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1) Any amplier channel pulls current through the SOA_PROTECT line for long enough to charge

up capacitors C5871 and then C5872 so that Q5874 turns on.

2) Any amplier channel pulls current through the OVERLOAD line for long enough to charge up

C5882 and turn on Q5882 and thus Q5884.

3) Any amplier channel has a large long term (DC) oset (typically greater than +/-3V) sμFcient

to charge up C5861 enough to turn on either Q5862 (positive oset) or Q 5864 (negative oset).

These then turn on Q5863. N.B. This circuit is also used to detect imbalances in both the Vcc/Vee

and +/-15V power supplies (the latter is generated on the Power Supply board).

4) When the PTC thermistor TH585 mounted at the top centre of the heatsink gets sμFciently hot

(around 100C) and thus high resistance enough to cause Q5855 to turn on via the +12V supply.

Intermediate temperatures will not activate PROTECT but will provide signals to the level detec-

tors associated with the FAN_1 and FAN_2 lines, to run the cooling fans at high or low speeds

respectively.

Note that the fans’ 12V supply is gated via Q5909 and Q5911. This means the fans will not run when

no signal is present on the FL, C or SR channels, so that during quiet passages no fan noise should be

audible.

AVR360 Main Power Supplies Circuit Description

The main DC power supplies are located on the Power Supply Board - a double sided PTH PCB adjacent

to the Main Board. Note that the mains fuses, standby power transformer with its associated unregulat-

ed DC supply and the relay for enabling the power amplier supply rails are located on the Main Board.

The two boards communicate via CON501.

Considering the Main Board rst, the power supply voltage is xed depending on which regional vari-

ant the AVR360 is (US or EU). The mains voltage is xed to a nominal settings of 115V (US) or 230V (EU)

+/- 15%. The 20mm fuse in line with the frame transformer is rated at 15A T (Time delay) for 115V units

and at 8A T for 230V units. Always replace this fuse with the same type and value. The standby transformer

T5941 is not fused but is designed to go open circuit in case of overheating (e.g. if left connected to a

230V supply for longer than a few minutes when the mains voltage selector is set to 115V).

Changing the power supply voltage

The AVR360 is designed for a single mains voltage only and cannot

be switched between 115V and 230V operation by the user. Conver-

sion of an AVR360 from 115V operation to 230V operation or vice

versa requires the following steps:

• Change power transformer to the appropriate voltage variant

• Re-wire links BN580/BN581 according to schematic Sheet 12

• Remove incorrect fuse from unused fuse holder

• Fit correct fuse to appropriate fuse holder

The standby transformer generates approximately +9V DC via the bridge rectier diodes D5495/6/7/8

and the 1,000μF reservoir capacitor C5947. This is sent via pin 7 of CN501 to the Power Supply PCB

(confusingly marked as 5V). The rail voltage is also routed to the system microprocessor (μP) via D5965/

R5965 and pin 6 of CN103 as POWER_MUTE.

Arcam AVR360 User Manual

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