A Beautiful Turntable With A Heart Of Concrete

On the face of it, playing a vinyl record is a simple process. You simply mount it on a turntable rotating at the right speed, and insert a needle into the groove. A learning exercise for youngsters used to be a passable attempt at a record player on the kitchen table with a pencil, a large cork, a sharpened matchstick, and a piece of paper. It sounded awful, but it demonstrated well how the audio was recorded.

If you have ever looked into the operation of a more conventional turntable though you’ll know that a little more care and attention is needed. There are many factors which affect the quality of the sound, and you quickly become obsessive about tracking, and sources of the tiniest vibration. Someone who has followed this path is [Mjhara], who has made a very high quality turntable. There is an unusual choice in this project: the tonearm is part of the build rather than fitting a commercial item like most turntable projects.

balanced-with-shotThe platter is machined from a piece of rosewood, weighted and balanced with lead shot, and laminated between two sheets of brass. It sits on a bearing aided by a ring of opposing magnets, and is belt driven by a two-phase induction motor. The base of the turntable is cast as a single piece of concrete, the idea being that the extra weight will aid the damping of vibrations. The tonearm is machined from a piece of wood, and its pivot from brass. The tonearm bearing is a ballpoint pen, a surprising yet inspired choice .

Sometimes audiophiles take their quest for better sound to extremes, and justification for their expenditure can be very subjective. But [Mjhara] assures us that this turntable has an exceptionally good sound, and it is certainly a thing of beauty. Full details are in the Imgur gallery embedded below the break.

We’ve featured surprisingly few home made audiophile turntables here at Hackaday, probably because classic examples aren’t hard to come by. This layered plywood example is probably the most striking we’ve shown you.

Thanks [Itay Ramot] for the tip.

22 thoughts on “A Beautiful Turntable With A Heart Of Concrete

  1. An impassioned piece of work, clearly.

    They use a simple AC synchronous motor — the turntable speed is determined by the instantaneous frequency AC line, and can’t be adjusted. The grid is generally pretty stable (see, e.g. http://fnetpublic.utk.edu/gradientmap.html ), but not at all guaranteed to be fixed frequency over short periods. The frequency and phase of the grid is allowed to (and must) drift a bit to adjust to varying load and generator mixes. (though averaged over 24 hours it’s kept at the advertised frequency).

    So I wonder if you put in that kind of work on all the other pieces, why not put a nice crystal-controlled drive on there? I suppose you could retrofit a stable AC power supply on it. That would be a nice project.

    Personally, I’d also complain about the bubbles in the concrete, but maybe that was a deliberate design choice.

    1. I’d wager the Doppler shift from moving around in the room would be more significant than the flutter induced by mains frequency variation. Not curious enough to do the calculation though. Pretty build but the things audiophiles worry about still baffles me.

      1. That’s about right. Over short time scales (seconds) normal mains frequency variation is pretty small (a few hundred ppm), roughly the magnitude of Doppler shifts from just moving around. However, large changes (though still a fraction of a percent) are normal in the usual course of grid operations. Much larger excursions happen in the case of weather events or other anomalies. UK-centric discussion is here: http://www.mainsfrequency.com/frequ_info_en.htm and a neat real-time meter is here: http://www.mainsfrequency.com/index.htm Some neat animations of excursions on the USA grid are here: https://www.youtube.com/user/PowerITLabUTK/videos

        1. That is what the mass of the the turntable is for. It is a flywheel after all. When I was young I had a turntable that used a DC motor and an LED to help adjust the speed of the turntable. The turntable had three series of slots cut into the rim and an LED that acted as a strobe. You picked the strip for the speed and then adjusted the speed until the the slots stopped moving.
          My question is why would anyone use a turntable that cares about audio quality? It is going to have much more noise, every time you play the record the quality will go down and CDs produce much more accurate replay. I thought that the point of a record was all of the defects, if you are going to copy records that only exist as records over to digital then trying to get the best audio possible make sense.
          BTW anyone that says that records are more accurate than CDs because they are analog or that the sample size or sample rates are too low…. Science says no you are wrong.

          1. Because audiophiles still think records are better than CDs or other recorded media. Most don’t realize that the audio is seriously manipulated before it goes onto a record because of the limitations of the medium. That’s why a lot of early CDs sounded like crap, they just stuck the record master recording onto the CDs which made apparent the manipulations of the audio. Its kind of like old video games that took advantage of CRT TVs and NTSC to make the games look better. Looks good on a CRT but display it through an emulator and you see behind the curtain.

  2. Sigh.

    I see so many of these made with massive bases…then mounted on solid feet/supports. While the mass will decouple a little vibration you’re depending on the furniture it sits on to act as the spring in a spring-mass system, so it usually doesn’t help much if at all. The whole idea is to detune the system from the environmental vibration using “soft”, low natural frequency supports/feet/mount and massive turntable base so that the natural frequency of the system is extremely low and acoustic/mechanical vibration effects are minimized.

    You don’t have to blow the budget on this, either. Optical benches also have to be set up to minimize vibration, and you can even use a flat piece of granite sitting on a couple of small innertube donuts and get good damping out of it.

    1. My thoughts exactly… there’s more damping in the piece of wood it’s sitting on. If you put that on the basement floor, every large truck driving by would make the needle skip.

      Also, those lead shot are left loose??? Maraca for a turntable.

      1. Also, if you disconnected the drive, pulled it forward on the stand so that the feet were in contact with the metal, and set the needle on a disk with the amp powered, you can probably record your toilet flushing…. and possibly do it where it’s sitting, depending on how loud your plumbing is.

    2. Look closer… to my eye it looks like he’s using brass isolation spikes (the tip of each brass cone rests in a divot on a brass puck). In that style of support, the only contact is the very tip of the cones, so the surface area of actual contact is reduced to near zero. In my understanding of that approach, that degree of isolation prevents vibrations of any of the audible wavelengths from getting through to the isolated unit (in this case, the record player). Each brass spike foot is essentially a mechanical highpass filter, with the poles at higher than audible frequencies.

      I could be all wet on this one, but that’s my understanding. I wish his documentation had been more thorough, but I love the project itself and what went into it! The finished project is gorgeous!

      1. It’s not even remotely a high-pass filter. They are quite rigid and will happily pass vibrations between the device on top and what it’s sitting on. I have a set of spikes too and you can happily pick up someone tapping their foot on the floor next to the unit through them. What they do give you is a very stable surface free of any kind of rocking balanced on 3 points, so any vibration that does couple up doesn’t ring around.

    3. Since when did “high-end” audio stuff have to make sense?

      99% of it is utter bullshit, at least this one took some skill and looks kinda cool. Bet it sounds no better than any half decent off-the-shelf unit, but meh whatever makes you happy.

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