Sansui AU-111 rebuild

Discussion in 'Exclusively Sansui' started by smurfer77, Jan 24, 2018.

  1. smurfer77

    smurfer77 Super Member

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    I got busy with amps over xmas and managed to do an AU-999, and a pair of HF-V60 & PR330. Well, I also managed to do an AU-111. I haven't officially signed off on it as I'm now trying to put together some kind of cover (mine didn't come with sides, or a cover) as well as fix up some blemishes on the front panel edging (the front panel and knows are in nice conditions, and the amp has no rust.

    The bias setup was 2-pot, but I changed it to 4-pot. Interestingly, where there are other differences between 2-pot and 4-pot schematic my amp usually follows the 4-pot version so I guess it was built right in between the 2 and 4 pot versions. I will have to add this one to the serial number database....

    I found at least 2 schematic errors. I'm not talking about small value changes or the like... have a look the phono section (btw, a very early demonstration of 'hybrid' semiconductor/tube, no?) Notice that B5 is positive supply (B6 is just a connection to share positive supply to the other channel of the phono section). Then notice that the first transistor is drawn as an PNP which should have higher voltage at the emitter than collector. In fact the 2SC-402 is an NPN, and my unit has Hitachi 2SC650 installed (also NPN). So yes, the diagram should have been an NPN, not PNP. I also confirmed that the supply to the collector is indeed positive (why? read on).
    [​IMG]

    How could this have happened? I have an wild suggestion. Someone started on the AU-111 schematic by a 'copy & paste' from the AU-70 which came just before the AU-111 and also used a similar hybrid phono section. However, the AU-70 does use Germanium PNP transistors used and the collector has negative supply; this negative supply comes from the power supply section feeding the negative output tube grids (the AU-111 also uses negative output tube grid supply). However, for the AU-111, the time was right to move from Ge to Si and an NPN was used (I don't think there were many PNP Si transistors at the beginning... correct me if I'm wrong, but I believe that is why the AU-777 and similar amps were all NPN rather than complementary).

    The other error which actually clouded some trouble shooting I had to do in the project, is related to a tone frequency adjustment and feedback loop on a later preamp stage. I will get to that later. This thread may move slowly... but it will happen. And then there will be a real sansui amp shoot-out! The amp is basically done, getting burned in with new output tubes but I will wait until I have finished the cosmetic side before putting it into full service. This will give a chance to observe it on the bench for extended periods and make sure all is well (as usual, things look good, but I always manage to find something fiddly to fix... and it's quite interesting and probably a problem on most AU-111 so I will share details as it can lead to significant channel imbalance if unattended).
     
    Last edited: Jan 25, 2018
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  2. _mano

    _mano Active Member

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    I have also worked on couple of AU-111's, never looked into the phono section in detail as it just worked. And you are correct, it should be a NPN. Always did wonder, if it could have been improved with newer phono section etc... and never carried it through.
    "related to a tone frequency adjustment and feedback loop on a later preamp stage" --- more thrills and spills, cant wait..
     
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  3. BLAH BLAH

    BLAH BLAH AK Subscriber Subscriber

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  4. stereofun

    stereofun Super Member

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    Can't wait to hear your impressions of this holy Grail piece, and what was given up and what gained as we moved into the transistor age.
     
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  5. craggd

    craggd AK Subscriber Subscriber

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    Great post and info, thanks! How are you thinking of fabricating the cover? I also have a AU-111 (with its cover) and live in the Bay Area if you need measurements or a template we could probablly work something out. PM me if interested.

    I have to believe you are going to love the AU-111, it is a wonderful amp.
     
    Last edited: Jan 29, 2018
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  6. smurfer77

    smurfer77 Super Member

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    Thanks for the kind offer! I think i am set with measurements for now but i may get back in touch if it doesn't work out. I originally drew the design in CAD with the view of having a shop CNC for me; I used simplified side panels with less folds and instead of side handle holds i drew up the sansui logo to form air holes. However the price of 3 panel cnc plus 2 folds seems to be the same price as buying a CNC machine for home (no joke!).

    So now i have taken an alternative route and had the 3 panels cut to size and i will do 2 folds myself, drill side holes (top panel i use a metal sheet with hole array from stock) and some extra bars to make the side and top panels mate flush.... Will explain with pics later when i get to it.

    If it isnt good enough i will buy a CNC machine as i really want one for making reproduction faceplates.

    Now i am repainting the faceplate trim which had some dings.... Going slowly doing one coat a day and 1000 grit sanding in between...
     
    Last edited: Jan 29, 2018
  7. craggd

    craggd AK Subscriber Subscriber

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    Sounds like you have a great plan, I like the Sansui Logo for air holes. CAD/CNC work is rediculously expensive, particularly for one off stuff. I wanted one knob fabricated and it was going to be ~$150. Was patient and found an origianl for much less. Do keep up the positngs I am enjoying them.
     
