Thursday, May 12, 2016

Sansui 8080 Receiver

Sansui 8080 Receiver

I wanted to take a posts and highlight a restoration of a Sansui 8080 Receiver. The 8080 is up there with the 9090/8080DB variants. Rated at a modest 80W @ .2%THD VS the 9090, the 8080 features some distinct differences in design apart from the 8080DB.  The 8080 features a quasi complimentary output stage where as the 8080/9090DB features a NPN/PNP push pull topography, the 8080 also only features a single RIAA input and formats the outputs to parallel rather than in series like the DB versions.  The 9090 and 8080 share an identical MOS FET FM front end unique to those two.

Power Supply F2546 Protection F2547 FM PS F2431
We started off with the regulated power supplies and protection networks. The main supply assembly F2546 also houses a insert card type connector for the driver assembly F2436.  All of the electrolytic includes the four 4.7/100 Bipolar capacitors were replaced with Nichicon UVP Bipolar and Nichicon low impedance PW and Panasonic FC high temp (105C) capacitors.  A common cathode blocking rectifier diode was replaced with a TO-220 type MUR1620 device with a common cathode configuration, along with the 2SD313 NPN transistor replaced with a 2073 type TO-220 and thermally coupled to the mounting plate. The FM Front End PS had the electrolytic replaced with the Panasonic FC type and remaining 2SD313 with a 2073 NPN BJT.  Along with the 6800MFD Filter capacitors updated.

The Protection assembly is located in the front end of the chassis under the FM PS assembly.  All of the electrolytics again were replaced with low impedance Nichicon PW’s and high temp (105C) Panasonic FC  and two Nichicon UVP Bipolar capacitors. The relay input mylar was replaced with a high quality Panasonic ECW polypropylene film along with the four remaining .1/50MFD mylar to ECW film capacitors.  The remaining 10D1 type diode were replaced with an Ultra-Fast UF4005 type diode and the MY4 Omron replaced.

Power Amplifier Assembly F2463
Like the 9090 versions the 8080 features a socketed single symmetric PCB design, fearing a differential front end and quasi complimentary output.  The electrolytics on this assembly were replaced with high temp (105C) Nichicon PW’s and Nichicon KL along with two UVP Nichicon Bipolar 100MFD capacitors.   The differential pair TR01-4 were replaced with 1% matched 1845 NPN transistors. remaining 2nd-3rd driver BJT’s were replaced with matched KSC2690/1220 compliments and 2073/940 BJT compliments with new thermal compound applied at the driver pairs TR11-14.  TR07/08 is thermally coupled to the collector of the driver pairs via a heatsink tab. The remaining2473 diodes were replaced with general 4148 type and the two VD1212 glass pack diodes to two 4148 in series. Going back and updated the 4.7K/1K to bourns potentiometers and thermal compound to the outputs once resistance points are obtained.  The bias breakdown is using an active mA measurement of 30mA or 15 (3mv<) at each .33 emitter resistor. (V=R(2)/I)

Tone Control & Assemblies F2544 F2543 & RIAA F2541
Mounted under the front end of the chassis next to the protection circuit the AF assemblies are fairly easy to get to after breaking the unit down.  As we typically, the AF electrolytic were replaced with a audio grade Nichicon KA and Nichicon fine gold (100MFD) capacitors.  Updating 1MFD> with high quality WIMA polypropylene film capacitors and Nichicon UPV Bipolar. 

Each PCB contain a low signal NPN BJT which is replaced with a quite, more reliable KSC1845 transistor, this consists the later network of the front end BA312 IC network, which is basically a
 NPN SET gain driver.

Similar to the above F2544, the RIAA F2541 uses a BA312 IC as a basic gain driver.  The electrolytic within this stage were replaced with audio grade Nichicon KA and low impedance Nichicon PW (470MFD) capacitors, two high grade WIMA polypropylene films were installed replacing an electrolytic (1MFD>).

New 8V SMD custom Fuse Lamps installed and function indicators and its ready for the verification tests...

Audio Notizen
Frequency Response
15hz-30Khz @ +/- .79dB

Continous Rated Output @ 8OHM
25.62Vrms  (82.04W/CH) @ .086% dB THD+N
@ 1.00W/CH @ 0.014%dB THD+N

Intermodulation Distortion
60Hz/7Khz 4:1 @ 0.031%
AV Gain @ 28.17dB

Zoomed in look at subsonic-reference-high frequency responses;

10Hz Sub-Sonic

1Khz Reference Mid Point

20Khz High Frequency Point