Arcam Diva P-1000 Service manual

DiVA

ARCAM

Bringing music & movies to life

P1000 Amplifier

Service
Manual

Issue 1.0

ARCAM

Bringing music & movies to life

Arcam P-1000 Amplifier Board functions and operation

The power amplifiers in the P-1000 are of class H design and use a three rail power
supply for high operating efficiency. These amplifier boards are field replaceable and
the unit can be safely operated with one or more boards out of the unit. The operating
descriptions below are divided into three groups. The input and signal control section.
The amplifier section and the power switching section. Signal net name references as
they appear in the schematic are designated here in bold type.

The line level audio path of the P-1000 very simple and short. Unbalanced audio
sources are buffered by U6-A and summed with the balanced input from U1-A. The
signal then passes through the gain set stage of U6-B and then on to the
amplifier drive. The
switching section via the

AMP-IN signal is also contoured by U2-A and on to the power

COMM output.

The gain switch S1 works by changing the local feedback around U6-B and has three
settings. The “A” gain position provides an overall gain of 31.5 dB and is compatible
with other Arcam amplifiers. The “B” setting is for use in THX compliant systems and the
low gain “C” position can be used to lower the overall system noise level in installations
where the speakers are very close to the listener.

Also at the input of the gain set stage are the mute transistor Q1 and the resistive
element of the clipping eliminator circuit. When the P-1000 is turned on, the global mute
signal at the

MUTE input of U3-A is low. This forces its output to +12V which activates

the mute transistor Q1 as well as the clipping eliminator circuit through D15. The

FLT_OUT from the emitter follower Q24 and also goes high. Q1 then shunts the audio to

ground and R11 goes to a low resistance state. The

FLT_OUT passes on out to the

channel status display board. When the global mute cycle finishes and the output from
U3-B goes low, Q1 turns off and passes the audio signal immediately but the resistive
element R11 has a slow release time which allows the audio output to ramp up in a
controlled manner.

The local mute circuit of U3-B also has two other inputs. The thermal shutdown circuit of
U2-B and R22 monitor the heatsink temperature of the amplifier. If the HS temperature
exceeds approximately 95 Deg C, the output of U2-B goes high and toggles the local
mute circuit on. Because of the hysteresis around U2-B, the thermal protection will
remain active until the amplifier has cooled down approximately 20 Deg below the trip
point. The second input is the

PROT line from the amplifier. This is a fast acting input

which goes to a low impedance state if a short circuit is detected at the amplifier output.
The clipping eliminator circuit has two inputs. The

signal and the

OPA-OUT signal from the output of U1-B. The OPA-OUT line is inside the

AMPOUT monitors the amplifier output

overall amplifier feedback loop and is very sensitive to any differences between the input
and output signals in the audio path. If the unit is driven into clipping the difference
signal from these two lines is amplified and used to drive the CLM5000 LDR. This
causes the resistance of R11 to decrease and work as part of a voltage divider against
R85 or R5. The effect of this is to reduce the signal level going into the amplifier thereby
reducing the output clipping to a very low value. Typically this circuit will hold the THD to
less than 1% with 10dB of overdrive at the input.

AMP-IN

Arcam P-1000 Amplifier Board functions and operation

In the amplifier portion of the board, Q2 acts as a level shifter and drives the class A
transistor Q13. The voltage source for the class A stage is from Q14 and is regulated by
Z1. This constant voltage causes Q13 to act as a constant current source and stabilizes
the output transistor bias regardless of changes in the AC mains. The class A drive
voltage is also removed from Q13 anytime the local or global mute circuits are activated.
In the un-muted state
which removes Q14s base voltage when Q25 is turned on.

The bias temperature tracking is from diode D8 and the initial setting is made by
adjusting RP1 for a voltage reading of .5 to 1.0 mV across either R51-R53 or R44-R45
after the unit has been on and running for a minute or two. A better method of setting
the bias is to use a distortion analyzer and adjust the amplifier output for 1 volt at 2 kHz
into an 8 Ohm load. After the amplifier has been on and allowed to warm up for a few
minutes, adjust RP1 until the crossover notch just starts to disappear.

