Specifications

AMP2-T assembly instructions. © 41Hz Audio / www.41hz.com Revision 1.0T boards
combine into half the equivalent value, increasing the corner frequency. It can also be noted that
the Tripath boards and measurement results given in the Tripath data sheets are usually done
with standard electrolyte capacitors as input caps.
Modulator gain
The AMP2 and TK2350 is a feedback topology. The voltage gain of the power section of the
amplifier is set by resistors that feed back the loudspeaker output voltage to the chipset. The
ground for each side has separate lead backs, for accurate sensing. This means there are four
feedback paths and four feedback resistors. For optimal amplifier use, the gain resistor values
could be changed, depending on the used rail voltage and the application. Some "over gain"
could be used so that the power stage will start clipping, i.e. output voltage is as high as the rail
voltage, when the input signal is a bit over the nominal maximum. If the gain is set to low then
the power stage will run below full power even when the input stage signal is high enough to
saturate the input stage. If the gain is to high, the power stage will start clipping at a low input
signal and this implies the preamp level has to be turned down, which may be unfavorable from a
THD+N point of view, especially at low volume. A reasonable balance has to be found.
Calculating the modulator gain / feedback resistor values
Description Typical value AMP2 Component
Vpp Rail voltage (+/-) 40-50V 50-60V
Rfba Typical value 1 K 1 K R105, R108, R205, R208
Rfbb = Rfba * Vpp/(Vpp-4) 1.1 K 1.07 K R107, R110, R207, R210
Rfbc = Rfba * Vpp/4 12 K 15 K R106, R109, R206, R209
Current limiting
The TK2350 chipset has built in over current setting. Actually, it senses the voltage over a
current sense resistor via set point resistors. The set point resistors are of the 0805 size. At an
over current situation the amplifier will go into mute and has to be power cycled off/on to reset.
The resistors supplied in the AMP2 component kit are 20 K and will trip the amplifier at 10A.
You may want to select other values for your application. The on-board power supply capacitors
are placed after the current sense resistors. Therefore the MOSFETs may draw current from the
caps and the current sense resistors will see a slightly smoothed current signal. The over current
sensing is still fast and will mute the amplifier even on short over current peaks. Please note that
the over current shut-off sets the chipset into mute state but if the MOSFETs are damaged, the
rail voltage can still be on the speaker outputs. The over current protection should therefore be
regarded as “soft” protection. Proper fuses are still required. But fuses may not blow before the
loudspeakers are damaged. For “hard” shutdown you can use a relay on the speaker outputs,
controlled by the HMUTE signal output. This will shut of the speaker outputs even if the output
FETs are damaged.