VK4PP CW Audio Filter

Centre Frequency: 700 Hz
Bandwidth: 200 Hz
DC Power: 5VDC
GAIN: Up to 20dB via R11 and R12 + trimpot.

Resistors 1206 SMD:

• R1 33k
• R2 33k
• R3 1M
• R4 47k
• R5 47k
• R6 36k
• R7 36k
• R8 10k
• R9 750k
• R11 100K
• R12 100K
• Note the 2 extra 10 K resistors, theses are additions in rev .02 board to bias the circuit.

Capacitors 1206 SMD:

• C1  0.1u  104
• C2  47n   473
• C3  36n   363 (33n + 3n3 stacked)
• C4  1n    102
• C5  39n   393 (33n + 5n6 + 390p stacked)
• C6  1n    102
• C7  2n2   222
• C8  2n2   222
• C9  0.1u  104 NOTE this should be 1n (102)
• C11 0.1u  104
• C14 220u  Electrolytic

Other:

• IC TLC274 / LM324
• Relay OMRON G6S-2-DC5
• 200K/100k trimpot

R11 and R12 are optional to parallel the 200k trimpot to make it a logarithmic 100k.
Or just use a linear 100k pot.

Use a switch connected to 5V to turn on the filter. 
This powers the opamp and switches the relay feeding the audio into the circuit.
When off the relay just passes the audio straight through unfiltered