Vintage Hi-Fi Audio Restorations: G. Widners Marantz 2270 Stereophonic Receiver Restoration

Marantz 2270 Stereophonic Receiver W/ Jupiter Condensers

The 2270 as I’ve highlighted in the past remains one of the most sought-after vintage receivers to date, fetching astronomical prices for a 70W receiver. The 2270 shares consistent design attributes as with similar 22XX series 2230/45 receivers with differences occurring in the PP amplifier design.

In this particular restoration we employed Jupiter Condenser’s extremely high quality (and priced) esoteric grade Red Astron and Vintage Tone series film capacitors.

P800 Power Supply

The 2270 power plant revolves around a 4A Full Wave Bridge Rectifier and two 9KMFD filter capacitors for the -/+48Vdc reserve. The P800 assembly employs a 1A full wave rectification array with a regulator derived 35V and 13 supplies for the RF and AF Front end stages. The P800 also contains the output protection network for DC deviation and excess current consumption actions.

The small signal devices here were all replaced with modern TO92L devices for better dissipation with low noise Fairchild type. The original rectifier diode array was replaced with a Ultra-Fast, Soft Recovery axial Vishay diodes. The bypass ceramics were also replaced with polypropylene high grade film Nichicon’s. The voltage adjustment was replaced to a sealed, precision Bourns potentiometer. The relay was replaced with a MY series Omron relay. Lastly the TO-66 regulator transistor was replaced with a modern, robust TO-220 equivalent.

The capacitors were replaced with a high temp (105C) low impedance Nichicon with an increase in operating voltage. The initial DC decoupling capacitor was increased to 1000MFD for better DC filtering.

BEFORE

AFTER

Regulated Confirmation35/13Vdc

Filter Capacitors

The original schematic indicates two 6800MFD filters, with most manufactured models touting 9000 filters. These were both replaced with a Computer Grade Panasonic and increased to 12000MFD for a total of 24,000MFD for better filtering and sub sonic reserve at higher output.

BEFORE

AFTER

Rail Confirmation -/+48Vdc

P400 Pre-Amplifier

The 2270 uses in my opinion one of the most popular Marantz designs outside of the PE01 (BA312) based design. The 2270/30/45 have a cap coupled input out, with a NPN differential voltage gain stage and push-pull output design. In this particular rebuild we focused on special esoteric film capacitors by Jupiter Condenser and their Red Astron style films.

All of the small signal devices here were replaced with a low noise, modern TO92 Fairchild devices, replacing the noise prone devices. All of the electrolytic capacitors to 3.3MFD were replaced with a audio grade KT/KA and the DC filter capacitor increased from 100MFD to 330MFD for better filtering with a low impedance PW type. The 1MFD capacitors were replaced with a high grade WIMA polypropylene type and the input .22MFD mylar replaced with a esoteric grade Jupiter Red Astron AM film capacitors.

BEFORE

AFTER

P700 RIAA/EQ (PHONO)

Like the above pre-amp stage, the phono stage concept was used in a half dozen 22XX series designs and a version of in the 1060 integrated. A very reliable and stable design with a warm cap coupled input out, push pull design and NPN voltage gain stage.

All of the small signal devices here were replaced with a low noise, modern TO92 Fairchild devices, replacing the noise prone devices including the notorious 458 type NPN devices. The VD varistor and other diodes were replaced with modern axial 4148 general type. The clipping adjustments were replaced with sealed, precision Bourns potentiometers. The DC filter capacitor was increased to 330MFD for better filtering with a low impedance PW capacitor, along with the remaining capacitors to a audio grade KT/KA Nichicon all with an increase in operating voltage. The input/output films were selected to use WIMA polypropylene in this restore for a specific, defined tone for the Astron capacitors in the pre-amp stage.

BEFORE

AFTER

RIAA Curve Response

P750 Amplifier Channels

The 2270 has a significant issue in the amplifier stages over the dozens of 2270’s I’ve done over the years, I consistently note skewed bias from factory and issues with proportional tracking. One of the solutions I employ for the 2270 is re-routing the thermal servo bias H760 to thermally track the 4th order driver dissipation versus the output stage heatsink dissipation with causes discrepancies in idle current consistency, along with choosing a device of higher beta range and wide Ft bandwidth.

New differential pairs were replaced with modern low noise Fairchild devices, Beta matched and thermally coupled with Wakefield synthetic thermal compound. Remaining devices were replaced with low noise, modern Fairchild devices and Vishay axial diodes. As noted above the bias modification was employed with a MJE series NPN TO-126 device. The bias and idle adjustments were replaced with seal, precision Bourns potentiometers.

Bias Modification

Differential Beta Mapping

All of the capacitors here including the tantalum were replaced with a audio grade KT/KA Nichicon with an increase in operating voltage. In conjunction with the pre-amp selection, films in the driver were complimented with esoteric grade Jupiter Condenser Vintage Tone film capacitors and high grade WIMA polypropylene compliments.