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Krell KRS-2

Discussion in 'd.i.y.' started by earthfield, Jun 27, 2014.

  1. 337alant

    337alant Negatively Biased

    Beautiful pre amp I am very envious ;)

    I would clean all that flux residue off the boards with Isopropanol and a tooth brush

    Only design flaw I see is lots of long wires ?. on the power supply why does the output run from one side of the case to the other and past the noisy rectifiers

    In the pre amp I would have put all switches and pots at the back of the amp on extensions and kept all signal leads as short as possible
    If you want to know the rail voltage why not just measure it

  2. Mr_Sukebe

    Mr_Sukebe pfm Member

    Simply stunning. Wonderful to see.
  3. sq225917

    sq225917 situation engineer

    Brilliant work, restoration wise and also on the initial design. I did 2 ksa 200's and a ksp 7b pre a while back.
  4. earthfield

    earthfield earthfield

    Glad your spirits have been raised!
  5. earthfield

    earthfield earthfield

    Will, really enjoyed working on that pre! Thats a rare statement! Well worth it, my ears love it, and everyone who hears it.

    Was that your efforts on the dual mono version too? In your opinion whats the Best Power amp ever made by Krell , KAS mono's, KSA 200's?

    It would have been great to connect with you before doing that refit! The guys at Krell -tho helpful- couldn't get me a circuit diagram of your work, one question put to them was how to truly bypass the C.D. filters by alteration, so full use of all inputs can be utilised for the studio. Time would not allow tracing the routes and transcribing them to make sense of it all. Sure it was a long time ago, but if diags could be sourced, please contact me via P.M. One other thing, having looked into sourcing the Large L.C.R rectifier caps, nothing came up. I suspect if you asked Krell, they might dig a little deeper?; they're unusual- low profile- three leg- 45v 16,000µF with the case numbers PC163 GW045 x twelve of. Also four x 35v 6800µF No. 329 680R.

    So much thanks for mastery of design to neutral sonics, rock solid reliability and functionality.
  6. Baldrick43

    Baldrick43 New Member

    I have a sick KRS-2 here in the UK and would be grateful for any help that you could give me to complete this upgrade.

    At present, it is believed that some of the caps have died in the amp, it has been inspected by various hi fi shops in the UK, but as yet I have not found one that inspires confidence in me to leave it with them, also, cannot afford the price quoted by Krell to repair it!

    This leaves the option of a self repair, this is not a big problem, but finding out what is the beat components to use is.

    As you have not only replaced the caps, but have also upgraded them, I would be grateful if you still have a detailed list of the caps and the values that you could pass on to me?

    This amp has been sitting dormant for a few years now and it would be great to breath some new life back into it.

    Many thanks

  7. witek

    witek Member

    i'm sorry i don't speak english, I am using a Google translator.

    I have a big request, you could read transistor names from one to twenty five according to photography.

    I am impressed and I would like to understand how this preamplifier works, but I do not know what Krell used transistors: bipolar, unipolar, mosfet, n-channel, p-channel.

  8. sq225917

    sq225917 situation engineer

    Usually Jfet, the KSP-7b i rebuilt used 2sk170 and the complimentary J74. (1-19, 21-23 in your image) The last three parts (20, 24-25) are voltage regulators, probably either Lm317 and Lm337, or LM78xx and LM79xx
  9. witek

    witek Member

    sq225917 thank you very much. "19" controls "20" so "20" is probably not LMXXXX I think so. 1-3 out of 100% is jfet. Maybe the earthfield will write something
  10. sq225917

    sq225917 situation engineer

    Let me see if I have a schematic on file. I've done a fair few krell rebuilds so I have a pile of circuits for power amps, maybe there's a krs in there.
  11. witek

    witek Member

    "maybe there's a krs in there" - wow, you are amazing, thank you very much for your help :), it would be sensational.
  12. sq225917

    sq225917 situation engineer

    Nothing for the krs I'm afraid, sorry.
  13. witek

    witek Member

    dont worry its ok, maybe you have a KSA-50S, KSP-7b?
  14. radelius

    radelius pfm Member

    I'm trying to find schematics/service manual for this Preamp. Anybody....?
    Last edited: Sep 7, 2018
  15. witek

    witek Member

    pleaseeeee help us
  16. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    Have you tried Krell themselves? They've sent me schematics in the past.
    If they can't or won't help and it's not on the internet you'll have to reverse engineer it.... If all you want to do is replace electrolytics you don't need a schematic. If it has only been switched on for an hour a day or so then it may well be fine anyway but if it has been left on 24/7 then I'd replace the lot!
  17. witek

    witek Member

    "Have you tried Krell themselves? " - I have not tried and I will not try because they will not send anything, that's why I am asking kind people for help
  18. witek

    witek Member

  19. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    They not only emailed me the diagrams I wanted but also rang me at their expense from America to discuss it... This was pertaining to a KSA200 I was working on at the time.
  20. earthfield

    earthfield earthfield

    Krell were contacted regarding this pre-amp and they were unable to supply circuit diagrams.
    As for capacitors just use what ever has the lowest ESR.
    Panasonic FM's are highly regarded.
    I put in Nichicon Fine Golds around the phono stage, Elna Silmic II's everywhere else, may replace those with Panasonic FM's.
    Low resonance Vishay cans on the last smoothing stage.
    The difficulty was mostly finding caps that would fit in the footprint of the board and height,
    Buying more capacitors than the list amount was also necessary for matching.
    PSU bridge rectifiers, replace with low noise singles, BYV29-600's/ MUR 420-480

    Walk to make the path!

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