Elektor Fortissimo-100, Руководство по монтажу

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Elektor Fortissimo-100 Power Amplifier Kit
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even cause instabilities and oscillations due to the high speed of the
amplifier as its gain-bandwidth product is 2.8 GHz! Star-Ground of the
amplifier is in the center of the PCB, located at the loudspeaker Ground
connection, K4. Only there, the Ground connections of power supply,
loudspeaker and combined input and feedback come together.
17 – Selecting BC546B/BC556B Transistors
for Differential Pairs
Figure 37. Test circuits for selecting matched transistors
for use in the differential amplifier stages
To select the transistors for the differential input stages, simple circuits
can be built on a breadboard. Use SIL or IC sockets to easily swap
TUT’s or use a solderless breadboard. For lowest offset, it’s best to use
two transistors placed or clamped against each other and then meas-
ure the potential difference between the 3.3-kΩ resistors as pictured
in Figure 37. The base currents can be measured across the 10-kΩ
resistors. Preferably the hFE of the NPN device is identical to that of
the PNP device. Swap transistors for the lowest offset between the
collector resistors. Always turn off the power supply before removing
or inserting a transistor as this measurement is less temperature de-
pendent. As a simpler way is to measure each transistor separately,
tabulate UBE and hFE values and select the best matches. This is much