SQ Quadraphonic Decoder -- Completed Build

For the quadraphonic enclosure case, I managed to find a broken SKY box that was ideal for my purposes. Due to continual development, these boxes go out of date within a short space of time, and then they can no longer be updated. Unfortunately, this one had also suffered water damage and all the electronics was fried. There are many sky boxes that look similar but are different sizes, and this particular box was the TDS850NB, which had sufficient space to house all the boards.

After building the quadraphonic decoder, I started listening to different sorts of music, and noticed that with classical music, there is definitely a discernable change in separation between the back channels and the front channels. Sometimes, you can hear one musical instrument come from the back channels, and another from the front and it sounds quite good. With pop and other types of music that has many instruments, there is also a definite separation giving a surround sound effect, but not as much.

I wish I had more money to buy better quality potentiometers than the ones I got from China. Unfortunately two of them crackled and I had to lubricate the wipers. The wipers essentially feed a DC voltage to the gain control chip, hence they have to be very good quality, otherwise they can introduce noise to the amplifier blocks within the IC.

Inside all the plastic, there is a metal case, and the front section of this box has plenty of space for installing potentiometers. Since the front part is plastic, it was very simple to drill some holes into the plastic and mount the pots. The dimension control, which would have been a preset, is also added to the front for convenience. In this particular box, there is a separate section for housing the power supply; hence it was only befitting to use it for my 20 V PSU board and transformer.

At the front, there is usually a board for the switches and LEDs; however I had to remove that to make space for the potentiometers. I was able to make use of the main LED, and I thought that the circular animation was very befitting to represent a rotating record. In the following pages of this multi-page article you can see photographs of the inside view and my installed circuits.

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