Arcam C30 pre sm
This is the 58 pages manual for Arcam C30 pre sm.
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Extracted text from Arcam C30 pre sm (Ocr-read)
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Contents List ! Circuit description ! Circuit diagrams o L958AY power supply board o L965AY pre-amp board o L928AY display board o L870AY phono board o L955AY multi-channel board ! Transformers o L923TX – 115/230VAC toroidal o L922TX – 100VAC toroidal o L907TX – 100VAC frame ! Exploded view diagram ! Mechanical & packing parts list ! Circuit board silk screen & parts list o L928AY display board o L955AY multi-channel board o L958AY power supply board o L965AY pre-amp board o L870AY phono board
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C30 preamplifier circuit description . Introduction The C30 pre-amplifier uses pre-amp input switching/control and display boards that are very similar in design to the boards used in both the Diva A85/A90 and Fmj A32 integrated amplifiers and as such you may already be familiar with the layout and topologies of these boards. The C30 boasts a very much over-engineered power supply and output stage that is designed to bring the very best out of the existing Pre-amp input switching board. The main PCB L958AY also contains output buffers for the unbalanced outputs to drive long cables and balanced line drivers. A headphone amplifier is included to drive low impedance headphones down to 32 Ohm. For description of the pre-amplifier switching and control board see the section... Power supply. The mains input comes in via SKT1. Two Y caps return common mode noise to the chassis ground and an X cap reduces any single ended noise. The 1M5 resistor following this is in place to discharge the capacitors when the unit is turned off. The mains selector switch, which follows the resistor, changes the configuration of the transformer windings from series for 230V to parallel for 115V. Tx1 is a standby transformer it powers the microcontroller at all times so that the unit can be put into and out of standby. To reduce voltage losses after this transformer, low forward drop diodes are used. A low drop out regulator follows to create the 4.5v(D) supply; this supply powers the micro and digital circuits. The primary of the Toroid supply transformer Tx2 is connected to CON3 and the power to this is switched on and off by the relay RLY1. The transformer has a number of secondary outputs and we use separate taps and bridge rectifiers networks followed by bulk capacitors to smooth the ripple. The voltages generated are +24V and -24V for the main analogue supplies, +46V for the HT supply to the VFD , and +18V , which is used to power the trigger output. The smoothed +/- 24V then goes through regulators REG 2 and REG 5 to create +/- 18V this is passed the pre-amplifier PCB via CON4. Another set of regulators REG 3 and REG 6 follow taking the 18V and creating a +/-15V supply that is available for add on modules such as the 7.1 channel input board. A 5v supply is derived via regulator REG 4 from the 18V to run the headphone amplifier. Mains detect. A mains present detector runs from the standby transformer, this detects the loss of mains using a peak hold circuit based around D7/TR1/DZ1 and TR2. If the power is lost this piece of circuitry sends a flag to the microcontroller so it can mute the outputs and shut down the unit. See Fig 1 for notes on protection modes . 12v trigger and RC5 receiver. The trigger output on SKT2 is driven through TR4 to provide a current limited supply at around 13V. IC1 A and B are used to demodulate incoming RC5 from socket SKT2. IC1A is a band-pass filter centred on 36KHz . This is followed by a peak detector circuit that demodulates the incoming signal. Fig 1. Protection and mute mode and measurements. Prot line Measured at. Working reading AC present Resistor R12 +4.5v Mute* Con 8 Pin 5 +4.5v Standby* Resistor R5 at point P18 .7v Trigger ResistorR10 at point P54 +1.8v