New project. Sansui 8080 recap. Advice appreciated.

Discussion in 'Exclusively Sansui' started by RR--, Apr 4, 2018.

  1. RR--

    RR-- Active Member

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    Update.
    I decided to recap the tuner as I had almost enough spare capacitors lying around and needed to buy more parts to qualify for free shipping from Mouser. All those new Wima caps look nice too!
    I also added an extra heat sink to the Tuner power supply transistor, even with the additional heat sink it gets very hot.

    [​IMG] [​IMG] [​IMG] [​IMG]

    I also decided to remove the Tape Rec/Play port and install a switch to change between stock and modded backlight states, I generally prefer to leave the tuner lights off but on occasion I like to show them off.
    The original port is taped up and tucked away inside in case the mod needs to be undone, I made it completely reverse able.


    [​IMG]

    Current pic of the bottom of the receiver showing all mods, I'm currently repainting the power transformer and will have a top pic when it's done.
    [​IMG]
     

     

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  2. RR--

    RR-- Active Member

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    So I think my next step is to replace some old noisy transistors, I have been using the receiver with the -20db mute enabled as it reduces the background hiss considerably but occasionally I like it unmuted and then the noise is annoyingly loud. After replacing a heap of transistors in my AU-719 the background hiss is almost nonexistent it's impressive.

    Looking at the schematics I noticed there's a few 2SC1313's on the Triple Control Tone board I can replace with some KSC1815's.
    I also noticed on F2436 that TR02, and TR04 don't match TR01 and TR03 so I think they should all be replaced, do you have any recommended transistors that should be replaced and some modern equivalents to purchase? [Edit, the schematics say they're 2SC1708(G)] remember you recommended replacing some transistors a while ago that I forgot about, any recommendations on what to replace those with too? http://audiokarma.org/forums/index.php?attachments/upload_2018-4-8_0-48-3-jpeg.1157685/some
    I don't mind replacing more than necessary, also I'll try and stick to RS Components this time as I won't be buying much. (I hope)

    Thanks again.

    [​IMG]
     
    Last edited: Jul 6, 2018
  3. petehall347

    petehall347 the brandy coffee man Subscriber

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    RS is free shipping here i feel bad when shipping costs more than my order
     
  4. RR--

    RR-- Active Member

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    Yeah that's why I do too, I prefer Mouser as they have more options but $25 shipping can hurt for individual components, unfortunately RS Components often only sell transistors in quantities of 200 so it's often a pain. At least I have plenty of spares.
     
  5. petehall347

    petehall347 the brandy coffee man Subscriber

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    tone boards should be fine for 1815 . i have more than a lifetimes supply of 2sc1815 here
     
  6. RR--

    RR-- Active Member

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    Thanks. I have three spare which should just cover it including the volume control board, they came out of another amp when troubleshooting the problem so I think they're still good.
     

     

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  7. Hipocrates

    Hipocrates Anti-Muppet Subscriber

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  8. RR--

    RR-- Active Member

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    Wow that post is a goldmine thanks! and thanks to Tnsilver.

    So it looks like I'll need to do the following:
    • Replace 2x 2SA818 at TR05 & TR 06 with KSA1381ES (in upper pin hole position)
    • Replace 2x 2SC1628 at TR09 & TR10 with Zetex ZTX694B (backwards orientation)
    • Replace 2x at TR11 & TR12 with On Semi NPN 863-MJE15030G (Same position)
    • Replace TR13 & TR14 with On Semi PNP 863-MJE15031G (Same position)
    TR01, TR02, TR03 & TR04 still puzzle me though, on my board TR01 and TR03 seem to be much older with the marking C639 while TR02 and TR04 say C1400. My thinking is that the C1400's have been replaced in the past although the soldering doesn't look like it has been altered.

    Any thoughts on what to do here? Searching through the forum KSC1845FTA seems to be the correct replacement for all four transistors.

    Also looks like I'll be paying extra for Mouser again, I'd buy more from RS if their minimum order quantities weren't ridiculous.
     
  9. Hipocrates

    Hipocrates Anti-Muppet Subscriber

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    That's why I end buying some dozens always, if all my projects are done, and have leftovers, I would just buy another unit to use them :rolleyes: (oops now I see why the hoarding).
    I think I used KSC1845FTA too, HFE matched If memory serves me right.
     
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  10. RR--

    RR-- Active Member

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    Thanks again Hipocrates, I'll go with the KSC1845's for all four although I wont be able to HFE match them, that shouldn't be a problem should it? Strange that the two transistors at TR02 and TR04 (right side) were replaced with C1400 transistors, but this driver board sure has been butchered a lot in the past so anything goes really.
     
