Audio Level Check for Line Input
for the PC sound card
Published in issue 315, November 2002
This simple control circuit allows the level of an external stereo audio source to be adapted to the sensitivity of, for example, a sound card. In addition, an LED indicates if any signal levels are present that can cause the input to be overdriven.Standardisation is a long way off in many areas. This is certainly true for audio signal levels — a phenomenon that many of you will have encountered at one time or another, usually at the most inopportune moment. With equipment such as cassette decks, tuners, CD/DVD-players, one can never be quite sure what signal level to expect. Anything is possible from around 200 mV to 2 V, or so.
R1,R10 = 270kΩ
R2,R6,R11,R15 = 1kΩ
R3,R12 = 56kΩ
R4,R5,R13,R14 = 4kΩ7
R7,R16 = 1MΩ
R8,R17,R26 = 100Ω
R9,R18 = 100kΩ
R19,R20 = 1kΩ8
R21,R22,R27,R28 = 47kΩ
R23 = 10kΩ
R24 = 6kΩ8
R25 = 820Ω
P1 = 47kΩ stereo potentiometer, linear
P2 = 100 k mono potentiometer, linear
Capacitors:
C1,C3,C4,C6 = 4µF7 63V radial
C2,C5 = 47pF
C7 = 47µF 25V radial
C8,C12 = 220µF 25V radial
C9,C10 = 100nF
C11 = 100µF 10V radial
Semiconductors:
D1-D4 = 1N4148
D5 = zener diode 5.6V, 0.4W
D6 = LED, red, high-efficiency
IC1 = TS924IN ST (Farnell)
IC2 = LM339
Miscellaneous:
S1 = rocker switch, 1 make contact, for chassis mounting
BT1 = 9 V battery with holder
Two 3.5 mm stereo jack sockets, chassis mount
PCB, order code 020189-1
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Click below to download a PDF copy of this article from Elektor magazine. Please note. In view of the complexity of international markets, Elektor cannot guarantee the availability of components for this project.
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