First Sansui! Au 555A ...and underwhelmed.

Discussion in 'Exclusively Sansui' started by toneriderMUC, Mar 18, 2017.

  1. stereofun

    stereofun AK Subscriber Subscriber

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    This may be a bit far out, but we've seen it happen before. Did you hook up the speakers correctly. The 555a and it's older colleagues hooks up with left/right on top of one another, not side by side.

    Adjusting is certainly something you can do - much easier than the recap. Bias is measured across fuse holder with fuse out - measure in mA !! I think it's 20mA, but verify.

    As smurfer77 mentioned, this is not a DC amp, but capacitively coupled. For that reason you don't adjust DC offset as usual. Now, you can still measure the off-set by probing the speaker terminals, but only with speakers ora load resistor connected. This exercise will give you some idea of the health of the amp as well as the coupling caps. Look for 5-10mV .

    As for adjusting DC-offset, or " centre voltage" as the manual calls it. You need a scope, but can still get a useable setting by measuring DC voltage at the supply cap, then divide by 2 and then probe the coupling caps plus side to chassis ground and use trimpots to set to the 1/2 value.
     
  2. The Fuxtor

    The Fuxtor AK Subscriber Subscriber

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    I've actually done the wrong speaker hookup....Very easy to do as the hookups are a bit different then what you logically think they should be.... I had one speaker on the top left, and then the other on top right.... That will mix up a+b channels together for just the left channel.... Screenshot_20170320-203201.jpg
     
  3. stereofun

    stereofun AK Subscriber Subscriber

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    Ok.....Just wanted to make sure. Then if you engaged both speaker selectors it plays, but sounds funny. Well, get the adjustments set. I'd be curious to have you probe the speaker terminals with speakers connected, amp turned on, speaker selected, but no signal. What mV are you reading for each side ?
     
  4. toneriderMUC

    toneriderMUC New Member

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    Guys, thank you so much for all your opinions and input. :)
    It is really strange that even the loudness switch doesnt do much - something must be really off. I have decided to give that little black beauty the treatment it deserves. A recap and a proper adjustment of bias and such.
    I'll probably mostly use Elna Silmic (and Nichicon KG 4700 super through for the bigger couplers) throughout the boards.

    Not sure about the power section though - will bump the original 2200uf to 4700uf. Any recommendation in terms of brand? What about the original 470uf and 1000uf?
    I was thinking all Nichicon KG, super through if possible?


    edit: speakers are connected correctly :angel:
     
    Last edited: Mar 21, 2017
  5. InSaNeBoY

    InSaNeBoY Active Member

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    recap! I have an AU-555 that I did a recap on about three years ago, loved that one so much its the only one I kept. I had kept it stock with the recap, but one of the 2sc781s just died so, I'm replacing all those now and upgrading the 2200uf to 4700uf. The UFOs are still fine, they look cool.... so not going to touch those unless they fail.
     
  6. quadmatrix82

    quadmatrix82 Active Member

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    Last edited: Mar 22, 2017
  7. quadmatrix82

    quadmatrix82 Active Member

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    Few example pics for you
     

    Attached Files:

  8. The Fuxtor

    The Fuxtor AK Subscriber Subscriber

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  9. slimecity

    slimecity Super Member

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    Glorious.
     
  10. quadmatrix82

    quadmatrix82 Active Member

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    I tried that initially also however I felt the sound signature changed a lot from stock. also I read another thread here from a few reputable posters that the output coupling caps on the 555a shouldn't be altered as they also act as a dc filter after my own experimentation and personal preference to minimise mods I kept the original 1500uf rating. I have two of these so I might experiment again up to 2200uf and compare the difference.
     
  11. quadmatrix82

    quadmatrix82 Active Member

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    http://audiokarma.org/forums/index.php?threads/output-coupling-caps-how-high.530344/ This was the thread that influenced me to maintain the original output coupling cap for the 555a apologies didn't mean to deter the original intent of this thread but it's great to see so many enthusiast people chiming in on these wonderful amplifiers. I look forward to hearing the progress made on this restoration once all done!
     
  12. stereofun

    stereofun AK Subscriber Subscriber

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    Any coupling caps, original or new, serves the main purpose of blocking DC. If they fail, you will fry your speakers in an instant. Question is, are you going to rely on 45 year old caps to continue to block DC...For another 1 year, 5 years, 10 ? We just don't know when they'll quit, but we do know they are at their end of expected service life.

