Flexible Single-Ended & Balanced Tube Preamp
Whether you have RCA gear, run with all balanced, or a mix of both, you don’t have to choose because the LDR3000T tube preamp handles both. There are 3 sets of RCA inputs and XLR inputs that you can use in any combination. The RCA and XLR outputs carry the same output signal regardless of the signal source type although the balanced output will only have one phase active (pin #2) if the input source is single-ended.
Elegantly Simple Signal Path
The single greatest challenge for any preamp is to remain true to the source material while delivering the selected and attenuated audio signal to the amplifier honestly and without editorializing. The LDR3000T achieves this by combining Tortuga Audio’s proven LDR volume/preamp controller with a hybrid zero/low gain tube input/gain stage followed by a simple yet highly effective solid-state JFET (transistor) current amplifier (output buffer).
Most tube preamps and amplifiers run their tubes at high plate voltages and current to achieve high linear gain. The truth is you need little to no gain at all in your preamp with today’s sources, amps and speakers. Because of this, we we run the LDR3000T tube at a low “slack” voltage of only 45 volts instead of 250 or even higher. At very low currents many tubes will operate linearly even at such low voltage. With a compatible tube the resulting zero/low gain sound quality is glorious indeed.
This elegantly simple design keeps the signal path short and simple without compromising performance. So you can hear more of the music and less of the hardware.
LDR Volume Control – V25
The LDR3000T is designed around our 4th generation remote controlled V25 volume/preamp controller that uses digitally controlled analog light dependent resistors (LDRs) to provide smooth 100 step volume control over a 60 dB range. Features include ramped muting, channel balance adjustment, input switching, both stereo and mono modes plus adjustable input impedance. Built-in calibration of the replaceable socketed LDRs ensures accurate attenuation, channel balance and optimal performance over the extended life of the preamp.
The LDR3000T is easy to operate via an intuitive interactive menu driven control interface designed around the 7-button Apple remote and a bright easy to see 256 x 64 pixel white-on-black graphic OLED (Organic Light Emitting Diode) display.
Tube Input/Gain Stage
The attenuated audio signal connects directly to the triode’s grid with no input coupling capacitor. We chose the 9 pin 6H30Pi Gold triode tube from Electro-Harmonix because of its growing reputation for sonic excellence, robust long-life, and the fact that it’s a contemporary tube that isn’t likely to go out of production for a long time to come.
While the 6H30 is a delightfully clean, neutral yet smoothly muscular sounding tube with just the right amount of tube euphonics, for those seeking a more lush sound, we also offer the Genalex Gold Lion E88CC/6922 triode tubes as an alternative. In fact the LDR3000T is great for tube rolling most any of the 6922 family of tubes.
A Little Gain But Only If You Need It
The only reason for your preamp to have gain (amplify the incoming signal voltage) is if your amp can’t put out enough power to drive your speakers loud enough for your needs. That is very rarely the case in the real world these days. Hence the LDR3000T has its default gain set at unity gain (0 dB). But if you do need some gain, the LDR3000T can be adjusted up to +6 dB gain (twice the voltage) for audio systems that need more volume headroom. While adjusting the gain is doable for most end users, the process to do so requires partial disassembly of the preamp and the use of a volt-ohm meter.
Matched Tubes | One For Each Stereo Channel
Each stereo channel has its own dedicated triode tube to ensure the best possible channel separation, sound stage, and stereo imaging. With single-ended audio, only half of each triode is utilized. When operating with balanced audio, each triode handles both phases of its own stereo channel.
Solid State Output Stage
The output stage is a discrete solid state current amplifier designed around a contemporary version of the vaunted Toshiba 2SK170 JFET. The JFET operates in Class A mode with a constant current source. This discrete buffer delivers powerful robust dynamics into practically any amplifier at a very low output impedance.
