Dilshan R Jayakody’s Web Log

This project is about a single-channel microphone echo generator circuit. This circuit builds around the Holtek HT8970 echo effect generator IC. It offers complete control of the echo effect by providing delay, mix, and output level adjustments.  HT8970 is an echo/surround sound effect generator IC with 20Kb SRAM. It also contains the built-in VCO stage, AD, and DA converters. The chip costs less than 0.5 US$ and is commonly available in the market. Prototype build of the echo effect generator circuit. The given schematic offers a maximum of 320ms time delay and works with a single-rail 9V DC power supply.  In addition to the HT8970 integrated circuit, this circuit uses an NJM4558 op-amp to amplify the input and output audio signals. HT7150 voltage regulator uses in this design to power up the HT8970 IC. The HT7150 is a low-power 5V regulator IC from Holtek, the same maker of the HT8970 IC. Top view of the prototype build. The circuit designs to work with 500Ω dynamic mic...

This is a single chip dynamic microphone preamplifier which is design to drive using commonly available 12V single rail power supplies. Preamplifier in this article is built around popular NE5532 dual low noise operational amplifier IC and this preamplifier is specifically constructed to drive professional 600Ω dynamic microphones. Internal view of a dynamic microphone preamplifier prototype. This preamplifier consists of two amplifier stages and the initial amplifier is designed 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 the output waveform. In prototyping stages, we test this preamplifier with few 600Ω dynamic microphones with a TDA2050 power amplifier . According to our observations, this unit produces excellent output with all of these microphones. To get professional results to use this preamplifier with 12V battery or with regu...

The phantom power supply is widely used in the 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 the same technique. The 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 an 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 using shorter wires between PCB and XLR sockets to reduce the noise. PCB and schematic of this power supply unit are available to download at...