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*  The voltages from the sensors are logic 'OR'd' through D1, D2, D3 and D10 into latching 

comparator U1a, PIN4. This voltage also controls U2 to drive Q1a and Q1b, which supply 
the cooling fans. The fan speed is proportional to temperature. U1b forms an additional 
comparator to switch relays RLY2, RLY3 via CONN1 PIN4 (on PCB712) at 
approximately 90°C. This reduces the output stage supply voltage to limit the available 
power. 

*  If the temperature rises above around 100°C, U1a, PIN2 will swing low when PIN4 

voltage exceeds PIN5 voltage and latch in that state because of R7, D5. 

*  The speaker outputs will be disconnected via D6, U1c, Q2A and Q2b and RL4 and RL5.  

*  D109 (D209) reduce the voltage on Q101 (Q201) drain to about 1.5V thus reducing the 

LDR resistance to very low, attenuating the audio signal. 

 

 

b.  EXCESSIVE DRIVE 

 

*  The limiter circuits prevent ANY continuous excessive drive condition, provided that the 

INPUT signal is less than +18dBu. 

 

 

c.  OUTPUT SHORT CIRCUIT 

 

    

*  In the event of a short circuit or very low impedance load being present on the amplifier  

 

 

 

output, excessive current will pass through the sensing resistors R156 (R274), R151  

 

 

 

(R253) on the emitters of transistors Q112 (Q216), Q107 (Q209). The voltage developed  

 

 

 

across the resistors will cause conduction of Q114 or Q115 (Q214 or Q215), which will  

 

 

 

pull current through the relevant OPTO coupler LED, OPT101 or OPT102 (OPTO201,  

 

 

 

OPTO202). The output transistor of the relevant OPTO coupler will cause comparator 

 

 

 

U1d to change state and latch (due to R12, D9). This will disconnect the speaker output  

 

 

 

relays RLY4 and RLY5 via D7, and mute the drive signal. (See Temperature, para. a.) 

 

 

d.  DC SHIFT 

 

*  R24 and R25 detect any DC shift at the output terminals. If the average voltage on
 

either output connection differs from 0V by a significant amount (approx. 100mV) U1c  
output will change state (high to low) disconnecting the speaker outputs via RL4 and RL5           
and muting the drive signal via the limiter circuit. Spurious operation due to AC signals is 
prevented by C18, C19. 

 
6.  STATUS LEDs – PCB703 and PCB701 

 

 

*  The status LEDs are mounted on PCB703 (display panel). 

 

*  The blue signal LEDs  are driven from the signal to the gain controls, via DU1a (DU1b) on  

 

 

PCB703. 

 

*  The remainder of the LEDs are driven via signals or voltages from PCB701 via CONN5 

 

 

(ribbon cable). 

 

*  The -3dB indicators are driven from U5a and U5b. (See paragraph 3 above.) 

 

*  The limit indicators are driven from U4a and U4b. 

 

*  The protection indicator (A/P) is driven from CONN6 PIN5 on PCB701, which connects to 

 

 

U1c PIN14 on PCB700. 

 
7.  SWITCHMODE POWER SUPPLY – PCB712 

 

 

The mains input, via in-rush and RF filter circuits, and switching is bridge rectified by BR1 and 
smoothed by C6 to C9. 

 

 

*  PTC1 is a protection device. 

Summary of Contents for E45

Page 1: ...E45 SERVICE MANUAL MC 2 AUDIO Ltd Units 6 7 Kingsgate Heathpark Industrial Estate HONITON Devon EX14 1YG England Tel 0 1404 44633 Fax 0 1404 44660 www mc2 audio co uk ...

Page 2: ... 3 MAINTENANCE 3 CIRCUIT DESCRIPTION 3 DIS ASSEMBLY 6 RE ASSEMBLY 7 ADJUSTMENTS RE ALIGNMENT 7 APPENDICES 1 EQUIPMENT REQUIRED 9 2 SPECIFICATIONS and PRC 10 CIRCUIT DIAGRAMS PCB710 x 701 x 712 x 703 x LAYOUT DIAGRAM PCB710 701 712 ...

