The latest offering from Rupert Neve Designs packs a range of their renowned tone-shaping circuits into a single, versatile processor. Described as the ultimate tool for musical colouration, the Master Bus Transformer combines EQ, compression and stereo width sections with the latest iteration of the company’s acclaimed Silk circuitry.

Input & EQ

The Master Bus Transformer’s first section houses a ±12dB Input Trim control and a high-pass filter that can be set between 15 and 150 Hz. An LED provides a visual indication of the signal level after the Input Trim control, illuminating green when the signal reaches -20dBu, and turning red once it exceeds +23dB.

A two-band shelf EQ section follows, which RND say has been designed with simplicity and elegance in mind, offering gentle slopes and minimal phase shifts. Each band has a ±9dB gain range, with the low and high band’s corner frequencies variable between 30 and 240Hz, and 3 and 24 kHz, respectively.

Compressor

The next section, Color Comp, features a new optical compressor design which promises to excel at accentuating the non-linear distortion and ‘colourful’ characteristics introduced by its opto cell. A push-button switch provides a choice of 2:1 (LO) or 5:1 (HI) ratios, and a Release control offers times ranging from 100ms to 1.5 seconds.

The compressor’s threshold can be set between 0 and +24 dBu, with gain reduction indicated by an LED. The company say that the section will introduce audible non-linear harmonic content even with just a touch of gain reduction, and recommend listening with it engaged even when no gain reduction is visible. The effect will, of course, become increasingly obvious at more extreme settings.

A high-pass filter ranging from 20 to 350 Hz can be engaged in the compressor’s side-chain to prevent low-frequency content from triggering the processing, and a Blend control allows users to easily dial in some parallel compression. The section is also equipped with 20dB of Class-A make-up gain, which in addition to matching the input and output levels of the section, can also be used to drive the Super Silk section’s interstage transformers even harder for more extreme effects.

Stereo Width

The MBP’s Width section has been designed to increase a signal’s perceived stereo spread without losing any low-end focus. Although inspired by the Stereo Field Editor (SFE) controls found on the company’s award-winning Master Buss Processor, the circuitry featured here has two key differences: firstly, the Width control is additive only, with a greater range allowing more extreme operation, and secondly, there is a variable 50 to 800Hz high-pass filter which allows low frequencies to be kept central in the mix. Additionally, there is subtle tapering of high-frequency content in the width signal to avoid harsher tones being overemphasised.

Super Silk & Output

Introduced almost twenty years ago, the company’s Silk circuitry has become a firm favourite of many users. It has evolved over time from a simple on/off switch to selectable Red and Blue modes that each emphasise different frequency ranges, as well as gaining a variable Texture control along the way. The latest advancement, Super Silk, features independent variable Blue, Red and Harmonics controls, along with a Zener Drive switch.

In previous designs, the Silk circuitry has utilised a device’s output transformers. When designing the MBT, however, RND decided to to include an extra set of transformers to allow for even greater control and flexibility. The new design means that signals can be driven into Super Silk for more dynamic saturation and transient clipping, and can be attenuated afterwards to maintain a sensible gain structure using an Output Trim control.

As before, Silk Red accentuates harmonics in the upper mid and high frequencies, and Silk Blue focuses on the low & low-mid frequencies, whilst the Harmonics control interacts with both circuits, saturating the device’s interstage transformers. The new Zener Drive function is a diode-based asymmetrical soft clip circuit that introduces mostly odd harmonics content as the signal approaches the edge of the MBT’s headroom, resulting in a more aggressive tonality.

I/O

The MBT features balanced line-level inputs and outputs on XLR connectors, and is capable of handling an input level of +26.8dBu and delivering an output level of +25.5dBu (both measured at 1kHz). Mains power is accepted via an IEC inlet, and a ground lift switch isolates Pin 1 of the XLR outputs from the chassis to combat ground loops.