Vectronics VEC-1604K - Manual (Page 16)

VEC-1604K Owner's Manual Portable CD Amplifier Kit
14
Sound Distorted: Check CD Player volume. If this is too high, distortion may
result. Also, operating voltage may be too low or battery condition poor.
Finally, speakers may be damaged or unable to handle power provided by your
amp.
Insufficient Volume: Check CD Player volume. If this is too low, insufficient
drive may be available for your amplifier. Also, check speaker wiring.
Insufficient Bass Response: Check speaker phasing.
If these checks fail to uncover the problem, repeat the "QC" check one more
time. Service records show that, for most malfunctioning kits, outright
component failure is relatively rare. In most cases, the culprit is a misplaced
part, reverse-polarized capacitor, improperly installed IC, or a faulty solder
connection. If, despite your best effort, you cannot solve the problem, kit repair
services are available through Vectronics. See the warranty on the inside front
cover for complete instructions.
THEORY OF OPERATION AND SPECIFICATIONS
Referring to the schematic, your VEC-1604K amplifier uses two (2) identical
pre-amp/power-amp ICs--one for each channel. For the left channel, volume is
controlled via a voltage divider (potentiometer R1). The divider output feeds a
fixed attenuator (R3, R4) to further reduce headphone level signals from the CD
player. A bridge-type tone control consisting of R13, C1, and C2 provides
adjustable attenuation of bass frequencies prior to amplification. U1 then boosts
the AF signal and provides power amplification for speaker-level output. Output
is single-ended with DC isolation provided by coupling capacitor C11. Snubber
circuit R9, C5 prevents high-frequency oscillation due to reactive speaker loads.
R12 provides a "safety" load to prevent over-voltage damage if no speaker is
connected. Vcc-line filtering is electronic, using R8 and C9 to establish the
proper LF time constant. Right channel circuitry is identical to the left.