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5.1 DC Bias Voltage Tuning
Since each tube might derivate a bit in parameters, especially from different
series, it needs to re-tune the DC bias voltages to guarantee the machine is
working in the best point and performing the best sound quality.
There are two blue precise adjustable potentiometers (P1, P2) for tuning the
DC bias voltage of each channel. The DC bias has been tuned in factory. But
after run-in for a period or changed another tube, it would be deviated that the
fine-tuning is needed.
Before you tune these, you need a screwdriver (take off the case), a small
screwdriver. (Turn the screw of the potentiometer) and a (digital) multi-meter
to detect the DC bias voltage:
1. Use screwdriver to take out the two upper level screws in the front panel &
another two screws in the back panel. Then, open the upper case.
2. Power ON the machine with no audio signal input.
3. Wait at least 5 minutes for the machine to run in.
4. Use the multi-meter to detect the DC voltage between the test point A (L)
[red] in the PCB & the GND [black] (e.g. the ring of the power switch or the
outer ring of those RCA sockets) of the LEFT channel.
5. Turn the screw on the top of the P1 potentiometer by a small screwdriver
clockwise or anticlockwise until the voltage as close as to +6~+8V.
6. Then, repeat step 4 and 5 for the RIGHT channel by changing the test point
to A (R) [red] and turning the screw on the top of the P2 potentiometer.
7. Power OFF the amplifier.
8. Cover back the upper case and tighten the screws.
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6. Troubleshooting
If your machine is out of order, it may not be very serious. Before you call your
local distributor or us to repair, you are suggested to check the following:
SYMPTOM POSSIBLE
CAUSE REMEDY
cannot power ON
indicator not bright
power cords not properly
connected
properly connect the
power cords
power switch is OFF
switch ON the power
no sound at all
the volume level is too low
turn volume level higher
The audio cable not
properly connected
properly connect the
audio cable
the audio source (e.g. CD
player) not started playing
start playing the audio
source
wrong input is selected
check input selection
the speaker cables not
properly connected
properly connect the
speaker cables
Hum
tube not fully pushed in
Insert Tube securely
audio connector plug not
fully pushed in
Insert plug securely
incorrect input switch
position
check the corresponding
input switch
sound
out(s)
loose
connection
check input and output
connections. When all has
been double-checked
reduce volume and switch
unit back on
