Monday, June 11, 2018

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.




AUDIO NOTIZEN