Dan D’Agostino RELENTLESS PREAMPLIFIER

Unrelenting Perfection

The Relentless Preamplifier represents the ultimate preamplifier design, playing a critical role in the reproduction stage when the music signal is particularly susceptible to compromise. The use of three separate chassis—a dedicated audio chassis for each channel separated by a power supply/control section—addresses these challenges and brings other benefits as well.

A Substantial Power Supply

Positioned between the two audio channels, the power supply has nearly as much power supply capability as many power amplifiers. Extensive electrical and magnetic shielding keeps radiated interference out of critical preamplifier circuits. Internal line conditioning circuitry filters RF noise on the AC power and compensates for asymmetric power waveforms and DC on the mains. Power comes from two 150 VA toroidal transformers—one dedicated to the analog circuitry and one for the digital and control circuitry. These transformers drive an 8-amp bridge rectifier and 26,400μF of filter capacitance. The two regulators for the analog stages are scaled-down versions of those used in the Relentless Series amplifiers.

The input stage in each mono preamplifier is the result of a design experiment for a circuit that hadn’t been used in any previous D’Agostino preamplifier. The audio circuit topology uses a discrete differential FET input stage featuring a voltage input signal capability of an extraordinary 30 volts. With an input impedance of over 1 MOhm, the preamplifier’s front end is immune to source-related electrical issues. Developed specifically for the Relentless Preamplifier, a unique circuit maintains a stable bias so that temperature-related anomalies are offset to preserve performance during extended listening. 

Featuring only balanced XLR inputs, the Relentless Preamplifier topology rejects common-mode input noise over an unusually wide bandwidth. All signal gain is realized in the current domain using proprietary multiple-output current mirrors with nearly 30 times the linearity of other designs. The use of four-layer circuit boards dramatically reduces distortion and propagation levels as compared to more commonplace, two-layer boards. The analog and digital circuit elements are isolated, including ground planes, from each other. Where necessary, digital control signals are optically coupled to analog circuits. The signal switching relays are hermetically sealed and use gold-plated contacts for maximum signal integrity. Utilizing no negative feedback anywhere, core D’Agostino circuit concepts include a signal path that is fully complementary and balanced from input to output, achieving a frequency response flat to 120 kHz. The overall result is a musically dense and dynamically rich signal presented to the balanced outputs. 

Separate But Linked

The most striking element of the Relentless Preamplifier is the pair of volume controls fronting the two audio chassis. Each volume control is constructed using 14 separate metal components ensuring the smoothest response and control of the military-grade, high-linearity solid-state switches and discrete precision resistors employed in the volume circuit. Bandwidth and transient response are completely unaffected by the volume setting. As a result, high frequencies sound smooth and extended, and music emerges from jet-black silence. The volume settings are displayed by elegant, Swiss watch-inspired volume wands or numerically, from 0 to 99.

Two Preamplifiers in One

This two-source/two-zone preamplifier can simultaneously control the switching and volume of two sources in two separate rooms or zones. Listening sources may be two analog sources, or when equipped with the optional Digital Streaming Module, one digital source and one analog source. In a one-zone system, either volume control will adjust volume in the main room or Zone 1. If two-zone operation is desired, the upper volume control manages Zone 1 and the lower volume control adjusts Zone 2.

Preamplifier Status in Your Hand

Housed in precision-machined aluminum and Delrin®, the Relentless Preamplifier’s remote control is a Bluetooth 5.0BLE-enabled device, rechargeable via USB, boasting an ergonomic design and featuring an LCD screen. Offering bi-directional functionality, the remote mirrors the information on the Relentless Preamplifier’s front panel onto its own display screen, including input, volume, and balance settings.

Integration Features

The Relentless Preamplifier can be the nucleus of the finest home theater system. Input Three can be configured for Theater Bypass, where the volume control is bypassed and the main loudspeakers are controlled by the connected surround-sound processor. RS-232 and12-volt triggers facilitate integration into advanced home control systems. Additional DC power outputs for future products, as well as two programming ports, allow future performance options. 

Optional Digital Streaming Module (DSM)

The optional Digital Streaming Module adds connectivity for legacy sources, USB functionality, and premier streaming capability. Field upgradeable, the DSM adds SPDIF coaxial, Optical, USB-A, and RJ-45 and Wi-Fi network inputs. For latency-free playback of high-resolution network content, 10/100/1000 GB Ethernet is supported. 

Customized apps for iOS devices provide easy control of music collections, streaming content, and unit control. Subscription streaming services Tidal, Qobuz, and Spotify are native within the app. With appropriately encoded music files, MQA decoding is standard. Additionally, Roon Music management is also available as an alternative music management program. 

Completely isolated from the analog circuitry, the DSM is housed in the power supply/control chassis. Requiring three separate circuit boards, the core element is a pair of DACs configured in differential mode, each one configured to handle the positive and negative signals for each channel. Capable of handling today’s highest resolution sources, PCM signals up to 32 bit/384 kHz and DSD signals up to DSD256 (11.2 MHz) are decoded natively. Often overlooked or downplayed, the analog section of a DAC significantly impacts the final sonic performance of digital music. Internal balanced connections carry the final analog signal to the connecting feet and onward to each audio chassis. From here, the analog music signal takes advantage of the entire power and analog circuitry within the three chassis of the Relentless Preamplifier. 

Coupling innovative circuitry, distinctive materials, and artisan manufacturing excellence in a sophisticated architecture, the Relentless Preamplifier is the perfect centerpiece for the ultimate music system.