Dilshan R Jayakody’s Web Log

A few months ago, I received this Onkyo PE-C50 stereo graphic equalizer from a friend because it was not working. He gave me this equalizer for free because he was planning to discard it due to some problems with its controls. Front panel of the Onkyo PE-C50. The Onkyo PE-C50 is a vintage, 7-channel, stereo digital graphic equalizer. This unit is manufactured in Japan and operates on 110V AC power only. Front panel controls allow me to adjust each channel separately or simultaneously. This unit also got 5-channel preset memory to save graphic equalizer settings. Besides a graphic equalizer, it comes with an attractive 2×7 channel spectrum analyzer. At initial testing, I found that the unit's controls and spectrum analyzer would randomly stop working. After controls at the front panel freeze, I have to restart it to get it back in working condition. PCB of the Onkyo PE-C50 graphic equalizer. To troubleshoot, first, I try to find the service manual for this equalizer, but I couldn...

If you are an audio enthusiast and if you have multiple audio systems and speakers, you may definitely need to have a speaker selector switch. These switches allow you to route a audio signal through a switching system and distribute it to various speakers. Using this listener can select single amplifier – speaker combination through the switch. We mainly design this switch to share our speaker system with multiple audio amplifiers. We design this switch to handle 6 stereo audio channels. Final view of 6 channel speaker selector prototype. This switch is based on PIC16F88 - 8bit MCU, ULN2803 Darlington transistor arrays and 12 DPCO relays. MCU is the core component of this switch and it control all relays, seven-segment display and store last channel in E 2 PROM memory and restore it during next power-up. In this system all audio lines are switching using 12 DPCO relays. To get optimal results we recommended to use good quality relays with thus switch. In our prototype we u...

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

Smart Audio Box (SAB) is microprocessor controlled audio switch and amplifier system, which is specifically design for audio composers and for audio engineers. SAB consist of 4 high impedance stereo inputs and two output modes. One output mode can drive stereo headphone/earphone and other output mode can drive pair of 8W speakers. In prototyping stages we identify those modes as " Personal Mode " (headphone output) and " Audience Mode " (power amplifier output). Another main feature of this system is its programmable 16 step attenuation controller. This attenuation controller helps to control the audio output level of each output-mode. Prototyping version of Smart Audio Box The main component of SAB system is ATmega8 MCU, other than that headphone amplifier is design around NJM4556 high current operational amplifier and power amplifier is based on TDA1521A. To operate, this system requires 2 power sources. Microcontroller, ADC interfaces and CMOS logic-s...