SPECIFICATIONS
"CORAL" Pre-amplifier (Line Stage)

TUBE COMPLEMENT

[2] 5814A [1] - 5687WB NOS JAN militrary dual Triodes

CIRCUIT DESCRIPTION

This line amp uses a grounded grid configuration which is isolated by a cathode follower stage before and after it. All three stages are non-inverting thereby maintaining absolute phase. The grounded grid configuration is known for its extremely wide bandwidth and high speed! The cathode follower output has a very low output impedance capable of driving two pairs of RCA output jacks to accommodate bi-wiring or bi-amping. All stages are DC coupled and only one capacitor is used in the output stage for DC blocking. No feedback is used and mirror image circuitry is implemented on the printed circuit board for the audio section. Overall amplifier gain is selectable via internal jumpers for 4.5db or 12.5 dB.

POWER SUPPLIES

The power supply uses a Toroid power transformer for low noise and reduced magnetic field radiation to surrounding areas. A Pi RC filter is used for the 250 Volt plate supply and a dual Pi RC filter is used for the 12 Volt filament supply. These filters, like the OPAL & JADE, are designed using only passive components that allow the speed of the power supply to keep up with the analog circuitry.

MECHANICAL CONSTRUCTION

CIRCUIT BOARDS

The components are soldered by hand on a dual layer Printed Circuit board that is masked on both sides to protect & insulate the circuit paths as well as a silk screened layer on top to label the components and their position on the board. High quality Teflon coated Silver plated OFHC copper wiring is used in all analog wiring to and from the circuit board.

AUTOMATIC POWER SEQUENCING & MUTING

To allow for extended tube life a 30 second delay is applied before the high voltage plate supply is engaged. To allow circuit stabilization and quite operation a 60 second automatic muting is activated during power up. Muting is accomplished using a 2-pole relay that shorts the preamp outputs. When disengaged the muting circuit is not in the signal path.

FREQUENCY RESPONSE

[ reference to a sine wave at 3.5 Vrms output ]

1. +/- 0 dB FLAT … 20 Hz to 120 KHz
2. + 0 dB/ -1 dB … 9 Hz to 425 KHz
3. + 0 dB/ -3 dB … 4 Hz to 825 KHz

INPUT IMPEDANCE:   50K ohms minimum
ABSOLUTE PHASE:   non-inverting
CHANNEL BALANCE CONTROL:   11 position for +/- 5 dB adjustment in 1 dB steps
ATTENUATION:   24 position stepped volume control [ -60 dB to 0 dB]
OUTPUT IMPEDANCE:   150 Ohms
RATED OUTPUT:   3.5 Vrms [ maximum = 7.5 Vrms ]
SELECTABLE GAIN:   High = 12.5 db. Low = 4.5 db [ Internal Jumper ]
OUTPUTS:   2 pre-amp outputs, 1 tape output, 1 line level output
INPUTS:   4 line level inputs, 1 tape input.
POWER REQUIREMENTS:   Switch selectable 115/230 Volt 50/60 Hz 35 Watts
NET WEIGHT:   12 lbs ( 5.5 kg)
SHIPPING:   16 lbs ( 7 kg)
DIMENSIONS:   15" W x 10.875" D x 3 3/4" H
LIMITED WARRANTY:   TUBES - 1 YEAR PARTS
    COMPONENTS - 5 YEARS PARTS & LABOR