Sansui AU-999 & Sansui TU-999
Today were showcasing the restoration of a customers two Sansui matching components...the AU-999 & TU-999 Integrated and Tuner combo, and in my opinion of the best looking compliments ever released! During this rebuild we also integrated the Gain Stage Modification for improved performance out of the AU-999 Pre-Amp stage.
Sansui AU-999 Integrated Amplifier
F-1230 -25V PS
The AU-999 has a three way power supply integrated with a Full Wave delivering the -25V source. The F-1231/77 Assembly establish the -/+42V source via a Full Wave Bridge with two 4700MFD filtering capacitors.
The common anode rectifier was replaced with a Ultra-Fast Soft Recovery MUR type Onsemi TO-220 rectifier. The regulator device was replaced with TO-126 modern Fairchild device with better dissipation. The electrolytic capacitors were all replaced with a high temp (105C) and low impedance Panasonic FC and Nichicon PW type with an increase in operating voltages.. A new polypropylene high grade WIMA bypass capacitor installed as well.
F-1231 / F-1277 -/+ PS
Establish via the bridge described above, both regulators were replaced with TO-126 modern Fairchild device with better dissipation. The electrolytic capacitors were all replaced with a high temp (105C), low impedance Nichicon PW type with an increase in operating voltages.. A new polypropylene high grade WIMA bypass capacitors installed as well.
Both of the 4700MFD was replaced with CDE computer grade capacitors, increased to a 6800MFD rating for better filtering.
The failure prone and slow crowbar type Protection assembly F-1313 was removed with the inline fusing retained. As well as the poor sub-sonic filtering stage between the pre-amp out and driver inputs, with the signal path now wired directly to the input/pre-amplifier for a cleaner signal flow.
The drivers are comprised of a common emitter differential stage and current type mirror/reg. with a tiered pre-driver/driver voltage/current gains stages.
Differentials were matched and plotted, new pre-drivers, drivers and constant current devices using low noise, modern TO-92 & TO-126 Fairchild devices.
DIFFERENTIAL PAIR PLOTTING
All of the electrolytic capacitors were replaced with a low impedance PW and audio grade KA/KT Nichicons with an increase in operating voltages. A high grade MKP polypropylene film input updated as well. Both diodes were replaced with general 4148 type as well as both potentiometers replaced with precision Bourns adjustments.
F-1209 Pre-Amp W/ Modification
Built around a full PNP compliment gain stage, the original design suffers serious gain deficiencies. Several years ago (Schematic/Modification Credits: Kevin Bennett) designed several modifications that increase the nominal gain output; You can read our initial detailed review of this modification with reports at our link below; (http://marantzhallo-fi.blogspot.com/2017/10/eds-sansui-au-999-with-pre-amp.html)
All of the associated electrolytic were replaced with audio grade KA/KT and low impedance PW Nichicon capacitors with an increase in operating voltages. All the small signal devices were updated with modern, low noise TO-92 Fairchild devices. New audio grade MKP polypropylene film capacitors updated as well.
F-1228 HeadAmp (RIAA)
The stereo phono stage consists of a PNP/NPN gain stage and coupled input/outputs. All of electrolytic capacitors here were replaced with audio grade Nichicon KA/KT with an increase in operating voltages. New MKP polypropylene audio grade films updated the input/output coupling type. 2SC458 failure prone devices were replaced with a low noise TO-92 Fairchild type.
F-1208 Filter Block
Preceding the pre-amp stage and the line gain controls is the F-1208 Filter block circuit. All of the small signal devices were replaced with a modern low noise TO-92 Fairchild devices. Electrolytic capacitors were replaced with a Audio grade Nichicon KT with an increase in operating voltages. Certain mylar were replaced with a high grade polypropylene and WIMA polypropylene film capacitors.
Sansui TU-999 Tuner
The TU-999 power supply is a simple regulated affair using a half wave and full wave rectification array. Each were updated with Ultra-Fast, Soft Recovery diodes, the initial filter decoupling caps were increased in capacity for better filtering as well as remaining electrolytic replaced with a low impedance Nichicon PW type with an increase in operating voltages. The regulating device was updated to a modern, robust TO-126 Fairchild device for better dissipation, the carbon resistors were updated to metal film 1/2Watt.
Each stage was gone over, updating and replacing tantalum and electrolytic capacitors to a high temp (105C) and low impedance Nichicon PW/ Panasonic FC types with an increase in operating voltages.
Custom SMD Multi LED Upgrades installed