K.Lovey Sansui 9090 Receiver Restoration W/ Upgrade

Sansui 9090 Receiver

The Sansui 9090 was released from 1975 to 1977 as a larger 8080 variant and remains an extremely popular Sansui today. Excellent rated performance and integration of the early BA312 made it a step above move available at the time and standard Sansui features such as the triple tone controls.

Power Supply F2546

The 9090 power supply assembly contains a full-wave bridge 5A for the 61 volt -/+ B supplies as well as a single full-wave for a 1A single ended 36 volt supply.

The full-wave bridge device was replaced with a common cathode 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 and VP Bipolar Nichicon capacitors with an increase in operating voltages. 

BEFORE 

AFTER

Filter Capacitors

The two 6800MFD filter capacitors for the B-/+ supplies were both replaced with a computer grade CDE type.

-/+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, often times 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 & Tone MIC Amp F2543 

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 F2543 & Filter Switching

Similar to the 9090DB the 9090 features a BA312 central Mic Amplifier stage.

The F2543 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 F2541

Like the 9090DB the 9090 RIAA EQ stages features another BA312 in the RIAA EQ stage. Upgrades for the 9090 RIAA EQ are hopefully coming in the future but the current design produces quite the impressive curve and a solid improvement over most of the NPN/PNP stages available at the time. 

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. 

BEFORE 

AFTER

RIAA Curve Response

Drivers F2463

The 9090 output stage differs quite a bit from the 9090DB version, 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. new pre-drivers were installed with low noise, 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

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 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

BEFORE RF PS Stage

AFTER RF PS Stage

LEDs

New 8V custom multi-SMD LED type lamps were installed in both display and meter assemblies. The wiring for the selector switch is modified to re-route the AC source from the selector due to possible long term damage and arching. 

AUDIO NOTIZEN

J. Trapani Pioneer SX-737 Restoration

Pioneer SX-737 Receiver 

The Pioneer SX-737 was introduced from 1974 to 1976 and shared construction the 35/36/38 series. Unlike its class sibling the SX-750 the 737 features far superior build qualities and overall reliability versus single PCB oriented units. Boasting a modest 35-40W at .5% THDN which is perfect for most listening sessions and a unique dual use recorder option. 

Power Supply AWR-057

The regulated power supply is comprised of a 3A  bridge rectifier for the two 6800MFD rail filter capacitors and a half and full wave rectified source developing the 13 and 35Vdc -/+ rails.

Many manufactures were limited in power supply filtering capacitor sizes due to high volume/costs, today during the rebuild we can see major improvements arise from increasing the factory DC filtering stage electrolytic capacitors as we do in our restorations. Here the full wave/half wave stages and mains -/+ rails were all increased for better DC filtering with low impedance Nichicon PW capacitors including remaining electrolytic, all with an increase in operating voltages. As axial offer an inferior construction in my opinion to radials, the original 1000mfd form factor was changed to a modern radial foot print. 

The 1A arrays were updated with Ultra-Fast, Soft Recovery Vishay diodes as well as 13/14V zener axial diodes. Small signal TO-92 devices were replaced with modern low noise Fairchild TO-92L devices with better dissipation. Both stand alone and thermally coupled TO-220 regulators were replaced with modern robust TIP devices, the thermally coupled TO-220 was coated with synthetic Wakefield thermal compound. 

BEFORE 

AFTER

Filter Capacitors

The 6800MFD bridge rectified dual rail 36V capacitors were replaced with computer grade CDE capacitors with a markable increase to 10,000MFD for better filtering and sub sonic frequency response. 

-/+ Dual Rail Vdc Confirmation

Protection AWM-025-C

The protection circuit in the 737 is shared across multiple SX series in A/B and C variants. The protection covers significant DC deviation across the output.

The electrolytic capacitors were replaced with a low impedance, high temp (105C) Nichicon PW with an increase in operating voltage. The series 330mfd capacitors were replaced with a single Bipolar 165MFD MUSE Nichicon capacitor ((C1XC2)/(C1+C2)tot).  The .22MFD capacitors were replaced with a high-grade WIMA polypropylene type. New small signal TO-92 and TO-92L devices were replaced with a modern low noise Fairchild. A new non TO-126 low noise Fairchild was also installed. 

BEFORE 

AFTER

Pre-Amplifier AWG-030 & MIC Amp AWM-066

The SX-737 pre-amp stage consists of nf type, direct coupled circuit and a simple gain stage with attenuated dual sub/hi controls. 

The electrolytic capacitors were replaced with low impedance PW and audio grade KT/KA Nichicons, operating voltages were increased and the initial dc filter capacitor was increased for better dc filtering. High-grade WIMA polypropylene films were installed. Small signal TO-92 devices were replaced with low noise, modern Fairchild devices. 

BEFORE 

AFTER

On the MIC amplifier assembler the low value capacitors were replaced with high-grade WIMA polypropylene film capacitors as well as electrolytic with low impedance PW Nichicon’s, a noted increase in operating voltages. New small signal TO-92 low noise Fairchild devices were installed.

BEFORE 

AFTER

RIAA EQ AWF-011

A multi-stage, NF type circuit, direct coupled with a npn output stage with a report deviation of +.3dB.

Electrolytic capacitors here were replaced with a low impedance PW and audio grade KT/KA Nichicon capacitors with an increase in operating voltages.. High-grade 1MFD WIMA polypropylene were also installed. All small signal devices were replaced with modern, low noise TO-92 Fairchild devices. 

BEFORE

 AFTER

RIAA CURVE RESPONSE 

Amplifier AWH-033

The amplifier stage in the SX-737 is built around a complete OCL type circuit, coupled input/output design. An initial differential gain stage and piggybacked bias compensating circuit and a pure complimentary 3rd-4th order stages. I do want to add however that the output rating of .5% THD is unrealistic as the unit is presented, their test must have involved isolating the amplifier stage, coupled as a AF-Driver receiver 0.9% THD+N is reasonable at rated output with a capable output of about 40Watts.

The differential pair devices here were replaced with precision matched low noise TO-92 Fairchild devices. New pre-drivers and 3rd order drivers were installed as well with robust, low noise TO-126 and TO-220 type Fairchild/OnSemi devices and thermally coupled with a synthetic Wakefield thermal compound. Precision Bourns bias and offset adjustment potentiometers installed. 

Differential Matching

Electrolytic capacitors here were replaced with low impedance PW and audio grade KT/KA Nichicon capacitors with an increase in operating voltages. High-grade WIMA polypropylene film capacitors were also installed. New axial general 4148 type Fairchild diode installed. 

BEFORE 

AFTER

BIAS Confirmation@ 20mV

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

(*new verification report in our long line of extensive testing now included with restorations*)

RF AM/FM Front End

The RF front end was designed well in this unit, with a 4-gang variable capacitor, Dual MOSFET FM Front end and proprietary FM/AM IC stages. Also implemented was the PLL or Phase Lock Loop tuning. All of the electrolytic capacitors here were replaced with a low impedance, high temp (105C) Nichicon PW type with an increase in operating voltages.

LED's

New high quality Multi-SMD LED type Warm White 3-35K spectrum lamps installed. 

AUDIO NOTIZEN
(Frequency Response/THD ~ Signal to Noise Ratio ~ Intermodulation Distortion (IMD) ~ Total Harmonic Distortion + Noise (THD+N) Thru Rated Specs ~ Clipping/Max Output ~ Av Gain ~ Separation (dB))