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Tips: Impedance Matching

We strongly suggest that you experiment with the 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.

Since the impedance of most loudspeakers vary over a wide range experimentation is essential.
Most speakers have a rated impedance of 4 or 8 ohms. We recommend starting with the 8 ohm
connection; after you know the sound if that connection, try the 4 ohm connection. Choose the
connection that sounds best to your ears.

If  you  bi-wire  your  system  (run  separate  speaker  leads  from  the  amplifier  to  the  high  and  low
frequency transducers) you may discover that two different impedance taps work best.

Contrary to popular misconception, no power is lost due to unused output taps.

For more information consult VAC Technical Monograph 90-9, which may be viewed on our wesite
(http://www.vac-amps.com).

Summary of Contents for ?200 Phi Two Hundred

Page 1: ...F200 The VAC Phi Two Hundred Stereo Beam Power Amplifier Operation Maintenance Information Valve Amplification Company Manual issued 01 02 2009 Revised 03 11 2009 01 21 2010...

Page 2: ...y high voltage and could present a serious possibly lethal shock If a tube breaks unplug the amplifier and wait 30 minutes then remove the tube Keep flammable objects away from the amplifier DO NOT LE...

Page 3: ...nstalling New Output Tubes Biasing Checking Output Tube Condition Replacement of Low Level Tubes Care Of Chassis Tips and Advice A Word About Tubes in General Output Tubes Low Level Tubes Impedance Ma...

Page 4: ...r circuit extremely fast and vivid sound is achieved from both single ended and balanced sources The Phi 200 may be used as a 100 watt channel stereo amplifier or can be connected as a 200 watt monoph...

Page 5: ...d goes to or Positive Follow the labels for the impedance that best matches your loudspeakers 06 Connect a12 volt trigger cable into the socket on the back panel if desired this allows the amplifier t...

Page 6: ...age to your loudspeakers or the amplifier Do not operate the amplifier without a loudspeaker or load resistor attached Do not allow anything to touch the tubes in normal operation they become very hot...

Page 7: ...s MONO CONNECTION without Mono Switch option early production units For 200 watt mono operation 1 Connect identical input signals to the two input jacks It is possible to use a Y adapter to do this or...

Page 8: ...amplifier off when you are not listening Any time that the VAC Power Amplifier has not been used for a few weeks the sound may be different This is also normal for high resolution audio equipment Opti...

Page 9: ...plifier first turns on at 60 seconds 90 seconds two minutes and five minutes In the earliest checks set the bias so that the meter read a bit to the left of center Final setting should be made after 1...

Page 10: ...lightly Do NOT touch the tubes themselves as they are hot enough to cause serious burns NOTE Some versions of KT88 will evidence a dull orange glow over a small percentage of the tube s anode see phot...

Page 11: ...ement tubes are available from VAC and other sources For further information refer to Tips Advice A Word About Tubes in General and Tips Advice A Word About Low Level Tubes CARE OF CHASSIS VAC chassis...

Page 12: ...of a tube amplifier can select those tubes which sound like the real thing in his her specific system Of course if the manufacturer you prefer is rare you may want to purchase a few spare tubes for th...

Page 13: ...er and driver tubes in the Phi is the 6SN7 medium mu octal twin triode Your amplifier is fitted with the current production VAC Tested 6SN7 from China which we find superior to the NOS types we have t...

Page 14: ...vary over a wide range experimentation is essential Most speakers have a rated impedance of 4 or 8 ohms We recommend starting with the 8 ohm connection after you know the sound if that connection try...

Page 15: ...z using the normal RCA input jack there are several steps you can take 1 Use the shortest interconnects possible 2 Use interconnects with good shielding properties 3 Keep the audio cables as close tog...

Page 16: ...it measures good and sounds bad it is bad If it measures bad and sounds good you ve measured the wrong things For those concerned with test bench performance the following describes typical measured p...

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