Ton Giesberts
About the article

Sound Pressure Level (SPL) Meter

the king-sized model

Sound Pressure Level (SPL) Meter
The measuring instrument described here distinguishes itself in one respect from all the others in its species. The display has been implemented in such a way that is – without exaggeration – not easily overlooked. This opens up entirely new possibilities for its application.The most salient feature of this circuit is that the display consists of a panel made from 10 incandescent lamps. This immediately catches the eye, and at the same time it is obvious that we’re dealing with a novel kind of measuring instrument. A typical sound pressure or VU meter makes use of a much more modest LED or moving coil indicator.
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Component list
R1,R9 = 10k?
R2 = 220?
R3 = 27k?
R4,R7 = 100k?
R5 = 3k?9
R6 = 3k?3
R8 = 39k?
R10 = 5k?6
R11 = 220k?
R12,R13,R14 = 10k?0
R15,R16 = 20k?0
R17 = 47k?
R18 = 1k?00
R19 = 30k?9
R20,R21 = 820?
R22-R31,R34 = 100?
R32 = 1k?2
R33 = 470?
R35 = 4?7
R36 = 2k?7
P1 = 500k? preset
P2 = 500? preset
C1,C2 = 22µF 40V radial
C3,C14 = 470µF 16V radial
C4 = 15pF
C5 = 56nF, lead pitch 5mm
C6 = 2n7, lead pitch 5mm
C7 = 4n7, lead pitch 5mm
C8 = 8n2, lead pitch 5mm
C9 = 10 n, lead pitch 5mm
C10,C11 = 2µF2 63V radial
C12 = 100nF
C13 = 100nF, lead pitch 5mm
C15 = 1000µF 6V3 radial
C16 = 470µF 10V radial
C17 = 10µF 63V radial
C18 = 470µF 25V radial
D1-D10 = LED, red (no highefficiency type)
D11 = 1N4148
D12 = BAT85
D13 = LED, green (high-efficiency)
IC1 = TLC274
IC2 = TLC272
IC3,IC4 = LM3915
IC5...IC14 = S202S02 (Sharp)
IC15 = 7808
JP1 = 2-way pinheader w. jumper
JP2 = 3-way pinheader w. jumper
K1-K11 = 2-way PCB terminal block, lead pitch 7.5 mm
K12 = cinch socket, chassis mounting
Tr1 = 9V 4VA8 e.g., Gerth 421.09
B1 = B80C1500 in rectangular case (80V piv, 1.5A peak)
F1-F10 = fuse, 500mA, fast, with PCB mount holder
MIC1 = MCE2000 (Monacor/Monarch) or equivalent
F11 = fuse, 32 mA, slow, with PCB mount holder
PCB, order code 020122-1
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