This repository includes a set of templates, diagrams and photographs, along with an elaboration of the process to seamlessly install a balanced tonearm output for Technics SL-12x0 MK7 turntables.
Please note that any change to the turntable will most likely void your warranty. You are accepting any inherent risk that may come with modifying your turntable. These instructions are provided as a means of sharing information and adding options to what is already an excellent product.
Turntable cartridges, specifically moving coil phono cartridges, are inherently floating devices. They provide both a hot (+) and cold (-) output in addition to a separate ground (G) connection. Such a configuration provides an alternative connection method - a balanced (professional) connection could be used to further protect delicate signals (typically less than 0.5mV) against external influences and factors.
Most commerical phono stages have only unbalanced input (RCA sockets) thus not taking advantage of the cartridge being a floating device. Some turntable phono stages (phono preamplifiers) feature the ability to accept balanced input, effectively providing a way to further decrease noise and potentially improve cartridge performance.
Now, all the changes made to the turntable aim to be fully reversible.
You obviously need a Technics SL-12x0 MK7. This guide focuses only on this specific model, and not on other models in this family due to the inherent chassis differences.
- Replacement rear panel. This is a readily available spare part for Technics turntable, called "Panasonic Jack Holder" and assigned a part number "TKFE46401". The panel is available at any official service center for Technics. One can always modify the existing rear panel, but that defeats the purpose of having a reversible modification.
- XLR connectors. One could use any standard XLR connector, but this modification relies on the standard Neutrik DL series, specifically model NC3D-L-B-1.
- Wiring. No specifics on wiring, reasonable quality wire needs to be used, preferably with PTFE insulation and color coded for easier installation.
- Copper tape. (Optional) Thin, self-adhesive tape that is used to shield cavities. Typically used in guitar bulding, readily available.
This repository has a number of templates to support installation.
- Drilling template. The drilling template is fit to the outside of the plastic rear panel. Should be printed on adhesive paper and fitted to the rear panel for easier modification.
- Screening can. The modification requires that the existing screening can is removed and discarded as it does not fit the XLR connector bodies. This repository includes a 3D model for a printable screening can that needs to be lined with the copper tape to facilitate its operation. Note that the screening can is optional and should be used in RF rich environments. Typical households should not experience any issues without.
A simple wiring diagram is provided to guide wiring decisions. A few notes:
- Technics use brown to designate R-. This is different than most as the widely accepted standard uses green for R-, and that is why the diagram makes note on both.
- The ground connection is crucial towards proper balanced operation. In a balanced configuration, the separate ground wire need not be used.
The repository includes a number of photographs that follow the modification steps.
Additionally, that folder shows a rendering of the model for the screening can.