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Leestereo's Restoration/Upgrade Of A Sansui AU-717

Discussion in 'Exclusively Sansui' started by Leestereo, Feb 10, 2015.

  1. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    See my answer in the other thread (same question). ;)
     
  2. Myounger

    Myounger Sansui Collector

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    Collierville ,Tennessee
    I have and thanks ....
    Mark
     
  3. Myounger

    Myounger Sansui Collector

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    Collierville ,Tennessee
    I have seen on other threads( there are many on AU-717 rebuilds) were that it was suggested that you could increase the output( WPC) by increasing the size of the 4 12000uF caps(C701-C704). I am wanting to really trick out my AU -710 . So any mod suggestion would be welcomed. I am collecting information/suggestion , ordering parts, etc. developing my battle plan before I crack the Au 710 open and start disassembling. Mark
     
  4. Thinker

    Thinker Super Member

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    For most of the film caps and C0G caps you didn't mention voltages, since most of them are signal path are they all low voltage? ~50v?
     
  5. Leestereo

    Leestereo Super Member

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    As a general rule, the signal path capacitors will be subjected to lower voltages than the power supply capacitors. The polyester stacked film capacitors are typically available rated at 50V or 63V. For the polypropylene capacitors, use the smallest capacitor that will fit the available board space (which is often the lowest voltage rating). For C0G capacitors you can use 50V or 100V rated ones.
     
    Thinker likes this.
  6. Thinker

    Thinker Super Member

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  7. ghamilton

    ghamilton Super Member

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    Very good. But how do you account (or allow) for higher uf values when the factory assigned the values that were in there? Higher voltage is one thing. But uf value is another. :lurk:
     
  8. Leestereo

    Leestereo Super Member

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    Generally, your parts order is OK. But I did notice some possible issues:
    *check the quantity needed for 2 Driver Boards.
    *the 0.47µF film capacitors you have in the Mouser cart are too big, use WIMA stacked film here
    *some of the film capacitors the 10% type, 5% or lower is preferred
    *the 27.4kohm resistor you have in the Mouser cart is back ordered
    *the 150ohm resistors should be metal film types
    *the 470µF 16V Nichicon ES may not fit on the phono board, use Nichicon VP
     
  9. Leestereo

    Leestereo Super Member

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    If I understand your question correctly, you are asking if increasing the capacitance value from the stock value is permissible. In the vast majority of the cases, there is no problem increasing the capacitance rating of the local decoupling capacitor, especially for small values less than 1000µF. IMO, a 2X-3X increase is acceptable for most small capacity capacitors whose purpose is solely DC filtering. In these cases, the extra load on the power supply transformer and diodes is minimal. However, the extra load would be a consideration when large main power supply capacitors are to be replaced; in that case, a more conservative approach is warranted, e.g., the stock main filter capacitors for the AU-717 are rated at 15,000µF and increasing them to 18,000µF (a 20% increase) would be acceptable, but beyond this value may be inviting problems.

    The original capacitance rating and types (e.g., electrolytic vs. film) specified during manufacturing were often limited by capacitor technology of the day, the cost of part and the physical size (finite space available on the PCB). I am certain that the original designers would have opted to use today's better parts had they been available or had not been constrained by profit considerations. Generally, today's best capacitors are often much better than their vintage counterparts and it is by leveraging this modern capacitor technology (e.g., long life/low ESR types, stacked film types) that the sound and reliability of vintage stereo pieces is often improved to better than when they were first manufactured.
     
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  10. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    ...and a side effect of the larger capacitance value for PCB mounted wire ended electrolytic capacitors (providing you know what you are doing), is that they more closely match the hole spacing of the originals, and thus reduce or eliminate the strain in the component leads and their seals.
     
    Last edited: Nov 15, 2016
  11. lbcgav

    lbcgav AK Subscriber Subscriber

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    Can I reuse the 2.2uF bypass caps on the main filter caps or should I order some new ones? I'm doing a full recap of my AU-717, but forgot to order the bypass capacitors.
     
