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Getting a recapped/serviced KA-8100. A question...

Discussion in 'Kenwood-Trio/Kensonic-Accuphase' started by ethangsmith, Sep 4, 2018.

  1. ethangsmith

    ethangsmith AK Subscriber Subscriber

    Messages:
    571
    Location:
    Manheim, PA
    Hi folks,

    I am getting a recapped and serviced KA-8100 integrated amp. In the recap, the technician upped the four main filter caps from the original 10000uf to 15000uf. I've heard some people say it's fine to up the capacitance, others say no. Will this hurt this unit to make that jump? Just surprised to see he did that.

    Thanks,

    -Ethan.
     

     

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  2. gort69

    gort69 AK Subscriber Subscriber

    Messages:
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    Steppin' up, eh?

    It's fine. The newer caps would likely measure at the low end of the +/- 20% range, so it's possible the jump isn't as big as it seems. It is a good idea to install sturdier rectifier diodes and and it's likely a bit tougher on the power switch. I redid my KA-8150 with 15K filter caps, installed 5A rectifier diodes and added a triac to the power switch after flipping it 180 to utilize the unused set of contacts and bridging both sides together.

    IMG_0306.JPG
     
  3. ethangsmith

    ethangsmith AK Subscriber Subscriber

    Messages:
    571
    Location:
    Manheim, PA
    How hard is it to upgrade to what you did? Is there a walk-through of how to do it? I'm a novice when it comes to these sorts of things. I have a KA-7100 that someone already recapped and added an extra relay to the switch and it works great. I have a difficult pair of EPI 201 speakers that the 7100 sounds fine with, but it runs a bit hot. My hope is the 15wpc and true dual mono setup of the 8100 is just what the doctor ordered!
     
  4. Grenadeslio

    Grenadeslio Super Member

    Messages:
    2,495
    The 15 extra watts won't make any difference, but utilizing those pre-outs to add a nice power amp will lol. Currently running my KA7300 as a pre only with a schveet Belles amplifier doing the heavy lifting for my AR's. The Kenny powered the AR's just fine, but the less analytical Belles just sounds so much sweeter.
     
  5. gort69

    gort69 AK Subscriber Subscriber

    Messages:
    1,094
    Location:
    Vancouver, WA
    I might know that guy ;)

    I would say the rectifiers are fairly easy if you have the skills and the tools to unsolder the old ones and solder in new ones. There are 8 of them - 4 on either side of the filter caps, evident in the photo above. Worth a look to pull the cover - maybe it's already been done.

    The power switch flip, bridge and adding the triac is a lot more involved. Hopjohn describes it in excellent detail here beginning with post #82, done on a KA-9100. Exact same power switch as the 8100. The triac is much simpler than the relay.

    I'm not expert enough to say either of these upgrades are absolutely necessary. I do them as a matter of insurance and consider it a part of a thorough job. From what I've seen, the chance is excellent that your power switch has significant deterioration on the original contacts. The switch in these has four sets of contacts, only one set is used as delivered.

    A quick and easy - but not as good - power switch trick on these is to simply move the two wires over the to the lugs on the other side of the divider and use that set of unused contacts, (use a new safety cap) This will get you back to an "as new" power switch, and no disassembly of the switch is required.
     
  6. ethangsmith

    ethangsmith AK Subscriber Subscriber

    Messages:
    571
    Location:
    Manheim, PA
    I couldn't remember if that was you that I got the 7100 from. I thought it was. A few months back, I almost replaced it with an Onkyo A7, but after some A/B listening, that Kenwood absolutely blew the Onkyo away. So much more pleasant sounding!

    Thank you for the info. I'll take a look at the 8100 when it comes to see what the diodes and power switch look like. In your opinion, how does the 8100 compare to the 7100?
     

     

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  7. gort69

    gort69 AK Subscriber Subscriber

    Messages:
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    I think the 8100 is a better amp. Two transformers, killer loudness setup, a bit more power, three position attenuator and pre-outs.
     