The output section is a complimentary feedback pair topology with Q9 and Q7,Q8 in the
positive leg and Q12 and Q10,Q11 in the negative leg. The advantage of this
configuration is higher peak output voltage and, because the emitters of the driver
transistors become the effective output of the amplifier, crossover discontinuities are
very fast and almost negligible without any bias setting. With the bias correctly adjusted
the transition through the crossover region is seamless and the very low bias current
holds the output stage dissipation to approximately 1 watt.

Output stage V-I limiting is through Q5 and Q6. The short circuit current limit is
approximately 10 Amps and is set to this high value in order to handle the out of phase
currents in highly reactive loads. At high output voltages, however, R37 increases this
limit to 20 Amps. For short circuit loads where the current is very high but the output
voltage is close to zero, Q4 is turned on and the
circuit. This mute removes the output signal momentarily and then releases, cycling
on/off until the fault is removed. To verify the short circuit protection, drive the amplifier
to an output of 5 volts or more and short the output terminals together. The shorted
channel output should cycle on and off and the front panel status indicator should toggle
between green and amber.

To increase the efficiency and reliability of the amplifier, multiple voltage rails are made
available to the output transistors. This addition of variable power supply voltages to the
amplifier circuit creates what is known as a class H amplifier. In conventional amplifiers
the output devices are simultaneously exposed to high voltage and high current. The
product of this current and voltage is dissipated in the form of heat. To make matters
worse, the efficiency of the amplifier is the poorest at lower power output levels. To side
step this problem the class H amplifier greatly improves the efficiency by running at low
power supply voltages when the signal level is low. The operating voltages increase
only as required by the program material. Another benefit is in the form of reliability
under demanding conditions. Because the output transistors are never exposed to the
maximum positive and negative supply voltages at the same time, the amplifier is able to
withstand both very high current, under short circuit conditions, as well as highly reactive
currents presented by some speakers. With the overall efficiency gain, amplifier
heatsink requirements are reduced by half.

CLA-MUTE is –12V. When activated this line goes high to +12V

PROT line activates the local signal mute

Arcam P-1000 Amplifier Board functions and operation

With the amplifier operating at low output levels (<20 W) only the +/-20V low voltage rails
are used. As the output requirements increase, the
increases and the peak value of this signal is compared to the low rail reference voltage
at the comparators U4-A and U5-B. When the peak value of the
the reference the comparators will toggle on and the middle rail voltage will be supplied
to the amplifier. For a positive signal, Q15 and Q17 turn on the 40 volt supply and on
the negative swing Q23 and Q19 supply –40 volts.

As the requirements continue to increase the same sequence takes place for the +/- 60
volt supplies. U4-B, Q16 and Q18 supply the positive voltage and U5-A, Q22, Q20 and
Q21 supply the negative voltage. The power diodes D7,D23 and D24,D25 isolate the
high voltage supplies from the lower voltage supplies. Under short circuit conditions the

COMM line signal goes to zero because of the mute drive to Q1 and only the low voltage

supply is present at the output transistors.
To verify the correct operation of the commutator circuits drive the amplifier to 30-35

Vrms into an 8 Ohm load at 200 Hz and observe the positive and negative supplies. The
positive rail voltage is monitored at the emitter of Q18 or at the junction of D7, D23
(cathode ends). To monitor the negative rail use TP2 which is connected to the junction
of D24, D25. The waveforms should appear as shown in figure XX. If any of the rail
voltages fail to operate, the output of the amplifier will be limited to a lower value by the
clipping eliminator circuit. Because of this and the fact that the output will still be a sine
wave, it may be necessary to remove the 8 Ohm load to determine which rail is not
switching.

COMM signal from U2-A also

COMM signal exceeds

FIGURE 1 POSITIVE RAIL SWITCHING WAVEFORM

FIGURE 2 NEGATIVE GOING WAVEFORM

FIGURE 3 BIAS CONTROL AT MAX CCW POSITION

FIG 4 BIAS PROPERLY ADJUSTED (COLD)

P-1000 Display Board functions and operation.