  12. Leestereo

    Leestereo Super Member

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    Yes, you can reuse the 2.2µF polyester bypass capacitors if they are in good condition; alternately, you can leave space on the main capacitors for an upgrade to polypropylene capacitors at a later date. Also you can increase the size, e.g., 4.7µF.
     
  13. calman46

    calman46 AK Subscriber Subscriber

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    Great thread , I am working on a AU-717now and on the tone control F2720 , C15 &C16 are not mentioned in the text (am I missing it ?) from the picture it looks like they were upgrade from 10uf @16v to 10uf @35v low ESR type.
    Also I have a question, same board I don't any 10uf @35v BP/ES caps for C21,22,45,46 I have 25V &50V .They both fit but is 50v to high for the signal path ?
     
  14. Leestereo

    Leestereo Super Member

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    On the F-2720 board, the capacitors C15 and C16 were replaced with audio grade types (Silmic II, 10µF/35V). In a blow-up of the original picture below, you can see the capacitor C15. But it was inadvertently not mentioned in the accompanying text. Regarding C21,C22,C45 and C46, use the 10µF/25V or 10µF/50V that you have on hand.

    [​IMG]
     
  15. calman46

    calman46 AK Subscriber Subscriber

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    moving right along here ... I couldn't without moving components on EQ board get the polypropylene caps in at C27/C29, C28/C30. So I use 2 Silmic II caps (10uf/50v) in series like the originals and I replaced the mylar bypass cap with a Wima polypropylene cap ,orignal value.
    How come the capacitance was lowered on the amp/ preamp switch , from 5.0 uf to 2.2uf ?
     
    Last edited: Oct 1, 2016
  16. Leestereo

    Leestereo Super Member

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    There isn't really enough room for large polypropylene film capacitors as replacements for C27/C29 and C28/C30 on the F-2723 board. However, 4.7µF stacked polyester film types (e.g., WIMA MKS2 or Kemet R82) will fit in the space originally occupied by the C35/C36 polyester bypass; see earlier post #20 for picture. Alternatively, a single 4.7µF Nichicon ES bi-polar electrolytic capacitor can be used to replace the original polarized capacitor pair and the by-pass kept.

    The impedance of the power amplifier is 50kohm, and with the 5.0µF electrolytic capacitors in the high pass input filter, the F3 is 0.64Hz; with the replacement 2.2µF film capacitors, the F3 increases to an inconsequential 1.45Hz.
     
  17. calman46

    calman46 AK Subscriber Subscriber

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    Thank you
     
  18. MBuras

    MBuras Restoration is an Addiction Subscriber

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    Wanted to throw out a big thank you to @Leestereo for the excellent initial write up and follow on discussion. After 2 years of working on various Marantz and Pioneer units I picked up an AU-717 for my first Sansui restoration. Definitely not disappointed. :thumbsup:
     
  19. calman46

    calman46 AK Subscriber Subscriber

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    I finished my AU-717 LeeStereo upgrade and its sounds great, thank you Lee. I went for the new filter caps , but I couldn't find all the polypropylene film caps I needed so choices had to be made . All the fuse-able resistors in my unit were open so I never heard it stock . The glue also ate the leg
    off a transistor. Grab a AU-717 if you can,the upgrade is great and the unit is easy to work on .
     
  20. deltalight

    deltalight AK Subscriber Subscriber

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    Minneapolis
    Hi Lee,

    On both the restored driver assys, it appears that you installed an additional .33uF film cap in parallel with R32, a resistor that sets the bias for TR09 protection transistor.

    Q1: The AU-717 schematic shows R34 is 270R whereas a 180R 1/4W is installed in several F-2721/F-2722 assys I have. Is the 180R a production change or have you seen 270R installed?

    Q2: Why the addition of the .33uF film in parallel with R32?

    Best,

    --Bill

     
    Last edited: Jan 29, 2017

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