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2. Amplifier Boards
2.1 120/230V Variants
To manufacture the separate SKUs for different AC mains voltages, a jumper (S100) on the
amplifier boards is changed.
2.2 DC Power
Each of the two amplifier modules is fed directly from the AC mains, and provides a +/-18VDC
nominal supply, referred to as +/-18V A and +/-18V B.
The A supply is used to power the DSP circuit board. It is converted to +/-15 VDC for the audio
circuitry, 5V, 3.3V, and 1.2 V to supply the circuitry.
The B supply is fed through the ethercon cable to supply the T1 ToneMatch
TM
Audio Engine.
Pins 4 & 5 are the +18V, and pins 7 and 8 are for the -18V.
2.3 Amplifier PCB Architecture
Note: Refer to the Amplifier Block Diagram, sheet 1 of 1 for the following. The information inside
the brackets [ ] is the schematic grid location on the sheet.
The amplifier comprises two PCB’s, a Switch Mode Power Supply (SMPS)/Amplifier PCB and an
Input/Limiter PCB. The SMPS/Amplifier PCB filters the AC mains power, converts it to the DC
voltages required by the audio amplifier and the input/limiter PCB, and provides a switching
audio amplifier with 30 dB of gain.
The block diagram shows the amplifier board PCB architecture. The amplifier uses a three-wire,
grounded AC power configuration, with the cast aluminum chassis connected to earth ground.
Connectors
The amp pcb has connectors for AC power (con300) [C1], line-level audio in (J301) [C4],
speaker out (con301) [D4], control signals (J302) [B/C4], and DC voltage output (J303) [B4].
Switches
S301 [A3] is a DC bypass option for the ground connection, left open in production for best EMC
performance. S302 [A1] was a design option to allow a second grounding point on the board, left
closed in production for best EMC performance.
2.4 AC Power Input Filter Section
Note: Refer to the SMPS/Amplifier PCB Schematic Diagram, sheet 1 of 3 for the following.
L100, L101, C100, C109, C110, C111, and C112 [all located at B/C2] provide filtering to keep
radio frequencies off the power supply for compliance with FCC and EN55103 emissions re-
quirements. R102, R103, and R104 [B/C2] provide a DC discharge path for the capacitors on
the input to discharge when power is removed.
L100 and L101 are progressively wound common mode chokes with an impedance peak greater
than 450 kHz.
Theory of Operation
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