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Monday, February 18, 2019

D.Deremo's Marantz 2285B Receiver Restoration

Marantz 2285B Receiver



The 2285B version was the latter 2285 adaptation with additional Dolby options and aesthetics. The 85B was available from mid 1977 to early 1980 with a nominal rating of 85Wrms @ .05%THD. The 2285B employed many of the latter B version build points such as the symmetric driver design.

P800 Power Supply
The dual secondary transformer is inline with dual section filter capacitors and each with its own full-wave bridge rectifier. The Regulated P800 supply utilizes a full-wave bridge and a separate full-wave rectifier array for the protection. 

All of the common cathode, common anode devices were replaced with state of the art Hex Fred ultra-fast, soft recovery MUR series TO-220 rectifiers. The TO-220 regulator was replaced with a OnSemi type modern, robust MJ series device with new synthetic thermal compound applied. All remaining small signal devices were replaced with modern, low noise TO-126 and TO92(L) Fairchild devices.



All of the electrolytic capacitors were replaced with low impedance PW and high temp (105C) Nichicon type with an increase in operating voltages, DC coupling capacitors were also increased in MFD value for better filtering. 


BEFORE

AFTER



Reg. Vdc & -/+B Confirmation

PE01 Pre-Amp
The PE01 employed in the 2285B is a vastly different design than a majority of the PE designs employed by similar Marantz PE01. This stage uses a series of common emitter PNP devices which are noise and failure prone. 

All of the common emitter devices were replaced with beta matched low noise, modern PNP devices in separate TO-92 Fairchilds. Remaining small signal devices were replaced as well with low noise Fairchild devices. 


All of the electrolytic capacitors and .22MFD mylar were replaced with a audio grade KT/KA and low impedance PW Nichicon capacitors with an increase in operating voltages. Mylar and 1MFD capacitors were replaced with a high grade WIMA polypropylene film capacitors. 


BEFORE


AFTER



P400 RIAA EQ (PHONO)
The phono stage is the similar concept to the Marantz 22XX series with a contained selector plus an additional FB stage.

All of the small signal devices here were replaced with a low noise Fairchild devices. All of the input capacitors were replaced with a bipolar audio grade MUSE Nichicon capacitors. Remaining capacitors were replaced with audio grade KT/KA Nichicons and the DC coupling capacitors increased for better filtering and replaced with a low impedance PW type, all with an increase in operating voltages. 


BEFORE


AFTER



RIAA Curve Response
P700 Driver
The 2285B driver is composed on a single symmetric PCB design with a shared complimentary output stage and convenient molex connection points. 

The differential pair transistors were beta matched and thermally coupled together. All remaining pre-drivers, drivers were all replaced with modern, robust TO-220 MJ series OnSemi and TO-126 Fairchild devices all thermally coupled with synthetic thermal compound. New precision Bourns potentiometers were installed for bias/offset adjustments. 



Differential Mapping


The input capacitors were replaced with audio grade MUSE bipolar Nichicon capacitors along with remaining capacitors as low impedance Nichicon PW type with an increase in operating voltages. Remaining film capacitors were replaced with a high grade WIMA polypropylene film capacitors.


BEFORE


AFTER




Bias Confirmation

RF Front End
All of the RF capacitors were replaced with a low impedance Nichicon PW type with an increase in operating voltages.

BEFORE


AFTER


AUDIO NOTIZEN



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