Compressor/limiter/clipper

Compressor/limiter/clipper - stereo version

Stereo version of the limiter includes common gain control for both channels. It does not affect the stereo information. Release time trimmer is common for both channels.

hlimst1.jpg (39836 bytes)

Characteristics:

Supply voltage:	9-16 V
Quiescent supply current (12 V):	30 mA
Output voltage:	linear adjustable 0-3.5 V p-p (0-1.2 V rms)
Lower cut-off frequency (3 dB):	input: 25 Hz, output: <2 Hz
Upper cut-off frequency (3 dB):	14.5 kHz
Min. input voltage:	0.6 V p-p (0.2 V rms)
Input impedance:	5000 ohm
Output impedance:	500 ohm
Signal-to-noise ratio:	>70 dB

Schematic diagram:

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:

If you have a possibility to measure static current gain of the transistor (h_21e), find a pair of Q1's with similar h_21e 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.

PCB:

Top side. Includes 3 wire-bridges.

Bottom side.