Simple Vacuum Tube Preamp Results in a Beautiful Build

We have no intention of wading into the vacuum tube versus silicon debates audiophiles seem to thrive on. But we know a quality build when we see it, and this gorgeous tube preamp certainly looks like it sounds good.

The amp is an attempt by builder [Timothy Cose] to give a little something back to the online community of  vacuum tube aficionados that guided him in his journey into the world of electrons under glass. Dubbed a “Muchedumbre” – Spanish for “crowd” or “mob”; we admit we don’t get the reference – the circuit is intended as a zero-gain preamp for matching impedance between line level sources and power amplifiers. Consisting of a single 12AU7 in a cathode-follower design and an EZ81 for rectification, where the amp really shines is in build quality. The aluminum and wood chassis looks great, and the point-to-point wiring is simple and neat. We especially appreciate the neatly bent component leads and the well-dressed connections on the terminal strips and octal sockets. There’s a nice photo gallery below with shots of the build.

As much as we appreciate the miracles that can be accomplished with silicon, there’s still magic aplenty with vacuum tubes. For more thermionic goodness, check out these minimalist homebrew vacuum tubes or these artisanal vacuum tubes.

32 thoughts on “Simple Vacuum Tube Preamp Results in a Beautiful Build

      1. Help me here, I was under the impression that on high Zout sources there was a specific follower required in any case, i.e. turntable pickup, microphone pickup, or guitar pickup. Likewise is there any hifi gear out there that is an amplifier with a high Zin? Given the potential for noise pickup that sounds like a design to avoid at all costs. I just don’t see the point in this.

        1. In the case of phonograph pre-amps, in addition to impedance matching, there’s an equalization curve that’s required as well (the RIAA actually had a job before Napster came along).

  1. Not knowing Spanish or even how to pronounce Spanish words, I read “Muchedumbre” as “much dumber”. Obviously, this beautiful amplifier is anything but that, and no offense was intended in any way.

    Bravo, well done. I would love to have the skills to do projects like this. Please consider my jealousy a compliment. :D

    1. Great build. Looks very professional! I love the component lead formations.

      Can I ask, were you unable to find a break-before-make input selector? The make-before-break switch you have will short two inputs as you switch from one to the next but that shouldn’t be a problem with the hi-z outputs (into pre-amp) it’s designed for.

    1. Sure, it’s called push pull. Extremely low THD possible, high damping factor, and odd order harmonics over even order. In most cases, when played below clipping, a transistor, opamp, and tube amplifier are all going to sound the same. It’s once you get into overload behavior that they start to differ.

  2. OK it’s a buffer-driver. It’s so old school, I wouldn’t want to push such construction on the younger ages. The can cap is a historical artifact that requires extreme mounting unless you happen to have a bench rack full of Greenlee punches from the older half of the 1900’s. Even the tube rectifier is unnecessary.
    A phono preamp is a good next project. There lots of turntables and DJ consoles but no phono preamps in common amps nowadays.
    I just stuffed a salvaged transistor preamp from a 70’s melted down rig into the base of a sweet linear tracking Technics I found at the curb a block away. It’s funny how the turntable had a square foot of printed circuits, two micros, and servos. But 4 TX’s more for when the next receiver don’t have a phono input was too much. I wouldn’t want tubes in the base of the turntable.

    1. Actually the can cap here is a motor run that I pulled from a (modern) dehumidifier. Judicious use of bimetal hole saws is all that’s needed for mounting:) Tube rectifier is definitely for show (and delayed B+ delivery, debatable advantage).

      Sounds like you have a cool phono project. That’s something I’ll tackle eventually, but the RIAA math is pretty involved so I didn’t want to make it the first “tubes for beginners” project.

  3. I totally don’t see what’s so nice about the look of this, sure the wood is a starting point with potential, but that ugly metal plate with the poorly slammed down connectors and tube and ugly knobs look unimpressive to me. Looks like something from the 70\s, maybe from a soviet satellite state.
    I think Dan is just dazzled by the photography/lighting

    But tastes differ. And there is no accounting for it I’m told.

  4. I was delighted to see this interesting work, until I saw so many swear words. We would do a review of this article in Filling the Vacuum, the new magazine for the Museum, or even ask Mr. Cose and Hackaday permission to re-publish this, but cannot due to the many swear words. You do not have to use swear words to get your message across.

    Invitation: Mr. Cose, if you want to see your work highlighted by the only formal vacuum tube museum in the world, we will work with you.

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