A 1watter Soon To Be Born..

Discussion in 'Building the Classics' started by johan.b, Apr 19, 2017.

  1. johan.b

    johan.b Well-Known Member

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    intended as preamp in my next rig, so no point in building 50watter and attenuating before fx's and poweramp. output tube is a 12au7 in cathode biased push pull. output transformer is a tiny toroid. I've used those before in similar builds.
    basicly its a 50watt jmp with a different powersuply and output. if I change my mind, I'll just mount octal sockets, and rebuild the powersupply and add a 50watt optx
    I dont need the bias supply, but built it anyway. the 50watt transformer I have laying around doesnt have a centre tap, so I reconfigured it like a 900 with class x capasitor
    [​IMG]
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    [​IMG]

    I'm not as tidy as some others, but thought you might like this anyway...
    ..still some things to do thou..
    J
     
    Geeze, Namkrad, kinleyd and 5 others like this.
  2. jensvonbustenskjol

    jensvonbustenskjol Active Member

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    Cool!
    I dig your concept!
    Have you tried it any cabinets?
    I played the 1w ann. Marshall on a 4x12. It got balls. More headroom than expected!
     
  3. soundboy57

    soundboy57 Well-Known Member

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    Very nice work, you are too humble. I bet it will sound awesome...
     
  4. Coronado

    Coronado Well-Known Member

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    That's amazing! Nice work!
     
  5. johan.b

    johan.b Well-Known Member

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    Thanks guys. I'll post more pics and some sounds soon. .between the house. The boat. the car. The two year old,working full time and some gigs the last week's. There's been too little time. .i'm tweaking it now and have it almost where i want it (feedback resistor. Bright cap. Those king of things)...I'll get back soon
    J
     
    Last edited: Apr 25, 2017
  6. johan.b

    johan.b Well-Known Member

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    quick and dirty..take it for what it is...

    more tweaking will probably be done after testing at loud volume...this just at home.
    j
     
  7. ampmadscientist

    ampmadscientist Well-Known Member

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    Dude, that thing shreads!

    What's the schematic for the trick output circuit?
     
  8. johan.b

    johan.b Well-Known Member

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    Thanks ams.
    no real trickery. Just the two sides of a 12au7 in place of the EL34's.
    B+ is 330 volt, so i went with cathode bias to take a few volts of the little tube.
    Initially i ran with Un-bypassed cathodes, to get a little local feedback, backing away from the triode-sound a little. The sound was even sweeter. "Cleaner overdrive" if you know what i mean. But it had a bit too little gain, so i threw a100uF across it. Nfb resistor at the moment is 22k.
    Output transformer is a tiny Talema brand toroid(the blue square thing). 115+115 volt primary, 9 volt secondary. Used with 8 ohm i get just over 5k plate to plate. ..i run it into 16ohm now to take some load of the little guy.
    Later on i plan on going back to Un-bypassed cathodes and see if paying around with nfb resistor and perhaps some filtering can get me where i want to be. I suspect though it'll render precens knob useless..but overall, I'm happy as is. .
    output load/master volume is an 15watt L-pad from the hifi store, sitting after the output transformer, so i always get "all the amp".
    With this low power it can run without speaker, so i can use the output for line out into whatever. ..
    J
     
  9. ampmadscientist

    ampmadscientist Well-Known Member

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    That's pretty cool.
    We are always looking for ways to get a good sound at low loudness. Seems like you are doing that w/ the 1W output stage / L pad.
     
  10. Geeze

    Geeze Well-Known Member

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    Sounds awesome! Could this rig be built into a smaller size? I've got a 12" wide quilted cherry head shell sitting empty that whispers to me....

    Russ
     
  11. johan.b

    johan.b Well-Known Member

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    The circuit, sans tubes. Transformers and pots.could with some creative layout fit in the palm of your hand, so anything is possible. .
    J
     
  12. ampmadscientist

    ampmadscientist Well-Known Member

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    Try building w/ Nuvistors?
     

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