Rupert Neve Designs 5025 Dual Shelford Mic Preamp  From Neve

Like Rupert’s designs from his time in Little Shelford, the Dual Shelford Pre uses a custom step-up transformer on the microphone input that provides the first 15 dB of gain. This specially-designed transformer, along with its careful integration with the surrounding class-A circuitry, is critical to the amplifier’s bold, mid-focused magic that can be heard on thousands of classic recordings.

While the majority of the harmonic richness found in Rupert’s designs is a product of the output transformer and surrounding class-A amplifiers, this step-up input transformer also imparts a unique musical enhancement of its own. The technical reasons for this are primarily a result of the reactive impedance characteristic of the input transformer and how that interacts with the connected microphone, resulting in subtle, non-linear harmonic enhancement of the lows and an unmistakable sweetness in the high frequencies.

While creating the input stage for the Shelford Channel and Dual Shelford Pre, the goal was not merely to recreate the classic designs, but to advance them: combining the unmistakable sound of the vintage technology with wide-bandwidth frequency response, consistently excellent amplifier performance at any gain setting, and extremely low noise operation. 

To achieve this, the custom transformer designs were carefully optimized and complete MuMetal shielding of the input transformer was implemented. The resulting preamplifier is flat from below 10Hz to above 60kHz, resulting in the purest possible tone and the very highest levels of versatility.

The Dual Output Level Transformers

Complementing the Silk circuit are the custom-designed output transformers, which use Rupert Neve Designs’ distinctive dual output topology. These offer both Main (+26 dBu) and -6dB (+20 dBu) outputs, allowing the engineer to drive the preamps fully into classic transformer saturation without clipping converters and other devices later in the chain.

The main outputs are designed to capture a more pristine sound at high levels, avoiding any nonlinear coloration of the output stage. The -6dB outputs allow an engineer to fully drive the Shelford – adding dynamic tone with these same nonlinear “colorations” – without clipping most professional interfaces. On drums, vocals, guitars and other instruments, these outputs let you easily hit the transformer’s “sweet spot” of nonlinear harmonic content, bringing a recorded performance to life in a way that other preamps simply cannot match.

Mic Gain

This 12-way precision rotary switch controls gain from 0 to 66 dB in 6 dB steps.

Trim

This rotary switch provides further continuous gain adjustment over a range of +/– 6 dB.

48V

This push button switch engages phantom power on the microphone input.

Polarity

This push button switch inverts the polarity of the signal path. It illuminates when engaged. (The symbol “Ø” is often used to denote opposite polarity.)

HPF / HPF FREQ

The HPF switch engages a 12dB per octave high pass filter. The HPF FREQ potentiometer is variable from 20Hz to 250Hz, and can be used to filter out unwanted low frequencies, or in conjunction with the EQ to help shape source material. Note that engaging the HPF to S/C switch moves the HPF from the primary signal path to the compressor side-chain signal path.

Silk / Texture

Pushing the Silk button cycles the Silk modes from Red to Blue to OFF. Silk reduces the negative feedback on the output transformer, adding harmonic content as the texture is increased. Red Silk accentuates the musical harmonic saturation from the mid and high frequencies, while Blue Silk accentuates harmonics from the low and low-mid frequencies. By manipulating the Texture control, the amount of Silk can be changed from essentially absent, to roughly 4-5% THD (mostly second order) depending on how hard the output transformer is being driven.

VU Meters

The VU Meters are calibrated to display average (RMS) output levels.

Peak LED

Red indicates near clipping of the output stage.

Dual Tap Output

In addition to the MAIN full-headroom output, the -6dB output creates a rich harmonic character while reducing the risk of clipping the next device in the chain.

Gnd Lift

This switch separates the direct connection from audio signal ground to chassis earth.

Universal IEC Power Input

Works worldwide, accepting voltages from 100-240VAC.