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

Modulo D

The world’s smallest full-fledged stereo amplifier

Modulo D

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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Gerber file

CAM/CAD data for the PCB referred to in this article is available as a Gerber file. Elektor GREEN and GOLD members can exclusively download these files for free as part of their membership. Gerber files allow a PCB to be produced on an appropriate device available locally, or through an online PCB manufacturing service.

Elektor recommends its business partner Eurocircuits as the company of choice for its own prototypes and volume production in selected cases.

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

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