Arcam (Cambridge) P1000 free download

File name Arcam-P1000 pwramp.pdf

DiVA 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 AMP-IN amplifier drive. The AMP-IN signal is also contoured by U2-A and on to the power switching section via the 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 AMPOUT monitors the amplifier output signal and the OPA-OUT signal from the output of U1-B. The OPA-OUT line is inside the overall amplifier feedback loop and is