Robust Power Supply
The LDR3000T power supply starts with a robust linear power supply composed of a large 50 VA linear shielded toroidal transformer, oversized bridge rectifer, and almost 38,000 uF of filter capacitors. This is followed by 2 independent DC-DC switching regulators with one dedicated solely to providing clean DC current to the tube heaters. The second DC-DC switching regulator provides 48 volts into a second stage linear regulator that in turn provides 45 volts to both the tube plate and the solid state JFET output buffer. The power supply can handle the current requirements of almost any 9 pin tube available today. Power supply will not be a limiting factor for those who consider tube rolling to be an official audio sport.
High Performance Capacitor Upgrade
The base price of the LDR3000T includes a modest yet high quality metalized polypropylene film capacitor at the output of the preamp. But to take the performance of the LDR3000T to the highest audiophile level, we offer (and highly recommend!) upgrading to either the VCAP ODAM (Oil Damped Advanced Metalized), or for ultimate performance, the reference grade VCAP CuTF (Copper Foil Fluoropolymer Film) output coupling capacitors. Click here to read more about what people are saying about VCAP capacitors.
We believe the LDR3000T with either VCAP coupling capacitor upgrade puts this preamp among the finest high performance preamplifiers available today at any price.
These specifications reasonably reflect the current model but are subject to updating and modification without notification.
|General||Summary||Remote controlled active tube preamplifier with 100 step LDR (light dependent resistor) attenuator, zero/low gain slack voltage triode tube input/gain stage, and a Class A solid state JEFT buffer output stage that handles 3 inputs of any combination of single-ended (RCA) and balanced (XLR) inputs.|
|Audio Signals||Inputs||Any combination of 3 single-ended RCA stereo inputs or balanced XLR balanced stereo inputs|
|Outputs||1 RCA stereo output and 1 balanced XLR balanced stereo output|
|Mixed Signals||* Output from single-ended inputs are available on one phase only (pin 2) of the balanced output.|
* Only the output from one phase (pin 2) of balanced inputs are available on single-ended output
|Input Coupling||Input signals are direct coupled to the tube grid (no coupling capacitors)|
|Output Coupling||Output signals are AC coupled through coupling capacitors|
|Input Switching||All input signal switching is done via LDRs (light dependent resistors) with signal isolation in excess of 10 megaohms when turned off|
|Output Isolation||Output signal isolation (disconnection and/or grounding) is done by a combination of LDRs and miniature relays.|
|Attenuation||Technology||Digitally controlled, optically isolated, analog LDRs (light dependent photo-resistors) in a series/shunt L-Pad voltage divider configuration. |
|Steps||100 steps of ~0.6 dB per step plus 1 additional muting step.|
|Range||-60 dB to 0 dB|
|Channels||Four (4) independent channels for handling stereo audio of both 2-channel single-ended and 4-channel balanced signal types with 2 LDR Modules per channel (total of 8 attenuation LDRs).|
|Channel Balance||Left/right channel within 0.5 dB over full attenuation range with +/- 20 step channel balance adjustment at ~0.6 dB per step for a nominal max channel balance adjustment range of +/- 12 dB and|
|LDR Modules||Each individual LDR is packaged as a compact easily replaceable 4-pin socketed plug-in module that plugs into a 4 pin header. LDR modules are not mechanically keyed so attention must be paid to aligning white dot on module with corresponding white dot on printed circuit board when removing/replacing.|
|LDR Calibration||The preamp includes a built-in software driven closed-loop measurement circuit that measures and calibrates each attenuation step of each LDR over the full attenuation range. Calibration compensates for any LDR performance changes over time or in the event an LDR needs to be replaced. During calibration the preamp operates "off line" and cannot play music. A calibration cycle typically lasts ~10 minutes.|
