• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

line pre amp

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P

phil

Member
2001-05-10 7:56 pm
www.xtra.co.nz
  • #1
    I would like to build a tube based line amp, nothing too fancy but
    with a great sound, an extended frequency responce, will match a ss amp input and not a kit. I have on hand a number of ecc81's.But I am willing to look at circuits using any other tubes/valves.
    I have had a quick look at a number of sites but cannot find anything suitable.
    Can anyone with experience of building such a project please point me in the right direction.
    Many thanks
    Phil.
     
    B

    bawang

    Member
    2001-10-31 2:52 am
    Malaysia
  • #4
    12AX7?

    From someone who's a green horn on tubes (but likes that sexy glow, and hates the output transformers on the tube power amps), what about a design based on the 12AX7 (or equivalent) series?

    This may seem to be the solution for a tube sound but with the grunt of solid state for the power amp! Correct me if I'm wrong........
     
    S

    stigla

    Member
    2001-11-09 10:49 am
    Trondheim
  • #7
    Hello phil

    I have a great page to recomend you. This article discribes a simple circuit with 12 different tubes suggested, and power supply. I think this is JUST what you are looking for. Figure 2 in the article would be my choise of circuit, but it inverts the signal. This is really no problem because you can compensate by switching the + and - on the speakers. All the tubes on the list ar well known and used by many.
    http://www.users.globalnet.co.uk/~valveamp/

    Your 81's can easily be used, check out
    http://members.tripod.com/~gabevee/mytubamp.html
    to learn how you can set up your own circuit from the ecc81.


    -stig
     
    D

    dice45

    Member
    2002-01-19 10:21 pm
    Munich, Bavaria
  • #10
    Hello Phil and Stig,

    Originally posted by stigla
    I have a great page to recomend you. This article discribes a simple circuit with 12 different tubes suggested, and power supply. I think this is JUST what you are looking for. Figure 2 in the article would be my choise of circuit, but it inverts the signal. This is really no problem because you can compensate by switching the + and - on the speakers. All the tubes on the list ar well known and used by many.

    http://www.users.globalnet.co.uk/~valveamp/
    Click to expand...

    when I read that Phil is intending to use the ECC81, I was tempted to disrecommend it as I had many occasions to listen to amps using this tube and none of them was sounding particularly pleasant or musical.
    But as I had no tried schematic to contribute, I stood mute.

    I followed the link and the 1st coming to attention was Simon Shilton's name. I know him as a transformer designer and he certainly is not sitting on his ears. I would follow his recommendations w/o hesitating.

    I observed he does NOT have the ECC81 in his list of recommended tubes. But he has the 6CG7 (noval/miniature9 socket version of the 6SN7), the 6SN7, the ECC82 and the 5687 in his list, and I know all these tubes make gorgeous music. The 5687 also fits for this but is a lil'bit high transconductant and I would rather use it with an output transformer. This is running at my place at the moment, just magic.

    Phil, my hint, keep the ECC81 as a deterioating example to try it out yourself but I would be surprised if you or anyone else prefers the ECC81 to one of the tubes I mentioned; this is not an audio tube and was never designed for that and has been tried out manytimes not to sound that well. (yeah, I know, the 5687 also was not deisgned for audio and was widely used in tube computers, but it has been tried out to sound gorgeous.)
     
    D

    dice45

    Member
    2002-01-19 10:21 pm
    Munich, Bavaria
  • #12
    Phil,





    the preamp i am currently using is a borrowed one, but as i know meanwhile, it is on AudioNote level or better; my friend Manfred lend it to me until my own differential PP preamp gets ready. So i had to ask him for specifics.





    Manfred's preamp has an input selsector and a 50kOhm ladder attenuator at the input. From that the 5687's grid is fed. The tube runs at 25 mA quiescent current. The used trannie is a Simon Shilton / SJS model PA102; it has a turns ratio of 5:1 and an impedance ratio of 15kOhm to 600 Ohm.





    Warning, the trannie is slightly uncheap, but AFA i can tell, it is worth it.


    At the moment, SJS has one pair of them on sale for UK-Pounds 85 a piece with chrome-plated shrouds. The normal retail price is at UKP 115, TMK. Recently, a British line preamp was reviewed in a German high-end audio magazine, Manfred reported, and the unit had a retail price of about US$ 9000.





    With this simple structure, you are launched directly to orbit :)


    Run and order as long as the sale trannies are available.
     
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