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My First Sansui (AU-101)

While I don’t like to crap on the OP’s thread/topic, I will try to be brief.

The AU-505 exhibits a more warmer tone with an excellent mid-range and nice deep bottom-end, the highs are a bit rolled off, not much, compared to my AU-999. Beautiful wide soundstage and depth. Overall the sound reminds me a lot of my Scott 222-b tube amp. Very easy to listen to, with zero listening fatigue, typical of cap-coupled amps. Very smooth. It sounds oh so good even at low volume, which is where I listen to most often. The mid-range this amp has is the best I’ve heard from a SS amp, at least of the ones I’ve listened to.

The 999 on the other hand, is more revealing, also presents a beautiful, wide soundstage, all across the spectrum. Bass is tighter and the highs are more airy and extended with all the detail present. Midrange is also glorious. More of an “audiophile amp” I would say.
To me it’s a well-rounded amp. It still has the warmth my old ears have to have to enjoy music these days.

Each one has their merits, that’s why I kept both. The Seven is a nice mix of the 505 and 999 all in one.

I honestly don’t think I will ever part with any of those three. I had a 9090 and a AU-9500 and they are both gone. Really a bummer as I really liked the looks of both of these early Sansui’s.

**Just to add, all of these comparisons were done with completely restored examples of each, using K-horn speakers.
 
No worries, it's no thread crap and at least the all the early cap coupled amps are closely related.

I think I need to look at transistor replacement on the 101 preamp, there's a constant crackle that comes and goes on the left channel, which originates somewhere in the preamp and I've cleaned and cleaned the volume pot to the point knob feel is getting bad. I had some lubricating cleaner I used after everything else, so at least it still feels smooth, but there's a lot less resistance to the knob now than there used to be. Oh well. The crackle is low enough to be completely inaudible during listening, even at very low volumes, but I can just about hear it when there's nothing playing and it's a bit annoying. Oddly enough it seems to disappear with the volume turned past 7, but even then I find it hard to believe it's the volume pot itself, because when the crackle happens to appear, moving volume between 0-7 seems to do just about nothing for it. I resoldered grounds on the preamp board + the transistors and anything immediately around them, but that did nothing. Might be my imagination but I think otherwise it did some good, reducing overall noise level.

I think I'll get me some KSC1845 or 2SC1815 and replace the old Mitsubishis, if I recall correctly there's only 1 per channel if you don't count the ones on phono end of the board. Or maybe there was 2. In any case, not a big job.
 
I think that will resolve your issue. All the small signal trannies were replaced in my 505. Cleaned up the sound a lot. Didn’t notice any noise before changing them, but new ones are better than 50 y/o ones for sure.
 
I got some parts today so I finally started giving the AU-101 some well deserved attention. First to go were the c871 transistors (TR701 & TR702) and that seemed to fix the crackle I had on the left channel, replaced them with C1845 by unknown manufacture, they are marked C1845 FCK44 and G-rated, Hfe was about 400. Balance was still leaning a bit to the left and the right channel was a bit hissy, looking at the schematic those 6.3V rated caps always get me suspicious, so next up I replaced the 47u/6.3 caps with 50V rated Panasonic FR. What do you know, hiss is gone and channels are now balanced.

I never worked like this part by part, I gotta say it's a really satisfying way to do this stuff, immediate feedback, hearing the part you just replaced make a change. The 47uF/6.3V caps both read well over 60uF and had around 5 percent Vloss, so while not completely toast they had definitely drifted out of spec.

Apart from better noise floor, sound also changed other ways, I'm inclined to keep this stock as much as possible. Might have to do something about those flying saucers on the power amp board, I have suitable replacements on hand. I also have new, slightly oversized (2200u) coupling caps on hand, together with a new PSU cap, again 2200u instead of the original 1000u. Figured bumping them up a notch would do no harm. But I'm not sure if I'm gonna change those. Might try and measure the originals and see what happens with the sound.

I also see some 1u electrolytic caps used for coupling on the preamp board, I will check if I have suitable PP caps lying about, I never replaced an electrolytic coupling cap with PP and went "oops, it was better before" :)
 
I replaced the coupling caps before the first transistor in preamp for both channels, I used a Russian 73-11 PETP cap, which I think is some kind of polyester film cap. I haven't used these anywhere before, got some a couple years ago when I was shopping for some Russian teflons. I noticed a change in sound, but it was not all for the better, so I didn't dare to touch the other ones yet. Overall better clarity, but bass lost something, some kind of distortion I hope :)

I noticed the power amp had a couple of those 47u/6.3V caps so I replaced those as well since the once in the preamp were a bit out of spec and seemed to be acting up. Can't say I noticed anything, but the ones that came out didn't measure well so let's just chalk that one up to preemptive maintenance. I also replaced the 1000uF PSU cap with a 3300uF Panasonic NHG. The original was still fine. Can't say I notice any change with the new cap, but maybe it would pay off driving a more difficult load.

There's still some hiss on the preamp, which seems to be worse at 2-4 and 6-8 or so on the volume dial. It's now pretty even between both channels and not at all intrusive but it's there. Not sure where that's coming from, but I'm not going to start hunting it down, it's only ever noticeable with nothing playing and it could be just everything adding up, old carbon film resistors etc.

How unreliable are those flying saucers and do they have the habit of failing with a bang taking other stuff with them? Everything on the power amp board seems to be fine, no extra noise or anything, so for now I'd be inclined to let them be but if it's an accident waiting to happen, I will change them.
 
