Audio Amplifiers & Voice Recorders
Click here for general information about power supplies for the audio amplifier modules.

K12 - Audio-To-Light Modulator Price Photo Docs
Introduces the Optocoupler-triac MOC3010 and triac. Complete electrical isolation between input audio signal (low voltage circuit) and output light modulation (mains supply voltage levels) is achieved.

K17 - LM386 Audio Amplifier Module Price Photo Docs
This Kit is designed as a building block in other projects where a battery-powered, variable-gain audio amplifier is required. Data sheet from National Semiconductor included.

K21 - Two Station Intercom Price Photo Docs
Simple two wire intercom. Each unit with its own speaker, microphone and amplifier (LM386.) Can be modified to a hard wired "bug". With 4 strand ribbon cable the power can be sent to the remote "bug" unit from the receiving unit.

K26 - Fibre Optic Audio Link Price Docs
Allows you to send sound through plastic 1mm fibre optic cable. Matched transmitter/receiver pair. Two circuit boards with a microphone at one end and a speaker at the other. 14 feet of fibre optic cable supplied. Will work over 200 meters.

K27 - TDA7052 1W Amplifier Module Price Docs
A 1W power amplifier building block designed to be part of a larger project needing a low power battery operated amplifier into an 8 ohm speaker.

K47 - LM383 Amplifier Module Price Photo Docs
A proven & popular power amplifier building block for use in any audio project. Power output is dependent on the supply voltage and load resistance. Over 10W is typical for a 16V supply into a 2 ohm speaker. A 12V supply into a 4 ohm speaker will deliver around 4W. Small heatsink provided.

K48 - Introduction To Class AB Amplifiers Price Docs
Using amplifier modules is modern, quick and easy but it teaches nothing about how they work. Here is a Class AB amplifier made from individual components which will deliver several watts of power into an ordinary 8 ohm speaker. Gives hands-on learning about cross-over distortion, bootstrapping, complementary pairs, and push-pull. Detailed explanations given.

K50 - 25W Hi-Fi Audio Amplifier Module Price Docs
This kit contains the essential components needed to build a high fidelity amplifier module using the National Semiconductor LM1875 IC. This kit will deliver 25 watts RMS into 8 ohms at 1% THD. The kit requires a split +/- 25V power supply (see K186 kit). Overload protection is provided by on board 2A fuses in each of the supply rails. PCB dimensions are a tiny 53 x 50mm (2.1" x 2"). Heatsink, speaker and cables not included.

K63 - One Chip AM Radio Price Photo Docs
Complete AM radio on a PCB. Tuned radio frequency front-end, single chip RF amplifier & detector and two stages of amplification of the audio signal into a speaker. All components supplied. Coil prewound. Excellent for schools.

K88 - 10W+10W Stereo Amplifier Module Price Photo Docs
The TDA2009 is a class AB dual Hi-Fi Audio power amplifier monolithic IC designed for quality stereo applications. This is the standard data book application circuit using a minimum of external components. Each channel is capable of delivering 10 watts into 4 ohm speakers using a 24VDC supply voltage.

K89 - Stereo VU Meter Price Photo Docs
A simple, low cost stereo VU meter. Two LM3915 dot/bar display driver ICs are used to drive 2 rows of 10 LEDs (4 green, 3 yellow, 3 red) in a moving bar display. Each row of LEDs spans a power range of 0-30 dB in ten 3-dB steps. This VU meter indicates "peak music power" when used with audio amplifiers. Ideal add-on for any of the amplifier kits. Dimensions = 65mm x 42mm

K90 - 3W+3W Stereo Amplifier module Price Docs
A simple stereo 3 watt per channel amplifier based on the BA5406 power amplifier IC. Minimum component count. Runs on 12VDC power supply. Good general purpose amplifier.

K97 - 4W Amplifier Module Price Docs
A text book amplifier built around the LM380 IC. It can deliver up to 4 watts into an 8 ohm speaker, depending on the supply voltage. No heatsink required - uses the PCB bottom layer. Soldered directly to the PCB.

K98 - Microphone Preamplifier Module Price Photo Docs
A preamplifier module to use with an electret or other microphone to boost the signal before feeding into an amplifier. Simple and easy to build using discreete transistors. Runs on 6-12V DC.

K100 - Stereo Preamp/Tone control Price Docs
A useful addition to any of the power amplifier kits. Extremely easy to built due to the use of a Philips TDA1524A IC. This IC contains all the circuitry required to provide up to 20dB of voltage gain, +/- 15dB of bass and trebble control, channel balance and switchable loudness contour. 12-15VDC supply required. See documentation for full specifications.

K105 - 18W BTL Audio Amplifier module Price Photo Docs
This kit contains all the components to build a low voltage, high power, mono 18W Bridge Tied Load (BTL) amplifier module using the Hitachi HA13118. Delivers maximum of 18W into 4 ohm using 18V/2A DC supply. Delivers >6W into 4 ohm using 13.2V supply - ideal for running off car batteries. Operating voltage: 8-18V. Speaker & heatsink not supplied.

K106 - 50W Hi-Fi Audio Amplifier module Price Photo Docs
The heart of this amplifier is a monolithic integrated circuit from SGS-Thomson, TDA7294. It is intended for use as an audio class AB amplifier in hi-fi applications. It has a wide voltage range and output current capability, enabling it to supply the highest power into both 4 and 8 ohm loads.

