Owner`s manual

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Ayon Audio – Hart 18 – 8101 Gratkorn – Austria – Phone: [phone]
www.ayonaudio.com
5. Intelligent Auto-Fixed-Bias (AFB) circuitry
The bias setting controls the current, thereby the operating point of the tube and therefore is vital for its
lifetime and sound. With the bias the power amp can be tuned to cooler/cleaner or hotter/more impure;
in the latter case the amp has more punch and can be overdriven more easily. However, too high a bias
leads to faster wear of the tubes. For tube amplifiers an "automatic" bias control of the power tubes
would be advantageous because differences, aging, or voltage shifting could be compensated more
easily or reliably. Furthermore the customer needs not care whether setting of the bias value is correct.
Unfortunately, this desirable automatic device has serious disadvantages such as significant deterioration
of sound and power. Creating a new automatic "fixed bias" circuit controlling the operating conditions of
the power tubes reliably in the specified way WITHOUT negative influence on the sound or output power
respectively was a very serious challenge for the Ayon development team.
This intelligent Auto-Fixed-Bias system must not be mistaken for a semi-automatic or so called fully
automatic bias fixture which can never achieve a result comparable with the new Ayon Auto-Fixed-Bias
circuit. The Ayon Auto-Fixed-Bias circuitry delivers the best possible combination of sound properties,
measured power and usability because it does not operate during music listening. This system does not
result in deterioration of sound, loss of output power, or any other negative concomitants.
Additionally the Auto-Fixed-Bias system is equipped with a sophisticated electronic two-way-protection
circuit which is always active during the tube test program or the switch-on period respectively.
In case of excessive bias current or a defective tube the high voltage is switched off immediately either
by a photo coupler controlled "comparator circuit" or by an analog-digital-converter. These protection
circuits do not lie in the signal path.
● An added benefit to this approach is that, should a tube fail prematurely, the single tube can be
replaced without having to purchase a matched set.
Mute LED remark: when the auto-fixed-bias adjustment or the tube test program is active the amplifier
always switches into the MUTE mode; this is indicated by the MUTE LED in combination with the blinking
ayon-logo.
Note: the auto-fixed-bias-system can also be activated manually when the amp is on by pressing the
bias-setup-button. Exception: during the 10 minutes after switching on the amp the system is deactivated
for safety reasons (the AA62B tubes first must have reached their operating temperature); i.e. in this
period you cannot perform a manual activation of the bias-setup. This function is mainly for servicing only
and is not really required for the user! The resulting actions are the same as in automatic mode, in
principle.
Bias meter: The successful operation of the auto-fixed-bias circuit can
be also indicated by an analog bias meter located at the top plate.
Every power tube can be checked by this bias meter too; the tubes are
selected by means of the bias selector switch at the rear panel. Switch
the bias selector to the desired tube V1 or V2. When the bias meter
doesn’t show the correct value (120-140mV), the particular output tube
is maybe defective. Press the “bias-setup” button to see if the bias
meter show the correct value again, if not, please changes the tube.
(The auto bias system is not able anymore to adjust the bias correctly
because of insufficient cathode emission). In this case this tube should
be replaced with a known good one and the bias meter should show
the correct bias value again. Note: Turn on Bias meter with NO music
signal going to the amplifier.
Bias meter