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Tube preamp scheme.

Discussion in 'Pickups & Electronics [BG]' started by sanyaalwaysbass, Feb 5, 2013.

  1. sanyaalwaysbass

    sanyaalwaysbass

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    Hello everyone! I'm in search of a good tube preamp scheme. It's assembling must not be expensive.
  2. sanyaalwaysbass

    sanyaalwaysbass

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    ... like alembic f2b or ampeg svt pro. Thanks!!!
  3. sanyaalwaysbass

    sanyaalwaysbass

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    Please note, that
    it has to be easy to assemble,
    because my friend-engineer will
    be in charge of that.
  4. Codger

    Codger Bradley Baker Supporting Member

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    I started with this R.G. Keen Schematic and made a couple of minor changes for voicing. I also added a MOSFET buffer to the output per R.G. Keen again.

    Power supply uses a doubler per the Alembic original. The transformer is from Antique Electronic Supply. It is capable of powering two 12A*7 type tubes. The doubled and filtered voltage under load is 300V. The filament supply is 12VDC regulated. The preamp has no hum, but has some hiss when volume is cranked.

    I made two PCBs, one for power supply which can also be configured for a conventional bridge rather than a doubler, and one for the preamp. All external connections are made using swaged and soldered turret terminals. This makes for an easy assembly that will fit in a 1U chassis.

    The second tube socket is for a 12AU7 SRPP transformer output stage per the Gyraf G9 preamp design but haven't needed it at this point due to how I am using it (driving the effect return in an amp). The output is hot and needs to be padded down.

    I'll add the final schematic later but it is pretty close to the Keen schematic with the exception of the regulated filament supply and the MOSFET buffer.
  5. Steve Dallman

    Steve Dallman Supporting Member

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    May I recommend a Kevin O'Connor projects book, "Tonnes of Tone." http://www.londonpower.com/catalog/product_info.php?cPath=3&products_id=11

    This is a book of tube projects and includes two bass preamps. One is an Ampeg B15 type, the other is a London Power design, with sensitivity adjust, three band Fender type tone stack, (tuned for bass). I've built both and have them in a Bassman 100. The projects have instructions for layout, and power supplies. Other projects include a 3 control, outboard reverb, Piezo buffer, channel switching guitar preamp, some bench tools, and other projects.

    I've built other tube preamps. In the late 80's, I built a rack preamp, combining features of the Alembic, the Peavey TB Raxx (the active tone controls) and added lots of shifts and switching. I loved it, and still have it, although it developed some noise after sitting on the shelf for years. I used it for around 12 years.
  6. sanyaalwaysbass

    sanyaalwaysbass

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    оk, thanks codger and steve. What in your opinion is more easy to assemble?
    maybe anybody have H&K Bassforce L also?
  7. Passinwind

    Passinwind Charlie Escher Supporting Member

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    London Power sells a board kit, plus a separate power supply one, doesn't get much easier than that. ;)
  8. Steve Dallman

    Steve Dallman Supporting Member

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    Judging the two London Power preamps in my 6550 loaded Bassman 100, I prefer the two band Ampeg/baxandall type to the more complicated London Power/Fender-ish type. It has more low end punch and authority, despite the simpler design.
  9. Clark Dark

    Clark Dark

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    fender dual showman = alembic f2b

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