• about Audio/Video/Photography
  • Published in issue 3/2010 on page 26
About the article
Modulo D

Modulo D

The world’s smallest full-fledged stereo amplifier

The external appearance of this small module with an LC display almost belies what it has inside: a complete stereo preamplifier and final amplifier with IR remote control, adjustable tone, volume and signal levels, and an output power of 2 x 20 W (Class D), all with a single 12-V supply voltage. This makes it perfect for use in a car, boat or motor home.

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Extra info, Update


issued: April 7, 2010

Constructors should note that the Modulo-D amplifier will only respond to commands sent by an RC-5 compatible remote control for CD players.



issued: April 28, 2010

The schematic in Figure 1 and the parts llst should be corrected as follows

R22,R23 = omit

C15,C24,C31,C32 = 220pF

These corrections do not apply to Modulo D units supplied by Elektor.


- 2 x 20 W continuous output power with 4-Ohm loudspeakers
- remotely controlled bass, treble, volume, and preset signal level
- can be used with RC5-compatible remote control transmitters
- all functions digitally controlled by an ATmega8 microcontroller
- operating status displayed on a three-line LC display with 20 characters per line
- stereo input on Cinch sockets
- auxiliary input on a pin header (selectable under software control)
- display board with IR receiver can easily be fitted separately using a 10-way flat cable
- expansion port for extensions, such as an MP3 player or manual control
- open-source firmware enables individual extensions for specific application areas
- extremely compact because no heat sink is necessary
- dimensions (module without enclosure): 65 x 40 x 35 mm (2.3x1.6x1.4 inch)
- efficiency up to 93%
- operating voltage range 11–14 V
- can be used with an onboard vehicle electrical network or an inexpensive 12-V power supply (4 A min.)


R7 = 0Ohm (SMD0603)
R26,R27,R28,R29 = 10Ohm (SMD0603)
R17, R18 = 22Ohm (SMD0603)
R5 = 100Ohm (SMD0603)
R22,R23 = 180Ohm (SMD0603)
R15,R16 = 2.2kOhm (SMD0603)
R6,R8 = 4.7kOhm (SMD0603)
R9,R10,R19,R20,R21,R22,R24,R25 = 10kOhm (SMD0603)
R1,R2,R3,R4 = 20kOhm (SMD0603)
R11, R12,R13,R14 = 47kOhm (SMD0603)
L1,L2,L3,L4,L5 = VHF choke (6-hole ferrite bead)
C44, C45 = 22pF (SMD0603)
C20,C21,C22,C23 = 470pF (SMD0603)
C33,C34 = 5.6nF (SMD0603)
C3,C4,C5,C6,C17,C18,C19,C41,C42,C43,C46,C48 = 100nF (SMD0603)
C35,C38 = 150nF (SMD0603)
C36,C39 = 330nF (SMD0603)
C29,C30,C40,C50,C51,C52 = 470nF (0603)
C1,C2,C7,C9,C10,C13,C14,C15,C24,C25,C26,C27,C28,C31,C32 = 1µF (SMD0603)
C37,C47,C49 = 10µF 16V (SMD tantalum case style B)
C8 = 100µF 16V radial
C11,C12 = 1000µF 16V radial
D1 = P6SMB16A (SMB)
T1 = BC847 (SOT23)
IC1 = 78L05 (SO8)
IC2 = TSOP34836
IC3 = LD1117-3V3 (SMD SOT223)
IC4 = MAX9744 (MLF44)
IC5 = 78M09 (DPAK)
IC6 = TDA7449 (DIL20)
IC7 = ATMEGA8-16 (TQFP32) (programmed, Elektor order # 090563-41)
X1 = 8MHz quartz crystal (HC49U-V)
LCD1 = EA DOGM 163 with backlight
K1, K3, K10, K11= 10-pin receptacle, straight, lead pitch 2.54mm (0.1''), h = 8.5mm
K2 = 10-way flatcable, l = 140mm (5.5'')
K4,K5,K6 = clamp connector SPRINGCON 6-way lead pitch 5.0mm (0.2'')
K7 = expansion port (optional)
K8,K9 = ISP Programming connector for Mega8, 6-pin (2x3) (optional)
K13,K14 = Cinch socket, PCB mount, lead pitch 7.5mm (0.3'')
4 plastic PCB standoffs, l= 4.8mm (0.18'')
20-pin pinheader
Kit of parts with SMD prestuffed boards and all parts, Elektor Shop # 090563-71
PCB design (.pdf); free download