|Input/Gain Stage||Type||9-pin triode tube running at slack voltage (45 volts) | Matched pair of Electro-Harmonix 6H30 Gold or Genalex Gold Lion E88CC/6922 triode tubes | Tube-rolling friendly design for 6922 family of tubes|
|Gain||Default unity (0 dB) gain adjustable up to +6 dB (adjustment requires partial disassembly and volt-ohm meter) |
|Output/Buffer Stage||Type||Discrete Class A fixed current JFET current amplifier with AC output coupling (capacitor) |
|Output Capacitor||* Standard: metallized polypropylene film output coupling capacitor |
* Optional: VCAP ODAM (Oil Damped Advanced Metalized) or TFTF (Tin Foil Fluropolymer Film) capacitors (additional cost)
|Isolation||Output signals are shunted to ground (effectively turned off) when preamp is powered down, muted, or running LDR calibration.|
|Impedance||Input||Default input impedance is 20k ohms with ability of user to configure up to 9 additional input impedance settings each between 1k and 99k that user can switch between to determine potential optimal input impedance for user's system.|
|Output||Output impedance is fixed at ~100 ohms|
|Performance||Total Harmonic Distortion||While not exhaustively measured is generally well below 0.5% under worst case scenarios.|
|Power Supply||Mains Input||IEC type socket with lighted switch and fuse drawer with external 3 A fuse plus spare|
|Mains Filter||Oversized RFI/EMI filter/choke upstream of transformer|
|Type||Classic linear DC power supply followed by independent switching DC-DC/linear subsystems as described below|
|Transformer||50 VA heavy duty shielded toroidal transformer|
|Fusing||* 2.5 A internal fuse on transformer secondary |
* 3 A external fuse in fuse drawer in the IEC mains input module
|DC Filtering||Over-sized bridge rectifier with 37,600 uF AC filtering|
|Tube Heater||Dedicated high efficiency, high current, DC-DC switching regulator capable of easily handling up to 2 amps of 6.3 VDC |
|Tube Plate & Buffer||Dedicated 2-stage regulated supply composed of DC-DC switching regulator with post-filtering followed by a second stage linear regulator|
|Controls||Controller||V25 Preamp Controller | Rev C | ARM M3 Cortex 32 bit microcontroller running at 72 MHz|
|Remote||Silver 7-button Apple infrared remote (38 kHz NEC protocol) |
|Encoder||Front panel control knob attached to a rotary stepped encoder with integral push button switch|
|Display||256x64 pixel white-on-black OLED display work in conjunction with software driven interactive menu driven control interface designed around the 7-button Apple remote. Please refer to online documentation for detailed explanation of the preamp controls.|
|Control Menu||Control menu items - see online product documentation for control operation details |
* Off (top menu item)
* Volume (default)
* No of Inputs
* Volume Units
* Volume Max
* Volume Display
Mono Mode: User can switch between stereo and mono mode via the remote by pressing Center button twice in a row
|Trigger Out||Rear panel mounted mono phone jack outputs 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.|
|USB Port||Rear panel mounted dual type A USB port allows external PC based bootloader application to update controller's firmware | USB cable provided | firmware updating instructions can be found in online product documentation|
|Enclosure||Case||Heavy wall extruded aluminum case with black powder coat finish|
|Front Panel||0.25 inch thick brushed anodized aluminum with dark grey acrylic inlay in front of visual display attached via socket head screws|
|Rear Panel||0.1 inch thick brushed anodized aluminum attached via socket head screws|
|Feet||Hudson Audio platinum silicone, non-skid, vibration absorbing, 1 inch hemispherical feet (four)|
|Other Design||Printed Circuit Board||High quality nickel immersion gold solder printed circuit boards with blue solder mask|
|Solder||Lead free solder with 3% or higher silver content|
|ROHS||Compliant or exempted|
|Ambient Criteria||Preamp must be operated in a stable, dry indoor environment only with stable ambient temperature within 60-90 degree F|
|Dimensions||3.5 inches tall | 12.0 inches wide | 9.0 inches deep|
|Weight||~ XX pounds | ~XX pounds as shipped|