE HPC-28-2U V2.
- Solder used is OYAIDE SS-47.
- Plugs are top-of-the-line silver rhodium-plated: OYAIDE P-3.5R and OYAIDE P-3.5/4SR.
- Ear pads are new 7506 (determined to be the best after listening comparison).

As a result, the weaknesses of the standard MDR-CD900ST have been eliminated, and the resolution has been significantly improved. Furthermore, by changing to a foldable design, it has become more compact and convenient for storage and transport.