Article

Audio Level Check for Line Input

for the PC sound card

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.

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Materials

020189-PCB.pdf

Gerber file

CAM/CAD data for the PCB referred to in this article is available as a Gerber file. Elektor GREEN and GOLD members can exclusively download these files for free as part of their membership. Gerber files allow a PCB to be produced on an appropriate device available locally, or through an online PCB manufacturing service.

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PCB

Download Gerber file: 020189-1.zip

Component list

R1,R10 = 270k?
R2,R6,R11,R15 = 1k?
R3,R12 = 56k?
R4,R5,R13,R14 = 4k?7
R7,R16 = 1M?
R8,R17,R26 = 100?
R9,R18 = 100k?
R19,R20 = 1k?8
R21,R22,R27,R28 = 47k?
R23 = 10k?
R24 = 6k?8
R25 = 820?
P1 = 47k? 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