NEDSP900 Development Board
5
2.1
SK6 Speaker/ Line signals
This socket allows for stereo speakers/headphone signals to be input, matched and attenuated.
The input connection Tip is connected to Channel 1 of the NEDSP900 module, while the first
Ring is connected to Channel 2 of the module. Each channel has attenuation/matching facilities
that can be selected using Jumpers JP 1 through to JP4 as given in the table below:
Low Impedance
Speaker Level
(8 Ohms/3 Watts)
Low Impedance
Headphone Level (33
Ohms/30mW)
High Impedance
Line level (10k
Ohm/ 0.707 v p-p)
Input 1- Ring
JP1 (Not JP3)
JP3 (Not JP1)
None
Input 2 - Tip
JP4 (Not JP2)
JP2 (Not JP4)
None
Below is a picture to assist in the location of the above jumpers.
Above: Jumpers set for Speaker Level Inputs Above: Jumpers set for Headphone Level inputs
Note: For Line levels, the Jumpers are removed altogether.
2.2
SK7 Microphone Input signals
A standard 3.5mm stereo jack socket is provided such that a Condenser Electret or other
microphone may be connected to channel 1 only as this has higher gain settings and an AGC
function that can be used if required.
When using SK7, ensure that JP8 (Mic) is removed
(this ensures no speaker signal is fed to Channel 1).
Speaker level signals will only be taken from the
Ring connection of SK6.
2.2.2 Electret Microphone Bias
Most Electret microphones require some form of
electrical bias. In some this is provide by an