The P-1000 display functions are divided into two separate blocks, power on/off and
channel status indications. The power on/off LED indicators are driven by the Standby
Power supply on the main board and are active any time the P-1000 is connected to the
AC mains supply and the rear panel power switch is on. The Channel Status LEDs
receive power from both the Main power supply and from each individual amplifier
channel.

With the P-1000 connected to the AC mains with the power switch on, the

is high which turns on the red Standby LED on. It also turns Q2 on which forces the run

LED off.

When the unit is turned on via the front panel power button or the rear panel 12V trigger

PWR-LED line goes low and +12V from the main power supply turns on the green run

LED.
The amplifier channel status LEDs, at turn on, are driven by the

FLT lines and show

amber for approximately 2 seconds. When the turn on mute cycle has finished the
lines go low and the LEDs receive their power from the –12V supply and are illuminated
green.

If one of the amplifier channels becomes hot enough to thermal out the
channel will go high until that amplifier channel cools down. During the off time the
status led will show amber. Other channels are not affected by this action.

If one of the amplifier channels has a short circuit across the output terminals the
line will be activated momentarily and the status LED will alternate between amber and
green. This amber/green cycle will continue as long as the fault is present and the
amplifier is trying to run program material. When the fault is removed the LED for that
channel will return to a steady green. No other channels are affected by this action.

In the event of a DC offset fault from the amplifier, the

OFFSET line goes high which turns

on both LEDs and the color changes to a steady amber. A DC fault condition will also
shut down the main power supply. This removes the power to the status LEDs and all
the channel indicators will go off. Although it very unlikely that a DC fault will ever take
place, it does trigger a latching circuit that receives its power from the standby supply.
This means that it will be unaffected by the front power button or the rear panel 12V
trigger. The only way to clear this condition is to completely remove the power either by
turning the unit off via the rear panel power switch or by disconnecting the AC mains
cord for a few minutes. This allows the offset latching circuit to reset to the off state.

PWR-LED line

FLT

FLT line for that

FLT

Arcam P-1000 Main Board functions and operation

In addition to the high current supply voltages for the seven amplifier channels, the Main
board also contains the circuitry for power on/off control, DC fault protection, the standby
housekeeping power and other control circuits as well as the bussing interconnections to
all channels.

Since the P-1000 is a multi rail class H amplifier, the Main board has three high power
plus/minus voltage supplies for the amplifier output stages. The +/- 12V for the signal
level amplifier circuits is obtained from the +/- 20 volt low rail supply. These 20 volt low
rails are also fused for added DC fault protection but under no operational conditions
including amplifier output short circuits should these fuses ever fail. The middle (+/­40V) and high (+/- 60V) rails are capacitive input filters and require no further
explanation.

Because the middle and high voltage supplies have no direct discharge path to the
output stages when the unit is turned off, Q8 and Q9 form dynamic discharge resistors.
This serves two purposes. First it discharges the main bulk capacitors when the unit is
off and second, this energy is redirected to the +/- 12-volt supplies which eliminates turn
off irregularities. Q8 and Q9 function only for a minute or so when the unit is powered
down.

The standby power supply is functional at all times when the unit is connected to the AC
mains and the rear panel power switch is on. The function of the
provide power for the power on/off logic, display and the DC fault circuit. One additional
function is to supply the amplifier circuits with a small (less than 1 volt) DC negative bias
which eliminates turn on “pops”. This is accomplished through R62 and D15. Because
the power requirements of these circuits is so low the power consumption when the P­1000 is in the standby mode is less than 2 watts.

The DC fault circuit, which includes Q2, 3 and 4, is a bi-directional DC level sensing
circuit. The output of each amplifier is monitored through the
networks. If a positive going DC voltage is present on any of these inputs, Q2 becomes
forward biased, turns on and forces Q3 on. Likewise, for a negative going DC fault Q2
operates in a common base mode with R12 holding the base close to ground potential
while the emitter goes negative and the circuit is again activated. Because of the
positive feedback through R26, Q3 latches on and, through Q4, pulls the base of the
emitter follower Q7 to ground. This action shuts down the Opto coupler U3 and the main
power supply Triac goes to the off state and turns the P-1000 off. The
drives the global mute circuit and the power LED will show as amber. The unit will
remain in this shutdown mode until all power is removed for a minute or so until the
standby voltage drops close to zero. If the offset circuit is activated, LED D12 on the
main board will be on and serve as a visual indication that the unit is in shutdown mode.
Shorting

TP1 and TP2 together on the main board will force the circuit to reset.

