This class A preamplifier has been designed in a symmetrical structure. In the input differential stages we’ve used the dual transistors T1 and T2. Polarisation correction is essential because of the amplification differences and is assured with T12. P2 brings the output voltage to 0. For maximum performances, T7 and T9 surfaces must be in contact, also T8 and T10 surfaces. The T9 and T10 repose current is adjusted to 20mA with P1. Frequency bandwidth is 2.4MHz.
Some measured characteristics at ±15V power supply and 1Vef/1Ω output voltage: