LDR1B.V2 Balanced Passive Preamp


The V2 model has been discontinued and replaced by the updated LDR1B.V25 model which can be found here. 

The LDR1B.V2 Passive Preamplifier is a fully balanced audiophile grade passive (unity gain) single input, dual (parallel) output preamp/volume controller designed around Tortuga Audio’s third generation light dependent resistor (LDR) technology. The LDR1B.V2 is a single input, dual output balanced version of the LDR3.V2.

SKU: LDR1B.V2 Category: Tag:
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Balanced Passive Preamp

The LDR1B.V2 Balanced Passive Preamp is a fully balanced passive preamplifier designed around Tortuga Audio’s third generation light dependent resistor (LDR) technology. The LDR1B.V2 is a unity gain (no active amplification) preamp with a single input and dual outputs. It is a balanced version of the LDR3.V2.

We believe the LDR1B.V2 may be our best sounding LDR preamp yet with all the benefits of true balanced attenuation plus the simplicity of no input switching hardware and straight in/out signal paths.

The LDR1B.V2 comes in silver anodized (as shown) and also black anodized, and lacquered bamboo front panels with Neutrik XLRs signal jacks in the rear panels.

Subjective Performance


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 Tortuga LDR passive sound.

Compared To Other Types of Passives

The consensus of customers and reviewers is you can expect performance  that is superior to conventional passive preamps utilizing even the best audiophile grade potentiometers, stepped resistive attenuators or even most transformer based volume controls.

Compared To Active Preamps

Independent reviewers have found that the Tortuga 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

The LDR1B.V2 is a true passive preamp insofar as 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

The LDR1B.V2 is built with our 3rd generation LDR3x (V2.1) preamp controller which employs microprocessor controlled analog light dependent resistors to provide audio attenuation and input switching with unparalleled audio quality.

Auto Calibration

Similar to tubes, LDRs are analog devices subject to aging and drifting over time. Unlike tubes, our preamps have self-contained auto-calibration to keep the unit in precise calibration. The ability to self-calibrate assurance that the preamp will hold its value over the long haul.

Software Updates via USB

If warranted, software can be easily updated by the customer via a USB port located on the rear panel. Software updates can downloaded from our website and uploaded into the LDRx from a laptop or desktop PC. Eventually, we hope to make the possible from a Mac as well.

Replaceable LDR Modules

While the useful life expectancy of LDRs are estimated to be upwards of 50,000 hours, just like tubes, some may fail earlier or go sufficiently out of spec over time to warrant replacement. And just like tubes, our LDR Modules are easily replaceable ensuring the lasting value of your passive preamp investment.

Available Options

  • Front Panel:
    • Clear silver anodized aluminum
    • Black anodized aluminum
    • Bamboo
  • Power Supply
    • US Domestic | 120 VAC – 12 VDC 0.5 amp linear regulated external “wall-wart” style power supply – 2.1mm pin (positive)
    • International | 100 or 240 VAC – 12 VDC 1.0 amp switching power supply “brick” with detachable IEC power cord with US AC plug – 2.1mm pin (positive)


  • Preamplifier Type: Passive unity gain without buffer | attenuation via light dependent resistors (LDRs) in an LPad configuration
  • Attenuation Range: –60 dB  to 0 dB in a 70 step attenuation schedule (see impedance/attenuation diagram below)
  • Compatible Amplifiers:  Works best with tube or solid state amps having input impedance of 20k ohms or higher
  • Impedance Characteristics: 20k ohms with ability to optimize impedance between 1 and 100k per channel
  • Control System: Software based 8 bit digital microcontroller driving 12 bit digital-to-analog volume control
  • Software :  Updateable via download from website and upload via USB cable from 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 if warranted
  • Display:  Dual numerical displays (blue) providing volume and status information
  • Control Methods & Functions:  Remotely  controlled via the elegantly simple Apple Remote | Front panel control via rotary encoder with integral push button switch
    • Power on/off toggle
    • Volume raise/lower
    • Mute/UnMute (with smooth ramping of volume)
    • Channel balance adjust & reset
    • Display brightness raise/lower
    • Channel input select
    • Auto calibration start/stop
    • Remote pairing (enabled via encoder bush button only)
  • Power Supply:
    • 115 VAC input, 12 VDC 0.5A output external “wall-wart” style with 5mm barrel plug with 2.1mm pin
    • 240VAC input, 12 VDC 1.0A output external switch mode “brick” style with 5mm barrel plug with 2.1 pin and detachable/replaceable IEC USA power cord
    • Low noise/ripple – maximum +/- 20 mv
  • 12 Volt Trigger Out: Heavy duty chrome plated through-hole threaded phone jack provide 12 volt signal when unit turned on
  • USB Port:  Dual type A USB ports updating control software if warranted.
  • Point-to-point Wiring:   All internal point-to-point wiring of power & audio I/O to PCB  utilizes milspec teflon insulated silvered copper wire. Optional Neotech UP-OCC solid copper wire is available for hookup of the audio signal path.
  • Inputs/Outputs: 
    • Inputs: 1 balanced XLR input
    • Outputs: 2 parallel balanced XLDR outputs
  • Audio Connectors: Standard black Neutrik brass/bronze XLR connectors
  • Enclosure:
    • Robust black powder-coated uni-boxy extruded aluminum box
    • 0.1 inch black anodized milled aluminum rear panel
    • 0.25 inch anodized milled aluminum or 0.375 3-ply bamboo front panel
    • Dark acrylic see-through front panel accent/inlay in front of display modules
    • Heavy duty non-slip black polyurethane rubber feet | it stays where you put it
  • Size (shipped package): Width – 8″ | Length – 12″ | Height – 6″
  • Size (unit): Width – 6″ | Depth – 8″ | Height – 3.5″
  • Weight (shipped package): ~7 lbs
  • Weight (unit): ~4 lbs
  • Items Included: Preamplifier | Apple Remote | External Power Supply | USB Cord

ldr3x.v2 attenuation and impedance curves

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