Nuts and Volts - August 2012

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