LDRxB Balanced Passive Preamp

LDRxB Balanced Passive Preamp

Price: $2,695

This is a legacy product and is no longer produced or sold by Tortuga Audio.

This model was eventually superseded by the LDRxB.V25.

The LDRxB is an audiophile grade balanced passive preamp combining LDR (light dependent resistor) technology with elegant contemporary styling. The LDRxB comes with 3 balanced XLR inputs and dual (parallel) balanced/XLR outputs, and also accommodates a single RCA input with a single RCA output.

The LDRxB is housed in an attractive, high-quality contemporary enclosure that combines the warmth of eco-friendly renewable bamboo with black-anodized brushed aluminum panels milled from high grade stock.

The elegantly simple Apple Remote provides remote control, along with a rotary encoder with integral push-button on the front panel. Volume level and status information are shown via a pair of digital displays that are invisible when the unit is off.

If you’re looking for a single-ended/RCA model, see the LDRx.

Subjective performance

Characteristics — colorless, transparent, neutral, articulate, clear, fuzz-free, clean, natural, high resolution, great mid-range, solid bass. These are words and phrases commonly used by both customers and reviewers to describe the sound.

Compared to other passives — the consensus of customers and reviewers is performance superior to conventional passive preamps using even the best audiophile grade potentiometers, stepped resistive attenuators, or most transformer-based volume controls.

Compared to active preamps — independent reviewers have found that Tortuga’s LDR passive preamps match the performance of even the finest high-end preamps costing many thousands of dollars more.

Key features under the hood

  • Optically isolated passive attenuation — there’s no amplification or buffering of the audio signal notwithstanding the presence of a power supply. Audio signals are optically isolated from both the power supply and the LDR control circuitry.

  • 3rd generation LDR technology — built with the LDR3x.V2.1 preamp controller, which uses microprocessor-controlled analog LDRs for both audio attenuation and input switching.

  • Auto calibration — similar to tubes, LDRs are analog devices subject to aging and drift over time. The LDRxB employs self-contained auto-calibration to keep the unit in precise calibration.

  • No relays in the audio signal path — the LDRxB uses LDRs for audio input switching. Auto-calibration does employ relays, but these are physically disconnected from the audio signal path during normal operation.

  • Firmware updates via USB — software can be updated by the customer via a pair of USB ports on the rear panel, downloaded from the Tortuga Audio website and uploaded from a PC (Mac support was never completed).

  • Replaceable LDR modules — LDRs have an estimated useful life upwards of 50,000 hours, but just like tubes, our LDR modules are easily replaceable, ensuring the lasting value of the preamp.

  • High quality power supply — AC mains pass through a high-performance EMI filter/choke feeding a low-EMI toroidal step-down transformer. An oversized DC filter supplies multiple high-performance switch-mode DC regulators providing quiet, stable 12V and 5V power to the controller board and peripherals.

An outside to match the inside

  • Stylish enclosure — poly-oiled bamboo side panels with black-anodized brushed aluminum front, rear, top and bottom milled from high grade stock.

  • Neutrik XLR connectors — high quality industry-standard Neutrik XLR connectors.

  • Controls — the elegantly simple 7-button Apple Remote, plus a rotary encoder with integral push-button on the front panel. Volume level and status shown via a pair of digital displays that are invisible when the unit is off.

Upgrades & customization

Because Tortuga Audio fabricates and assembles most of its products in-house, it was able to offer options, upgrades, and customizations rarely available with mass-produced audio gear. Hookup wire, for example: standard wiring was high quality Milspec teflon-insulated silver-coated copper wire, with optional 26AWG Neotech UP-OCC solid copper available for point-to-point wiring in the signal path.

Specifications

  • Preamplifier type: passive unity gain without buffer; attenuation via LDRs in an L-Pad configuration

  • Attenuation range: -60 dB to 0 dB in a 70-step attenuation schedule

  • Compatible amplifiers: works best with tube or solid state amps having input impedance of 20k ohms or higher

  • Nominal input impedance: 20k ohms

  • Control system: software-based (updateable) 8-bit digital microcontroller driving 12-bit digital-to-analog volume control

  • Software: updateable via download from the website, uploaded via USB cable from a PC

  • Auto calibration: user enabled/disabled, self-contained auto-calibration of LDRs to correct for drift/aging

  • Replaceable LDR modules: similar to tubes, LDR modules can be easily unplugged and replaced

  • Display: dual numerical displays (blue) providing volume and status information

  • Control methods & functions: remote via the Apple Remote, or front-panel rotary encoder with integral push-button switch — power on/off, volume raise/lower, mute/unmute with smooth ramping, channel balance adjust & reset, display brightness raise/lower, channel input select, auto-calibration enable/disable, remote pairing (via encoder push-button only)

  • Input switching: via LDRs — no electromechanical relays in the signal path

  • Power supply: IEC AC socket with removable cable; switchable 120/240 VAC; EMI noise suppressor/choke on AC entry; 10 VA low-noise toroidal transformer; oversized low-ripple DC filter; stable low-noise 5V and 12V DC via dual switch-mode regulators. Power draw: on < 0.4 A @ 12 VDC, off < 0.25 A @ 12 VDC

  • 12V trigger out: heavy duty chrome-plated through-hole threaded phone jack, 12V signal when the unit is on

  • USB port: for control software updates

  • Point-to-point wiring: milspec teflon-insulated silvered copper wire for power & audio I/O to PCB

  • Solder: lead-free with high silver content

  • Inputs: 3 balanced XLR, plus 1 unbalanced RCA (only 2 XLR inputs available if the RCA input is used)

  • Outputs: 2 balanced XLR, plus 1 unbalanced RCA

  • Signal conversion: internal unbalanced-to-balanced conversion done with passive transformers

  • Audio connectors: Neutrik or Cardas Gold XLR; Cardas GRFA-L rhodium over silver plated brass RCA jacks

  • Custom enclosure: poly-oiled bamboo side panels; front, rear, top and bottom milled from high grade aluminum stock; brushed and black anodizing on all visible aluminum parts; dark acrylic front panel accent/inlay in front of the display modules; MDF hockey-puck feet with non-slip black polyurethane rubber

  • Size (shipped package): 14" W x 14" D x 6" H

  • Size (unit): 12.5" W x 10.5" D x 3.75" H

  • Weight (shipped package): ~11 lbs

  • Items included: preamplifier, Apple Remote, power cord, USB cord

Owner reviews