Battery operated tube pre-amplifier with phono stage
The PL-P vacuum tube pre-amplifier is a high quality pure class A tube based pre-amplifier including a high precision phono stage for vinyl records. With its unique internal rechargeable battery power supply, the highly sensitive phono stage, features individually hand-wound NAGRA built transformers, is entirely isolated from the mains power supply and hence avoids any form of hum loop. Able to handle both moving coil and moving magnet cartridges and up to 4 independent sources the PL-P is an extremely flexible preamplifier.
Uncompromised power supply
In any pre-amplifier, the power supply is a sensitive and significant component. This is especially true when dealing with phono levels. That’s why the PL-P power supply uses a set of rechargeable “D” cell batteries, operating through an external current charging AC supply. This design eliminates all disruptive effects of AC powering from wall outlets and may solve persistent hum problems. The internal power supply regulation circuitry of the PL-P uses proprietary, dual DC-to-DC converters to eliminate power supply ripples and assures a clean power source for all active electronic stages and components.
Unique design phono stage
The phono stage is built around the best tubes out of our selection and especially designed Nagra transformers for impressive noise figures, dynamic and high-resolution performance with both moving magnet and moving-coil cartridges.
Variable capacitive (from 47 pF to 837 pF) and resistive (30 Ω to 330 Ω) loading is provided to allow ideal matching with most available cartridges. Switches for selecting the appropriate loading options are internally mounted on the circuit board to protect sensitive low-level signals from undesirable interferences.
A class tube
Two triode sections, biased for pure class-A operation, are implemented in each channel for additional amplification. The PL-P has two stages, the first one for level input management and the second for output level management and record loop.
As in all vacuum tube circuits within the PL-P, precise DC filament voltage regulation from the power supply ensures low-noise, high-resolution performance and a long lifetime. The output stage vacuum tubes, operating in pure class-A, are directly coupled to the output connectors; they can accommodate loads as low as 600 Ω. To facilitate tape transcriptions and external signal processing, a full tape loop facility is also provided.
Input selection is made on the left side of the front panel using a precision rotary switch. One phono and three line level inputs are provided. Input levels for all sources can be adjusted via left and right potentiometers on the front panel. A clever geared clutch mechanism, allows these channel adjustments to be made either independently or together.
Attention to detail
To reduce unwanted interference, the main circuit board is mounted on elastomer dampers to eliminate the effect of external vibrations.
To conserve component life and battery reserve, only those vacuum tubes required for the selected input are turned on. The audio output is automatically muted when switching between input sources.
Tradition – Level matching through the Nagra modulometer
A highly precise, Nagra-made modulometer, identical to the legendary NAGRA IV-S, provides a multitude of functions through two coaxial, internal pointers representing the left and right channels. The Nagra modulometer is a true measurement device that allows precision over a large scale. The modulometer can be used to adjust the volume and balance potentiometers for:
- Reaching a proper balance between left and right channels ;
- Compensating the level differences between various recordings ;
- Controlling the power supply DC input level ;
- Controlling the output level of the amplifier (if correctly sets)
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