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Concordant Excelsior - who knows about history of this pre?

Discussion in 'classic' started by _webwasher, Apr 10, 2019.

  1. audiojoy

    audiojoy pfm Member

    I did indeed find the capacitors in the power supply very critical as well on the main board as well. Tried many different brands, my conclusion is to choose components that stay close to the original sound which is excellent IMO. Please read my old thread, but Black gates as the main filter on the main board was the best there not the replica LCR.
    To get rid of that graininess some people have noted here is what i did
    by passed all the switches
    changed the pot for a bournes
    parallel the black gate filters on the main board with Jantzen Superior (very very important to get the right overall sound) (note audio note now make black gate replicas but i feel they sound a touch more polite than the originals)
    use a super regulator on the heater supply
    replace every single signal cabling to western electric.
    Do not change the original main cord for something fancy neither the umbilical cord, the originals will keep the original sound intact.
    Use Toshibas for the pre valves, best i could find and closest to the original sound Doug wanted.
    No grain, wonderful PRAT but with valve timbre kept intact and a very wide sound stage.
     
  2. eastone

    eastone pfm Member

    Quiz question: my Exhilarant uses 12AX7s; if I introduce 5751s to reduce gain by approx 30% am I increasing or reducing the amount of feedback in the circuit?
     
  3. Dan K

    Dan K pfm Member

    Stays the same. Works as a percentage of the output.
     
    eastone likes this.
  4. Dan K

    Dan K pfm Member

    But is the same level of feedback appropriate for a 5751?
     
    eastone likes this.
  5. eastone

    eastone pfm Member

    Is 5751 inherently lower distortion than 12AX7? I have nice Sylvania Triple Mica gray plates, if that makes any difference.
     
  6. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    Gain will stay the same but feedback reduced. Always best to stick to the correct valves.
     
  7. eastone

    eastone pfm Member

    Interesting - I was looking for a reduction in gain, why does that not happen?
     
  8. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    Because the negative feedback is doing its job! I keep saying that negative feedback is the single most important aspect of amplifiers... period. It decides virtually everything about an amplifier... gain, frequency response, distortion, damping factor (in power amp), output impedance etc...

    So long as you just want to reduce gain of line section then you can probably get away with increasing feedback to reduce gain but ideally it should be checked on an oscilloscope to make sure it doesn't cause instability.
     
    Julf, eastone and _webwasher like this.
  9. rmcin626

    rmcin626 pfm Member

    I owned this pre amp and also Quad II amps that were modified by Doug Dunlop, also spent a very interesting day at his house once while upgraded the pre amp.
     
  10. eastone

    eastone pfm Member

    What upgrades did Doug perform on the pre?
     
  11. rmcin626

    rmcin626 pfm Member

    To be honest, I can’t remember the exact changes, every time I spoke to Doug he was changing something and this was probably about 30 years ago. The Quad amps didn’t change much apart from different valves. His workshop was basically a converted cupboard in his house.
     
    _webwasher and eastone like this.
  12. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    There was a pair of the Concordant Quad II's in a cupboard of the office of local petrol station... Since changed hands so no doubt taken away by original owner...
     
  13. _webwasher

    _webwasher pfm Member

  14. eastone

    eastone pfm Member

    Lid off I see! That’s how I run mine when my daughters not around. One of these days I’ll get round to making a Perspex lid... smoked black / brown like the teachers’ teacups of me youth!
     
    _webwasher likes this.
  15. rmcin626

    rmcin626 pfm Member

    One of my many regrets in hifi, should never have sold the Concordant equipment
     
  16. awkwardbydesign

    awkwardbydesign Officially Awesome

    On mine, I have switchable NFB to reduce gain if I need it, depending on what's downstream. Some of my power amps are overly sensitive. One day I may get round to changing to the valve PSU, but I need a suitable trafo for that. And as it's just the loft system, it is down the list.
     
  17. eastone

    eastone pfm Member

    Quoting the above from another Concordant related thread.

    Am intrigued by your comment on the 'excess' of valves here. Are you suggesting the amp could be run off one ECC83 and one cathode follower valve?
     
  18. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    Sorry 'fraid I can't recall exactly what this was about...

    With regard to line pre amps in general yes it could easily be done with either one ECC83 shared between channels and a cathode follower, which could be half of another dual triode but preferably not an ECC83. or it could be done with a whole ECC83 per channel and again a cathode follower using half of a dual triode.

    The first type would be phase inverting and not really very suitable if it must have over say 50K input impedance.
    The second non phase inverting and as high as you like on input impedance.
     
    eastone likes this.
  19. eastone

    eastone pfm Member


    Yes, sorry, a little short on context. I came across your comment in an older thread of mine this morning and it got me thinking.

    I was really just mulling in what ways the Concordant Exhilarant circuit, which uses two '83s + two 5965s as cathode followers, would be changed by halving the number of valves used. Would it reduce gain for example?

    Impedance-wise my unit is fed by a USB dac and nothing else.
     
  20. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    I just googled that model and it shows pics of a pre with 6 valves! Hmmm...
    Odd that it uses 2 5965's if they are used as followers as it's a dual triode and one could do both channels....

    Anyway unless a schematic turns up the original circuitry will be a matter of speculation...

    Negative feedback sets the gain and so it can be whatever you like. With one ECC83 half per channel the max would be about x 80-90 or so and that would be with no feedback.

    With a ECC83 per channel anything up to about x 8000 possible with no feedback. Of course in practice feedback would be used (not much choice with the very high gain of the ECC83!) and with all that gain available distortion down at less than 0.01% easily possible.... maybe 0.003% or so.

    With some difficulty it is possible to use 3 triodes per channel in the "ring of three" configuration as a DC amplifier with no capacitors at all.... A version with just one cap (output cap) rather easier...
     

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