VAC PA160 "UNIVERSAL" MONOPHONIC POWER AMPLIFIER Operating Instructions Index: Introduction Unpacking Installation Operation Bias Adjustment Fine Tuning Your System Operating Mode Feedback Ground Configuration Switch Load Impedance Sonic Troubleshooting Tube Selection Installing New Tubes Care of Chassis How to Contact VAC Specifications Location of Tubes & Controls Warranty Information Registration Form 2 3 3 4 4 5 5 6 6 7 7 8-10 11 12 12 13 14 15 15 DO NOT OPEN THIS UNIT - THERE ARE NO USER SERVICEABLE
Introduction The PA160 is a wideband low-feedback monoblock power amplifier producing approximately 160 watts per chassis in standard trim. It is largely based on the critically acclaimed VAC PA90C-1 circuit, which was has been praised by many authorities since its introduction in 1990. This improved version delivers a new level of performance, musicality, flexibility, and convenience.
Unpacking Do not lift the PA160 by the transformer cans! Each tube socket on the amplifier is covered by a small round sticker. The color of this sticker corresponds to the color of the sticker on a tube. Fit each tube into the matching socket, first removing the sticker from the tube and socket. Handle tubes by the bases, not the glass. The bias levels for the output tubes have been factory set, but should be checked during the installation procedure.
Operation Continuous operation is not recommended. If the amplifiers will not be auditioned for a few hours it is best to turn them off. This avoids undue stress to the KT88 output tubes, whose lives average between 3,000 and 8,000 hours depending upon brand fitted and random variations within the tubes themselves. Do not operate the tube type switch while the unit is turned on. As with all high fidelity products, the sound characteristics of the VAC amplifiers change somewhat as they warm up.
Fine Tuning Your System The VAC PA160 offers unparalleled opportunities for fine tuning your system for best subjective reproduction. At first glance this may seem a bit intimidating, but it's actually quite easy to do. The possible adjustments are output stage operating mode, adjustable negative feedback, output impedance matching, and output tube type. Before critical tuning, be sure that the amplifier is fully broken in, having operated for at least 150 hours.
Feedback The feedback controls are provided for adding controlled amounts of loop negative feedback to the amplifier. The exact amount depends on the tube type fitted and the output operating mode selected. The exact numbers are given in the specifications section. The "A" setting indicates no loop feedback, while "B" through "F" correspond to increasing amounts of negative feedback. A given amount of feedback reduces the sensitivity of the amplifier by that amount.
Output Impedance Matching We strongly suggest that you experiment with the three available impedance connections for the best sonic match with your system. Since no loudspeaker represents an unchanging impedance at all frequencies, it is impossible to assert with certainty which output tap is appropriate to use. In many systems an amazing difference in sound will exist between the various impedance taps.
Tubes in General It is a truth that each brand of tube sounds different in a particular high resolution circuit. This is because no two manufacturers make a tube type in quite the same way, and the central tendencies of the performance parameters will differ slightly with each maker. To emphasize the point, examine the plate structure of any two 12AX7 from different manufacturers will probably find that they may not even the same shape and size.
Output Tubes Your VAC Amplifier can use the following output tube types: KT88, 6550/6550A, KT77, EL34/6CA7, KT66, 6L6GC. DO NOT MIX TUBE TYPES. Set the tube type switch to correspond to the tubes fitted and adjust bias level for proper operation. The standard output tube is the new Golden Dragon KT88, which possess a nice combination of image size, tonal weight, and openness. By contrast, the Golden Dragon EL34 provides a leaner, sharper sound. The Golden Dragon KT66 is darker in tone than a KT88.
Phillips/ECG/Sylvania 6550A: Similar to the GE tube, perhaps a bit better. Sovtek 6550: Samples tested do not bias correctly, having insufficient current flow. Not recommended. With regard to the EL34/6CA7/KT77 family, the following observations apply: M-O Valve Company/Genalex/GEC KT77 (U.K.): Accurate and dramatic imaging, great nuance, control of dynamics, sweetness, and bass quality. Quality is surprisingly variable for a premium tube, and we have had to reject about 10% of the KT77s we have purchased.
Installing New Output Tubes Replacement tubes are available from VAC and other sources. It is not necessary that they be matched pairs, although a slight improvement in measured performance may be achieved in this way. Make certain that each tube fits firmly in its socket. A tube that fits loosely may not make correct contact on all pins and might "run away" (read on). It is best not to mix brands of tubes. ALL POWER MUST BE OFF.
Care of Chassis VAC chassis are aluminum for superior electromagnetic performance. The finish is matt and textured powder coat paints. This finish is durable but can be scratched or chipped, just as that of a fine automobile may be damaged. Cleaning with a slightly damp cloth WHILE THE AMP IS SWITCHED OFF AND UNPLUGGED should suffice. Need Help? Please call us with any questions you may have. It is better to ask than to guess.
SPECIFICATIONS The VAC System has been developed with the critical ear as the major arbiter of quality, with both conventional and unique measurements providing insight and guidance as necessary. The lack of emphasis on measurements is due to the fact that engineering's arsenal of equipment and techniques do not operate on the pattern recognition principals that control human perception of sound. In the immortal words of Daniel von Recklinghausen, if it measures good and sounds bad it is bad.
