Reference Stereo Preamplifier

L5 Reference Stereo Preamplifier

Following in the BSC design tradition, the L5 preamplfier represents a different approach to conventional preamplifier architecture.

The L5 preamplifier utilizes a multi-chassis solution for noise and crosstalk reduction, all consolidated on its own custom designed platform. The (i) Power Supply, (ii) Control System, and (iii) Audio Circuitry are separated into individual machined aluminum enclosures.

  • The Power Supply is based around massive, but separate, internal Analog and Digital power sections. The L5 preamplifier remains stable even in the most challenging electrical environments.
  • The Control System is located in a physically separate command module that houses the following key control interfaces: volume control, remote control, input selection, RC5/RS232, LED display, and other basic control interfaces. This separation significantly reduces the occurrence of parasitic noise or other similar interference.
  • The Audio Circuity is physically isolated in a 3rd separate chassis, which is electrically and mechanically disconnected from the other two chassis.

All three enclosures are centrally located on a solid aluminum base, minimizing the overall space requirements.

The L5 preamplifier relies on Discrete, Complimentary, Direct coupled, Differential and Class A circuitry from input to output to ensure the very best in signal transmission speed and accuracy.

At the heart of every preamplifier is the volume control, and to this end, BSC Audio pulled out all of the stops to create an incredibly accurate and mechanically stimulating linear volume control. Based on a precision R2R resistor network, volume position is selected via the motorized linear slide mechanism. The volume control offers 255 quarter-decibel steps to make finding the perfect listening level much more simple.

The L5 is a perfect complement to any audio system but in particular to our M5 or S5 amplifiers where it transfers the speed, dynamics and sense of palpability fully realized only through a BSC Audio Class A playback system.

Inputs: 2 balanced, 2 single-ended, 1 combo.
Outputs: 2 balanced, 1 single-ended
Input Impedance: 1M Ω
Output Impedance: 1,000 Ω
Gain: -64.00 dB to +10.00 dB
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Multi-chassis Design

The L5 preamplifier is not the first preamplifier to adopt a multi-chassis solution for noise and cross-talk contamination, but may be the first to consolidate its components into one organized space. The traditional problem with multiple chassis is where to locate them in the typically overcrowded rack or space-lean environment. BSC Audio has avoided this problem by providing an integrated Base that unites the three separate chassis modules onto one pedestal. Additionally, all of the inter-chassis wiring is neatly tucked away inside of the base, joined only by short cables connected to each separate chassis.

BSC Audio has taken the concept of power supply isolation a step further by not only placing the power supply in its own, separate chassis, but by also isolating the digital control circuitry and placing it into a separate chassis as well. In this configuration, the Analog and Digital sections of the preamplifier are completely isolated.

The three independent aluminum modules rest atop the aluminum base unit, separated by machined DELRIN™ feet.

The increased electrical and mechanical decoupling translates into a lower ambient noise floor and an increase in low level inner detail, adding handsomely to the listening experience.

Power Supply

The power supply chassis is comprised of two independent power sections: Analog power and Digital power.

Analog Power - This section is dedicated to powering the analog circuitry, including all of the audio input and audio output circuit boards. The analog power supply is built around a low noise, 150 VA toroidal transformer feeding four double-regulated analog circuit power supplies, as well as a regulated motor control supply.

Digital Power - This section is dedicated to powering the digital switching and logic circuitry as well as the volume control and input relay select logic. The digital supply utilizes a low noise, high current 75 VA toroidal transformer to feed the critical digital bus voltages. An overbuilt, regulated design ensures precision performance.


The control chassis contains the microprocessor and associated display related circuitry. A long-life 7-segment LED display reduces noise contamination and enables maximum visibility. The programmable interface allows for future software upgrades via a convenient RS-232 Port.

The control unit also houses direct RS-232 and RC-5 communication, as well as input selection and operation adjustments.


The audio module contains all of the critical input, output, and volume control circuitry. All of the circuit boards are multi-layer with gold plated traces. Circuit boards are mounted in a centrally located area to reduce long signal connections. The modular design allows for easy updates or circuitry upgrades by an authorized BSC Audio Dealer or Distributor should they become available in the future.

The 255 step volume control is also a separate circuit board centrally located to minimize connection distance. The motorized, linear volume control assembly is located at the front of the chassis, eliminating any interaction with the audio circuitry.

Input and output connections located at the back of the chassis transfer the delicate audio signals through the highest quality XLR and RCA connectors.

Input and Output Stages

The input and output stages of the L5 preamplifier are all discrete and complimentary. Simply put, the circuitry is done with standard transistors, resistors and capacitors, relying on the circuit design to achieve the desired performance as opposed to a packaged component like an OP amp that forces you to work within another designer’s sound. Complimentary circuits use transistors that are natively designed to work with positive or negative signals respectively, and this ensures the greatest linearity between the components, thus allowing the circuit to “breath” naturally. Class A biased, differential circuitry (balanced) is used from input to output, to further reduce any potential signal contamination.

The first input gain stage has a High input impedance, allowing a very simple load for any front end component while the output stage of the L5 preamplifier is extremely fast and powerful, that can easily drive long lengths of interconnect cable and consequently an amplifier input. Additionally, there are no capacitors in the signal path throughout the L5 preamplifier circuitry eliminating any additional coloration due to component interference.

Volume Control

The centerpiece of the L5 preamplifier is the volume control. From the motorized linear sliding mechanism to the discrete precision Resistor-to-Resistor (R2R) network, no expense was spared in its implementation. The linear volume control was directly influenced by studio recording consoles utilized on virtually all of our favorite recordings. The flying fader provides instant visual stimulation, as well as precision, motorized control. The L5 preamplifier linear volume control is comprised of a custom cage machined from a solid block of aluminum, housing the linear bearing based slide mechanism and associated components. A high speed, high torque DC motor controls the linear motion through a Kevlar belt. Volume position is indicated via a precision optical encoder, which in turn determines the correct resistor value combination for the given gain level. The R2R network consists of several high-precision resistors switched via very fast, precision relays in combinations to raise or lower analog signal level. This, in our opinion, is the very best way to attenuate gain in a high performance audio product.


16.50 in (W) x 10.90 in (H) x 20.75 in (D)

or 419.10 mm (W) x 276.86 mm (H) x 527.05 mm (D)

Full Specifications

Inputs: 2 balanced via XLR connectors, 2 single-ended via RCA connectors, 1 Universal/ Theater Throughput via XLR or RCA
Outputs: 2 balanced via XLR connectors, 1 single-ended via RCA connectors
Input Impedance: 1M Ω
Output Impedance: 1K Ω
Frequency Response: -3dB @ 10Hz – 100KHz
Signal to Noise Ratio: > 116.00 dB, 1K Ref 2V
Gain: -64.00 dB to +10.00 dB
Volume Steps: 255 steps in 0.25 dB increments
Power Consumption: < 75 W
Dimensions: 16.50 in (W) x 10.90 in (H) x 20.75 in (D)
or 419.10 mm (W) x 276.86 mm (H) x 527.05 mm (D)
Weights: unit only weight: 86.00 lbs (39.01 kg)
shipping weight in carton: 92.00 lbs (41.73 kg)