Stereo Microphone Preamplifier

There are still a lot of hobbyists who enjoy making high-quality live audio recordings of concerts, interviews, radio broadcasts, natural sounds, and so on. Professional equipment such as Nagra and the like is simply too expensive. We can thus be thankful that many MP3 players are equipped with an analogue input and a high-performance MP3 or WMA encoder.

1. The circuit diagram shown in Figure 2 should be corrected to reflect that the negative terminal of capacitor C3 is connected to junction R10/R18/T2 base, i.e., not to the emitter of T2 as indicated. The same applies to C12 and T6. The printed circuit board design (Figure 4) is correct.
The indication with connection point ‘C1’ should be moved one level down, i.e., from GND1 down to the same level as C9.

2. On the PCB component overlay, the labels of SMD resistors R29 and R32 have been transposed. Resistor 29 (2 kΩ) should be the top device in the row of resistors fitted to the right of S1 and S2. R2 (6kΩ8) should be directly below it.