SPECIFICATIONS
"OPAL" Pre-amplifier (Line Stage)

TUBE COMPLEMENT: (5)

4 6SN7WGTA dual triode
1 6x5 dual diode

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 was the reason we chose this topology! The grounded grid stage drives two cathode followers which provides two isolated outputs for each channel. All stages are DC coupled and only one capacitor is used in the output stage for DC blocking. No feedback is used and dual mono construction is implemented using separate circuit boards for each channel.

POWER SUPPLIES

A unique design for the power supply was implemented in order to eliminate all ripple & noise while maintaining a constant voltage regulation of the 200 Volt DC power line effectively acting like a large battery power source. A combination of large chokes, electrolytic and polypropylene capacitors are used to implement three stages of filtering. The output from the second stage is split in two to form a dual third stage filter to eliminate any channel crosstalk through the power supply. This is accomplished using a tube rectifier in a choke input filter configuration followed by successive LC and RC filter stages using only passive components to accomplish regulation and noise suppression. A 3 element pi-filter is used to provide DC to the filaments. Further noise reduction was accomplished by containing the power supply in a separate chassis.

MECHANICAL CONSTRUCTION

CIRCUIT BOARDS
(Hand crafted Vectorboards using precision double turret terminal posts)

The components are mounted on Vector boards which contain swaged terminal post. These posts are divided into two areas. The wiring used is laid out on both top and bottom of the board and is soldered to the bottom layer of the terminal post. This point to point wiring allows the highest possible component density while maintaining the shortest possible SIGNAL PATH! The components are then soldered into place on the top layer of the terminal which allows the replacement of any part without removing the circuit board. High quality Teflon coated Silver plated OFHC copper wiring is used where appropriate and silver solder is used throughout.

AUTOMATIC POWER SEQUENCING & MUTING:

About 10 seconds after the filaments light up the DC rails are slowly brought up to full voltage of 200 Volts over a period of 60 seconds. At the end of 90 seconds the auto-mute is disengaged completing the turn on sequence. Muting is accomplished using a 4-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 V RMS output)
  1. +/- 0 dB FLAT... 20 Hz to 100 KHz
  2. + 0 dB/ -1 dB ... 6 Hz to 375 KHz
  3. + 0 dB/ -3 dB ... 2.6 Hz to 750 KHz
INPUT IMPEDANCE:
50K ohms minimum
ABSOLUTE PHASE:
non-inverting
MASTER GAIN CONTROLS:
L & R variable from 9 db to 15 db [ in 1 db steps ]
CHANNEL BALANCE CONTROL:
Use left or right channel gain controls.
ATTENUATION:
24 position stepped volume control [ 12 steps of 1.5 db's/step ]
OUTPUT IMPEDANCE:
425 Ohms
RATED OUTPUT:
3.5 Vrms [ maximum = 20 Vrms ]
SLEW RATE:
Greater than 40 Volts/microsecond.
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. 50 Watts
WEIGHT (NET):
Preamp: 38.5 lbs (17.5 kg)
Power Supply: 18 lbs (8 kg)
WEIGHT (SHIPPING):
66 lbs (30 kg)
DIMENSIONS:
Preamp: 19" W x 14 3/8" D x 5 1/4" H
Power Supply: 9" W x 12" D x3 1/2" H
LIMITED WARRANTY:
Tubes: 1 year parts
Components: 5 years parts & labour

HAND BUILT LIMITED EDITION

24 CARAT GOLD PLATED SOLID BRASS NAMEPLATE WITH ENGRAVED SERIAL NUMBER


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