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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K.Lovey Sansui 9090DB Receiver Restoration W/ Upgrade

Sansui 9090DB Receiver

The Sansui 9090DB was released from 1976 to 1979 as the advanced/larger 9090 brother. However similar in appearance and projection the build features are very different in the 9090 and 9090DB. With an increase in output to 125Watts and integration of the Dolby Noise Reduction circuit. This article is can be read in comparison to the previous Sansui 9090 article here; http://marantzhallo-fi.blogspot.com/2018/06/klovey-sansui-9090-receiver-restoration.html

Power Supply F2656

The 9090DB power supply features two full-wave bridge rectifiers, a 1A and 5A with a dual single ended 36/44+ volt supply.

The 1A full-wave bridge device was replaced with a common cathode and common anode ultra-fast, soft recovery MUR OnSemi type TO-220 device. The TO-220 regulator was replaced with a robust, modern OnSemi and coupled with synthetic Wakefield thermal compound. All small signal devices were replaced with low noise TO-92L Fairchild type for better dissipation.

The electrolytics were replaced with a high temp (105C) low impedance PW and VP Bipolar Nichicon capacitors with an increase in operating voltages. 

BEFORE 

AFTER

Filter Capacitors

The two 1200MFD filter capacitors for the B-/+ supplies were both replaced and increased to 15,000MFD with computer grade CDE type capacitors.

-/+B Supply Confirmation

Protection F2547

The protection assembly involves a DC deviation and thermal cascade protection. This board also contains components for the LED’s, just like the 9090 often times we see R12 appears to suffer cracking and will no longer operate correctly. The meter calibration circuit operates here as well.

All of the fusible resistors in this stage were replaced with KOA equivalents and the R12 resistors increased in current capacity with a MOX type. New ultra-fast, soft recovery axial Vishay diodes were installed. The meter calibrating potentiometers were replaced with Bourns precision type. 

Electrolytics were replaced with a low impedance PW and VP Bipolar Nichicon capacitors with an increase in operating voltages. Films were replaced with a high-grade WIMA polypropylene film. 

BEFORE 

AFTER

Pre-Amp F2544 W/ BA312 Upgrade

For the pre-amp stage were proud to offer the BA312 Upgrade we assisted in designing and now available online. The BA312 Upgrade offers a substantial improvement to the original “pre-amplifier” IC, with a modern Class-A fully discrete Op-Amp..the results are significant to say the least.

Two new BA312 Upgrade Modules with the Sparko’s Labs SS3601 Op-Amp are installed per channel. Electrolytics were replaced with a audio grade Nichicon KT/KA and low impedance Nichicon PW type with an increase in operating voltages. DC filtering stages were increased in overall capacitance.  New high-grade WIMA polypropylene film capacitors were also installed. The secondary gain stage devices were replaced with a low noise, modern TO-92 type Fairchild devices. 

BEFORE 

AFTER

Mic Amp F2617 & Filter switchinging

The 9090DB features a BA312 central Mic Amplifier stage.

The F22617 requires the change of two resistor values due to the increase in current consumption of the BA312 modules. The electrolytics were replaced with low impedance PW and KT/KA audio grade Nichicons with an increase in operating voltages. The single small signal device was replaced with a low noise modern TO-92 Fairchild device.

BEFORE 

AFTER

On the filter switch assembly both electrolytic capacitors were replaced with a audio grade KT/KA Nichicon capacitors.

BEFORE

 AFTER

RIAA EQ F2653 W/ BA312 Upgrade

For the 9090DB the RIAA BA312 version has been perfected and released with outstanding reports from folks! Like above, the BA312 Upgrade Modules replaces the original BA312 IC's. On this assembly retrofitted the selector switch making it somewhat awkward. 

New BA312 Upgrade Modules installed. Electrolytics were replaced with a audio grade KT/KA and low impedance PW Nichicon capacitors with an increase in operating voltages. New high-grade WIMA polypropylene film capacitors were installed. Two resistors are increased in current capacity due to the increase in consumption from the Op-Amps employed. 

BEFORE 

AFTER

RIAA Curve Response

Drivers F2626

The two receivers employ vastly different driver designs with the DB version capable of additional output with a decrease in THD. Both featuring a PP complimentary output and gain differential stage.

New precision matched differential pair transistors were installed with modern, low noise TO-92 Fairchild type. Current mirror circuit and new pre-drivers were installed with low noise,TO-92 and  TO-126 type Fairchild devices. VD series diodes were replaced with a modern axial 4148 series type. All fusible resistors were replaced with carbon film type and precision Bourns potentiometers installed. 

Electrolytic capacitors were replaced with a low impedance PW, high temp (105C) and Bipolar VP Nichicon capacitors with an increase in operating voltages. New high-grade WIMA polypropylene film capacitors were installed. 

BEFORE 

AFTER

Bias Confirmation

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

RF, Dolby (F2654) & RF PS F2619

The nice part about the front end of the 9090/DB series is that the chassis completely lifts off for easy access to the RF front end and AF stages.  The RF stage utilizes its own regulated 12.5V power supply from the 36+ single end supply. The DB features are more advanced regulated supply.

BEFORE

 AFTER

F2654 Dolby Switching (Vol Adjustment)

The 9090DB has an integrated Noise Reduction/Dolby decoding circuit, one of the first dual-sided soldered PCB’s available at its time. A prior technician had replaced with appropriate application,  capacitors on board. We reflowed the switch and wire-tap connectors as these often become problematic. 

New high-grade WIMA polypropylene film capacitors and KT/KA Nichicon audio grade capacitor installed. Precision Bourns potentiometers installed for the 270mV Output adjustment. 

BEFORE 

AFTER

The TO-220 regulator was replaced with a modern, robust OnSemi type device and coupled with synthetic Wakefield thermal compound. A new axial Vishay ultra-fast soft recovery diode installed as well. Electrolytic capacitors were replaced with a low impedance, high temp (105C) Nichicon PW with an increase in operating voltages. 

BEFORE 

AFTER

LEDs

New 8V custom multi-SMD LED type lamps were installed in both display and meter assemblies. A new 100MFD Nichicon PW was installed across a meter. The wiring for the lamp was routed different on this model versus the 9090.

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