Page 3: ...less it is within a clean room Replacement filter material is available from MC2 Audio No other regular maintenance is required NOTE Any internal cleaning should only be carried out by a competent person CIRCUIT DESCRIPTION 1 GENERAL The E45 amplifier operates in modified class H with mixed bi polar and FET output stages powered from a switchmode power supply This ensures optimum sonic quality and...

Page 4: ...ove ve when PIN3 exceeds the reference set on PIN2 Hence the limiter threshold is set The PRC switches control the gain and therefore the voltage into PIN3 of U102a U202a thus the threshold of limiting can be lowered to reduce the maximum output of the amplifier 4 OUTPUT AMPLIFIER PCB710 The unique MC2 Audio sliding op amp drive circuit combined with multiple bi polar output transistors form the p...

Page 5: ...se conduction of Q114 or Q115 Q214 or Q215 which will pull current through the relevant OPTO coupler LED OPT101 or OPT102 OPTO201 OPTO202 The output transistor of the relevant OPTO coupler will cause comparator U1d to change state and latch due to R12 D9 This will disconnect the speaker output relays RLY4 and RLY5 via D7 and mute the drive signal See Temperature para a d DC SHIFT R24 and R25 detec...

Page 6: ...relays RLY2 and RLY3 which step down the Vcc Vss rails The base of Q4 is driven from PCB700 via CONN1 PIN4 NTC4 senses the IGBT heatsink temperature within the power supply D12 adds a small d c voltage to that on C37 to also control the limiter circuit as above SAFETY COMPONENTS FS1 is a 1AT fuse to protect the low voltage circuits Th Trip1 is the main unit thermal trip fitted to the rear panel 24...

Page 7: ... pillar Disconnect ribbon and audio cables from PCB701 Cut tie wraps as necessary Withdraw display assembly through front panel d PSU PCB712 WARNING ENSURE CAPACITORS ARE DISCHARGED BEFORE PROCEEDING LEAVE UNIT SWITCHED OFF FOR 30 MINUTES Remove spade terminals LIVE NEUTRAL Remove CONNs 2a 2b and CONN1 Remove spade terminals RED BLACK BLUE WHITE YELLOW Remove 5 x M4 retaining nuts and 1 x PZ2 M4 s...

Page 8: ...ct suitable dummy 4 ohm load to relevant speaker output Inject 4dBu 1kHz balanced into relevant input XLR Monitor the output across the 4 ohm load on a suitable audio analyser capable of measuring THD N down to 0 003 If possible monitor the residual signal from the analyser monitor output on an oscilloscope Set VR104 VR204 fully anti clockwise Slowly adjust VR104 VR204 clockwise The THD N should r...

Page 9: ...y Ch A and adjust VR105 on PCB701 to match Ch B in output power NOTE THAT POWER MEASUREMENTS OF BOTH CHANNELS TOGETHER CAN ONLY BE MADE USING A BURST TONE IF A SINE WAVE SOURCE IS USED CONSULT MC2 FOR FURTHER INFORMATION IF REQUIRED There are no further adjustments but a check of power and frequency response should be made with reference to the specification in Appendix 2 ...

Page 10: ... 1 Signal Generator 10Hz to 40 kHz 0 001 THD Burst tone for power measurements 2 Audio analyser capable of measuring dBu Watts 4 ohms THD to 0 003 accuracy Recommend Audio Precision AP1 or similar 3 Oscilloscope 10MHz band width minimum 4 Dummy loudspeaker loads 4 ohm 2000W Qty 2 5 Voltmeter D C volts 1 to 100V 6 Suitable screwdriver trimmer for POTs ...

Page 11: ...ency response 20Hz 20kHz 0 0 5dB Input impedance actively balanced 20k ohms Dimensions mm 2U 88x482x428 Weight 11kgs Power requirement 230 VAC 20 amps max 115 VAC 40 amps max Table of PRC settings and resulting Output Output Per Channel Watts Bridged Mode Watts Max Power into 4ohm 2250 6400 2dBu PRC Setting 1400 4000 4dBu PRC Setting 900 2500 6dBu PRC Setting 560 1600 Max Power into 8ohm 1200 4400...

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