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  8. The Fuxtor

    The Fuxtor AK Subscriber Subscriber

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  9. slimecity

    slimecity Super Member

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    Nice - good luck!
     

     

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  10. smurfer77

    smurfer77 Super Member

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    I'm in the process of making an amp cover and side panels for my AU-111 and want to get the colours as close to original as possible. Can anyone out there confirm the colour of the side panels on the original Sansui AU-111? While the top perforated panel is always black, the side panels seem to have some variation, even within the original 1960s model. I see the side panels with anything from an off white (like the AU-777), to a light non-metallic grey, to a darker metallic grey/silver like the AU-999 or even a bit bronze-grey like the AU-9900.

    I think the most common is the light non-metallic grey, and the off-white pics might just be this colour with funny lighting or image processing.
     
  11. _mano

    _mano Active Member

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    Mine is Light Grey/Silversih, almost aluminium grey I would say.
     
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  12. smurfer77

    smurfer77 Super Member

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    Some of the pics look almost silver in the right light. Is the light grey/silverish metallic at all?
     
  13. _mano

    _mano Active Member

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    not perfect lighting, with a closer look, I would describe it as a pearlescent, speckled effect grey, giving it a shiny look to the grey
    [​IMG]
     
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  14. smurfer77

    smurfer77 Super Member

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    Thanks mate. Now I understand why some of the pics out there look grey, others silver, and some white-ish. Alright, this gives me a good starting point for a match. thanks a lot
     
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  15. Sebastien

    Sebastien AK Subscriber Subscriber

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    Subscribed, your posts on Instagram surrounding this are mouth watering.
     
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  16. smurfer77

    smurfer77 Super Member

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    oh you are following me on there?
    Cheers. I actually have scrapped that cover I was showing on IG so far... the measuring device I used was off and I have to start over. Sigh. But I am also learning how to make bends better and the final product is going to benefit! New sheet metal is in the post and thanks to @Mano I've now decided on a paint that is much closer than what I used previously.

    BTW, for those who don't know, I am on instagram as California_Audiophool and @Sebastien has a killed feed under the handle vintagehifistereo . I'm actually much more real-time on there, than on AK
     
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  17. Sebastien

    Sebastien AK Subscriber Subscriber

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    What do you mean am i following you on there, of course i am!

    Well tha's right the experience points always count, the final product should be great - and a worthy amp for all the effort too.

     

     

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  18. smurfer77

    smurfer77 Super Member

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    Ha. I know you are following me on IG! :)

    I learned a few things in the first attempt. (a) 2 of my tape measures, which I checked against each other, are both inaccurate; (b) I need softer/thinner metal to fold my sheet metal (neatly) with my hand tool; (c) if possible, drill/pattern after folding as the hole array near the fold was actually weak and the fold was kind of uneven near the hole array as it tried to fold in the hole array.
     
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  19. timmatt

    timmatt New Member

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    Heavy metal - I calipered it at approx. .065 inch -- needs to be strong, the weight of the transformers puts a lot of flex on the chassis -- needs stiffness the sides provide. (also, a faraday cage?) How about making four sides from thinner metal -- 2 smaller ones to nest inside outer ones - just a thought - not my area of expertise.
    Color?
    As I read your post, without looking -- mine are what they called 'grey hammertone'. Checking my cover pile (under the Akai M7 & Citation V covers - FIFO), yup, grey hammertone. Lots of stuff in offices, businesses and industry had iterations of that color in the 50's and 60's. Nice texture, think very shiny orange peel.
    Took the covers outside under cloudy but bright conditions for some pictures and blew one up --- wow, my covers are purple, green and grey. Pearlescent? I suspect additives in the paint plus application expertise causes various components of the paint to separate as it is applied and begins to cure, creating the grey color and hammertone texture. (Purple+Green=Grey, add White to lighten). The insides of the covers are a grey satin/flat texture. Photos of the inside covers show a definite greenish cast in one area, purple in another. The greenish/purplish cast is only visible in the photos - to my eyes and brain it actually looks uniformly light grey. --- it's how the camera sees reflected light -- sees things the eyes cannot.
    My AU-111 was a curb find in the early eighties. One of the caps has December 1966 on it, so I'd assume my amp was made mid-1967, four bias pots, all aluminum knobs.
    OK, your post has re-inspired me, my covers have been off for over a year, soon I'll know what I've been missing...
    I love soldering, I hate desoldering.
    regards

    .. DSC01869.JPG DSC01868.JPG DSC01872.JPG
     
  20. smurfer77

    smurfer77 Super Member

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    Thanks for the info. curb side AU-111 find?!!!! you are one lucky SOB.

    I should probably update this thread... my cover has long been fabricated and painted and it looks the part (although there are some weaknesses). Will share some pics and details soon. I've been enjoying my AU-111 as my daily driver now for some time..... love it. Glad you find the finish to be 'hammer' as that is what I did in the end.

    Also thanks for the detailed pics; this is pretty useful because good pics of construction (especially the air hole hand-hold) of those panels are not readily available on the web.
     
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