Logic Control Circuit -- Quadraphonic SQ Decoder

Block Diagram

The MC1315P, quadraphonic logic control system is an extremely complex IC that contains a plethora of circuitry for enhancing the front and back channel separation in the CBS SQ four channel decoding system. It has variable logic enhancement that controls the dc gain and balance signals on the MC1314 IC. According to the manufacturer, this enhancement improves the back separation to 12 dB, which is impressive.

  • Provides logic enhancement to extend front to back separation to 12 dB
  • Low external parts count
  • Provisions for enhancement controls
  • Provides DC gain control signals to the MC1314P

Board Layout

Board Layout
return

The original schematic diagram around the MC1315 was unworkable, because not only was the IC upside-down, the pins were mirror reversed, which makes it extremely difficult when building on strip-board. Ideally, I prefer pin 1 of the IC to be on the top left corner, and therefore, I decided to redraw that part of the circuit diagram as well. I felt it was best to have a layout that did not require much thinking, because, if you have to hang upside down from the chandeliers with your eyes-crossed and tongue hanging out every time you need to figure out how to map each component then you are liable to make a mistake for sure!

Component List

TypePart NumberValueDescription
ResistorsR16.8 kΩMetal-film, 1/4-watt, 1 %
R23.3 kΩMetal-film, 1/4-watt, 1 %
R330 ΩMetal-film, 1/4-watt, 1 %
R450 ΩMetal-film, 1/4-watt, 1 %
R4A100 Ω (Optional)Metal-film, 1/4-watt, 1 %
R510 kΩMetal-film, 1/4-watt, 1 %
R610 kΩMetal-film, 1/4-watt, 1 %
R710 kΩMetal-film, 1/4-watt, 1 %
VR110 kΩPotentiometer
CapacitorsC12.2 µFElectrolytic, 63 V
C22.2 µFElectrolytic, 63 V
C310 µFElectrolytic, 16 V
C410 µFElectrolytic, 16 V
C51 µFElectrolytic, 100 V
C61 µFElectrolytic, 100 V
C70.15 µFElectrolytic, 50 V
C82.2 µFElectrolytic, 63 V
C920 µF (or more)Electrolytic, 25 V (or more)
C101500 µFElectrolytic, 25 V
C111500 µFElectrolytic, 25 V
C121500 µFElectrolytic, 25 V
SemiconductorsIC1MC1315PPDIP
MiscStripboard36-strips × 50-holes95 mm × 127 mm

For all the components, you need to get the ones with best tolerance. Ideally, the resistors should be 1 % tolerance and capacitors 5 % tolerance (if possible). I got all the components from the auction site and nearly all were to the specification I needed.

C9 is for the power supply rail and not so critical, hence, I managed to find 22 µF/50 V which I am using in this project.

R4 is meant to be a 50 Ω resistor, however it may prove difficult to find, hence I have included space for an optional resistor R4A to go in parallel with R4. Yes, you guessed it! Two 100 Ω resistors in parallel make a 50 Ω effective resistance! I can see that your doctorate degree was not all due to "charity donations", ahem...

Board Cuts

Board Cuts
return

This is a reversed view with the board flipped over along the horizontal axis. Hopefully, you will have some nice tools to make neat cuts to the tracks. Great thought went into the design of this board so it would require minimal cuts.

Board Links

Board Links
return

This Article Continues...

Logic Control Circuit
Board Completed Build
Faulty MC1314P and MC1315P ICs