Bose T1 ToneMatch, Руководство по обслуживанию

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Numerous small capacitors in the range of 100-500pF are used to reduce susceptibility to
incoming EMI.
Line inputs 4 and 5
Note: All reference designators apply to Channel 4. The circuits for channels 5 are identical.
J2 is a balanced ¼” TRS connector that provides a short to ground when no jack is inserted to
keep input noise low. R3 and R4 provide a DC reference at ground to avoid DC shifts when
inserting and removing cables. D15 and D16 provide clamping for high DC voltage inputs as
well as other fault conditions like ESD. U12A is a low pass filter (f = 33 kHz) with medium input
impedance for line level signals in.
Channels 4 and 5 are summed at U12B and passed to the U21 codec.
Preamp Outputs
For channels 1, 2 and 3, the preamp outputs after the diff amp are routed through another set of
buffers to convert them to balanced (U7 for channel 1) and present them at a ¼” output jack at
line level.
The output jacks have 100 Ohm resistors in series to provide a low but finite output impedance.
The signal is capacitively coupled for protection against external DC voltages, and referenced to
ground through 47k Ohm resistors. Capacitors to ground provide paths for RF and ESD.
CODECS/DSP
Channels 1 and 2 are converted to balanced signals in U3 and U6, and then applied to codec
U20. D30 – D33 provide clamping to the 5V rail to avoid latching up the codec inputs.
Similarly, channel 3 is applied to codec U21. Channels 4 and 5 are summed in U12 then ap-
plied to U21.
Signal Processing
The Figure below shows the signal processing flowchart
Figure 1: Audio Signal Processing (without USB)
Theory of Operation