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Sansui AU-Alpha907Limited service manual

Discussion in 'Exclusively Sansui' started by smurfer77, Oct 4, 2018.

  1. smurfer77

    smurfer77 AK Subscriber Subscriber

    Messages:
    1,477
    Location:
    San Francisco
    I've been lucky enough to obtain a Sansui AU-Alpha-907limited. According to the audiodatabase this was limited to 2000 units only back in 1994 at 410,000 Yen. I do question a bit the production number as there are hardly hard to come by in Japan.

    We know from a previous thread that the 907limited and 907XR share service manual but to best of my knowledge the service manual is not publicly available, although we know it exists and snippets are available in various threads. A few years ago an former sansui engineer contacted me via LinkedIn and we have been penpals ever since. Let's call my penpal 'T'. A few weeks ago I told T that I've gotten interested in the alphas and explained that there are very few service manuals available. He asked "which model are you interested in?". Of course I was tempted to say all of them! But I thought that would be rude :). So I explained I already have 607/707/907/MR/MRX and 907KX..... but what I really need is the 907 Limited. T says he will ask around and get back in touch. Just over a week later, I get an email with an attachment!!! As far as I understand T has scanned this for us himself from a hardcopy!

    It's in Japanese but the schematic is legible (and the test points are labelled n English actually), and with the 907MR manual which has English, the 907Limited japanese adjustment procedures are clear.

    At the very begining before all of this I asked T if the service manauls are secret and received the response "There are no secret because the property holder does not exist". Now, I totally understand (1) personal promises and (2) pro-tech business protection are separate issues, but as far as Sansui itself is concerned there is likely no problem at all since Sansui is no longer an entity. I asked T if I can share the 907Limited manual with everywhere and received the response "of course no problem to share with anyone who is interested the documents online. We (I and the person who found the Service Manual), are rather happy as exSansui." I lightly edited the English (although T's English is very very good), but the meaning is unchanged. I think T is not working on amplifiers these days and gains nothing from this, except sharing the joy of Sansui history. I think this passion from an ex-employee is really exemplary and this is the passion that shows in the product Sansui made! T was already very interested in the mystery 907 Extra over on Stereonet forums...

    About the pdf, I've just uploaded on hifiengine; if it doesn't show in a few days give a shout and I will share via dropbox (I find the ak db doesn't let me upload for some reason so if someone could do that, please go ahead).

    A few other notes:
    - as noted by skippy, some panel screws are different length. Be sure to replace same length screw when you put it back together (there is a risk of shorting out the phono board on the right hand side).
    - the 907Limited poweramp section might have been recommended by Sansui as power amp for "best preamp of the time", C-2302 VINTAGE (1992, 1,280,000 Yen!). The original matching power amp B-2302 was dated to (1990). gathering this info from the audio database site.

    BIAS Voltage:
    - 28.6mV for Limited (8.8mV for 907XR). This gives about 130mA idle current.
    - Need top and bottom cover off. Left panel off also needed if doing premap DC. Probe from bottom, access VRs from top. Stand on right hand edge, so VRs for preamp near front left panel can be accessed.
    - the manual refers to TP on the amp board, but you will actually find two pins, not one. The two pins connect to either side of an emitter resistor. I used a 2.5mm female plug to make life easier and just probe across those two test pins (it just skips the output coil but that is only 0.01Ohm so it hardly matters), but you could also follow the manual, but you will need to know which test pin to grab hold of (which is easy to find with DVM (the test pin you want is the one that is 0.22 Ohms from the 'out', not the one that is shorted with 'out'). Other alphas, like 607NRAII pretty much require such a 2.5mm connector plug (5-pin in the 607NRAII, which I also used on the 2-pin 907LTD (whereas the 607MR has easy to access TPs and no need for a connector/extension)).


