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.

Tube Rolling

Designing the LDR3000T around the 6H30 tube means the LDR3000T has a very robust power supply due to the high current demanded by the 6H30. This opens up the possibility to trying a wide variety of alternative high transconductance pin-compatible 9-pin triode vacuum tubes including the 6DJ8, ECC88, E88CC, 6922, 6N23P, and 6N11 including both current and NOS versions.  Let the tube rolling begin!

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, to do so requires disassembly of the preamp and flipping around 4 plug-in gain resistor modules located on the tube board.

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.

Specifications

These specifications reasonably reflect the current model but are subject to updating and modification without notification.