Tuesday, January 17, 2017

Mike's Sansui G-8000 Pure Power DC Receiver

Sansui G-8000 Pure Power DC Receiver 





The Sansui G-8000 is the little brother to the popular G-9000 receiver, featuring many of the same construct and quality. The G-Series shares many cosmetic qualities together with over-sized tuning and volume knobs with the classes brushed anodized and crest finishes, unique is the left and right chassis mount input/output banks versus the traditionally rear mounted location.




Power Supply F2808-F2807 & F-2809 AF PS/Protection
Each of the G-8000 driver assemblies are fed by separated regulated +/- 75V  power supplies and a large Toroidal transformer with dual AC windings along with 30,000 microfarads of filtering and reserve which were replaced with separates vs the G-9000 that uses a dynamic oval capacitors.

The two F808 and 2807 assemblies had the large mount 2200 and 100MFD capacitors replaced with high temp (105C) long life Nichicon PW capacitors with an increase in operating voltages along with all the 10D diode to Ultra-Fast UF400# type diodes. Several resistors were replaced with KOA 1/2 type that were originally coating in the glue that was removed from the PCBs. 





Protection &  AF PS
The G-8000 features a trifecta of protection features such as significant DC Deviation, Over-Current protection when output fails and a thermal detecting sensor at the main heatsink.

The remaining of the AF PS is located on the F809 assembly under the chassis along with the Protection circuit. As above the PS components were replaced with high temp (105C) low impedance and long life Panasonic FC and Nichicon PW’s along with VP Nichicon BiPolar capacitors with an increase in operating voltages. The regulating  2SB/2SD TO-220 devices were replaced with heavy duty On-Semi MJE TO-220 devices with new thermal compound and MICA applied. All of the 10D diodes upgraded to Ultra-Fast UF400# type.  The relay contact were all Brandished and/or replaced with Omron LY2 and a MY4 DC24V type. Associated fusible were replaced with KOA 1/2W resistors.



F27086 Drivers
  The following input stages in the G9/8000 series use a differential FET or dual FET 2SK device. The driver stage installs a 2SK97 dual FET device with non cap-coupled NFB. Constant current/mirror source circuits were updated with modern TO-126 and TO-92 low noise Fairchild devices. Pre-Driver were updated to a TO-126 low nose Fairchild devices. New Bourns precision trimmers were installed (100/2.2K) The lower bank of resistors (fusible type) typically report heat issues as these displayed, the array was replaced with 1/2W KOA resistors.



BEFORE

AFTER

The capacitors were replaced with 470MFD/100V low impedance Nichicon PW capacitors along with KT audio grade capacitors with an increase in operating voltages. New High grade ECW Panasonic  and Polypropylene WIMA film capacitors installed.





F2798 RIAA EQ
The initial differential input stage is achieved with a tied FET 2SK117 device with a final Class A/Buffer to inverted Class A darlington complimentary output.  The capacitors here were replaced with VP Nichicon Bipolar capacitors and KT  and FG Fine Gold audio grade and low impedance PW Nichicon capacitors with an increase in operating voltages.Small signal devices were replaced with Fairchild TO-92 low noise devices. High grade WIMA .1 polypropylene were installed replacing the original mylar films.



F2799 Tone Amp/Control
As with the RIAA circuit the tone amp employs a tied FET 2SK117 input circuit with a constant current/mirror source and two-stage tiered darlington-complimentary output.  Again the Bipolar’s were replaced with VP Nichicons as well as KT and FG Fine Gold audio grade and PW low impedance Nichicons with an increase in operating voltages. The .22 films were replaced with high grade polypropylene MKP film capacitors and 3.8K fusible resistors to KOA film resistors. Small signal devices were replaced with Fairchild TO-92 low noise devices.





Audio Notes







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