Toa A-503A Manual page 12

TOA Electronics Amplifier Guide
Figure 5 shows a simplified block diagram and a level diagram, indicating gain stages inside a mixer-
amplifier, from mic and line level inputs to 70.7 volt speaker level output. The signal is amplified in
stages, with attenuators (volume controls) between each stage to reduce the overall gain when needed.
The mic pre-amp provides 32 to 52 dB of gain, bringing the mic level signal up to a level that can be
matched with other line level sources. The summing amplifier provides additional gain, bringing all
sources up to 0 dBV. The power amplifier serves to boost the power up to a level that can drive a
speaker. It also provides a low output impedance for efficient power transfer. Lastly, the output trans-
former matches the amplifier to the 70.7 volt line and increases drive voltage to a maximum rated out-
put of +37 dBV.
PBX
Phone System
Matching
B-series Transformer
Input Module
Microphone
M-series
Input Module
+40
+20
B-series Line Input
0 dBV
-18 dBV
-20
-40
-60
M-series Mic Input
-72 dBV to -52 dBV
Figure 5: Block Diagram and Level Diagram of Mixer/Amplifier
Bridge
Input
Level
Gain
Mic
Preamp
Mix Bus
-20 dBV
Pre- Power
In/
Amp Amp
Out
Out In
Master
Level
Link
Summing
Amplifier
A-900MK2 series
Mixer/Amplifier
Pre-Amp
Output
0 dBV
9
Trans-
former
Power
Amplifier
Power Amp
70 Volt Output
+37 dBV