The power on/off switching can be done three ways. Turning the rear panel switch on or
off, pressing the front panel power button (assuming the rear panel switch is on) or by
applying a 12 volt DC trigger to the rear panel 3.5 MM jack. The logic switching
functions of the P-1000 are then controlled by U1 and U2 which maintain a zero crossing
on/off drive to the main triac.

STBY supply is to

CH1 through CH7 R-C

OFFSET line

Arcam P-1000 Main Board functions and operation

To perform these functions an AC mains sine wave from the standby transformer
secondary is applied to the input of U2-D. This
rectified and the output of gate U2-D is a square wave clock signal to the CLK input of
U-1B. By using a clock signal derived from the AC mains, zero crossing turn on/off is
assured regardless of which method is used. If the unit is turned on via the rear panel
power switch the SET input of U1-A goes high and the Q output becomes the DATA
input to U1-B whose Q output goes high on the first clock cycle from U2-D. This high
output then turns on the Optocoupler U3 and the main triac is gated on thereby turning
on the main power. If the front panel power button is pressed again, the Q¯ output is
clocked through the DATA input of U1-A causing its Q output to go low. This low state is
passed through U1-B, on to the Opto and the unit is turned off. Since U1-A is a divide
by 2 circuit subsequent button presses will switch the unit on and off. The
from U1-A drives the front panel standby LED and the
power to Q5 in the power on/off mute circuit.

The rear panel 12 volt remote input is independent of the front panel power button and
will cycle the unit on or off depending on the whether a 12 volt input is present. The
remote switching, unlike the front panel switching, is voltagelevel dependent and
operates by forcing a SET or RESET on U1-A. The main power triac switching,
however, is still controlled by the clock signal from U2-D. The rear panel control also
incorporates a time delay of 1-2 seconds through the R-C pair R2-C4. This allows for a
staggered turn on sequence if an entire system is powered on by a single 12 volt trigger
source.

Because triacs and SCRs remain conductive only when a current is flowing through
them, a constant load circuit is included on the transformer secondary windings. The R­C network of R64 on the 20 volt winding and the 3 uF 250V capacitor across the 60 volt
windings correct this by holding the triac on through the zero crossing point. This
equalizes the transformer flux and prevents mechanical transformer “buzz” due to
unequal conduction cycles across the windings.

When the P-1000 is turned on, the global mute circuit is activated by the network around
Q5. Initially Q5 will be off and the

MUTE output will be –12 V. This mute voltage is

distributed to all seven channels and will activate the local mute circuit on each of the
amplifier boards. As C30 discharges, the voltage eventually exceed the zener drop of
Z4 and turn Q5 on which then toggles high for a
global mute line is high (-4V), the individual channels are active and will pass a signal.
The

FLT outputs from the amplifier boards are used to provide the channel status LED

drive. If any amplifier channel is in the muted state its
corresponding channel status LED will show as amber.

As shipped the P-1000 is meant to operate at either 230Vac or 120Vac. To change the
AC mains operating voltage it is necessary to replace the main power transformer with
one of the desired voltage. In addition it is also required that the standby transformer
primary windings are rewired to accept the new voltage. JP1,JP2 and JP3 determine
which voltage the standby transformer is set for. For 230Vac operation JP1 is used and
JP2 and 3 are removed. For 120Vac operation JP2 and 3 are installed and JP3 is
removed. The fuse F1 is an F50mAL type and remains the same value for either
voltage.

LV_AC_IN signal is then half wave

PWR_LED line

PWR_ON line is used to supply

MUTE line voltage of –4V. When the

FLT output is high and the