LDR300x.V3 Passive or Active Preamp


The LDR300x.V3 is an affordable high performance LDR (light dependent resistor) preamp available as either a passive or active type for single-ended (RCA) 2-channel stereo applications for up to 3 separate switchable single-ended (RCA) sources.

Remote controlled (Apple remote) or from the front panel (rotary encoder) with a high contrast, white-on-black, interactive menu driven OLED display.

The passive model utilizes our latest ePot.V3 stepped attenuator/controller with precision closed loop LDR current control for arguably the best sounding purely resistive passive attenuator available today.  The active model adds a minimalist solid state gain plus JFET buffer stage that delivers power when and where you need it with no impedance concerns or cable length limitations.


Mains AC Voltage Level (120 or 240 VAC) *

Output capacitor upgrade options

Takes the performance of your active preamp to the next level with a high quality output capacitor upgrade

Oil Impregnated Metallized Polypropylene film capacitor...."one of the most transparent and musical oil capacitors ever made".

Copper Foil & Fluropolymer film capacitors - the ultimate upgrade to "the soul of the music"

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SKU: LDR300x.V3 Categories: ,


A flexible passive or active preamp

The “x” in the LDR300x stands for fle”x”ible in that the LDR300x is available as either a passive or active preamp for single-ended (RCA) 2-channel stereo applications able to switch between 3 single-ended line-level (RCA) sources.

If  you purchase the passive version you can opt later to convert to an active by adding a solid state buffer board.  If you have an active version you can bypass the active buffer and operate as a passive by swapping 2 internal jumpers.

A great sounding preamp

The LDR300x delivers exceptional high fidelity the belies its small size and understated packaging.  Built around our latest ePot.V3 Max stepped attenuator & preamp controller, the LDR300x is arguably our best sounding preamp to date whose subjective performance will please even the most discriminating listener.

An affordable preamp

In redesigning our previous LDR3 into the LDR300x we sought to retain and improve upon elements that really mattered sonically while forgoing things that raised costs with dubious sonic benefits. As a result we are able to offer the LDR300x at a more aggressive price as our new flagship value line preamp product.

Advanced ePot.V3 LDR stepped attenuator

The heart of the LDR300x is our latest preamp attenuator/controller, the ePot.V3 Max (the “V3” or “Max”  ). The V3 is the culmination of over a year of development and refinement of our evolving 10+ year LDR attenuation technology. The V3 combines exceptional sonic performance in an integrated, software driven, preamp controller that includes input switching, remote control and a menu driven interactive high contrast OLED display interface.

Features of the ePot.V3 Max include:

  • 100 step attenuator over 60 dB range
  • Smooth volume stepping with no sonic artifacts
  • No mechanical switches in the signal path
  • Menu driven visual control with high contrast 256 x 64 OLED display
  • LDR (light dependent resistor) attenuation
    • precision closed loop LDR current control
    • integrated offline self calibration of the LDRs
    • replaceable plug-in LDR module
  • Switch between 6 single-ended stereo sources (3 in the LDR300x)
  • Remote controlled (Apple infrared remote)
  • Manual control via rotary encoder with integral push button
  • Smooth muting/unmuting
  • Left/right channel balance  (+/- 10 db)
  • Updateable firmware

High performance SSPB.V2 solid state JFET buffer

Combined with the ePot.V3 front end, the active SSPB.V2 Solid State Preamp Buffer (the “SSPB” or “buffer”) delivers robust current drive to enhance the performance when a passive attenuator connected to sources with less robust drives may not satisfy.

The SSPB.V2 employs a high performance audio op amp input stage with just the right amount of gain to ensure ample volume control headroom without introducing noise. Gain can even be optimized through the use of plug-in gain modules including the ability to go with unity gain if desired. The op amp employs an 8-pin DIP socket so op amp enthusiasts who are so inclined can explore alternatives.

The buffer output stage employs a discrete high performance LSK170 JFET transistor that provides robust current amplification with low output impedance and minimal DC offset.

A dedicated 2 stage split voltage power supply powers both the op amp input stage JFET output stage. This power supply is separate from the power supply for the ePot.V3 attenuator/controller.

sspb.v2 solid state preamp buffer simplified schematic
(the JFET in the above image is mislabeled – it’s an LSK170)


(coming soon)

Weight 7 lbs
Dimensions 14 × 8 × 4 in
Preamp type | passive or active?

Passive, Active

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