Tuesday, January 3, 2017

Telefunken HiFi Studio 1 restoration

HiFi Studio 1 is portable boombox manufactured by Telefunken in around 1979. This player consist with 4 band radio (with LW, MW, SW and FM), cassette player / recorder and with 2 × 30W audio power amplifier.

Restored HiFi Studio 1

This unit is designed using both ICs and transistors. Receiver of this unit is build around TDA1047, TBA570 and BA1320 ICs. Tape player/recorder is mainly build using NPN transistors and special Telefunken IC and 4066 ICs are used to get Telefunken's proprietary HIGH COM tape noise reduction feature. Power amplifier of this boombox is transistor based and it uses pair of TIP130 and TIP135 transistors in it's final stage.

Monday, January 2, 2017

Sony TC-252 reel to reel player restoration

TC-252 is 3 speed reel to reel player manufactured by Sony in around 1970 – 1972. This is transistor based tape player with 4W × 2 audio output power, sound-on-sound and sound-with-sound recording features.

The TC-252 which we got to restore had many problems. Major problem is someone alter the circuit in that recorder and attach LA4440 power amplifier into the circuit. Apart from that, motor speed of that recorder also starts to decrease after 10min of continues playback. Other than above two major problems it had some mechanical problems in playback position and all the potentiometers in the front panel are damaged beyond repairing.

TC-252 main PCB after restoration.

As a first step of the restoration we remove the LA4440 module attached into that recorder and rewire the player with original wiring layouts. After rewiring we check all the transistors in that player and find-out that the couple of 2SC634 transistors are damaged in that player. Because 2SC634 is not available in the market we replace those damaged transistors with BC548 transistors.

For the front panel potentiometers we use standard 10K and 20K (log) potentiometers available in the market.

To fix motor speed problems we replace 1.5MFD + 0.5MFD multi-section can capacitor with two separate 1.5MFD and 0.5MFD (450V) AC fan capacitors.

Internal view of restored TC-252 player.

After cleaning and reassembling the mechanical unit TC-252 player starts to work. Compare with most of the reel to reel players TC-252 looks like a basic player, but we really like it's playback audio quality and audio output power.

Thursday, December 15, 2016

Pioneer PL-250 turntable restoration

Pioneer PL-250 is direct drive auto-return turntable with s-shaped tonearm. This turntable is manufactured by Pioneer in around 1979 - 1982.

The PL-250 which we got had many electronic and mechanical issues. The main electronic problem in this unit is it's varying speed. The speed controller of this turntable is based on PA2004 and PA2005 ICs. After checking each an every electronic component in speed controller PCB, we figure out that the problem is in the "Pitch Control" potentiometer (VR1) of this unit. After replacing VR1 with 5K (log) potentiometer, the speed problem got resolved and motor starts to spin with correct speed(s).

Servo motor and speed control assembly of Pioneer PL-250 turntable.

The turntable which we got comes with original Pioneer cartridge with "broken" stylus. We test several  cartridges with this player including cheap US $ 3.00 cartridges (which are available in eBay), Audio Technica AT-91 and Audio Technica AT-95E cartridges. Out of all these cartridges, chap Chinese (US $3.00) cartridges produces worse results and the most noticeable thing with that cartridge is it's heavy distortion in 1.0kHz - 6.8 kHz range. Both Audio Technica cartridges produces excellent results with this player.

After fixing all the issues this unit starts to work perfectly and produces excellent results. We mainly test this turntable with Pioneer SA-420 power amplifier system.

Monday, November 21, 2016

HTML5 Mandelbrot Generator

This quick post is to introduce "HTML5 Mandelbrot Generator", which is simple JavaScript application to generate Mandelbrot set and Julia set fractals in HTML5 complaint web browsers. This application is derived from Mandel source code (which is available at http://www.cylog.org) and it covers most of the features available in that original application.

Online version of this HTML5 Mandelbrot Generator is available at https://dilshan.github.io/mandelbrot-js. Few fractals generated with "HTML5 Mandelbrot Generator" are shown in below:

Mandelbrot and Julia set fractals generated from "HTML5 Mandelbrot Generator".

All the source code of this application are available to download at https://github.com/dilshan/mandelbrot-js under the terms of MIT Licenses.