New (to me) Kenwood KA - 8100

Discussion in 'Kenwood-Trio/Kensonic-Accuphase' started by rbspop, Sep 5, 2017.

  1. rbspop

    rbspop rbs55pop Subscriber

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    61
    Location:
    Reno, NV
    I have a KA-8100 that is in pristine visual condition. I have it tweaked (+1.5 db bass) to sound pretty good thru a pair of Sennheiser HD 800's. I want to rehab it so that it will last for a long time (10 years anyway). To date I have replaced all of the caps and zeners on the Control Amp board and am wondering if there is anything else to do to that board to a) make it sound better. b) make it last longer. c) improve on the original circuity?
    I have also replaced the main filter caps on the Power Amp board. Same question: Anything I can/should do to that board to improve performance/longevity? I'll probably replace the caps on the Pre Amp board and have the same questions for that board. I know that I am asking a lot of questions but hopefully someone might want to wade in with some answers?
     
  2. gort69

    gort69 AK Subscriber Subscriber

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    I'm just finishing the details on one. I'll sit down with the service manual and post what other items I replaced in addition to caps. I can't go from memory so it will be a little while.
     
  3. rbspop

    rbspop rbs55pop Subscriber

    Messages:
    61
    Location:
    Reno, NV
    Great .. Looking forward to the details.
     
  4. gort69

    gort69 AK Subscriber Subscriber

    Messages:
    795
    Location:
    Vancouver, WA
    I replaced all electrolytic caps in the amp. All 1uf 50v (control amp) were replaced with 1uf 50v Wima films. Orange jacketed caps got Nichicon UKL (except 1uf) There are 4 caps directly in the signal path, Cd17,18 on the preamp and Ci9,10 on the control amp. Those all got Elna Silmic II.

    Control amp board:

    Qi13 (2sc1419) to MJE15032G
    Qi14 (2sa755) to MJE15033G

    Ri97,98 (1.5k ohm 1/4W) to 1.5k ohm 2W http://www.mouser.com/Search/Produc...irtualkey61300000virtualkey71-CPF21K5000FKE14

    Main board (power amp board):

    De1,2 (EQA01-24R) to 1n5252B 24V zeners
    De3,4 (EQA01-30R) to 1n5256B 30V zeners
    De16,17 (W06B) to 1n4007

    Protection circuit
    Qe31 (relay driver - 2sc1735) to KSC2690AYS
    Qe29 (2sc1222) to KSC1845
    Qe30 (2sc1681) to KSC1845

    I went from 10,000uf to 15,000uf on the filter caps, so I beefed up the rectifier diodes De18-25 to these 5A jobs http://www.mouser.com/ProductDetail/STMicroelectronics/STTH5L06RL/?qs=sGAEpiMZZMtbRapU8LlZDytFE9CP7yanLYq6cp%2bqI78=

    A previous owner had already replaced the trimmers for bias and DC offset with Bourns multi-turns. A very worthwhile upgrade. Hopefully someone can help you pick the correct ones - it's very confusing to me.

    And of course a new relay - http://www.mouser.com/ProductDetail/Omron-Automation-and-Safety/MY4-02-DC24/?qs=sGAEpiMZZMtSzCF3XBhmW7nRSRDOvRrSF7fzJd2EGBw=

    If I think of other stuff I'll post it, but I think that's it.

    Credit isn't to me on most of this - I referenced other threads and mainly culled info from hopjohn, roger2 and Echowars
     
    Last edited: Sep 6, 2017
  5. roger2

    roger2 . Subscriber

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    The trimmers I used in my KA-8100 project were Bourns 3386F. There are two @ 100 ohms and two @ 1k ohms. The "F" suffix is one of many available, and it indicates lead arrangement, where the adjustment screw is, etc. You can download .pdf spec sheets for these trimmers on their product page at either Digikey or Mouser. The spec sheets will explain in detail all of the options available.

    On two of the trimmers I extended one leg by j-hooking a leg cut off of a resistor then soldering. The leg spacing of the original trimmers is not (I don't believe) available now. The other two trimmers fit OK without alteration.

    FWIW, digging through old EchoWars posts is the source of the bulk of my information, especially where anything Kenwood is concerned, as it is (or should be) for anyone who takes this stuff seriously. Google advanced search using "audiokarma.org" in the site text box, "EchoWars" as one search term and a Kenwood model number as another search term...will get you pretty far.
     
    Last edited: Sep 6, 2017
  6. rbspop

    rbspop rbs55pop Subscriber

    Messages:
    61
    Location:
    Reno, NV


    Aaah .. Thank you very much. Exactly what I needed.
     
  7. rbspop

    rbspop rbs55pop Subscriber

    Messages:
    61
    Location:
    Reno, NV

    Good on the Trimmers info. I was wondering how to search old "EchoWars" posts. I wasn't having any luck going through his 'billions' of posts. Now I know. Thanks ..
     
  8. gort69

    gort69 AK Subscriber Subscriber

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    Location:
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    I corrected typos on Qe30 and on the rectifiers
     
  9. hopjohn

    hopjohn Kenwood Krazy Subscriber

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    Location:
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    If you haven't seen it already, here is a nice KA-8100 thread. It provides solutions for filter cap replacement issues you'll run into if you decide to replace those.
     
  10. rbspop

    rbspop rbs55pop Subscriber

    Messages:
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    Location:
    Reno, NV

    Very cool solution .. Thanks
     
  11. gort69

    gort69 AK Subscriber Subscriber

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    Location:
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    The KA-8100 could probably be considered to be tough on the power switch. There are a few options to address it if reliability is the goal.

    - Add a triac. This is what I did and it's fairly easy. Do not use a safety cap across the switch contacts when doing the triac mod. Details: http://www.audiokarma.org/forums/in...orth-5-and-an-hour-or-so-of-your-time.504673/

    - Add a relay. More complicated and more expensive than a triac. Here it is done on a KR-9600 - the principle is the same. http://www.audiokarma.org/forums/index.php?threads/kenwood-kr-9600-power-switch-workaround.464045/

    - The power switch is actually two separate switches side-by-side with a divider separating the two. There are 4 sets of contacts available and Kenwood only used one set. The simple method would be to simply snip the wires from the current lugs and move them straight over to the other side of the divider and replace the safety cap. http://www.mouser.com/ProductDetail.../ynH9T8ROa3QcXkjshqNCAZaUwa3akN1LJjKrfc7C9yhm

    - You could also separate the switch body from the toggle assembly, rotate it 180 degrees and reattach. This will give you two sets of unused contacts, which can be bridged together so that both sides of the switch share the load. I did this also, and along with the triac it should outlast just about all of us, me for sure. http://www.audiokarma.org/forums/in...witch-used-in-ka-7100-ka-8100-ka-9100.606012/
     
    roger2 likes this.
  12. rbspop

    rbspop rbs55pop Subscriber

    Messages:
    61
    Location:
    Reno, NV

    Interesting. At this point I am not having any problems with the switch. Always nice, though, to have solutions .. Thanks
     
  13. hopjohn

    hopjohn Kenwood Krazy Subscriber

    Messages:
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    Location:
    Dallas, TX
    The triac or relay modifications come strongly recommended. It makes sense to do it while you are in there. Your switch, like all other like Kenwoods I've seen, already has some damage on the contacts. It's just a matter of time before the arcing takes a complete toll. The more it's switched on, the more it gets damaged. If you aren't going to do it, at the very least plug the unit into a surge protector and switch it on and off from the switch there.
     

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