    Coupling caps do make a difference in sound imo - you can't go wrong with some Nichicon KG's - There is nothing wrong with replacing to stock capacitance and I am not sure upping the capacitance always sound better. You really have to test. Keep in mind here that when Sansui picked a capacitance back in the day, they probably also looked at size and cost, and then settled on an appropriate cap rating, without it being an exact science.
     
    Last edited: Mar 22, 2017
  13. The Fuxtor

    The Fuxtor AK Subscriber Subscriber

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  14. restorer-john

    restorer-john Super Member

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    Before jumping in and changing everything, get a decent tech to put the amp on the bench, run a frequency response sweep on it, check the tone circuit and the filters/loudness and get him to give you a printout of the stacked FR curves. Run the sweeps at low power (1 watt) and at full rated power into 8 ohms. This will tell you what and where the problems lie. If he can't do that- get a new tech.

    Have a look at square wave responses too, many problems can be pinpointed with a range of square wave visuals.

    Then go down your restoration path, otherwise you will a) destroy the originality possibly for no good reason and b) possibly not solve the deficiency you are hearing and c) waste time and money.

    Attached is an example I tested 10 years ago (2007) on for a Sansui AU-505. Note, this response is stock and DID NOT change after a like for like modern re-capping and restoration. The AU505 was the baby in the range and its response was tailored, just as your 555A is also. As you can see, the AU-505 was not remotely 'neutral' or flat- ever.

    AU505.jpg

    (flat, high/low filters, loudness) done on my trusty old Audiolab hardware (now retired as it needed dos direct hardware access)
     
    Last edited: Mar 22, 2017
    zaibatsu likes this.
  15. restorer-john

    restorer-john Super Member

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    I may be able to get hold of a mint AU-555a myself (my dad has one) and bench test it, and post the results if you are interested before jumping in on the resto.
     
  16. toneriderMUC

    toneriderMUC New Member

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    This is a really interesting discussion!! I read load of threads about 555A (and 505) restorations and almost everywhere there is a general consensus about upping coupling caps and the big psu one at least to 4700. To hear some voices speaking out for leaving couplers at stock value, is interesting (and confusing :-D ).
    As we are talking couplers... for the 505 i have read about the popular mod of bypassing the two couplers with two smallish film caps. Does this also apply for the 555a?

    Ok, Nichicon KG Superthrough for Couplers are set (either 1500uf stock, 2200 or 4700... we will see!).

    As for the 2200uf Power cap... also 4700 KG Superthrough? Or is something else better suited for that position?
     
  17. pete_mac

    pete_mac Super Member

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    Very interesting indeed!

    I've lost count of how many 555As that I've restored, along with other cap-coupled Sansuis (from the lowly 101 upwards). I've never been disappointed with upgrading the capacitance of both the output caps and filter caps.

    The latest 555A that I'm currently testing features 4700uf output caps by-passed with 3.3uf polypropylene caps, and 2 x 3300uf and 2 x 2200uf power supply filter caps with upgraded rectifier diodes. I've seen some people fit power supply caps which are similar in capacitance to the originals, but MUCH higher voltage (ie. suitable for switching power supplies or tube amps!) to maintain the same capacitor diameter. I much prefer upping the capacitance and keeping voltage ratings sane.

    Add some polypropylene caps in select locations in place of the original polyesters, use Nichicon UKL low leakage caps in signal path locations in the phono stage and preamp, and replace the known troublesome small signal transistors with new low noise substitutes and my word, you'll have a superb sounding amp (in my opinion anyway!).

    AU555A first listening test closeup.jpg AU555A first listening test.jpg AU555A preamp recapped.jpg AU555A underside new rectifier diodes and poly bypass caps.jpg
     
  18. The Fuxtor

    The Fuxtor AK Subscriber Subscriber

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  19. InSaNeBoY

    InSaNeBoY Active Member

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    1500uf? I have the 555, it uses 2200uf caps stock. I had always thought the difference between the two was mainly cosmetic, I guess not.
     
  20. ConradH

    ConradH AK Subscriber Subscriber

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    Whenever I order new snap-caps, they usually come in at the minimum end of tolerance. Now I just order the next size up. Going a bit larger than that is probably OK, but I try not to get carried away.

    Output caps will spend decades sitting at 1/2 the supply voltage. It's typical for caps to eventually reform to their actual operating voltage, and draw large currents if you then try to go above it. Though very rare, if a positive output were to fail, the cap would see the full supply voltage. It could then pass a lot of current and possibly short out, taking the speaker with it. I've no idea how realistic this scenario is, but it seems like a good justification for replacing old output caps.

    I've also seen the factory caps develop bad connections where the rivot holds the solder terminal, resulting is wonky operation, even if the cap itself is good.
     

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