Bose Personalized Amplification System Troubleshooting Manual page 13

Point Nominal
Line In, Trim -30dBV un-
@ Max bal
Line In, Trim -1dBV dBV
@ 12:00 un-bal
Line In, Trim +12dBV un-
@ min bal
Mic., Trim @ -50 dBV
max balanced
Mic., Trim @ -21 dBV
12:00 balanced
Mic., Trim @ -8 dBV
min balanced
Ch1, Ch2 +6 dBV
Line out XLR balanced
Dig. Vol. 0 dBV
Control, input
Dig. Vol. -10 dBV
Control,
output
Insert Send -10 dBV
Insert Return -10 dBV
A/D input -10 dBV
D/A output 0 dBV
Bass Out 0 dBV
Amp In 0 dBV
Amp Out 30 dBV
The minimum input level that would allow the system to reach full output (with all gain controls
all the way up) is -72 dBV. This is the output level of a Shure SM58 being exposed to about 78
dB SPL and should be sufficient for almost any application.
This gain scaling puts the main responsibility for the high-signal performance of the system on
the digital limiters. The limiters need to make sure that the output never exceeds 0dBV. The extra
6 dB headroom in the DSP can be used to compensate for gain variance in the power amp and
to allow the DSP to overdrive the power amps for very short periods of time. It may turn out,
that, for certain instruments, this will be required to achieve maximum SPL at acceptable sound
quality.
THEORY OF OPERATION
Peak Comment
- 12 dBV Ch1 / Ch2 Vol. + Master @ 12:00. Maximum input
limited by input INA163 output clipping.
+17 dBV Ch1 / Ch2 Vol. + Master @ 12:00. Maximum input
limited by input INA163 output clipping.
+18 dBV Ch1 / Ch2 Vol. + Master @ 12:00. Maximum input
limited by input Buffer.
-32 dBV This nominal = the output level of a Shure SM58
balanced microphone that is exposed to 104 dBSPL.
-3 dBV
Balanced
+10dBV This nominal = the output level of an AKG C4000
balanced microphone that is exposed to 120 dBSPL.
+24 dBV
balanced
+18dBV
+18dBV The nominal gain setting here is -10dB for the
volume control +20 max out assumes Volume @
Max. (+10 max)
+8dBV, Peak @ 12:00 / Max Volume. Nominal is
+18dBV conservative but should also work well for cheap
stomp boxes
+6dBV Assumes FX device in loop is set for unity gain
Peak limited by A/D input overload.
+4.5dBV Assumes max voltage at the A/D = +6dBV=0dBFS,
D/A output filter gain = -1.5dB
+4.5dBV The total excess gain in the DSP will be 16 dB, with
(debug) a nominal setting of +10dB. Again we assume
0dBFS = +6dBV. It is the responsibility of the digital
0dBV
limiter to ensure that power amp does not clip, i.e.
(normal)
that the output will not exceed 0 dBV
0/+4.5dBV Limiter engaged (normal operation) / Debug
+6/10.5bal Bass Out can be used Balanced / Un-balanced
0 dBV Nominal levels throughout the system are
referenced to full output power, so nominal & peak
are the same
30 dBV This is maximum output at clip level ~250W
@ 4 ohms
Table 2. Nominal and Peak Signal Levels
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