This application circuit is stereo audio compressor limiter with clipper for processing your FM audio signal. Limiter is a device, which weakens loud signals and intensifies silent signals. On its output there is signal with constant level. Signal clipping on the limiter output allows to increase the signal level without exceeding maximum frequency deviation limit 75 kHz. It's very suitable since preemphasis is used.Be careful if you want to buy any simple compressor/limiter board available on the market! Although a big list of features is mentioned, some of these toys have no signal overshooting protection and have no precise preemphasis with HF clipping option. With these devices it's not possible to keep loud sound AND meet the frequency deviation limit. So there is no reason why to pay for them.
Circuit Schematic:
Left Channel Schematic
Right Channel Schematic
Printed Ciruit Boards (PCB):
Part list:
Left channel:
R1, R3 - 10k
R2 - 1k
R4, R5 - 1M
R6 - 18k
R7, R8, R15-R17, R19 - 33k
R9 - 1M5
R10, R12, R14, R18 - 470R
R11 - 270R
R20, R23, R25 - trimmer 5k
R21 - trimmer 5M
R22 - trimmer 1k
R24 - trimmer 500R
C1 - 4n7 (EU) or 6n8 (USA), plastic
C2 - 470n plastic
C3 - 4n7 plastic
C4 - 330n plastic
C5, C7, C8, C12 - 10n ceramic
C6 - 22n ceramic
C9 - 330p ceramic
C10 - 470p ceramic
C11 - 82p ceramic
C13 - 10u/25V tantalum
C14 - 470u/25V electrolytic
C15, C16 - 220u/10V electrolytic
U1 - TLC272
Q1 - BC557B
Q2 - BF245C
D1, D2 - Red!!! LED diode 5 mm, medium luminance (eg. 200 mcd)
J2 - jumper
Right channel:
R1, R3 - 10k
R2 - 1k
R4, R5 - 1M
R6 - 18k
R8, R15-R17, R19 - 33k
R9 - 1M5
R10, R12, R14, R18 - 470R
R11 - 270R
R20, R23, R25 - trimmer 5k
R22 - trimmer 1k
R24 - trimmer 500R
C1 - 4n7 (EU) or 6n8 (USA), plastic
C2 - 470n plastic
C3 - 4n7 plastic
C4 - 330n plastic
C6 - 22n ceramic
C7, C8, C12 - 10n ceramic
C9 - 330p ceramic
C10 - 470p ceramic
C11 - 82p ceramic
C14 - 470u/25V electrolytic
C15, C16 - 220u/10V electrolytic
U1 - TLC272
U2 - 78L05
Q1 - BC557B
Q2 - BF245C
D1, D2 - Red!!! LED diode 5 mm, medium luminance (eg. 200 mcd)
J2 - jumper
Tips:
Following steps are recommended for the stereo version:
- 1. If you have a possibility to measure static current gain of the transistor (h21e), find a pair of Q1's with similar h21e from about 5-10 pieces.
- Place a temporary 3-pin IC socket piece instead of Q2's. Set the same input level value for both channels. Find a pair of Q2's from about 5-10 pieces which results in the same output level in both channels (you may follow the LED luminance if clipping is set). Then remove the sockets and solder the Q2's found.
Transistor Q2 temporarily placed in socket.
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See more : Transistor FM Transmitter - Stereo Encoder - FM Transmitter Antenna
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