How to make 4 Channel Mic echo preamplifier board... 

4 Channel Mic preamplifier board, assembled by Salcon Electronics. This board contains 2 ICS
PT 2399 and F4558.
A PT2399
The PT2399 is a single-chip echo processor.
Features
1.CMOS technology
2.Least external components
3.Auto reset Function prevent POP noise
4.Low noise, SNR better than 90dB (typical)
5.Low distortion, THD= 0.5%(typical) •
6.User adjustable VCO clock frequency.
B.F4558Features
1. Internal frequency compensation
2. High DC voltage gain (about 100dB)
3. Unity gain frequency bandwidth (about 1MHz)
4. Low input bias current
5. Low input offset voltage and offset current
6. Wide range of common-mode input voltages, including ground
7. Wide differential input voltage range, equal to the supply voltage range
8. Large output voltage swing (0 to Vcc-1.5V)