D. Stoner Marantz 2270 Receiver Restoration

Marantz 2270 Stereophonic Receiver 

The 2270 is one of today’s most popular and prized receivers from the era and Marantz. Produce from 1972 to 1974 featuring an output of 70Watts @ 0.3THD. The 2270 uses an almost identical pre-amplifier stage and RIAA phono stage of the 2230 and 2245. 

P800 Power Supply & Protection

The 2270 power supply consists of regulated 35V and 13.5V single-ended outputs around a full wave quasi bridge. The large 48V supply consists of a 4A full-wave bridge rectifier. The P800 assembly also contains the protection network which guards against DC deviation and excessive current consumption. 

The electrolytic capacitors were all replaced with a high temp (105C) low impedance Nichicon PW with an increase in operating voltages. Original axial rectifiers were all replaced with a ultra-fast, soft recovery axial Vishay type diode. New precision Bourns voltage adjustment potentiometers replaced. 

BEFORE 

AFTER

All the small signal transistors were replaced with a low noise, and robust modern TO-92L and TO-126 devices for better dissipation. The TO-66 NPN regulator was replaced with a modern, robust TO-220 type OnSemi device with new synthetic Wakefield thermal compound applied.

BEFORE

AFTER

35Vdc Confirmation

Filter Capacitors

The original 9000MFD filter capacitors were replaced with a CDE computer-grade 15,000MFD filter capacitors for better subsonic response and DC filtering for the 48 -/+ dual rails. 

48V Rail Confirmation

P400 Pre-Amplifier 

The 2270 pre-amplifier design was used in a few different 22XX series such as the 2230 and 2245. The cap-coupled input/output design offers a warm, classic Marantz tone.

In this stage all of the small signal devices were replaced with a low noise, modern TO-92 Fairchild type. The electrolytic capacitors were replaced with a audio-grade KT/KA and low impedance type PW with an increase in operating voltages. The DC filtering capacitor was increased to 220MFD for better DC filtering. The original films were replaced with a high-grade MKP polypropylene film capacitors, small value electrolytic were replaced with a high-grade WIMA film capacitor. 

BEFORE 

AFTER

P700 RIAA EQ

Like the pre-amp stage of the 2230 and 2245, the phono stage is mirror in a large number of 22XX and 23XX series. Again with a modest cap coupled input/output and NPN gain stage, as the curve report details below its quite accurate too.

The capacitors in this stage were replaced with a audio grade KT/KA and low impedance PW Nichicon capacitors with an increase in operating voltages. The DC filtering capacitor was increase to 220MFD. The original films were replaced with a high-grade MKP polypropylene film capacitors.  The VD type varistor was replace with modern axial 4148 type diodes and the clipping adjustments replaced with a precision Bourns potentiometers. 

BEFORE 

AFTER

Marantz 2270 RIAA Curve Response

P750 Driver Stages

The 2270 Driver stages can have a unique history of unstable biasing and output. This is related to improper positioning of the servo-bias type transistor at the heatsink versus the driver heatsink to appropriately monitor difference in gain/dissipation. 

The 2270 driver design also features a  ASO (symmetric clipping) adjustment that can act as a current limiter. Due to the age of components these tolerances and settings can drift and change, in this particular unit one unit had skewed quite significantly. Below is a graphic I compiled adjusting the 2270 ASO calibration for this unit;

ASO Adjustment Highlight

New precision Bourns potentiometers for the Bias and Offset adjustments. New low noise, robust TO-92 devices including matched differential pair transistors were installed. 

Differential Pair Mapping

The capacitors on each stage were replaced with a audio grade KT/KA and low impedance PW Nichicon capacitors with an increase in operating voltages. Film capacitors were replaced with a MKP and Nichicon polypropylene film capacitors. 

BEFORE 

AFTER

BIAS Confirmation

Amplifier Square Wave Applications with FFt (Fast Fourier Transform) Analysis

Hardware

New 8V custom SMD LED fuse-type were installed as well as new vellum for the display and both meters. New SMD/LED indicators and the common 12V stereo replaced. 

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