Sansui AU-555A Rebuild Cap Coupled Goodness

Discussion in 'Exclusively Sansui' started by patfont, Mar 19, 2015.

  1. SoundOfSound

    SoundOfSound Super Member

    Messages:
    4,050
    If the UFOs are good leave them in. They are much better build quality than those little plastic transistors.

    What brand of COGs did you use?
     
  2. c.coyle

    c.coyle Fighting the Dunning-Kruger Effect Subscriber

    Messages:
    2,655
    Location:
    40.333468 -76.423711
    When I re-did my AU-555A, every flying saucer I pulled, I think there were six, had an hFE under 100, I think one was 40. That's a reason to change them.
     
  3. patfont

    patfont AK Subscriber Subscriber

    Messages:
    3,076
    Location:
    South Jersey
    sent you a PM, want to sell any?





     
  4. patfont

    patfont AK Subscriber Subscriber

    Messages:
    3,076
    Location:
    South Jersey
    me too, I pulled the first just to check for pin out and the Hfe was pretty low, but I am wondering what the original rating was?





     
  5. c.coyle

    c.coyle Fighting the Dunning-Kruger Effect Subscriber

    Messages:
    2,655
    Location:
    40.333468 -76.423711
    I think the 8002 and 9002 had low hfe to begin with, under 100.
     
  6. patfont

    patfont AK Subscriber Subscriber

    Messages:
    3,076
    Location:
    South Jersey
    Just for FYI here are my pulls with Hfe:

    8002
    #1 100
    #2 83
    #3 69
    #4 56

    9002
    #1 51
    #2 46

    495's
    #1 62
    #2 83

    anyway the new transistors are in and running and the 555 sounds intoxicating! Need to get the preamp board and phono done. Also need to re-grease and new mica on the outputs.
     
  7. stereofun

    stereofun AK Subscriber Subscriber

    Messages:
    1,081
    Location:
    Tucson, AZ
    Beautiful work. What's the reason for the NP muse caps ? Feedback caps ?

    What are these cog ceramics for the signal - is there a mouser part number ?

    PS. My impression of the UFO's are not that they are failure prone, but rather noisy.
     
  8. patfont

    patfont AK Subscriber Subscriber

    Messages:
    3,076
    Location:
    South Jersey
    Hey Tom,
    Thanks for the kind words!

    Yes C807/C808 are in the feedback loop and an audio grade bi-polar is recommended, I will let Ben chime in on this if he is following.

    For C801/C802 in the signal path (low pass filter) I used these:

    Mouser # 581-SR211A470JAR CORRECTION TO THE BELOW*******The JAR suffix is the packaging, they will come loose which saves time and damage pulling from tape, The SR21 Prefix is the kinked leads.

    I always use the JAR suffix because they are kinked leads and drop right into the 5mm spacing.

    As for the other caps on the amp board I like mine to fit flush to the board, so I just do not order any 220uf cap, I check each one to make sure the lead spacing will drop in and fit flush, that means ordering right diameter and maybe bumping up the voltage to do so.

    As for the UFO's they are built very well and look amazing. I think I got a little caught up about pulling these little charmers. Bottom line is sounds more focused and less diffuse now.

    I will also be installing a set of C0G's on the phono board, when I get there I will post that Mouser part number also.









     
    Last edited: Mar 27, 2015
  9. Leestereo

    Leestereo Super Member

    Messages:
    1,891
    Location:
    Ottawa, ON
    Pat is correct about the bi-polar capacitor: it determines the F3 cut-off for the -ve feedback loop which should be <5Hz; using a bi-polar capacitor will minimize distortion.

    As Pat said, C0G capacitors are excellent in low-pass filter applications; here's a link to a distortion comparison of C0G to "regular" ceramics and polypropylene capacitors: C0G vs. Ceramic vs. Polypropylene.
     
  10. super98lsc

    super98lsc AK Subscriber Subscriber

    Messages:
    981
    Only version I can or could find is the FTA from mouser which as you noted had significantly less gain than the 1845. My issue was the use of the 1845fta in place of the 871 on EQ amp input section on a 2000x.
     
  11. patfont

    patfont AK Subscriber Subscriber

    Messages:
    3,076
    Location:
    South Jersey
    Got a chance to pull the outputs install new mica and thermal compound. Made the amplifier adjustments, and ran it for a couple hours. All outputs run cool, and are within less then 1 degree of each other, nice!


    [​IMG]
     
  12. petehall347

    petehall347 the brandy coffee man

    Messages:
    23,521
    Location:
    uk.. the middle bit
    nice job ..i got to look for those transistors today to see the gains .but in my infinite wisdom i have moved them so cant be found yet.
     
  13. patfont

    patfont AK Subscriber Subscriber

    Messages:
    3,076
    Location:
    South Jersey
    Thanks for looking!


     
  14. patfont

    patfont AK Subscriber Subscriber

    Messages:
    3,076
    Location:
    South Jersey
    Well you can not get much easier then this EQ board, one screw and it comes right out of the socket!

    Board is out, caps are out. The Phono board will get a pr. of C0G's.

    [​IMG]


    [​IMG]
     
    smurfer77 likes this.
  15. patfont

    patfont AK Subscriber Subscriber

    Messages:
    3,076
    Location:
    South Jersey
    Anyone know where to get a set of pre in/main out jumpers for this OEM style. This one just has short RCA's.:scratch2:
     
  16. slimecity

    slimecity Super Member

    Messages:
    1,752
    Location:
    New Zealand
    I've never regretted pulling a flying saucer transistor. They may look cool, but after replacing mine in a 555a, 999 and 6500, the amplifier did sound better to me. I also had some crackling symptomatic of a failing transistor in a 6500 that went away once those transistors flew away.....

    Are you going to replace those trimpots also, or do you think there is no need? I personally only do it when they contribute to noise at the outputs (from not holding their value properly) or where you get wildly fluctuating values on adjustment....
     
  17. patfont

    patfont AK Subscriber Subscriber

    Messages:
    3,076
    Location:
    South Jersey
    As to the trim pots, for all adjustments I use proper plastic adjusting tools. The pots in this 555A had nice feel and adjusted to spec without jumping around, and are holding rock solid.

    -In some Pioneer units the trim pots are known to be flakey and can short out, those I replace.
    -When I do Marantz same thing if jumpy I replace.
    -Advent 300 I always replace them

    I like Bourns trimmers: 3386 or 3329 series single turn.





     
    Last edited: Mar 31, 2015
  18. patfont

    patfont AK Subscriber Subscriber

    Messages:
    3,076
    Location:
    South Jersey
    Phono Board is now done, took a short break to deoxit, and flush all the controls, switches, and inputs. Just need to do the tone board now!

    Installed a set of C0G's in the RIAA feedback loop.


    pics:


    [​IMG]


    [​IMG]
     
  19. patfont

    patfont AK Subscriber Subscriber

    Messages:
    3,076
    Location:
    South Jersey
    Preamp/Tone Board is up next. I will do this board in place I see no reason to remove it-easy access!


    [​IMG]
     
  20. slimecity

    slimecity Super Member

    Messages:
    1,752
    Location:
    New Zealand
    I've never worked out what the metal round thing is thats mounted on this board, (with the number 401003 stamped on it) - can someone enlighten me? Is it an inductor?
     

Share This Page