I had symptoms similar to what you describe with my 101,with it being such a simple amp i de fluxed the boards and reflowed all of the solder joints and it all went away.

Coincidently i get the same volume related hiss on my 505 when i get time i'll try the same thing.

I'm just enjoying it too much at the minute.
 
Trw said:
I had symptoms similar to what you describe with my 101,with it being such a simple amp i de fluxed the boards and reflowed all of the solder joints and it all went away.

Coincidently i get the same volume related hiss on my 505 when i get time i'll try the same thing.

I'm just enjoying it too much at the minute.
Click to expand...

I reflowed a lot of the solder joints when I was trying to fix the crackle, not all of them but everything around the transistors and pretty much all grounds if I recall correctly and it helped some for the overall noise floor, but didn't really fix anything. It seems the crackle was the left channel C817 transistor, since changing that fixed it. Most of the hiss was the caps in the RC circuit between emitter and ground.

To be honest I'm not sure how much of a 'problem' the remaining hiss is, since I can just about pick it up with the amp idling, and I'm sitting nearfield. But since it seems slightly more on the right channel, maybe "something" would make it better still, but I'm inclined to let things be for now. It was really the slight crackle that started to drive me a bit nuts, because it was a constant, barely audible (on idle) reminder that the poor thing needs some loving care :)

It's still sounding fabulous, even more so now, so I think I'll let it be for now and take a look at the AU-317 next, it developed an issue with constant, pretty loud noise on the left channel that comes from the preamp, I'm guessing either a transistor got really mad or some of my resoldering of grounds didn't stand the test of time.
 
muovimies said:
I reflowed a lot of the solder joints when I was trying to fix the crackle, not all of them but everything around the transistors and pretty much all grounds if I recall correctly and it helped some for the overall noise floor, but didn't really fix anything. It seems the crackle was the left channel C817 transistor, since changing that fixed it. Most of the hiss was the caps in the RC circuit between emitter and ground.

To be honest I'm not sure how much of a 'problem' the remaining hiss is, since I can just about pick it up with the amp idling, and I'm sitting nearfield. But since it seems slightly more on the right channel, maybe "something" would make it better still, but I'm inclined to let things be for now. It was really the slight crackle that started to drive me a bit nuts, because it was a constant, barely audible (on idle) reminder that the poor thing needs some loving care :)

It's still sounding fabulous, even more so now, so I think I'll let it be for now and take a look at the AU-317 next, it developed an issue with constant, pretty loud noise on the left channel that comes from the preamp, I'm guessing either a transistor got really mad or some of my resoldering of grounds didn't stand the test of time.
Click to expand...

I would be tempted to swap out all of the transistors in the pre/phono pre amp i've had good success with bc550c which should be cheap and readily available in your part of the world
 
The AU-101 has been sitting in the same spot for these past years, other than the indicator light giving up the ghost it's been trouble free and a really good fit in my desktop setup. But yesterday I noticed the transformer started buzzing. It's physical buzz from the transformer and doesn't come through the speakers. I'm sitting right next to the amp so it's a bit annoying to be honest. It's not super loud or anything, but it used to be completely silent. It's never done this before but as I recall I think it started after a short power out. The electrical company is doing some repairs in my area so it might be the AC is dirtier than usual because of it. There's also plenty of switching PSUs in the same outlet, but they've always been there, but it could be one of those has started to act up.

I suppose I should try to unplug everything else and see if it still buzzes and if it does, try it in a different room and check the transformer to see if a screw came loose or something. Just feeling too lazy for any of that and the way things are set up it's a bit of a hassle to move the amp.

Just wanted to sort of whine a bit in the meantime before I get to troubleshooting this :)
 
muovimies said:
The AU-101 has been sitting in the same spot for these past years, other than the indicator light giving up the ghost it's been trouble free and a really good fit in my desktop setup. But yesterday I noticed the transformer started buzzing. It's physical buzz from the transformer and doesn't come through the speakers. I'm sitting right next to the amp so it's a bit annoying to be honest. It's not super loud or anything, but it used to be completely silent. It's never done this before but as I recall I think it started after a short power out. The electrical company is doing some repairs in my area so it might be the AC is dirtier than usual because of it. There's also plenty of switching PSUs in the same outlet, but they've always been there, but it could be one of those has started to act up.

I suppose I should try to unplug everything else and see if it still buzzes and if it does, try it in a different room and check the transformer to see if a screw came loose or something. Just feeling too lazy for any of that and the way things are set up it's a bit of a hassle to move the amp.

Just wanted to sort of whine a bit in the meantime before I get to troubleshooting this :)
Click to expand...

Those power outages, depending on the cause, can deliver voltage surges into the home. Surge protectors at the panel and at the point of use are good precautions. Could have also been an under voltage which can't really be protected against without a battery backup. Hope your AU-101 hasn't been damaged!
 
bolero said:
Could be a failing power switch or cap, buzzing power transformer was the symptom for me.
Click to expand...

And the buzz is gone... might have been a dirty power issue like I suspected. Caps shouldn't be failing, they are only few years old - I did a full recap. Didn't think about power switch, thanks for bringing that up. I'll be sure to check that out if it becomes necessary. Both this one and my AU-317 had some switch issues from another dimension - they've both been fine since cleaning but before that the symptoms were unlike anything I've experienced before.

Fingers crossed the buzz stays gone now.
 
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