LDRxB.V25 Balanced Passive Preamp


Note: This preamp model is no longer available and has been replaced by the LDR3000P.V25 High Performance Passive Preamp

The LDRxB.V25 is a high performance balanced passive preamp that combines Tortuga Audio’s advanced LDR (light dependent resistor) attenuation technology with elegant contemporary styling designed to satisfy the most demanding audio enthusiast. The LDRxB accommodates up to 3 balanced XLR inputs and a single unbalanced RCA input. Dual (parallel) balanced XLR outputs are provided along with  a single RCA output.

The LDRxB.V25 delivers clear, articulate and honest sound with a dead quiet background together with satisfying dynamics and surprisingly powerful bass.

If you haven’t experienced a high performance balanced passive preamp, find out what your’re missing with Tortuga Audio’s LDRxB.V25

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SKU: LDRxB-V25 Category:
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A Really Nice Balanced Passive Preamp

The LDRxB.V25 is Tortuga Audio’s flagship balanced passive preamp for the discerning audiophile with balanced audio gear who appreciates what is possible from a high performance balanced passive preamplifier. The V25 version of the LDRxB is an update to the original model and employs our most advanced LDR.V25 preamp controller board along with an updated graphical OLED display.

The result is a beautiful elegant  audiophile grade balanced passive preamp that combines advanced LDR (light dependent resistor) technology with elegant contemporary styling designed to satisfy the most demanding audio enthusiast. .

What To Expect

If you haven’t tried a balanced passive preamp before, or even if you’re already a fan of passive preamps, the LDRxB.V25 will likely surprise and delight you.

The words people use to describe our LDR preamps include colorless, transparent, neutral, articulate, clear, fuzz-free, clean and natural. Paired with a high quality source component you can expect satisfying dynamics, a beautiful mid-range, and surprisingly solid bass.

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 attenuators  and most transformer based volume controls.

Will the LDRxB out-perform your favorite active preamp? Ultimately, that will depend on the quality of the output stage in your source component(s) which you can only determine by trying it out.  When well matched,  you’ll be hard pressed to find a better preamp anywhere regardless of price.

Key Features

LDR Volume Control

Light Dependent Resistors (LDRs) are at the center of Tortuga Audio’s passive preamp technology. LDR based volume control deliver a clean, neutral yet satisfying sound that defies explanation but is nevertheless undeniable.  The result is a super smooth 100 step analog volume control complete with channel balance adjustment, muting and mono mode.

OLED Display & Remote Control

We’ve done away with all conventional buttons, dials and switches and replaced them with a single multi-function encoder control knob and a contemporary menu driven OLED display and a simple 7 button Apple remote. Audio gear for the 21st century.

Unity Gain – No Amplification

Being a balanced passive preamp, the LDRxB has no active signal amplification stage and is thus a true unity gain preamp designed solely to provide passive volume control and input switching. The absence of actual signal amplification (gain) is rarely a problem since nearly all source components have sufficient line stage output voltage to drive most amplifiers to ear splitting volume levels. Why amplify when you don’t need to. Go passive.

Built-in LDR Calibration

Just like tubes, LDRs are analog devices subject to aging and performance drifting over time. Unlike tubes, the LDRxB has built-in calibration to tune up the the LDRs as they age and to calibrate a new one if it requires replacement (all LDR modules are plug-in replaceable). This provides added assurance that the LDRxB will hold its value over the long haul.

No Relays In The Signal Path

The LDRxB also employs LDRs for audio input switching eliminating the use of electro-mechanical relays and their mechanical switching interface points.

Replaceable Plug-in LDR Modules

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

Firmware Update via USB

The LDRxB is controlled by a software driven microcontroller. If warranted, software (firmware) can be easily updated by the customer via a pair of USB ports located on the rear panel. Software updates can downloaded from our website and uploaded into the LDRxB using a simple PC application.

High Quality Stylish Enclosure

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

Neotech Point-to-Point Signal Wiring

All signal wire connections are hand-wired point-to-point using top quality 24 AWG Neotech UP-OCC solid copper hookup wire.


