Op-Amp for KA-5500

Discussion in 'Kenwood-Trio/Kensonic-Accuphase' started by Spenser, Aug 31, 2017.

  1. Spenser

    Spenser AK Subscriber Subscriber

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    Hello there. Can you take a look at this?

    Original op-amp on the KA-5500 was the in-line, TA7136P -- a long time ago "...when op-amps were still young." (Echowars) Far better op-amps are made today.

    So what I am wondering...

    Would an op-amp upgrade improve performance enough to justify?

    Which reasonably priced, readily available op-amp (ideally Mouser-stocked), would be a good choice?

    What other modifications would be needed?

    Some weeks ago Hopjohn (THANKS), suggested to me -- IF one were to switch out the op-amp -- possibly go with 595-OPA2132PA. He added caveats. One, 'op-amp rolling' is not his specialty. Two, there is give and take, from what he understands. Three, it would be advisable to seek counsel from others.

    In 2002 Echowars posted a thread on an op-amp upgrade he did on his KA-5500; said performance enhancement was significant. He noted that improved performance also was attributable in-part to electrolytic capacitor upgrades. In any event the op-amp Echowars selected was the now, no longer available / outdated (Burr-Brown - later Texax Instruments), OPA604AP with a .18uF stacked film cap soldered directly to the leg of an IC socket to deal with "supply voltage outrageous by opamp standards (+/- 19V)." The OPA604AP was an eight-pin DIP. To adapt he had fashioned a small PC board which he wired to the Kenwood PC board; incorporating a a gold DIP socket, in case someone came up with another op-amp that might be fun to try.

    Edit: I think I left out that he may also have adjusted resistors, as follows: "... the preamp supply voltage resistors are dropping the supply voltage from +/- 19V to about +/- 17.5V. I was prepared for this, and changed the resistors to get the supplies back up to 19V."

    Tin pin gold DIP socket 575-11043308?
     
    Last edited: Sep 1, 2017
  2. ferninando

    ferninando AK Subscriber Subscriber

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    how about the BB/TI OPA2604. 8pin dip dual.
    Definate sound imprvement in my sony CDP302 output stages compared to sony origs..
    If all specs match with the 604 it should work ok.
     
  3. rjsalvi

    rjsalvi Active Member

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  4. Spenser

    Spenser AK Subscriber Subscriber

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  5. Spenser

    Spenser AK Subscriber Subscriber

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  6. ferninando

    ferninando AK Subscriber Subscriber

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  7. Spenser

    Spenser AK Subscriber Subscriber

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  8. Beau Geste

    Beau Geste Super Member

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    I replaced the NJM 2068 and M5238 of my Denon POA 6600a with the BB OPA 827 and OPA 627 mounted on dual mono adpater...I advice this mod..You can find these OP Amps on Ebay.com..They are genuine and work very fine..But before of thise, read this :http://nwavguy.blogspot.it/2011/08/op-amp-measurements.html
     
  9. Spenser

    Spenser AK Subscriber Subscriber

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    Hey Beau Geste, That was very nice reading you suggested. The op-amp NE5532 mentioned in the article was part of the exploration in year 2002 on the preamp section we are talking about here in a Kenwood KA-5500. It was tried but ruled out due to its greater input current demands.

    Your comments and suggestion made me think to go back and add an edit to my original post:

    how the power supply resistors for the preamp section (where the IC is), got adjusted to get the voltage back up from its decrease to +/-17.5 (due to the more modern IC), to where it belonged by specifcations +/-19V.

    It is pretty involved this matter of op-amp rolling. Well beyond my current analytical and engineering abilities on my own.

    How about the OPA2134 mentioned in the article? (Hopjohn see initial post offered perhaps look into OPA2132).
     
    Last edited: Sep 1, 2017
  10. Beau Geste

    Beau Geste Super Member

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    Ok..Take a look here..These are the newest IT Op Amps ..You have a wide choice about the max total voltage supply.. The OPA 827 , for example, has a max voltage supply of 40 V ( V+ V-) and the optimal supply voltage at 18 +, -http://www.ti.com/amplifier-circuit/op-amps/audio/overview.html :)
     
    Last edited: Sep 1, 2017
  11. Beau Geste

    Beau Geste Super Member

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  12. Beau Geste

    Beau Geste Super Member

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  13. Spenser

    Spenser AK Subscriber Subscriber

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    I understand. At the same time judging from the article I would not want something like the OPA 627. Overkill on performance for the type of amplifier we are talking about here, and way too expensive for me.

    The OPA 1642 is perhaps more in range (at least in terms of price). Only comes in the SMT/SMD mounting format on Mouser.

    Back to the OPA 2134. While not the latest and greatest, would it nonetheless be a significant performance improvement over the original factory IC (remember we are talking here replacement of circa mid-1970s TA7136P)?

    IF looking at OPA 2134 or the OPA 2132, which would be the better choice of the two?
     
    Last edited: Sep 1, 2017
  14. rcs16

    rcs16 Super Member

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    I do not think that you will notice any differences. have to make sure that you do not exceed the supply ratings and that you may get oscillations/instability as these faster devices are more sensitive to supply decoupling. The best is to use 100n MLCC cap as close to the supply leads as possible and short ground connections.
     
  15. Spenser

    Spenser AK Subscriber Subscriber

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    OK.
    This is good. I will look at datasheets; might get a couple different ones to try; these specific tips are helpful. Thank you!
     
  16. Spenser

    Spenser AK Subscriber Subscriber

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    rcs16, what do you think of this, reference your suggestion "...100n MLCC cap as close to the supply leads as possible and short ground connections."
     

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