Monday, November 9, 2015

Dynamic microphone preamplifier

This is single chip dynamic microphone preamplifier which is design to drive using commonly available 12V single rail power supplies. Preamplifier in this article is build around popular NE5532 dual low noise operational amplifier IC and this preamplifier is specifically constructed to drive professional 600Ω dynamic microphones.

Internal view of dynamic microphone preamplifier prototype.

This preamplifier consists with two amplifier stages and initial amplifier is design to get 36dB gain and final preamplifier is used to get 16dB of gain. Preamplifier gain controller is placed in between those two amplifiers and this separation allows reducing clipping in output waveform.

In prototyping stages we test this preamplifier with few 600Ω dynamic microphones with TDA2050 power amplifier. According to our observations this unit produces excellent output with all of these microphones. To get professional results use this preamplifier with 12V battery or with regulated power supply unit and use screened wires for both input and output connections.

Schematic, wiring diagrams and PCB design of this microphone preamplifier are available to download at

Tuesday, October 27, 2015

48V Phantom power supply

Phantom power supply is widely used in audio industry to power the active microphones over single audio cable. Most of the phantom power supplies deliver 48V DC over the balanced audio link and power supply unit described in this article is also based on same technique.

Phantom power supply in this article is based on TL783 high voltage regulator IC and 230V - 50V step down transformer. Like most of the phantom power supplies this power supply is also design to connect in between active microphone and audio mixer devices.

PCB of 48V Phantom power supply.

Schematic of this power supply unit is self explanatory and PCB design is also based on commonly available through-hole components. For the step down transformer we use commonly available 230V - 25V-0-25V 1.5A transformer.

During the construction we recommended to use shorter wires between PCB and XLR sockets to reduce the noise.

PCB and schematic of this power supply unit is available to download at

Monday, September 7, 2015

DIY resistor box

Resistor box is a quiet useful instrument in analog electronic based design and prototyping tasks. It can easily build with few sets of resistors and with couple of rotary switches.

This quick post is about resistor box which we construct recently using 5W wire-wound power resistors. For this resistor box we use five, single pole 12 position rotary switches and 50 wire-wound resistors. It gives 5 dials to controls 10Ω, 100Ω, 1KΩ, 10KΩ and 100KΩ steps.

Final view of homebrew resistor box.

Internal view and high resolution photographs of this resistor box are available at my Flickr page. Schematic of the resistor box is available in here.

Sunday, August 30, 2015

Low cost TEA5767 based FM stereo radio receiver

TEA5767 is electronically tuned FM stereo radio receiver from NXP for low voltage applications. TEA5767 based radio modules are now common in the field and this project is based on Samsung TT-502 radio module. The main objective of this project is to design low cost FM tuner based on this TT-502 / TEA5767 module and commonly available electronic components.

In this receiver the main controller is ATmega8 MCU, except to that TDA2822 is used as AF power amplifier, PT2257 is used to control the volume. In this given design MCU, PT2257 and TEA5767 radio module is set to work with 3.3V power source. LD33V voltage regulator is used to obtain 3.3V from supply voltage.

To control the receiver, MCU provide five push buttons. Those can be used to control volume, perform automatic scan and manual tuning.

Final version of TEA5767 based FM radio receiver.

The firmware of this receiver is developed using MikroC for AVR and it is available to download with project package.

This receiver is design to drive using 9V - 12V DC power source and we recommended using regulated AC power supply to drive this tuner.

While at the testing we got very good results with this tuner and it perform similar to the commercial grade portable FM stereo radio receiver. All the schematic and firmware related to this project are available to download at