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.
“looks like it sounds good.”
Now *there’s* audiophile thinking for you.
And “zero-gain preamp”. Here’s a hint: Try putting a pot in a box.
missing the point
Pot in a box works just fine in some systems. This is for when it doesn’t due to impedance issues (high Zout on sources and/or low Zin on amps).
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.
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).
Consider a pot between a source and an amp as well as cable capacitance, output coupling caps, and any input capacitance at the amp. This has the potential to create high and low pass filters depending on the values used.
Perhaps they mean to say zero voltage gain, or unity gain – a buffer amp. The transistor equivalent would be an emitter follower.
The application is an active attenuator. He does mention the option of switching between active and passive, and obviously understands the issues.
We called it common collector – but same thing. In the article he refers to cathode-follower.
Gain isn’t the only function of a preamp. A zero-gain amp can act as a bridge between a high impedance input and a low impedance output.
Other than the fact that you got those backwards, what kind of hifi gear has those problems that this would solve?
Yes, backwards. Sorry. I wasn’t so much speaking of this particular preamp, merely what purpose a unity gain buffer serves generally.
“looks like it sounds good” — that is the funniest thing I have read in a long time.
Zero gain preamp? I missed that. Isn’t that a buffer (or maybe just a cable).
You are exactly right. ‘Preamp’ is a misnomer in this case in the sense of voltage amplification. This is just a current buffer to provide high Zin, low Zout, volume and source selection control.
It’s like a HDMI cable – it doesn’t have any gain but it gold plates the ones and zeros – you can tell by the price!
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
Thanks! Muchedumbre means crowd in spanish and with this design I was going for extremely simple for the masses who are curious about tubes but don’t know where to start. Kind of an inside joke that only I’m in on :)
Fascinating to read his write-up and I don’t understand a thing he’s saying. All I understand is chips whereas he has the Real Knowledge.
“Muchedumbre” cn be interpreted as a mass of things/people united in a single purpose
Thank you for the love, Dan! I have plenty more simple tube designs to come (headphone and speaker amps currently on the burner).
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.
Break before make can create pops when switching sources, so I went the make before break. And thanks for the compliment!
Nice!
So you can make an amp out of transistors that sounds like tubes fairly easily, but can you make a tube amp that sounds like transistors?
Sacrilege!
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.
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.
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.
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.
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.
Hi Charles,
Please email me through the site (email address at the bottom) so we can discuss. I promise not to swear at you :)
Ok, I am sending you an email.
And for anyone that’s reading, we’re not prudes at the Museum, just have to follow typical requirements of formal Museums.