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Rebuild of classic Krell KSA50 fan heater

Discussion in 'classic' started by Arkless Electronics, May 5, 2019.

  1. mandryka

    mandryka pfm Member

    A couple of quick questions about my favourite amp.

    1. How much space does it need to have above to be sure it’s ventilating properly? I’m thinking of putting it in a place with shelves above. What will happen if I make a mistake and it overheats (I.e. will it just cut out and then be fine when it’s cooled down? I want to get clear about the risk!)

    2. Is it too heavy at 30kg for the top shelf (I suppose the turntable shelf) of a regular hi fi rack with glass shelves.


    This is what it looks like right now, i.e. a dog’s dinner, not acceptable

    [​IMG]
     
  2. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    It really need to be completely out in the open. A shelf or table of whatever sort that will take the weight is of course fine but it must not be closed in. It does not want to be sucking in already warmed air that its just blown out!
    So nothing with sides or a top basically!
     
  3. sq225917

    sq225917 Bit of this, bit of that

    Do your fans blow down or up? I'd give it an open sided shelf with 10cm minimum above and around. My ksa 200 was out in the open, and needed it.
     
  4. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    The actual heatsink internally runs at a steady 67C and this thing needs all the fresh air it can get!
     
  5. mandryka

    mandryka pfm Member

    I'm not going to take any risks.

    I may try to learn to love its brutal beauty and put it on a table in the middle of the room.
     
  6. mandryka

    mandryka pfm Member

    Well I’ve plucked up the courage. So far so good, no bowing or cracking of the stand . . . so far.

    [​IMG]
     
  7. Hooch500

    Hooch500 pfm Member

    I had one of these for a short while back in the 80's, whilst initially very impressive, I found myself listening to less and less music. I picked up an Audio research D76 which was a little the worst for wear, but was many leagues better in terms of involvement. The brother of a friend who was a BBC technician managed to sort the D76 issues without a circuit diagram, as Absolute Sounds would not supply a circuit diagram.
     
  8. mandryka

    mandryka pfm Member


    why was that then? I mean was it the amp that made the difference or a change in your mood?
     
    Last edited: Nov 7, 2019
    cooky1257 likes this.
  9. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    All Audio Research gear used to have the circuit diagrams actually in the instruction manual! They are also freely available on-line.
    I built myself an SP8 phono stage from the diagrams in the handbook 25 years ago...
     
  10. cooky1257

    cooky1257 pfm Member

    Care to compare and contrast with the BBC/Quad 520?
     
  11. mandryka

    mandryka pfm Member

    Contrast what with the Quad 520 - the Krell KSA50? I have run both with no preamp to control the main speakers in a Quad ESL system - the bass is taken care of with Gradient subs.

    The Krell image is more dynamic, more detailed, more 3 dimensional, more wide, more high, more deep, more firm, more open. The texture of instruments is more lively and life like with the Krell - the sound of horsehair on cat gut when a violin plays, for example, or the sound of the percussive attack of a piano hammer attacking the piano string, or the chiff of an organ pipe. My Quad 520 runs more quietly, there’s less (there’s no) transformer hum.

    what is the 520, is it a studio 606 or 405/Mk ?

    It’ll be interesting to compare the Krell with the Radford STA 25. In a few weeks some builders will be working in the room with the Krell, at that time I’ll put it with my JR 149s and see, the Radford sounds very good with them.
     
  12. cooky1257

    cooky1257 pfm Member

    The 520 is a 606 with fewer output transistors but a beefier power supply, I ask as I'm in the process of swapping out 521 and a 240(306) for a Mark Levinson 333(similar muscle/US over build). Thanks, you like it by the sounds of it!
     
  13. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    I was unimpressed by the 520. Sounded like a generic high feedback solid state amplifier... the same criticism I have of the vast majority of SS amps.
     
  14. TheDecameron

    TheDecameron Unicorns fart glitter.

    stop it, stop it, stop it!
     
  15. TheDecameron

    TheDecameron Unicorns fart glitter.

    Are they also easy to work on Jez? Everything inside them looks supersized- big boards with fat tracks and plenty of space round the components.
     
  16. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    Generally yes. Personally I would avoid anything modern enough to have remote control. I was unimpressed by an LS25 pre amp I must say. SP9 is a sleeper.... generally not regarded as one of their finest hours but I've always really liked them. 80's gear is the stuff to have IMHO... SP8, SP10 etc
     
  17. Hooch500

    Hooch500 pfm Member

    Like I said it was impressive at first, detailed with solid bass etc. Just didn't engage me musically. Reminded me of the old Crown amps I used in the studio. Always preferred the Yam B1's and B2's.
     
  18. mandryka

    mandryka pfm Member


    Ha, I was thinking of using a Crown DC 300 to drive the subs of the system with the Krell driving the main speakers!

    I’d like to hear a good Yamaha amp but they’re not so frequently for sale in Europe, and import charges can be off putting.

    The Krell sound is more like a live sound, with all its asperities, than anything else I’ve heard in hifi. That’s exactly what I wanted to achieve, but I’ve learned from posting here that not everyone wants that from their hifi, they look for something more polished and soft.
     
  19. Hooch500

    Hooch500 pfm Member

    The B2 was a lovely amp,the B1 too - but they are getting old and an overhaul is a bit daunting. No idea how the new ones sound. The Technics R1 with the GaN FETs looks interesting though.
     
  20. cooky1257

    cooky1257 pfm Member

    I've used quite a few muscle amps, particularly worthy of mention for sheer grip and low end grunt were an MC2 MC1250 and BGW 750B, The BGW sounded similar to the Crown/Amcron DC 300 in its mids/top(a bit hard tbh), the MC2 was just a superb all rounder. The Muscle Amp moniker tends to generate some expectation bias as to their presentation when in reality many are capable of great subtlety.
     

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