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  11. Hipocrates

    Hipocrates Anti-Muppet Subscriber

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    I don't think it will be and you will be probably getting same batch. And yes I remember that board, some weird values. Anyway KSC1845 will do the job
     
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  12. RR--

    RR-- Active Member

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    Hey quick question, My parts have arrived and I'm currently installing them. When removing the transistors mounted to heat sinks no thermal compound seems to be present although some have been slightly oily.
    How should I go about mounting the new transistors to the heatsinks?

    Below is a picture for reference (TR02)

    Thanks
    [​IMG]
     
  13. RR--

    RR-- Active Member

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    Also I was planning of replacing the four BiPolar capacitors on F-2546 with regular Nichicon Gold electrolytics, however I just noticed they're rated at 85° where the BiPolars are at 105°, is this a bad idea?
    I got the idea from this post http://www.tapeheads.net/showthread.php?t=49795
     
  14. Hipocrates

    Hipocrates Anti-Muppet Subscriber

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    I cleaned them and put a tiny amount of thermal paste and spread it on the back of the transistor, that's just to help thermal conductivity.
    I don't think it will be a problem.
     
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  15. RR--

    RR-- Active Member

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    Update.
    All new transistors, capacitors and trimmer pots are in. I've also finished the very time consuming rust removal and painting work. I sanded back and repainted the top of the transformer, driver board cover, baseplate (bottom black and top with clear coat) and top metal case grill. I painted the case grill with the same satin black paint I used for everything else rather than the stock grey/olive because I already had it. It looks pretty sharp being black too. Bias and DC Offset adjusted as according to the schematics exactly.

    Sonically the distortion is noticeably lower similar to when the transistors were replaced on my AU-719. It's not night and day different but very well produced electronic music is very clean sounding.

    This is a very very nice sounding amplifier, it's very soft yet powerful sounding with the best separation and soundstage I have heard so far. With the increased capacitance in the bass potentiometer everything sound very flat with a deep powerful clean bass I didn't know my bookshelf speakers were capable of, far better than the stock midrange/bass boom.

    I'd still like to re-veneer the wooden case in a dark walnut but finding a supplier in quantities smaller than an entire kitchen is difficult, plus I don't know much about veneering so I think I'll leave that for the time being.

    Question: Unfortunately while the noise floor is dead silent while the -20db mute engaged and the volume past 12 o'clock without doing so it is still quite noisy even at a much lower volume at 0. Any ideas why this is the case? Maybe I'm just fussy but this isn't a thing on my AU-719.

    Another small thing that still needs addressing is the wood case itself tends to resonate when the amp is powered on, jamming some cardboard in the centre of the back seems to help but isn't perfect, anyone have any experience with this too?

    [​IMG] [​IMG] [​IMG]

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    Fun game: Try and spot what is stock on this board. I count 42 new components.
     
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  16. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    Nice.

    It looks like you have changed what needs to be changed, and not wasted your time and money on pointless component replacement, kudos to you. :thumbsup:

    (I would likely have changed the two trimmers in the 3rd pic down, but if they could be adjusted nicely - then perhaps not ;) )
     
    Last edited: Jul 18, 2018

     

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  17. RR--

    RR-- Active Member

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    Thanks, I couldn't have done it without all your invaluable advice, this amp was in pretty rough shape to start with too although through it all is still worked.
    I have to admit I hadn't even thought to adjust those two trimmer resistors yet. My record player has a phono pre-amp built in but 99% of my use is through AUX with external DAC to my computer.
    I have adjusted the two trimmer pots for the VU meters but one reads slightly differently even when in mono, not enough to worry a lot about though.
     
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  18. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    Well, I was actually zero help in this particular thread, so I hope 'your' refers to the excellent AK members that did help. ;)

    A special shout out to @Hipocrates who has been wonderfully helpful, here, and in many other threads.
     
    Last edited: Jul 18, 2018
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  19. Hipocrates

    Hipocrates Anti-Muppet Subscriber

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    Great work, I think this receivers are kind of noisy(a little bit of hiss the back ground) compared with the AU's o the G's, in my case just noticeable when I put my ear close on my speakers.

    What kind of noise are you having?
     
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  20. RR--

    RR-- Active Member

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    Haha yeah my bad Hipocrates is the real champ in this thread, The H's and different profile pictures is throwing me off. You were a lot of help for my AU-719 fix though, it had been having issues for years and a "professional" couldn't even find the problem.

    It's just a normal white noise hiss, the same as what you'd hear with no music playing but the volume at 100%, with the amp muted -20db the hiss level drops so I've just been using it muted all the time.
     

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