Hej - blev netop faerdig med denne restaurering for et par uger siden. Jeg er Sansui fan og havde altid haft et godt oeje til topmodellen Au-999 fra foerste generation af deres solidstates. Den er utrolig velbygget og meget let at arbejde paa da alle prints er plug-in style. Saadan lydmaessigt synes jeg ikke den er exceptionel som f.eks dens lillebror Au-777a. Den er lidt "flad" MEN via nogle modificationer der aabner forforstaerkeren op, samt en mod. der aendrer bassen EQ slope bliver det en ganske habil amp. Faktisk ret god!
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Her billeder af restaurering - text kopieret fra AudioKarma: http://www.audiokarma.org/forums/showthread.php?t=646156
Picked this 1972 AU-999 up a few month ago. Had some issues - popping in the left channel and very hot outputs on the left as well - The minute I touched the bias for a left turn, I got magic smoke. Outputs had already been changed in the left side, and the work done looked suspicious at best.
First, I strip down the chassis for a good clean.
...Then time to build her back up nice and clean. The less than humble filter caps are some brawny 12k/100v. Only option for a 40 mm fit to bracket in CDE 38x series.
First up for redo is the bottom - I remove the subsonics, crowbar and install a new 400v/25A rectifier - all else down here is recapped with Nichicon PW series. New transistors on the minus and plus ripple filter blocks and some 2.2 / 250 Polyprop bypass for good measure.
I pay extra attention to matching transistors on this one. The two differential pairs are matched within 1 % and set aside.
Then new outputs, mica and grease. Only two original transistors were left, so I replace the entire set with some rugged onsemi's MJ21194's
Next up are the driver boards. All new trimmers, diodes, caps, transistors and a Mundorf Polyprop for the input coupling. The bipolar feedback cap gets extra attention with a nice Nichicon Muse at highest voltage possible in order to lower distortion. Pre-drivers are robust 1220's/2690's.
Finally done - but not without a battle. One driver board keeps on blowing fuses. After having checked transistor pin-outs, measured all resistors, I turn to the traces where I continuity test and find two separate culprits. Both hidden from view under a seemingly sound looking blob of solder. In both cases the foil base have ripped from the copper trace right before the blob, like a hairline crack.
The remaining boards are recapped with Silmic II's and repopulated with ztx795a signal trannies, except for the head amp where two 458's are swapped with ksc1845's. In the end, Dc and bias smoothly locks in. I got 1-turn trimmers, thinking the problem with old trimmers weren't the one turn, but rather the 40 year old pots acting up from age. I was wrong. Next time I'll go for 5 turns.
Close to 90 parts swapped.....
Cosmetically she is a real beauty. Not much to do here really.
LISTENING:
I first give it a run without the pre-amp / bass EQ mod. I am a tad disappointed. It is a good sounding amp, no doubt, just not quite what I thought. On a positive note, the amp is very quiet.
But the battle is not yet over. We still have the mods, so off to the bench.
The Pre-amp mod was rather straight forward. Here is the EQ bass mod...Oh boy oh boy - this is not hangover day work. Steady now...steady.
A good hour later and WOW - a completely different animal - Kevin - Kudos to you. That pre amp and bass eq mods are brilliant little engineering hacks that makes her sing to the high standard she was build.
This is a truly great sounding amp. No lack of bass output to my ears, super sweet mid and a great separation well into the higher notes.
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P.s efter lidt break-in lyder den endnu bedre. Har besluttet at skifte pre-drivers til nye onsemi mje15032/33 samt re-bias, dertil skifte alle koblings polyester caps til dobbelt value polypropulene samt give feedback resistor et bump til .5 watt for bedre temperatur coefficient.
Hilsener fra Tucson, Arizona