This module will deliver 50 watts RMS into an 8 ohms at 0.1% THD and is powered by a split +/- 30V supply (see K186 kit). A heatsink, rated at 1.4 deg C/W, is required but not supplied. The heatsink can be mounted directly on the PCB.

K126 - Mini-VOX and relay Price Photo Docs
VOX stands for "voice operated switch". Basically this kit picks up audio via a microphone input, amplifies it and uses it to operate a relay. Sensitivity can be adjusted by an onboard trimpot. Use it to give you hands-free control of things like tape recorders, lights, sirens, etc. Relay contacts rated ar 12/24VDC @ 1A. Based on a circuit published in Silicon Chip, Sep 1994, p31

K139 - Stereo 1W Amplifier module with Volume control Price Docs
The TDA7053A is an integrated stereo power amplifier IC with volume control input. All work is done internally in the IC. 5 - 18VDC operation. PCB dimensions = 4 x 4.2cm (1.6" x 1.7").

K143 - 6-10W Stereo Amplifier module with Volume control Price Photo Docs
This kit is a class AB stereo audio power amplifier designed for hi-fi applications using a TDA2005 module. It is easy to construct and has a minimum of external components. The TDA2005 has output current protection and thermal protection. On board volume control. This is the data book circuit which produces excellent sound. Kit requires a supply voltage of 8-18V DC at 1 to 2 Amps.

Maximum power output will only be obtained with a power supply of at least 2A at 15V DC, and using 2 ohm speakers (or 2 x 4 ohm speakers in parallel). However approximately 4W per channel can be obtained with only a 15V DC, 1 Amp supply into 4 ohm loads. The power supply should be well filtered to reduce mains hum.

DC Input
8 - 18V at 1 - 2A (15 to 30VA minimum)
Power Ouput
> 8W RMS / channel, 2 ohm load, 16V DC supply
> 6W RMS / channel, 4 ohm load, 16V DC supply
> 4W RMS / channel, 4 ohm load, 12V DC supply
< 0.1% @ 1W, 4 ohm load
S/N Ratio
> 80 dBA
Frequency Response
~ 15 Hz to 50 kHz, -3 dB
~ 30 dB maximum
Input level
~ 150 mV for full output
Size 75mm x 45mm (3" x 1.8")

K188 - 40 Second Voice Recorder Price Photo Docs
K189 - 120 Second Voice Recorder Price Photo Docs
K188 is the replacement for K146 whilst K189 replaces K64. Both those older kits used the now obsolete ISD2500 series of chips. These kits use the ISD1700 series chips. These chips have much the same specifications as the ISD2500 series but with some extra features that make them easier to use.

The ISD1700 series of chips offer a wide range of message durations, ranging from 30 seconds up to 240 seconds depending on the chip. The sampling frequency of each chip can also be adjusted from 4kHz to 12kHz with an external resistor, giving greater flexibility in duration versus recording quality.

Recordings are stored in on-chip Flash memory, providing non-volatile storage when power is removed. The audio data is stored directly without digital compression, giving better quality voice and music reproduction.

These chips are designed for operation in either standalone or microcontroller (SPI) mode. These kits provide interfaces for both.

Specifications & Features
Operating Voltage
8 - 24VDC (see documentation for battery powered use)
Sampling Frequency
8kHz default (can be changed - see documentation)
Message Length
K188 - 40 seconds @ 8kHz (see documemnation)
K189 - 120 seconds @ 8kHz (see documentation)
Standalone Mode
SPI Mode Interface
Yes (requires 5-pin header - not supplied)
Input Source
Onboard electret microphone
Analog Line In
Direct drive to 8 ohm speaker
Analog Aux Output
Visual Indicator Onboard LED. Stays ON during recording - BLINKS during playback, etc
Connectors Power Supply - 2.5mm DC jack, center positive.
Line In - 3.5mm mono audio jack. Suitable for connecting to audio source such as MP3 player or PC sound card. Slide switch must be set to 'LINE' position.
Aux Output - 3.5mm mono audio jack. Use for connecting to external power amplifier.
Speaker - 2-way screw terminal block.
Buttons/Switches LINE/MIC - Selects recording source between external source (LINE) or onboard microphone (MIC).
RECORD - Press and hold to start a new recording. Release when done.
PLAY - Plays the current message. Press and hold to play each message sequentially.
ERASE - Press to erase the current message. Press and hold to erase ALL messages.
FWD - Advance to next message.
VOL - Change playback volume (speaker output) in eight steps.
RESET - Return to default state.

A63 - 20 Second Voice module Price Photo Docs
This pre-assembled module measures a tiny 3.5cm x 2cm (1.3" x 0.9"). It uses a chip-on-board device from Vtech. All components are fitted on the PCB, including the pushbutton switches and electret microphone. One button is pressed to record the message. An LED turns on during record. The other button is momentarily pressed to replay the message. A second momentary press during playback will stop the playback. All you have to add is a speaker and 5V DC power.

The record/playback time is determined by a 52K resistor. If you change it to 89K you will get 30 seconds but at a reduced sampling rate. Operating current is 25mA. Standby current is 10 uA. The module comes supplied as you see it in the photo.