Marantz 2285 Receiver
Today were featuring a somewhat rare Marantz 2285. The 2285 with a limited one year production run in 1977 is the sibling of the popular Marantz 2285B version.
The 2285 and B are vastly different units and in my opinion from a technical point of view, the 2285 is far better built in every way. Featuring a far more robust 35V supply along with two single core filter capacitors versus the single dual caps of the B versions which tend to fail far more often or premature defects than single core. The other major difference is the driver assemblies, whenever we can separate channels and provide better thermal take off we gain better results and a lower noise floor. The 2285B uses a single symmetric PCB assembly and one large heatsink versus the 2285 that utilizes two separate driver assemblies and heatsinks.
Power Supply P800 & Filters
The 2285 has a fairly robust power supply compared to similar 22XX series receivers by Marantz include a large 2200MFD capacitor which was replaced with a Nichicon low impedance long life PW with an increase in operating voltages. The remaining electrolytics were replaced with Nichicon PW and high temp (105C) FC Panasonics along with an increase in operating voltages and large filter capacitance t0 330MFD.
The common cathode diodes were replaced with ultra-fast UF400# type diodes and the 7.5V zener with modern diodes. The regulator 2SD TO-220 devices were replaced with new modern and robust On Semi TO-220 MJE transistors with new thermal compound as well.
BEFORE
AFTER
This PCB also house the protection Relay for the output stage, which was replaced with a new Omron MY2 Relay.
The original 13,000MFD 55V filter capacitors were replaced with high grade Nippon Chem-Con with an increase to 18,000MFD 75V capacitors and new terminations.
P700 Drivers
Similar to the 23XX series drivers the 2285 has a heavy heatsink and thick PCB mounts for a very sturdy design. With a similar topology of the other drivers seen in the 2275 etc. The initial differential pair transistors were replaced with 1% matched low noise Fairchild TO-92 BJT’s thermally coupled together and heatshrinked along with the 2nd stage and pre-drivers to new Fairchild low noise TO-126 BJT’s.
The electrolytic were replaced with FG and KT audio grade Nichicon capacitors with an increase in operating voltages. All of the films were replaced with high grade polypropylene MKP and WIMA’s. New thermal compound and MICA installed as well as lubricated the heavy plastic potentiometers and cleaning. As I’ve noted on other Marantz driver rebuilds I tend to prefer these older white plastic heavy bodied potentiometers even over Bourns IF they track well and reliably after cleaning.
BEFORE
AFTER
PE01 Pre-Amp & PH01
Again, similar in construction to the 2325 assemblies and better 23XX series chassis. Like the 2325/ 2275 etc the 2285 uses a BA312 IC for an initial differential stage and an effective Audio Pre-Amp IC (pre-cursor to OPAMPS), the proceeding NPN/PNP compliments here were replaced with modern low noise TO-92 Fairchild devices.
New high grade WIMA and MKP polypropylene films were used along with low impedance and audio grade KT/FG PW Nichicon capacitors. All the controls were heavily cleaned and lubricated. The electrolytic on the filter amp stage were replaced with audio grade KT Nichicons.
BEFORE
AFTER
P400 RIAA EQ
The RIAA stage used in the 2285 is one of the most common Marantz RIAA EQ stages they integrated into both receivers and some integrated. Its is the main stay of their popular vinyl sound!
I have done many trial and errors over the years getting the best film compliment here. What differs is the use of NPN device versus the early 2SC458 transistors. Albeit this stage was still updated to low noise Fairchild TO-92 devices in compliment along with general diodes to modern 4148 and the epoxy diode replaced with 4148 in series. The electrolytic axial was replaced with my preferred radial type low impedance PW and remaining electrolytic with KT audio grade with an increase in operating voltages. The tantalums and output films were replaced with high grade MKP and WIMA polypropylene film capacitors.
BEFORE
AFTER
RIAA Curve Response
New Vellum paper on both meters and dial display was installed. You can see effect of years of grimy air on the vellum! New custom SMD LED 8V fuse types were installed along with all Bi-Pins to LED upgrades. (recently lost all hope with original type Bi-Pins)
Audio Notizen
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