    Original bias on mine:
    - if you see about 38mV at cold start up dont touch VRs just yet, it really takes some warming up to get to steady-state. Read on:
    - cold start-up (Right (37.8mV, 37.8mV); Line pulling 1.49A
    - Warm up took well over 60 minutes and the above settled to:
    {Right (27.6 ('hot' (non-inverting), 28.6 ('cold' (inverting));
    {Left: 29 (non-inverting) and 28mV (inverting)}
    - at warmed up idle line pulling 1.25A

    TEMPERATURE:
    - On all 3 of my alphas the side with the phonoboard (right) runs 2 C hotter. The thermal situation is just non-symmetric with the left being coupled more directly to larger chunks of metal.
    - My 907Limited runs about 50C at the top of the heatsinks and 53C near the bottom where the transistors are situated. That is the right side. As mentioned Left side runs slightly cooler.

    OFFSET:
    - for 'hot-to-cold' probe between the two ‘out’ (one for hot (non-inverting) and one for cold (inverting), which go to positive and negative speaker terminals). Just take care you negative probe isn’t grounded by your measuring device as 'cold' does not mean grounded, but in fact refers to an active output designated 'cold' (is just what they called the inverted amp in a bridged setup). ''hot-to-ground' yoy can work out and must be set simultaneously with 'hot-to-cold' as they are interlinked (one setting balance between either side's DC and other setting magnitude of one).

    Power: I got 101W, both channels into 8Ohms before obvious clipping. Didn't go into detail with the distortion meters, but this thing is clearly making more than the prescribed 80W.

    Side Panels:
    The side panel pattern is Birds Eye Maple. I recovered mine with new vinyl as the original got dinged in shipping and it looks fantastic... I should probably post. Did think about solid wood but I thought it might look better, but less original.

    Further thoughts on listening:
    - I think very few people have compared the newer models with the older ones using an amp selector box and volumes set equal using SPL meter. When I did a quick comparison of the 907Limited and 607MR, without doing it properly (just changing the wires and doing volume by ear), I swore the 907Limited was bright and disappointing. I even mentioned that too a few people.
    - Then next weekend I setup properly and redid comparisons. It's amazing how much the mind plays tricks. The 907Limited is in fact very very smooth and a bit warm souding, similar in sound to the 607MR and 607NRAII, on my speakers at least and driven to moderate volumes (I rarely listen loud). The differences are extremely subtle, and in fact I'm the only person on my setup who can tell the difference in blindfolded tests. I am now comparing to older amps and will report elsewhere. But summary is it's pretty useless for me to trust my own ears/brain without proper comparison setup, let alone someone else's comments with unknown conditions.
    - One thing I will say now is these later Alphas all sound a lot like the AU-777A (to be fair, my AU-777A is not stock at all). Will compare some earlier alphas soon. And will compare to AU-111 (but I think for now they sound more like AU-777A/AU-70 as my memory of my AU-111 is slightly more clinical/accurate/damped).

    If you have a chance please give a thumbs up or comment to thank T, as I will share this with him later.
     
    Last edited: Oct 5, 2018
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  2. skippy124

    skippy124 Super Member

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    Location:
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    Hi David,

    That is fantastic, any many thanks to "T" for his generosity in sharing the 907 Limited service manual.

    And your write up re the adjustments, the temp difference etc is very well put together.

    Looking forward to hearing more about your listening comparisons.

    Cheers
    John
     
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  3. mjs1

    mjs1 AK Subscriber Subscriber

    Messages:
    382
    Location:
    Ithaca, NY
    Bravo smirfer77 (David?) with a heartfelt thank you to Mr. T. Not to press to hard, would you ask him what manual would be good for getting settings for an 07 Anniversary? If we can’t get schematics or manuals for these Japanese only Sansuis perhaps we can compile a list of settings? I do have an 07 that I obtained using Buyee. It was partly trashed in shipping ( they do a much better job of packaging now ) and is mostly functional. I got a full refund. Phono is out however. Thank you.

