Halcro DM88 Owner'S Manual Download Page 18

 

17 

 

If the loudspeaker cable is inadvertently 
shorted out, these sorts of currents are quite 
capable of causing some cables to catch fire. 
We know of one such instance with an 
amplifier rated according to the table! 

As we do not wish to set your house on fire 
we have limited the peak output current to 
15 A. 

One also has to question the belief that an 
amplifier should be capable of such 
unreasonably high output currents. Consider 
the following facts: 

 

most loudspeakers have impedances of 
4 ohms (not 1 or 2 ohms) 

 

all valve amplifiers are output current 
limited, and yet the industry does not 
consider this a problem, which is 
inconsistent with the belief that maximum 
available current limiting is a problem 

 

all well designed loudspeakers have 
impedances that do not deviate 
excessively from their nominal 
impedances and hence no excessively 
high currents are required anyway 

 

if indeed a 4 or 8 ohm loudspeaker does 
have an impedance of 1 ohm at a 
particular frequency, one must wonder 
where the heat generated is dissipated if 
this load is predominantly resistive or why 
the coupling is so poor if this load is 
predominantly reactive 

Hence we believe that these excessively high 
output currents are: 

 

not required for well designed 
loudspeakers 

 

highly dangerous 

Many people have listened to maximum 
available current limited amplifiers played 
through different loudspeakers without 
encountering any current limiting problems 
that is, obvious “cracking” sounds at very loud 
listening levels, except for loudspeaker or 
voltage overloads which are independent of 
current limiting

Output transistor protection 

Halcro uniquely incorporates circuitry that 
accurately calculates the mean power 
dissipated in the power output transistors 
(power FETs). Another calculating circuit then 
may reduce the maximum available output 
current according to the heat-sink 
temperature and calculated average 
dissipated power in the transistors. The higher 
the heat-sink temperature, and the higher the 
mean power dissipated in the output 
transistors, the greater this reduction. This will 
only occur at very high heat sink temperatures 
and very high mean output powers. 

Summary of Contents for DM88

Page 1: ...Monoblock Power Amplifier Owner s Manual www halcro com dm88 dm78...

Page 2: ...Break in period 11 dm78 Inputs 12 dm88 Inputs 13 Operation 14 Electronic Protection and Reliability 15 Components 15 Output Current Limiting 16 Output transistor protection 17 Unusual output condition...

Page 3: ...ectronic design was to create an amplifier that did not color the sound with its own electronic characteristics to recreate the original sound as it was at the time of recording Please enjoy the Halcr...

Page 4: ...gle is intended to alert the user to the presence of important operating and maintenance servicing instructions in the following pages The CE symbol indicates compliance of this device with the releva...

Page 5: ...outlet The unit should be installed in a position where the mains plug is easily accessible Disconnect the unit from the mains if it is to be left unused for a long period WARNING No naked flame sourc...

Page 6: ...h the same type and rating as specified F 10 A L 250 V DANGER Always disconnect the unit from the mains before touching the loudspeaker terminals or replacing the fuse Protection from overheating The...

Page 7: ...ways bend at the knees when lifting Do not strain your back Wiring to the loudspeaker terminals to Class 2 wiring US wiring regulations This equipment has been classified as having a Class 2 loudspeak...

Page 8: ...two blades with one wider than the other A grounding type plug has two blades and a third grounding prong The wide blade or the third prong is provided for your safety If the provided plug does not f...

Page 9: ...owever there is no guarantee that interference will not occur in a particular installation If this equipment does cause harmful interference to radio or television reception which can be determined by...

Page 10: ...sed of in general household waste but recycled in compliance with local government regulations or environmental requirements o Please dispose of this equipment via a recycling service or centre or by...

Page 11: ...l it clears the top of the amplifier o With an assistant remove the plastic wrapping and foam pieces then lift the amplifier from the base of the container o Remove the plastic covering from the unit...

Page 12: ...8 are equipped with a separate ground terminal which may be used to reduce hum and ripple in some circumstances There may be high vol ages present at the loudspeaker terminals which may present an ele...

Page 13: ...likely to have an RCA output socket The advantages of this source are that Earth loop generated mains hum and ripple are minimized and cable plug and socket generated interference is minimized from po...

Page 14: ...e minimized and cable plug and socket generated interference is minimized from poor connections which may be affected by sound vibration for example The unbalanced input is quite satisfactory so long...

Page 15: ...mode In this mode a small current is drawn from the mains supply but the unit will not drive the loudspeakers o Press the mode switch once to switch between Standby and ON modes The mode switch is a s...

Page 16: ...at least industrial grade rather than the usual commercial grade Industrial grade components are rated at least from 40 C to 85 C whereas commercial grade components are only rated from 0 to 70 C In...

Page 17: ...ns the first and third amplifier types above highly obvious cracking overload sounds may be heard Note that this overload sound may also occur if a loudspeaker overloads or if any amplifier suffers vo...

Page 18: ...e must wonder where the heat generated is dissipated if this load is predominantly resistive or why the coupling is so poor if this load is predominantly reactive Hence we believe that these excessive...

Page 19: ...will only cut in under fault conditions Internal power supply protection There are numerous power supply protection circuits for example two independent over temperature cut outs two independent maste...

Page 20: ...ohm input impedance to minimize cable reflections to be fed from an infinite impedance current source The voltage gain of the balanced and unbalanced inputs is 60 V V The gain of the current mode is 9...

Page 21: ...in the power amplifier to minimize stray magnetic fields and to accurately define voltages four layer PCBs are used in the power supply to minimize E M I and voltage transients which improves reliabil...

Page 22: ...edance to minimize cable reflections to be fed from an infinite impedance current source a minimal path voltage mode with an input impedance of 660 ohms The voltage gain of the balanced and unbalanced...

Page 23: ...emperatures is protected against most mains transients Components Footnote 4 For reliability all semiconductors are at least industrial grade in both the power supply and amplifier All electrolytics a...

Page 24: ...ight 120 lb or 55 kg Height 31 in or 79 cm Width 16 in or 40 cm Depth 16 in or 40 cm Shipping weight one pair including pallet 385 lb or 175 kg Footnotes 1 THD specifications of our typical best compe...

Page 25: ...rly from the heat sink area o Add 15 ml 0 5 oz of very mild household dishwashing detergent to a four liter one gallon bucket of tepid water o Immerse the soft cloth in the bucket of water and then wr...

Page 26: ...e Master Switch is ON Check fuse Red light is on no sound Press the Standby ON switch to ON Green light is on No sound Ensure Input Selector switch is set to the correct input Ensure loudspeaker cable...

Page 27: ...Halcro products Product warranty Halcro warrants the dm78 monoblock amplifier to be free from defects in materials and workmanship for a period of five years from the original date of purchase Halcro...

Page 28: ...ct Warranty Registration form provided or request a copy from your Halcro dealer If service is required We suggest that you work with your authorized Halcro dealer when the need for technical service...

Page 29: ...horization number a detailed description of the situation and signature of authorized Halcro representative Freight damage claims If a unit being returned to Halcro is damaged in shipment Halcro will...

Page 30: ...Copyright and acknowledgements This product is manufactured by Extraordinary Technology Hi Fi Pty Ltd trading as Halcro and Halcro Audio USA Inc Halcro dm78 dm88 Owner s Manual Revision 1 2 Halcro 20...

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