Specifications

AMP2-T assembly instructions. © 41Hz Audio / www.41hz.com Revision 1.0T boards
b. The leads of the current sense resistors R1, R2, R15, and R18. These should
preferably be mounted with some standoff that helps keeping them cool. The
whole supply rail current will pass through these resistors.
c. Mount the gate diodes and resistors D1, D2, D3, D4, R3, R4, R11 and R12.
d. Mount the other axial resistors.
7. Solder the offset trim potentiometers R104 and R204
8. Before connecting the final components, now is the time do a first test of the board. Do
not proceed further until the test described below, has completed successfully. Please
look at APPENDIX 4 for the connector pin assignments. Testing:
a. Check the resistance on the power supply connector J1. It should be about 1
Mohm between positive and ground, about 1.3 Mohm between negative and
ground and about 2 Mohm between positive and negative rail.
b. The +5V input should measure something like 0.5 kohm to ground.
c. The +5V supply should be well stabilized and fused, (before the voltage
regulator), at 200mA. Use a shielded cable for connecting the +5V and connect +
to pin 8 and negative to pin 7 of J2. The +5 supply should never go above +6V,
or be connected with wrong polarity, as this will damage the Tripath chipset.
Do not turn on the power yet.
i. Note, the +5V is used for both the analogue preamp section of the Tripath
chip and also for the logic level signals in the chipset. It is essential that
the +5V supply is quiet / well stabilized. Using shielded cable for hooking
up the +5V prevents feedback of high frequency EMI from the power amp
into the analogue section.
d. Connect the rail positive, ground and negative leads to J1. Double check the
polarity! Connecting the wrong polarity will damage components. The amp
may draw around 100 mA on the positive rail and around 200-250 mA on the
negative rail at “transistor radio volume”. Do not turn on the power yet.
i. As a protection you should use current limiting resistors in series with the
power supply lines. If the amp draws unexpectedly high current, the
voltage will drop below the level where under-voltage limit shuts off the
amp. Suitable resistor values can be 68 to 100 ohms, 3W for the positive
rail and 33 ohms to 47 ohm 3W for the negative rail. With the default
components, the amp will mute if the supply voltage drops below about
+/- 34V. Do not turn on the power yet.
ii. Alternatively, the amp could be protected with a 100mA fuse, placed on
the AC side of the supply. This way, both rails de-power in the case of
failure. The down side is that the energy in the supply capacitors may
discharge through the amp, even if the fuse has blown. Other fuse values
may be required, depending on your transformer and capacitors. Do not
turn on the power yet.
e. The onboard LED is connected via R90 (2.2K). Optionally, instead connect an
external LED from pin HMUTE (J2 pin 9), for example on the front panel of your
amp. An external LED needs its own 2.2 k resistor to ground. A LED helps a lot
when testing.
i. Do not connect two LEDs at the same time, as this may draw too much
current from the HMUTE output