    Marc
     
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  4. smurfer77

    smurfer77 AK Subscriber Subscriber

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    Location:
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    John, those temp difference observations are based on just 3 units, so I could still be wrong, but that is my feeling for now. Luck has it that a couple more Alphas are headed my way so I can confirm. Listening comparisons aside, I can say that I have to admit the build quality on some of the later units is outstanding.

    There were some settings listed, I think over in skippys 907limited thread or another alpha thread here that had a few settings listed. Since I've only gotten into the Alphas a few weeks ago maybe I'm not the best person to head it up, but I may start a parallel thread on "Alpha Notes" in general, as I have already amassed quite a bit of info and data in the last few weeks. As for your specific question about the 07 Anniversary, I think the 907MR manual (which is available at hifiengine thanks to another AKer), would be a very good place to start. I've never seen many details about the Anniversary, so I wouldn't assume this is correct (and would do some checks of output transistors and PCB layout etc) but it might it's entirely possible that the 07 Anniversary is a kind of MR version of the 907Limited (the possibility was pointed out to me recently by Jeff/Cafad from Stereonet). Others may have better advice (I don't think T will have an immediate answer and I would like to pace my questions to him on a reasonable rate :)). However, something is definitely different between the 07 Anniversary and the 907MR; the power of 90W on the Anniversary versus 160W on the 907MR. So either there are some power supply or driver circuit changes, or the 07 Anniversary idled a lot hotter.... I guess we will have to wait for better advice, or I will see what I can find out from Japan.

    Cheers
    David
     
    Last edited: Oct 4, 2018
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  5. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    Really excellent write up David, thank you for taking this up with 'T'. As you know I have reason to be very grateful to both of you for getting this manual made available.

    As for the temperatures, in the fullness of time I'll do some temperature readings on the one I have for comparison with the 3 you have already done this to.

    In the meantime a special thank you to 'T' for his kindness and generosity regarding the manual. :thumbsup:
     
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  6. mjs1

    mjs1 AK Subscriber Subscriber

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    Location:
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    And thank you David for starting the Alpha thread. I may have some contributions to make over the weekend.

    Marc
     
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  7. craggd

    craggd AK Subscriber Subscriber

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    Location:
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    This is very cool and genrous of T and you to share. Many Thanks!

    It is a wonderful amp with incredible build quality, I enjoy mine very much. Look forward to downloading the service manual. I have previously posted the owners manual in the AK depository if anyone is interested (also in Japanese).
     
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  8. smurfer77

    smurfer77 AK Subscriber Subscriber

    Messages:
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    Location:
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    Thanks for that. I also have the owners manual but didn't upload it yet. Is the 907limited brochure available? I have it.

    Also I'm copy and pasting below some voltages from @mjs1 over in the general Sansui Alpha thread (originally provided by Czubsi and I have not confirmed them via schematic or my own measurements yet).

    -----------------
    between kR63-kC1 = 29,5 V

    between kR7-kR5 = 22,0 V

    between kR6-kC9 = 12,0 V

    between kR7-kR8 = 12,0 V

    between kR15-kQ2 = 28,0 V

    between kR16-kQ3 = 28,0 V

    between kR22-kQ4 = -28,0 V

    between kR23-kQ5 = -28,0 V

    between kR64-kC2 = -28,5 V

    between kR17-kQ2 = 13,0 V

    between kR18-kQ3 = 13,0 V

    between kR20-kQ4 = 11,0 V

    between kR21-kQ5 = 11,0 V

    between kR31-kQ9 = -28,5 V

    between kR30-kQ7 = 28,6 V

    between kR29-kQ8 = -28,5 V

    between kR28-kQ6 = 28,6 V

    between kR43-kQ12 = 2,6 V

    between kR43-kQ14 = -2,6 V

    between kR44-kQ13 = 2,6 V

    between kR44-kQ15 = -2,6 V

    between kR46-kQ19 = -2,0 V

    between kR46-kQ17 = 2,0 V

    between kR45-kQ18 = -2,0 V

    between kR45-kQ16 = 2,0 V

    between kFT23-kFT27 = -29,5 V

    between kFT22-kFT25 = -29,5 V

    between kFT20-kFT24 = 29,5 V

    between kFT21-kFT26 = 29,5 V
     
  9. smurfer77

    smurfer77 AK Subscriber Subscriber

    Messages:
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    Location:
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    Here is a pic of her. Can you believe she came to me with no headphone jack and every single knob shaft bent, and a busted wood veneer/vinyl on front-left? ... typical shipping.

