Today were showcasing two customers Marantz 2275 receivers we restored recently. One of the units as you will see below was a very very early production model prior to foil silk screening, with suitable variations in topography, the biggest being a different in bias feedback for the P700 amplifier stages. Both of these units had the new Analog Esoteric BA312 upgrade modules installed in the PE01 tone stages. One customer opted for a new production black faceplate as photo’d.
The 2275 is a particular favorite Marantz of mine, built exceptionally well, akin to the 2325 versus the 2270 which I despise from a technical point of view due to its amplifier design shortcomings. The 2275 has excessive RF shielding, robust filtering reserve, PE01 oriented pre-amp stage etc.
P800 Power Supply
The regulated 35/14V power supply is a tried and true Marantz design used in many series, composed of two full-wave rectifiers with a TO-220 regulator and full wave bridge rectifier for the B-/+ rails. The protection circuit is housed on the same PCB, acting as a DC deviation/thermal monitor.
All of the capacitors were replaced with a low impedance, high temp (105C) Nichicon PW capacitors with an increase in operating voltages. New high grade WIMA polypropylene films were also installed along with precision Bourns adjustments.
Common array diodes were replaced with more robust MUR TO-220 devices, as well as new TIP TO-220 robust voltage regulators, all remaining devices were replaced with modern Fairchilds TO-92L devices for better dissipation.
BEFORE
(note one P800 had previously had capacitors replaced but was all redone)
AFTER
The original 15,000MFD filter capacitors for the B-/+ were replaced with a Nippon Chem-Con computer grade capacitors and increase to 18,000MFD for better subsonic response and handling.
PE01 Tone Board W/ Analog Esoteric BA312 Upgrade
The PE01 used in the Marantz 2275 is identical to the 2250,2250B, 2265, 2285, 2325, 2330 models using two monolithic BA312 IC’s as a differential gain stage with a proceeding NPN/PNP coupled output stage. The New AE BA312 Upgrade modules are one of the biggest upgrades to these vintage units in decades, results from peer/customer reviews have been absolutely outstanding, with the modules adding a great degree of dimension and clarity to the Marantz presentation and associated decrease in distortion, increase in gain and damn near linear frequency response!
After the modules were installed replacing the old inferior IC’s all the capacitors including tantalums were replaced with a audio grade and low impedance KA/KT and PW with an increase in operating voyages, audio grade Muse BiPolar were used for the output R/C. High grade MKP polypropylene capacitors were installed for the input R/C network. The decoupling capacitor was increase in value for better filtering. New low noise TO-92 Fairchild devices were installed.
BEFORE
AFTER
P700 Drivers
The 2275 driver section employs a dual differential pair which drivers the output via H703 and predriver/driver H711/12/13 devices per channel with a global feedback circuit and dynamic bias control via H709/10 and a complimentary output stage.
As mapped below the differential pairs were matched within 1% and thermally coupled together, new constant current/ detect, pre drivers were installed using low noise, modern Fairchild TO-92 and TO-126 devices. New general axial Vishay diodes installed as well.
Differential Mapping
New low impedance, high temp (105C) Nichicon PW’s installed with an increase in operating voltages, as well films to a MKP polypropylene input and PP .1MFD type including high grade WIMA polypropylene type.
BEFORE
AFTER
P400 RIAA (Phono)
The phono stage is the same stage present in many of the 22/23 series Marantz receivers, most which feature the problematic 2Sc458 devices and VD diodes. The P400 is a coupled input/output stage which is quite linear compared to the RIAA standard when low noise, higher gain devices are used.
All of the capacitors here were replaced with low impedance PW Nichicon, including the axial to a more reliable radial, and increases in operating voltages. All the VD diodes were replaced with modern axial viceroy 4148 type and all NPN replaced with low noise Fairchild devices.
BEFORE
AFTER
RIAA Curve Response
Illumination
New vellum for both displays and meters were installed along with new custom SMD lamps and function indictors.
Audio Notizen
No comments:
Post a Comment