UNI-QUAD UQ-1A

QUADRAPHONIC DECODER

The page author took the idea for the Dynaquad device, and expanded it into an adjustable decoder. It can decode any of the regular matrix formats. The following are instructions on how to build and use this decoder. The instructions for use are placed first.

SAMPLE FRONT PANEL OF UQ-1A
 

USING THE DECODER

Calibration

Before the UQ-1A decoder can be used, it must be calibrated. To calibrate the decoder, follow the following steps:

1. Choose a monaural audio source (or select MONO on the amplifier, if possible).
2. Turn down (counterclockwise) the FRONT LEVEL, CENTER, and SUBWOOFER controls.
3. Play the source.
4. Move the NULL switch to the NULL position.
5. Adjust the amplifier's BALANCE control.
6. Move the NULL switch away from the NULL position. The NULL position is used only for calibration.

Using the Decoder

Use the following table to adjust the decoder.

• 0 % = full anticlockwise
• 100% = full clockwise.
• The exact positions depend on the particular manufacture of the controls.

Using Autovary

The decoder is equipped with Autovary separation enhancement logic. Autovary must be adjusted for each matrix according to the following instructions:

1. Play the program source.
2. Turn the Autovary control to 0 %.
3. Adjust the Depth control to the widest the back channel separation desired.
   • For most matrix systems, use the setting in the table above, or use a lower setting.
   • For the EV matrix, use 60 %.
   • For Dolby Surround, use 60 to 80 %.
4. Adjust the Autovary control so the light is on when front-center program material is present.
5. If more enhancement is desired, increase the Autovary setting.
6. If the image seems to shift abruptly, reduce the Autovary control setting.
7. To turn off Autovary separation enhancement, turn the control to 0 %.
    

TECHNICAL DETAILS

How the decoder works

The decoder works in the following way:

• The front left-to-right separation is reduced by the Width control according to its setting. The control provides a blending between the left front and the right front speakers that reduces as the Width control is turned toward 100 %. The 3-ohm resistors keep the Width control from affecting the other channels.
• The amount of blend in the front speakers is a tradeoff between higher front left-to-right separation at low blend, and higher front-to-back separation at maximum blend. Most matrix systems are based on this tradeoff.
• The back left-to-right separation is reduced by the Depth control according to its setting. The control provides an antiblending between the left back and the right back speakers that increases as the Depth control is turned toward 100 %. The 3-ohm resistors prevent damage if the amp does not have common grounding. The Depth control resistance causes part of the signal sent to one back speaker to go through the other back speaker in reversed polarity.
• The amount of antiblend in the back speakers is a tradeoff between higher back left-to-right separation at low antiblend, and higher front-to-back separation at maximum antiblend. Most matrix systems are also based on this tradeoff.
• The center speaker and the subwoofer are fed from the 5-ohm resistors. A crossover network determines what sound goes to the center speaker and what sound goes to the subwoofer.
• The Null switch disconnects the Depth control from the back speakers. This makes the back speakers reproduce only the difference between the incoming left and right stereo channels. Adjusting the Balance control on the amplifier for minimum sound removes any imbalance from a mono source.
• The Autovary separation enhancer uses the nonlinear resistance characteristics of the #49 lightbulb to change the amount of antiblend on the back speakers. When the bulb is not lit, its resistance is lower, so it increases the back left-to-right separation, while reducing the front-to-back separation. When strong center front material is present, the increased current through the bulb causes it to light up. This causes the resistance of the bulb to increase. This increases the amount of antiblend, increasing the front-to back separation, while reducing the left-to-right back separation. This keeps the center soloist out of the back speakers.
• The filter switch in the filter position rolls off all signals above 7 KHz in the back channels. This removes noises in the back channels, and creates the back signal for Dolby Surround.

How the matrix systems work

The matrix systems are designed in the following ways:

• The Sansui QS matrix is designed for equal separation between speakers all around the room.
• The Dynaquad matrix was designed to maximize front left-to-right separation, at the expense of front-to-back separation and back left-to-right separation.
• The EV Stereo-4 matrix was designed to favor front left-to-right separation and front-to-back separation, at the expense of back left-to-right separation. It is best for recording classical music with concert hall ambiance.
• Dolby Surround is designed with full front separation and no back separation.
• The Hall setting is designed to maximize front-to-back separation (for recording concert hall ambiance) while sacrificing some front left-to-right separation and almost all back left-to-right separation.
• The CBS SQ matrix, Denon BMX matrix, and several other phase shift matrix systems are designed with modulations beyond the capabilities of this decoder.

Building the decoder:

Use the schematic diagram to wire the decoder.

Parts list:

• A case to hold the parts
• Two stereo L-pads*
• Two mono L-pads*
• Either three mono L-pads* or three log-taper 50-ohm 10-watt rheostats*
• One double-pole double-throw toggle switch
• One single-pole single-throw toggle switch
• One #49 miniature lamp***
• One panel mount miniature bayonet lamp socket
• Four 3-ohm 10 Watt resistors*
• Two 5-ohm 10 Watt resistors*
• Two 200-microhenry 5-amp inductors* **
• One 12-millihenry 5-amp inductor* **
• One 200-microfarad 100 volt capacitor* **
• Solder-lug terminal strips for making connections
• Four 4-gang screw to solder pin terminal strips for the back panel
• Knobs for the controls (my be supplied with the L-pads)
• Materials to label the panels

*These parts need to be higher wattages, amperages, and voltages for higher power systems.

**Double the capacitances and halve the inductances if the speakers are 4 ohm.

***Connect multiple #49 lamps in series-parallel for higher wattages. Only one lamp needs to be on the front panel.

Construction:

1. Make sure there is room between the front and back panels for the stereo L-pads, the terminal strips, and the resistors.
2. Drill the holes and mount the parts on the front and back panels.
3. Mount the terminal strips and connect the resistors, coils, and capacitor to them. Parts that are connected together can share the same terminal.
4. Wire the decoder according to the circuit diagram at right.
5. If high amplifier power is used, provide enough ventilation for cooling.
    

Connections:

1. Connect the amplifier to the input terminals as indicated. Be sure to observe polarity.
2. The speakers used should be nominally 8 ohms.
3. Connect the left and right front speakers to the indicated terminals. Be sure to observe polarity.
4. Connect the left and right back speakers to the indicated terminals. Be sure to observe polarity.
5. If a center speaker is used, connect it to the center speaker terminals.
6. If no center speaker is used, turn the center speaker control to 100 %.
7. If a subwoofer is used, connect it to the subwoofer speaker terminals.
8. If no subwoofer is used, turn the subwoofer control to 100 %.
    

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