    [​IMG]

    This shot gives a better view of my side panel recovering job. The colour is bit lighter than original but the pattern is perfect, it's durable and easily replaceable.
    [​IMG]
     
    Last edited: Oct 6, 2018
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  10. mjs1

    mjs1 AK Subscriber Subscriber

    Messages:
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    Location:
    Ithaca, NY
    Hi David,

    My AU-07 came to me in bad shape too with no functioning headphone socket and trashed side panels. Unfortunately the faceplate was scratched and the phono board was damaged (or is missing since I haven’t looked inside it). Buyee gave me a full refund and I can listen to it using the tuner input but I was too discouraged to go through the torture of taking this 34 kg/75lb amplifier up the flight of stairs to my second floor listening area (bad 70 year old knees).

    Any way, great job on the side panels. Where did you find the veneer and did you do it yourself?

    Marc
     
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  11. smurfer77

    smurfer77 AK Subscriber Subscriber

    Messages:
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    Location:
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    I actually found my headphone socket, smashed into two pieces, floating around inside of the amp. The rear panel took a hit and the speaker outlets are still out of shape. During this hit the chassis flexed enough to crack the headphone socket. I glued my socket back together and reinstalled it and so far it is holding nicely.

    The phono board will be located on the right hand side - just four screws to check. But yes I understand these amps are heavy to play around with.

    About the recovered side panels, I did it myself and believe it or not, the entire job only took a couple of hours. The pattern on the 907LTD is Birds Eye Maple which is a very common pattern. I thought about making solid blocks of wood but worried that this would actually look better but less original. So I used a vinyl, which can be bought in Birds Eye Maple just about anywhere, including amazon etc. I should post a couple more pics of the process i guess.... I'm surprised how well it turned out.
     
    Last edited: Oct 7, 2018
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  12. mjs1

    mjs1 AK Subscriber Subscriber

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    Location:
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    Hi David,

    Thanks for the reply. I planned on retiring at the age of seventy only to be called back into service but will retire again at the end of the week. I have family visiting as well, But, you’ve inspired me to have a go at the AU-07 in the near future. When a son visits I’ll get some help moving this thing. Best wishes.

    Marc
     
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  13. smurfer77

    smurfer77 AK Subscriber Subscriber

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    Location:
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  14. MP984

    MP984 AK Subscriber Subscriber

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    This is an absolute stroke of luck, and many thanks to smurfer77 and his good friend T. I'm the owner of the 907 Limited which Hyperion is currently looking at, so this is great news.

    It seems a couple of people here have bought these amps, and they've arrived in poor shape from lousy packing jobs. For the record the one I bought is a result of stalking 907 Limiteds and various other late era Sansuis on Rinkya for several months. The one I bought was advertised at a buy it now price considerably lower than the ones I'd seen previously, so I jumped on it.

    I've bought on Rinkya before, and I have to say that the packing job they do is excellent. The 907 arrived in very good shape, and is pretty close to mint condition.

    Anyway, I'll watch this thread with interest. Because obviously if I have a 907 Limited it would also be good to find an 07 Anniversary..................... just for comparison ...................
     
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  15. pete_mac

    pete_mac Super Member

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    Please pass on an enormous virtual man-hug to T on my behalf!
     
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  16. stereofun

    stereofun Super Member

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    "T" for prez ! - please tell him he would be very welcome if he wanted to hang out with us here. Thanks for generously sharing and advocating on behalf of the community :thumbsup:
     
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