Trends Combo One Hi-Fi System User Guide
Section 7. Technical Notes
11
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7.1 Offset the DC bias voltage of the speaker terminals
There are two blue adjustable potentiometers (Rt) inside Trends TA-10.2P SE
Class-T Power Amplifier for offsetting the DC bias voltage between the positive (+ve)
and negative (-ve) terminals of each channel. Offset this DC bias voltage can
enhance the purity of the sound and minimize the “pop” sound when power on and
off. The DC bias has been pre-set in factory. But after run-in for a period, it would be
slightly changed 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 top level screws in the front panel &
another two screws in the back panel. Then, open the upper case.
2.
Power ON the amplifier.
3.
Use the multi-meter to detect the DC voltage (200mV) between +ve & -ve
terminals of the RIGHT channel.
4.
Turn the screw on the top of the LEFT (near the front panel) potentiometer by a
small screwdriver clockwise or anticlockwise until the voltage as close as to
±0mV.
5.
Then, repeat step 3 and 4 for the LEFT channel by turning the screw on the top
of the RIGHT (near the back panel) potentiometer.
6.
Power OFF the amplifier
7.
Cover back the upper case and tighten the screws.
7.2 Jumper Setting for Different Tube Series
Trends Audio
has already pre-set the jumpers and fine-tuned the DC bias voltage
of each PA-10 with the packaged vacuum tube before shipping. However, changing
different tubes to taste for different sound is the great fun for many audiophiles and
also a great feature of PA-10. There are some important notes should be aware
before changing tubes.
Trends PA-10 supports two major tube series:
(1) 6DJ8, 6922, 6N11, 6H23n,
ECC88, E88CC, etc…
, and
(2) 12AU7, 5963, 5814, ECC82, etc…
If you change
the tube within the same series, it needs to re-tune the DC bias voltages ONLY. If
you change the tube from another series, it needs both to re-tune the DC bias
voltages and re-set the jumpers.
Otherwise, the tube may be burnt out
.
You can simply configure the amplifier to support the two different tube series by
resetting the jumpers in J3, J4, J5 in the PCB as follows. (Remember to power OFF
the machine before setting)
6DJ8 Series
12AU7 Series
J3
O O O
O O O
O O O
O O O
J4
O O O
O O O
J5
O O O
O O O
Trends Combo One Hi-Fi System User Guide
Section 7. Technical Notes
12
7.3 DC Bias Voltage Tuning
Since each tube may 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 (R3, R13) inside Trends
PA-10 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
R3
potentiometer by a small screwdriver
clockwise or anticlockwise until the voltage as close as to
+16.5V
.
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
R13
potentiometer.
7.
Power OFF the amplifier.
8.
Cover back the upper case and tighten the screws.
