feeds the negative input of U1B. The output of U1B is fed
back to the treble and bass controls, and to the volume
control R13 which has an audio taper.
The signal is coupled through C5 and R14 into the
negative input of U1A. The double inversion maintains the
proper phase from input to output through the signal
chain. The fixed gain of the output stage is 10. Thus, the
user has a choice of either 0 to 50 or 0 to 200 signal
gain, depending on the input signal level and the output
signal level desired.
The output of U1A is fed
through R16, C6, and C7 to the
output jack. The MCP6024 is an
RRO (rail-to-rail) output op-amp.
The input is linear from 0 to Vdd
- 1.2 V. By using four AA
batteries (six volts) and a reverse
polarity protection diode D1
(-. 6 volts), the supply to the
MCP6024 is 5. 4 volts. The
op-amp inputs can go as high as
4. 2 volts in the linear range.
To maximize the voltage
swing, the amplifier bias level is
set by R17, R18, and U1D. The
values selected give a reference
voltage of 2. 2 volts which is
roughly half of the linear range.
The output of U1D is the ground
reference for the unit and is connected to the
input/output jack grounds, as well as the positive input
reference for the three other op-amps in the signal chain.
The green LED shows if the power is on and the
relative health of the batteries. The shelf frequencies for
the treble and bass controls are 1.6 kHz and 200 Hz,
This gives more adjustment (about ±1.5 dB) of the
sound’s brightness to the treble control.
42 November 2013
■ FIGURE 3. Control side of PCB.
QTY REF# SOURCE DESCRIPTION/VALUE
3 C1.C3.C5 DK .1 µF metalized poly, ±10%, Panasonic ECQ-V1H104JL, Digi-Key P4525-ND, or equiv
1 C2 DK .001 µF metalized poly, ±10%, Panasonic ECQ-B1H102JF, Digi-Key P4551-ND, or equiv
1 (Opt) C4 DK 47 pF ceramic cap
2 C6,C7 DK 10 µF alum elec, 35V, Panasonic ECA-1CM331, Digi-Key P5161-ND, or equiv
1 C8 DK 470 µF alum elec, 16V, Panasonic ECA-1CM471, Digi-Key P5141-ND, or equiv
1 D1 DK 1N4005, 1A, 400V, diode, Fairchild 1N4005FSCT-ND, or equiv
1 D2 DK LED, GRN (green), Lite-On LTL-4232N, or equiv
3 R1,R9,R14 DK 100K resistor 5%, YAGEO 100KQBK-ND, or equiv
1 R2 DK 10K resistor 5%, YAGEO 10KQBK-ND, or equiv
2 R3,R15 DK 1 meg resistor 5%, YAGEO 1.0MQBK-ND, or equiv
1 R4 DK 51K resistor 5%, YAGEO 51KQBK-ND, or equiv
1 R5 DK 220K resistor 5%, YAGEO 220KQBK-ND, or equiv
R12,R18 DK 8.2K resistor 5%, YAGEO 8.2KQBK-ND, or equiv
1 R16 DK 2K resistor 5%, YAGEO 2KQBK-ND, or equiv
1 R17 DK 12K resistor 5%, YAGEO 12KQBK-ND, or equiv
1 R19 DK 1K resistor 5%, YAGEO 1KQBK-ND, or equiv
2 R7,R11 DK 100K linear pot, BOURNS PTV09A-4225F-B104-ND DK
1 R13 DK 50K audio pot, BOURNS PTV09A-4225F-A503-ND
2 S1,S2 DK SPDT miniature slide switch, STS121PC04 450-1609-ND
1 U1 DK MCP6024-I/P quad RR op-amp, Microchip Tech MCP6024-I/P-ND
2 J1,J2 DK 1/4" phone jack, Switchcraft 35PM1, SC1455-ND or equiv
1 Enclosure DK SERPAC, 5.62x3.25x1.50 Blk, SR151-IB-ND
1 Bat Hldr DK Four AA battery holder w/leads, Memory Prot Devices BC4AAW, BC4AAW-ND
3 Knobs Mouser Eagle control knob, . 55 D T18 BLK, 450-AE141
MISC. Fellows sheet laminates
4 Screws #4 x . 25" sheet metal screws for mounting PCB in enclosure