R6, and C3. The part number of C3
(810-CGA5L2X7R1C225K given on
the schematic) is a surface-mount
ceramic. If you need a thru-hole part,
use 2. 2 µF, 35 volt tantalum.
I chose the LM6492 op-amp
because it is rail-to-rail input and
output, but LM358 or similar will
work.
The output switch, Q1, is rated
70V 10A, and has RDSon of 0.1
ohms max. Any TO-220 MOSFET
with low RDSon (less than 0.1 ohm)
should work without a heatsink.
HEADSET AMPLIFIER
QI participate in a lot of conference calls and have difficulty understanding some of the other
participant’s audio. Although I have a
substantial high frequency loss, many
of the other participants come through
loud and clear. However, many other
caller’s audio sound is “muffled.” It’s
loud enough — just lacking sufficient
highs to make it clear. Can you
provide a circuit and parts list for an
amplifier with an adjustable high
frequency boost that I could plug in
between my headset and the cordless
phone ( 2. 5 mm)? There may be a
product out there that will work but I
haven’t found one.
— Bill P-MA
AI’m not sure this circuit (Figure 7) will solve your issue, but it provides a max of 20 dB boost above 1 kHz.
Both the gain and boost frequency
vary with the pot setting. NV
24
August 2012
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