Bill's Marantz 4230 Quadradial Restoration

Marantz 4230 Quadradial Receiver

Here were showcasing a customers Marantz 4230 that came in for a restoration.  The 4230 is a X2 Stereo + Quadradial Receiver released from 1973-1977.  The Quad Marantz are a unique approach to the dimensional listening session. The Marantz 4230 features a Discrete Mode which direct each input to each respective output, or 2/Ch listening. Using the Vari-matrix mode the rear inputs are internally shunted, Left/Right Input drive the front output and the Left/Right output Rear is synthesized and further attenuated via the Dimension Feature. Optionally a SQ Decoder can be utilized which shunts the signal similar to the Vari-Matrix operation but after plug-in decoder processing. 

P800 Power Supply

The 4230 Power supply is relatively unique for the regulated Marantz PS as it utilizes two full wave bridge rectifiers where as they often employ a full wave bridge and full wave pair.  The Full wave bridge has the + output shunted to ground for a single rail supply. 

The Full Wave Bridge was upgraded with Ultra-Fast, Soft Recovery axial Vishay Diodes and a new .01MFD ECW polypropylene Panasonic Film, the 330MFD decoupling film was increased to a 470MFD/63V type low impedance PW, the 1/2 wave for the lamps was also upgraded to a UF, soft recovery diode. New axial 4148 general and 14V zener installed as well. The adjustment was replaced with a Bourns precision potentiometer. The TO-92 small signal devices were both replaced with NPN TO-92L Fairchild devices for better dissipation as well as the regulator 2SD315 to a more modern, robust TO-220 TIP device and new synthetic Wakefield thermal compound.  Electrolytics were replaced with a low impedance, high temp (105C) Nichicon PW with an increase in operating voltages. New high grade WIMA polypropylene bypass were installed as well. 

BEFORE

AFTER

Confirmation 14/35V Source

The Filter cap was increased from the original 4700MFD capacitor to a Cornell 6800MFD computer grade filter capacitor for better transient noise filtering and power reserve. 

P700 Drivers (X4)

The 4230 designed two separate driver assemblies with two mirror driver circuits per assembly, which is switchable via a rear 30WX12W(X4) selector. Each circuit is comprised of a simple differential,  pre-driver/inverter phase and drivers to output coupled stages.

The differential/pre-drivers and H701 were all replaced with TO-92 and TO-92L low noise, modern Fairchild devices. Pre-Driver and Drivers were replaced with TO-126 low noise, modern Fairchild/On devices. General 4148 axial diodes updated and the original robust plastic frame “Clipping” potentiometers removed, debri’d, cleaned and lubricated and re-installed, the bias points were updated with precision Bourns potentiometers.

All of the electrolytic were updated with a low impedance PW and audio grade KA/KT Nichicon with an increase in operating voltages. New high grade MKP polypropylene/pp films were installed. Two service bulletins pertaining to gain and output devices were addressed on this model. 

BEFORE

AFTER

X4 Channel Bias Confirmation 

PE01 Pre-Amp & PD01 Buffer

Feed after the buffer and monitor/Dolby pathways the PE01 is a much different PE01, using a simple gain NPN/PNP stages for the input/output. Both Tone Controls were removed from the PCB's for a deeper clean and better access.

All of the electrolytic capacitors here were replaced with audio grade KT/KA Nichicon capacitors with an increase in operating voltages. The input were replaced with high grade WIMA polypropylene film capacitors. All of the small signal devices were replaced with a low noise, modern TO-92 Fairchild devices. 

BEFORE

AFTER

On the PD01 Buffer Stage All of the electrolytic capacitors here were replaced with audio grade KT/KA Nichicon capacitors with an increase in operating voltages.  All of the small signal devices were replaced with a low noise, modern TO-92 Fairchild devices. 

BEFORE

AFTER

P600 Dolby & PL01 400Hz Tone

The initial Dolby circuit is a selectable Noise/Reduction/Calibration control for the RIAA/Line playback. Inserting itself prior to the PE01/PD input, normal operation should rest in Off Mode. 

All electrolytic here were replaced with low impedance PW Nichicon capacitors with an increase in operating voltages. New .33MFD ECW polypropylene film capacitors were also installed. 

The PL01 Stage is used for calibration of the record input level of dubbing for reference, as above all the electrolytic’s here were replaced with low impedance PW Nichicon capacitors with an increase in operating voltages.

P500 Vari-Matrix

The P500 enables the synthesized option of buffering the front to rear inputs, the P500 uses a pair of monolithic TA7122 integrated-circuits.  All of the electrolytics here were replaced with a low impedance PW Nichicon capacitors with an increase in operating voltages and high grade WIMA polypropylene film capacitors. 

BEFORE

AFTER

P400 RIAA (PHONO)

The 4230 has a very unique phono stage employing two monolithic TA7129 integrated circuits for gain stages and output.

The decoupling C413 capacitor was increased to a 220MFD PW Nichicon for better noise reduction, the electrolytic were replaced with audio grade and low impedance KA/KT /PW capacitors with an increase in operating voltages. IC bypass capacitors were replaced high grade WIMA polypropylene film capacitors. 

BEFORE

AFTER

Hardware

New custom SMD 8V Meter and Dial Display LED’s installed along with new Vellum diffusion paper and two 100MFD meter capacitors to Nichicon PW type.  All the function/Stereo indicators were replaced with a SMD LED type. 

Audio Notizen