Quasar Project # 3115V2 - Low Voltage Stereo Amplifier

as necessary to achieve full output, with the input

T his is a 1 watt per channel, stereo amplifier reduce the S/N ratio by a similar amount, since the
module Kit using two LM386N IC’s from equivalent input noise figure is constant. The jumper
National Semiconductor. It is basically two of may be replaced with a resistor if an intermediate
our 3017 modules on a single PCB, with a dual gang gain level is required. See the National data sheet for
pot. It will operate best from 6-12V DC and will more information.
work well from a battery since the quiescent current
drain is only 10 mA. It requires no heat sinks for If driving a pair of headphones, you may require a
normal use. The input and output are both ground 100 ohm resistor in series with each output to reduce
referenced. Maximum output will be obtained with a the output level, depending on headphone
12V power supply and 8 ohm speaker, however it is sensitivity. Make sure you start with the pots right
particularly suitable for driving headphones from a down to check. A number of headphones may be
supply as low as 4V. driven from the one amplifier if you wish, as long as
the total impedance is more than 4 ohm per channel.
Specifications :
Testing :
D.C. input : 4 – 12 V at 200 – 500 mA max.
Idle current : ~ 10 mA Check the voltage and polarity before connecting
Power output : > 1 Watt max. @ 8 ohms, 12V DC the battery or power supply. If it does not work,
~ 0.4 Watt RMS cont. per channel recheck all component positions and polarity. Check
Freq. Resp. : ~ 40 Hz to 100 kHz, 8 ohm all solder joints, and all external wiring. Poor solder
< 20 Hz - 200 kHz, 32 ohm, G=20 joints or solder “bridges” are the most common
THD : < 1 % @ 400 mW, 8Ω,12V DC cause of faults. The IC itself is quite robust, and
< 0.2 % @ 1Volt RMS, 8Ω, 12V there is very little else to go wrong. Remember
Gain : x20 (26 dB) OR x200 (46dB) when testing, it will not produce full output for more
S/N ratio : > 80 dB, (>90dBA) G = 20 than a short duration because of limited heat
> 60 dB, (>70 dBA) G = 200 dissipation. We found it easily exceeded the
Sensitivity : > 100 mV, G=20 manufacturers specifications however.
> 10 mV, G=200
Input Z : ~ 10 k ohm Circuit Description :
There are only a few external components, the IC
Assembly Instructions : contains most of the necessary circuitry. C1, C5 are
Assembly is very straight forward, just follow the the input coupling capacitors, which block any DC
PC board overlay. Make sure you get the integrated that might be present on the inputs. C2, C9 maintain
circuit and the electrolytic capacitors the correct way DC bias levels in the gain adjustment (feed back)
around. The electrolytic capacitors are polarized, circuit. C4 provides power supply decoupling, and
they have a - marked on them and they must be C6, C8 are the output coupling capacitors. C10, R1
inserted correctly into the PCB. The IC’s and and C11, R2 act as zobel networks providing a high
sockets have a notch at one end, which is marked on frequency load to maintain stability where loud
the PC board overlay. Solder the sockets in place speaker inductive reactance may become excessive.
first, and then the 100 nF capacitors, making sure The pot provides adjustable input level attenuation.
they are not above the IC sockets, before installing
The National data sheet contains further information
the IC’s themselves. Leave the potentiometer until
about the LM386N. You may download it from the
last.
software download page on our website :
The gain is adjustable from 20 to 200, i.e. 26 to
46 dB. Start with the jumpers J1 and J2 removed, http://www.quasarelectronics.com
this will give a gain of 20 which should be adequate
for most applications. If you require more gain,
short circuit the pins with the jumpers provided. We
have also provided input attenuation via the
potentiometer. You should keep the IC gain as low

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Quasar Project # 3115V2 - Low Voltage Stereo Amplifier
Circuit Diagram
.
One channel only shown
+ +
DC input C4
4 - 12 V 100 uF
_ 6
C6,8
470 uF
C3,7 7 5 Output
C1,5 100 nF +
2u2 F
IC1,2 1
High C10,11

Jumper
47 nF
+
LM 386N
Pot 1 3
+ Speaker
Signal (not supplied)
Input 10 kΩ
Log. R1,2
C2,9
8 10 uF 10Ω

Gnd 2 4 Gnd

Components :
Capacitors :
C1, C5 2.2 uF / 50Vecap 2
C2, C9 10 uF / 25V ecap 2
C3, C7 100 nF mono (104) 2
C4 100 uF / 16V ecap 1
C6, C8 470 uF / 16V ecap 2
C10, C11 47 nF mylar (473) 2
Resistors :
R1, R2 10 ohm (brown, black, black) 2
Pot 1 10k ohm dual gang log pot. (A) 1
Misc. :
Kit 3115V2 Printed Circuit Board 1
IC 1, 2 LM386N Integrated Circuit 2
8 pin IC socket 2
2 pin header and jumper 2 sets
PCB Pins 10

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Quasar Project # 3115V2 - Low Voltage Stereo Amplifier

THD @ 1kHz, 1 Volt RMS output

THD @ 1kHz, 1 Volt RMS output

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