Sansui AU-7700
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Choosing a vintage amplifier that "sounds good" based on subjective opinions...is not easy..
There is no shortage of amplifiers in this house, but a few months ago a Sansui AU-7700 came up for sale on the local Ebay. I had been reading for a long time about Sansui and the start-up in Tokyo in 1947 by the company's founder Kosaku Kikuchi, and how people listened to the "right" sound back then. In addition to the many measurement data, each amplifier had to go through several listening tests before actual production could begin. A typical Japanese attitude that reflects how a Japanese person approaches life by making things just a little better every day! It was one of the reasons for Japan's success in the electronics industry in the seventies and eighties.
So a choice had to be made and it was a Sansui AU-7700 : Power: 54 watts per channel into 8Ω (stereo), Frequency range: 10Hz to 50kHz, Distortion: 0.1%, Size: 434 x 130 x 315mm, weight: 12.3kg
Reason for purchase:
1st the Sansui AU-7700 appears in good condition.
2nd reason for purchasing the AU-7700: that I could carry it home in a "blue Swedish suitcase" from Ikea!
3rd reason: that I heard the Sansui pull a pair of JBL Lancer 101. The Lancer 101 contains a driver.. LE175DLH that covers the range from 1500Hz and up. The AU-7700 made the slightly active driver sound "completely civilized"?...
The AU-7700 feels right when you turn the knobs... The AU-7700 is mechanically well made..
about 54 Watts is plenty for a pair of speakers with a sensitivity of 2.5Watt/96dB ..... plenty for my speakers... The net: there are countless opinions about the sound from Sansui's various amplifiers... the "warm" sound that the AU-7700 apparently delivers together with a good sense of space and fine resolution meant a lot....... ...when purchased, the AU-7700 turned on the relay when we pressed "power on" and played stereo ....looking forward to fixing switches and contacts etc...
The AU-7700 gives off a strange feeling of something historical after 51 years of use!
The Sansui AU 7700 is without exception the most dust-free old amplifier I have seen...and there have been many on the repair table......
The AU-7700 doesn't look like it has been opened and repaired? ...after 51 years?
Apart from a little dust by the open switch for AUX, Phono and tuner....the AU-7700 is very service minded, and by looking at the output transistors at an angle you can find a little dust, but that part is also "outside" the box itself....
...the components look as if they were mounted with your fingers...by bending the transistors over resistors?? ...you might be a little "stunned" to see it !
Cleaning Silver
Oxygen and "raw" pure silver = oxidation... a method that cleans and removes the black tarnish without damaging the silver coating. An old lady gave me a recipe that can clean silver and brass without scratching. She used: flour, a little water and vinegar, a teaspoon of salt, a teaspoon of citric acid powder, which she stirred into a "paste". The paste was spread over the silver item for a few minutes, then rinsed and dried...the silverware was shiny again. I have successfully used the same treatment for open switches with silver contacts.....
Ford contact grease then manages to maintain the electrical connection..
The switch silver contacts has black oxydation surface and needs cleaning
The silver contacts after cleaning and Ford's contact grease
All signal serial capacitors changed from electrolytic type to film capacitors
Many repairs of erlier Luxman amplifiers such as the L100, L11, L58a and M12 have shown, that changing the signal transfer electrolytic caps to long-term stable film capacitors does not destroy the amplifier's sound signature.
All replacement capacitors bought from Nichicon , Nippon Chemicon and Wima film caps...
As replacement used the Erni 24VDC relay
As can be seen from the photo, the Sansui AU-7700 is incredibly easy to access when it comes to RCA sockets, but the easy access is also a small mechanical weakness, as the RCA sockets are soldered directly to the PCB. Although the solder pads and PCB tracks are strong, small cracks can occur in the solder joints after long-term use. Therefore, all solder pads were cleaned and re-soldered....there are many hundreds of solder pads so it takes time to do it!
Warm-up started and after one hour bias adjustment can be made....
The Sansui AU-7700 is one of my absolute musical favorites
and I can only recommend buying it.
The Sansui AU-7700 has made me buy a smaller integrated amplifier called the Sansui AU-505. It will be exciting to hear the sound from the AU-505?
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