  8. hopjohn

    hopjohn Silver Face Subscriber

    Messages:
    1,092
    Location:
    Dallas, TX
    Let's not forget the 8100 /8150 has the added benefit of making your left arm stronger too.
     
    ethangsmith and gort69 like this.
  9. neevo

    neevo Super Member

    Messages:
    1,414
    Location:
    Sydney, Australia
    I went from a 7100 to an 8100. Threads on here about the work I did on both too I think.

    I have LS50’s which are pretty power hungry and I found a significant improvement in their performance with the upgrade. The LS50’s have impressive bass for their size but I never heard it with the 7100. Instant change with the 8100 though to the point where I had to check whether I’d turned the subs off.

    I also run a miniDSP and have found preouts to be essential to my needs now.
     
  10. ethangsmith

    ethangsmith AK Subscriber Subscriber

    Messages:
    571
    Location:
    Manheim, PA
    Good to hear. Hopefully this 8100 makes the journey here without damage and it's an excellent performer.
     
  11. ethangsmith

    ethangsmith AK Subscriber Subscriber

    Messages:
    571
    Location:
    Manheim, PA
    The 8100 seems to have made the journey just fine. FedEx in our area is brutal, but this is the first amp I received largely undamaged in a long time- one dent in the top cover and 2 switches slightly bent. Fixed them both already. The amp really sounds nice. I was expecting loads of deep bass, but it's actually very balanced. I run my EPI 201 speaker in 16 ohm mode, so flipping the gain switch to +10 helps things quite a bit. With this amp, I'm probably safe to run the speakers in 4 ohm mode. I've found that if I put the Loudness on the 50hz setting and then set the level to 1, it sounds great. Any more and there's too much bass! Definitely a nice amp.

    On the idea of upgrading the power switch, I looked through the triac instructions, and I understand what's happening and how to construct it, but I'm not sure where I would find the correct parts. I did some digging around but couldn't find exactly what he was using.
     

     

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  12. ethangsmith

    ethangsmith AK Subscriber Subscriber

    Messages:
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    Location:
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    Also, output heat sinks get quite hot with moderate volume playing after a while (About 30-60 minutes). Is this normal for these units? My 7100 has a wood case around it, so it's hard to tell how much heat that generated in comparison.
     
  13. Grenadeslio

    Grenadeslio Super Member

    Messages:
    2,495
    You did mention the speakers are a bit of a difficult load, that said my 7300 never had a problem driving my AR's. I will say my Belles gets rather warm when really cranking the AR's at concert levels for extended periods. The 7300 wasn't connected to the AR's all that long so never really cranked it for any extended listening, but moderate levels only warm to the touch.
     
  14. hopjohn

    hopjohn Silver Face Subscriber

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    Here's the part I'd use in an 8100. Q6040J7TP Mouser - Digikey
     
  15. ethangsmith

    ethangsmith AK Subscriber Subscriber

    Messages:
    571
    Location:
    Manheim, PA
    What would cause the heat sinks to get hot? High bias or offset? Or is it simply the EPI 201's giving it a workout? It's not painfully hot, but the outer case is hot to the touch.

    Easy enough. What about the safety cap? I'm having a hard time finding the one he used. Is it something special?
     
  16. gort69

    gort69 AK Subscriber Subscriber

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    Location:
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  17. hopjohn

    hopjohn Silver Face Subscriber

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    Yes, it is special in that it is specifically designed for across line voltage, X2 safety cap spec. No ordinary cap will do. Use the one @gort69 linked you to.
     
    Last edited: Sep 8, 2018
  18. ethangsmith

    ethangsmith AK Subscriber Subscriber

    Messages:
    571
    Location:
    Manheim, PA
    Excellent! Thanks guys for the help. I'm slowly trying to figure more of this stuff out so I can remedy problems myself.
     
  19. Watthour

    Watthour Electron Rancher - JS3600

    Those larger filter caps could be helpful it you install a power switching triac, since they may be enough to reduce the noise produced. They would not, however, help with any of the other potential problems created by a triac switching the transformer primary, such as voltage/current lag (dV/dT), transformer heating, etc. Using an incorrect triac with no snubber network and excessive gate voltage/delay can be problematic (something a relay contact will not cause).
     
  20. ethangsmith

    ethangsmith AK Subscriber Subscriber

    Messages:
    571
    Location:
    Manheim, PA
    So are you advising against a triac?
     

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