Attenuation typePassive series/shunt (L-Pad) voltage divider using two (2) light dependent resistors (LDRs) per channel | total of 4 attenuation LDRs for single-ended attenuation & 8 for balanced attenuation
Attenuation Range-60 db to 0 db in 99 ~0.5 dB steps plus 1 additional muting step.
LDR ModulesAll LDRs are easily replaceable plug-in modules
GainUnity (1x) gain | no amplification, processing or active manipulation of the audio signal | audio signal optically isolated from control system
BufferingNo input or output stage buffering
Self CalibrationBuilt-in calibration algorithm that calibrates the four attenuation LDRs at each of the 99 attenuation steps to compensate for any drift or aging or in the event an LDR needs to be replaced. Pre-matched LDRs are not required | Enables adjustable impedance feature
Adjustable Impedance Nominal 20k by default | User may configure up to 9 additional impedance settings adjustable between 1k and 99k each | Once additional settings are initialized user may switch between the settings with live music to optimize input impedance for their system.
Number of Channels 2 channel stereo
Channel Balance Adjustment+/- 10 dB channel balance adjustment range in 0.6 dB increments
Channel Balance AccuracyWithin 0.5 db over full attenuation range
Channel IsolationEach channel signal is 100% isolated and independent from the other | audio signal grounds are tied to a common star ground point
Audio Inputs/Outputs** INPUTS **
Balanced - 3 pair of Neutrik XLR
Single Ended - 1 pair of Cardas RCA
Balanced - 2 pair of Neutrik XLR wired in parallel
Single Ended - 1 pair of Cardas RCA from single phase of balanced output
Input SwitchingInput switching via LDRs | typical 50 ohm resistance when on | in excess of 5 megaohms when off | no relays in signal path | total of 6 LDRs used for input switching
Output IsolationOutput signal is switched off and isolated when AutoCalibration is enabled | Switching is done using LDRs | no relays in signal path | Isolation between inputs and output when switched off in excess of 10 megaohms | total of 2 LDRs used for output isolation
Total Harmonic DistortionTypically ~0.2% under normal operating conditions
Power SupplyUS : Nominal 12 volts DC linear regulated "wall wart" rated at 0.5 amp
International: Nominal 12 volts DC switching "wall wart" rated at 1.0 amp
Power Regulation 2 stage regulation | 5 V 1st stage via low noise switch mode regulator followed by 3.3 V low noise 2nd stage linear regulator
ProcessorARM M3 Cortex 32 bit microcontroller running at 72 MHz
Controls | RemoteAccepts control inputs from silver Apple infrared remote or equivalent using 38 kHz NEC protocol and Apple commands | infrared commands received via infrared receiver module located on right display module.
Controls | EncoderAccepts control inputs from rotary stepped encoder with integral push button switch | encoder attaches to right display module
Display Interactive menu driven 256 x 64 pixel white graphic OLED (Organic Light Emitting Diode) display
Mono ModeUser can switch between stereo and mono mode via the remote | switching uses an LDR switch
Firmware UpdatesUser can update firmware using PC based HID bootloader application (no MAC option) | User can download the bootloader application and updated firmware files from company website | Firmware is custom interrupt driven application code written in the C language provided in hex format
USB PortType A female USB port allows processor to communicate with external HID bootloader application for updating firmware | USB cable provided
WiFi Module | Future Future ability to plug in a simple WiFi module to allow control via smartphone app | will require WiFi module, firmware update, and upgrade to future OLED display
Trigger OutOutputs a 12 V DC signal when unit is turned on. Signal can be used to turn other devices on/off that are equipped with a Trigger Input.
Enclosure* Milled anodized aluminum front panel with acrylic inlay lens
* Anodized aluminum rear panel
* Powder coated top panel
* Lacquer finished 3-ply bamboo side panels
* 4 non-skid bamboo feet
Printed Circuit BoardHigh quality nickel immersion gold solder printed circuit boards with blue solder mask
SolderLead free solder with 3% or higher silver content
ROHSCompliant or exempted
FusesNo internal or external fuses
Ambient RequirementsPreamp must be operated in a stable, dry indoor environment only with stable ambient temperature within 60-90 degree F
Dimensions~ 3.75 inches tall | ~12.5 inches wide | ~ 10.5 inches deep
Weight~8 pounds as shipped
Items IncludedPreamplifier | Apple Remote | External power supply | USB Male A to Male A Cord

LDR3000P.V25 High Performance Passive Preamp

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