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18
This is the heart of the Velleman mixing panels: the actual mixing amplifier with volume,
balance, treble and bass control, and three buffered outputs (2.5V, 1.55V, and 775mV
RMS; output impedance of 1K each). In addition this module contains also a small VU-
meter, a headphone amplifier with selection switch, and the voltage regulators for the
power supply of this module, the monitor and effects module, and the big VU-meter.
ASSEMBLY
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Fit switch SW1, AT THE SOLDER SIDE. Proceed as follows (see also fig. 1) :
Put the pcb, with its SOLDER SIDE UP, on a hard and flat table. Put the switch with its
pins in the holes (the pins are now flush with the pcb-surface at the solder side), and
solder the central pin. Check if the switch stands perfectly upright. To make
corrections, you must reheat the solder, because otherwise you may break off the
copper trace! Now solder the remaining pins too. Although this assembly is quite
strong, care is needed whilst proceeding, in order to preserve the p.c.b.
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Fit the wire jumpers J.
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Fit the resistors:
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R1R and R1L,
for a 12 channel mixing panel: 3K9 (orange, white, red, gold)
for a 6 channel mixing panel: 8K2 (grey, red, red, gold)
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R2R, R3R, R4R, R2L, R3L, and R4L, 1K (brown, black, red, gold)
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R5R through R8R, and R5L through R8L, 10K (brown, black, orange, gold)
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R9L and R9R, 3K3 (orange, orange, red, gold)
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R10R and R10L, 1K (brown, black, red, gold)
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R11R and R11L, 1K8 (brown, grey, red, gold)
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R12R, R13R, R12L, and R13L, 1K5 (brown, green, red, gold)
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R14R through R17R, and R14L through R17L, 10K (brown, black, orange, gold)
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R18R and R18L, 33K (orange, orange, orange, gold)
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R19R and R19L, 1K8 (brown, grey, red, gold)
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R20R and R20L, 180 Ohm, (brown, grey, brown, gold)
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R21R and R21L, 82 Ohm (grey, red, black, gold)
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R22R and R22L, 47K (yellow, violet, orange, gold)
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R23R, R24R, R23L, and R24L, 100K (brown, black, yellow, gold)
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R26L and R26R, 1K (brown, black, red, gold)
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R27L and R27R, 2,7 Ohm (red, violet, gold)
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Fit the jumpers VU-R and VU-L, if you are not going to install a big VU-meter. In this
case the small VU-meter responds to what you hear in the headphone: the output or
PFL.
Fit the resistors R25R and R25L, 3K9 (orange, white, red, gold), if you do install a big
VU-meter. In this case the small VU-meter remains connected to the output,
regardless of the position of the headphone selection switch.
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Fit the sockets for IC1and IC2. NOT for IC3L, IC3R and IC4 !
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Fit IC3L and IC3R, KA2285 or equivalent, with its notch towards selection switch SW2.
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Fit IC4, LM2877 or equivalent, with its notch towards the C10.
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Fit C1R and C1L, 100nF MKM capacitors.
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Fit C2R, C3R, C2L, and C3L, 4n7 MKM capacitors.
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Fit C4R and C4L, 47nF MKM or ceramic capacitors.
