User manual HAFLER XL-600

[. . . ] Please peel off this coating following installation. When cleaning the faceplate, we advise a soft cotton cloth with a non-abrasive cleaner that is safe for Lexan and painted surfaces. DO NOT use paper towels or any coarse materials to clean the faceplate as these materials may scratch the insert. Ventilation Adequate air flow is important to the continuing reliability of any power amplifier. The XL-600 uses a quiet, continuously variable speed fan to cool the entire chassis Cool air must circulate freely into the side vents and out the rear vent. [. . . ] The XL-600 is supplied with 5 ampere fast blow fuses installed. This value will afford minimal protection for most speakers. A spare pair of 10 ampere fast blow fuses has been included, for testing purposes, or high power applications. This fuse value will offer no speaker protection. IF THE MANUFACTURER OF YOUR LOUDSPEAKER RECOMMENDS A SPECIFIC FUSE VALUE, OBTAIN TYPE 3AG OR AGC AGC 3AG FUSES AND INSTALL THEM IN THE BACK PANEL FUSE HOLDERS. THE EXCELINEAR CONCEIT The purpose of the Excelinear technology is to detect and then minimize all possible non-linearities, or distortions. This is done by subtracting the output of the amplifier from its input, A perfect amplifier would have no residual signal. The less difference signal that remains, the better the amplifier. The test described below enables you to hear only the difference signal- the sum total of all audible 6 amplifier distortion, It will already be exceedingly low on the XL-600 as you receive it because each amplifier channel has been factory adjusted using a typical loudspeaker load. But when the XL-600 is connected to your own speakers, careful readjustment by a technician may yield some slight improvement. The test is as sensitive as one's hearing, and much more precise than available measurement technology because it is able to reveal the audible effect of all distortions - even those which have not yet been identified or quantified!This is a very useful amplifier comparative technique which supplements conventional distortion measurements. With the XL-600, the total of all residual distortion products will be on the order of 60 dB or more down across the audio band - a substantial improvement over other amplifiers, where 40 dB figures are among the best. Only a few amplifiers cannot be subjected to this test: those which are phase inverting, and those which have floating (not grounded) outputs, or those which cannot tie together the output grounds. The XL-600 provides a unique internal adjustment for "fine tuning" each channel when it is connected to your speakers. This "tweaking" may fairly be described as significant only to those persons with "golden ears". The rest of us who simply wish to indulge ourselves with fine sound need not be concerned with this consummate pursuit of perfection. The range of adjustment provided is within the defined operating specifications of the amplifier. Misadjustment will not damage or impair the performance of either amplifier or speaker. The region of change is several octaves above the range of human hearing. Yet we have found that minute differences in absolute linearity can be heard, and this "tweaking" can minimize them. Do not change the factory's setting until you have at hand the appropriate gain control circuit described below. You will need the special tool provided, patience, quiet, and good hearing, but no test instruments to complete the task. [. . . ] Before returning any unit to the factory for service, please call us. All units being returned (regardless of warranty status) must receive a Return Authorization (RA) Number. In addition, we can offer trouble-shooting assistance that may often simplify or even eliminate the need for factory service. The Hafler XL-600 is warranted for 3 years from date of purchase, including parts, labor, and return shipping costs from the factory to the owner within the Continental USA. [. . . ]