Hier folgt zwar das gesamte Inhaltsverzeichnis wegen der Beschreibungen, doch ein Teil der nicht ineressierenden Komponenten ist bewußt weggelassen !! (zurück zum Hauptartikel)
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Wir müssen die propagierten super tollen Qualitäten des ganz normalen Audio- Verstärkerteils definitiv trennen von den Qualitäten / Spezifikationen des Phono-Entzerrer-Vorverstärkers und der Quadro-Vorstufen.

Die Entwickler-Spezifikation von CD-4 begrenzt die Bandbreite schon von der Theorie her auf 15 kHz - für alle Kanäle !!, also auch die Front-Kanäle. Hatte mir Herr Brüggemann in seinem Platteschneidstudio gezeigt, daß er keine Frequenzen oberhalb von 18 kHz auf die Neumann- Schneidemaschine läßt, also alles mit 18 db/Okt. "absägt", wird bei Quadro Platten allgemein, also auch bei QS und SQ bei 15 kHz alles (weg-) gefiltert. Die eventuellen Mischfrequenzen könnten die Phasenauflösung der hinteren Kanäle empfindlich stören.

Man kann das ganz simpel nachrechnen. Die CD-4 Trägerfrequenz von 30 kHz wird mit 15 kHz nach unten und 15 kHz nach oben "moduliert". Damit bleiben für die Stereo-Information eben nur noch 40Hz bis 15 kHz übrig.

Und damit auf die beiden Frontkanäle auch nichts Unerlaubtes drauf kommt, hat der QX-949 Entzerrer-Vorverstärker dort ein "Low Pass" Filter am Ausgang.
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WICHTIG : Hier steht es explizit : The other two form a buffer amplifier (sie (bilden einen Impedanzwandler), which supplies the CD-4 subcarrier signal (das sind die 30 kHz) to the sub-channel assembly.

After phono equalization, the signal passes through a low pass filter and thence to the matrix assembly. The purpose of this low pass filter is to prevent leakage of the supersonic subcarrier signal of CD-4 discs into the main signal path.

Sub-channel (CD-4) demodulator
The subcarrier signal from a CD-4 record first passes through the carrier level control and enters the sub-channel assembly. This subcarrier is a 30kHz signal frequency-modulated with front-minus-rear difference information.

Demodulation takes place in a PLL (Phase Locked Loop) circuit. The resulting audio signal then passes through the ASC (Automatic Sensitivity Control), sub-equalizer and muting circuits, and thence through the ANRS (Automatic Noise Reduction System) circuit to the matrix circuit.

Matrix circuit (in CD-4 signal path)
The main CD-4 signal (from the equalizer) and the sub-signal (from the CD-4 sub-channel assembly) are added and subtracted in a series of algebraic operations to obtain four independent channel signals.

This is done in the matrix circuit. Different phono cartridges produce different output voltages and, therefore, main signals of different levels. The sub-signal, however, being FM modulated, does not vary in level (after demodulation, of course). To obtain optimum channel separation in the matrix operation, the main and sub-signals must therefore be first matched in level.

This is done by the separation control on the front panel which regulates the main signal level. It controls the amount of negative feedback current at the transistor's emitter.

RM, SQ decoder circuits RM (Regular matrix)
The signal from the equalizer (Vorverstärker) enters the decoder assembly, if the MODE switch is at RM or SQ position. The decoder comprises two phase shifters and a matrix circuit. By changing the position of the MODE switch, the decoder can be made to operate according to the RM or SQ system.

Control amplifier (Lautstärke und Klangregler)
The control amplifier is a negative feedback circuit comprising one FET and two transistors. To obtain stable operation, this two-stage direct coupled circuit constitutes a buffer amplifier of high input impedance but low output impedance.

Power amplifier and protection circuit
The power amplifier is basically an all-stage direct coupled pure complementary design. Power supply is of course of the balanced positive and negative type.

With the mode switch in 2CH position, the rear channel inputs are grounded, only the front channel inputs remain operative. The protection circuit incorporates 4 transistors (one for each channel) for four channels, which are used to detect overload.

DC potential at the junction points of the output stage transistors is done by a differential amplifier consisting of two transistors. Additionally, three transistors are used to drive the cut-off relay. At the first sign of trouble, the relay contacts are opened to safeguard the output transistors and speakers. The protector circuit also serves as a muting circuit, keeping the unit silent during the first few seconds after switch-on.
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8. PARTS AND P.C. BOARD LOCATION / 8.1 TOP VIEW (Aufsicht von oben)

MATRIX CIRCUIT ASSEMBLY AWM-048-0
DECODER CIRCUIT ASSEMBLY AWM-031-0

8.2 BOTTOM VIEW (Ansicht von unten)

SUB-CHANNEL CIRCUIT ASSEMBLY AWX-051-B

10. ALIGNMENT PROCEDURE
10.1 REQUIRED MEASURING INSTRUMENTS (die Meßgeräte)

• FM Signal generator
• MPX signal generator
• AM signal generator
• Millivolt meter
• Distortion meter
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Note, however, that unless the test record (PQX-1011) and the phono cartridge used for the audition are both new, adjustment is impossible. (Beachten Sie jedoch, dass eine Anpassung nicht möglich ist, es sei denn, die Testaufzeichnung (PQX-1011) und das für das Audit verwendete Abtastsystem sind beide neu. - Muß man das verstehen ?)

1. Terminal 19 of the sub-channel assembly must be to ground. (This ensures that muting is inactivated.)
2. Connect an oscilloscope to terminal 14 (L channel). (For the R channel use terminal 5.)
3. Turn the carrier level control up to its maximum (fully clockwise).
4. Play band 1 of the test record (Band 2 for the R channel). The warble-tone waveform will be displayed on the oscilloscope.
5. Turn the carrier level control to the left until the point where the warble-tone waveform distorts is reached. This adjustment is extremely critical, and should be performed with great care.
6. Adjust VR10 until the warble-tone distortion disappears. (For the R channel use VR1.)

It is preferable for the adjustment to be made with the lowest possible carrier level, so the oscilloscope used should have as high a vertical sensitivity as possible (approximately lOmV/cm).
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