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Revisiting the Sansui AU-999 - repair, rebuild and mods

bolero said:
It still didn't sound that great IMO,
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Sometimes one have to accept the equipment for what they are, hardly installing a CCS will change much. IME with this amp the main limitation is on the power amp section and power supply, so I very easy speakers to drive was what worked the best, after all the mods.

Off course one comes here, read all the hype about it and expect a lot (that's ok since is a fan club), but as one get more experience realize that is just, It is a very cool piece of history with a weak power supply using capacitance multipliers. an a unsophisticated amp section with low PSRR, certainly gorgeous. But sound wise IMO is lean with no headroom at all and extremely load dependent.

That doesn't mean that one can't enjoy it, but to be honest I have piles of gear that sound way better... None of the are that good looking to me :P
 
Oh don't get me wrong: it sounds excellent after doing the mods & rebuild!!

I was just saying that stock, without the subsonic filter, it wasn't particularly great. Original (old) parts too.
 
bolero said:
Oh don't get me wrong: it sounds excellent after doing the mods & rebuild!!

I was just saying that stock, without the subsonic filter, it wasn't particularly great. Original (old) parts too.
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Cool, is fun how different people have different perspectives... IMO, without mods and with filters is bad, without filter is kind of blah, with mods is average/good, paired with I consider good quality efficient speakers.
Did I mention how good looking is that amp?:p
Cheers
 
This remains me that I have to order some parts and start to invest time to test the boards for the AU-999, but this year have been challenging health wise, with a ton others projects on hand so I is kind of a slow process for me, but I hope by February I'll have everything on place to write about for all of you modders and part swappers :p .
Simulations are promising tho, with a constant current source, current mirror and NFB changes.

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Question: shouldn't a constant current source mod improve the power supply rejection ratio? Isn't that the whole point?
 
bolero said:
Isn't that the whole point?
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Basically improves the linearity of the amp section, yes it improve PSRR, to what degree? I don't know,
There's very knowledgeable people that likes a tail resistor.
Xraytony have a video on a CCS mod on a 2240 that explains it very well, and Johnaudiotech, have a very good couple videos about it, if you want to look into it.
 
Hipocrates said:
This remains me that I have to order some parts and start to invest time to test the boards for the AU-999, but this year have been challenging health wise, with a ton others projects on hand so I is kind of a slow process for me, but I hope by February I'll have everything on place to write about for all of you modders and part swappers :p .
Simulations are promising tho, with a constant current source, current mirror and NFB changes.

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Hi Hipocrates

I'm modifying and improving my AU 999, I actually have 2.
A few days ago I bought a board on eBay very similar to the one in the photo, maybe it's the same one and now reviewing AK's posts on the subject I see your post.
I'm very interested in the constant current source, as well as the current mirror and NFB changes.

Do you have something to show?
Thanks
 
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