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Thread: Lenco #2, plinth comparisons, plans etc.

  1. #1
    Join Date: Mar 2015

    Location: Finland

    Posts: 237
    I'm Kai.

    Default Lenco #2, plinth comparisons, plans etc.

    Since I got my 2nd Lenco and my first stock plinth I decided to do some experiments. I know this would be far more fun with some pictures, but I'm lazy with the camera.

    One Lenco, two plinths. Big one is 60x40cm, 3 layers of 18mm acacia sandwiched between 18mm layers of Bamboo, so 5 layers in total. Mounting of the turntable with 4 bolts that go through the whole plinth construction. For footers this one has 3 hockey pucks which rest on cradles made of rubberbands & little glass cups. (Think ash-tray feet like I hear DJs of old used to do with SL-1200).

    Second plinth is the original one, but with some modifications. Springs were gotten rid of and replaced with small wooden blocks with some furniture rubber footers for a little bit of isolation from the bottom board. I also installed a cross-brace and damped the sides with acrylic mass. Both of these things helped a lot as far as knuckle test for plinth resonances go - it's not as dead obviously as a more substantial plinth, but it doesn't ring anymore and when rapped with knuckles produces a reassuring sounding little thud instead. I've seen several different variations of the stock plinth, this one seems a later production one which is made of chipboard with very thin veneer on top.

    I recorded a lead-in groove and analyzed the spectrum for rumble. For first test the top plate was mounted like stock, so the 4 rubber grommets on corners and two screws on the pan. Now these figures don't follow any standard obviously and as such don't hold any meaning compared to anything published anywhere else, but they are comparable (within +/- 2dB or so) between each other. So here they are:

    Big plinth
    50Hz -59.6dB
    100Hz -71.5dB
    150Hz -74.1dB

    Modified stock plinth
    50Hz -59.9dB
    100Hz -54.2dB (!!!)
    150Hz -75.6dB

    That 100Hz was clearly audible, not distracting while listening to music, but between tracks you could hear it, either very faintly or quite clearly depending on the volume Very disappointing result for the modified plinth in any case and removing the springs didn't seem to do much for the rumble even with the additional damping of the plinth. Sadly I didn't measure the TT in completely stock form, but using ears alone it was improvement, but a pretty slight one. I traced most of the rumble coming through the idler arm, so I damped it using electrical tape, rotated the rubber grommet 90 degrees just in case and in a different test (not directly comparable to this one, because platter wasn't installed and stylus rested in a resonating hollow plastic cap) that reduced the 100Hz rumble by 6dB and also spread the spectrum a bit. In the above test I doubt the difference would be as great, but probably a few dBs anyway. Next I altered the mounting and got rid of the rubber grommets at corners and the results were as follows:

    50Hz -58.2dB
    100Hz -64.3dB
    150Hz -75.3dB

    A whopping 10dB reduction @ 100Hz, which means with the rubber grommets in place (and idler arm undamped), the rumble @ 100Hz was about 3 times as loud. While the modified plinth still falls short of the big one (with better footers) the deck sounds splendid now and is practically silent.

    I've heard some people be happy with the stock arrangement with the springs and all, but at least this one didn't sound good at all like that, plus it rumbled. The worst part seemed to be the rubber grommets though. I might try it with the springs yet just for kicks, though the upper plinth that rests on the springs is probably 2-3 kilos heavier now. Based on this, if you want a good sounding Lenco with minimum hassle, just getting rid of the springs and rubber grommets might get you quite far already with the stock plinth. However I noticed at high volumes it was prone to feedback, which doesn't happen at any volume with the big plinth and rubberband cradle footings. I attached two of self-adhesive rubber foam footers into each 4 stock feet on the bottom board and that cured it. I was just curious about what's the minimum effort and money to spend on a Lenco to get good results, and it's also further learning towards the eventual proper plinth.

    I plan to try out what more solid mounting does to it - now the top plate is fastened to the plinth with only two puny woodscrews through the pan. I should've installed some additional blocks into the insides to faciliate bolting the deck down, but can't really do that easily anymore. Only easy option is to drill holes into the bottom board and bolt through it, but that means my little isolating rubbers in place of springs would become pretty much meaningless, but seeing they didn't work all that well to begin with, maybe that's not a bad thing.

    Now, in stock form I don't think two 50 year old Lencos will perform exactly the same, there have been little variety in production and also the springs and rubber grommets, idler arm rubber grommet etc. have aged differently depending on the life of the deck. If after service the performance is not up to par in stock form, the above modifications cost me about 5 euros in the form of two 310ml tubes of the acrylic mass, and two pieces of scrap wood for the braces. These mods are still more or less reversable if wanting to go back to stock.

    I don't know what maintenance (if any) has been done to this new-to-me Lenco, but since it came with a properly mounted Sumiko MMT and no extraneous noise is present I'm assuming at least the main bearing has been cleaned and oiled ... haven't actually opened it up yet, but I can tell it's not running dry. It came with an original 5-hole idler wheel. Just for kicks the results for my first Lenco, for which I've done motor and bearing maintenance and replaced the idler wheel with a Norbert one:

    50Hz: -61.4dB
    100Hz: -75.3dB
    150Hz: -75.1dB

    So a little quiter all-in-all, could be many things, probably mostly the idler.

    What can be taken away from all this is resonances, the paths they take, damping, coupling/decoupling in mounting and the actual construction of the plinth do matter, not only in perceived sound qualities but in very easily measurable noise levels. Not exactly breaking any new ground here, but I wanted to have some actual numbers for myself to have some reference which is not dependent on my ears and how I happen to feel on a given day.

    Btw. my hat off to people who make detailed threads with pics and all for tweaks and modifications they are doing, takes some real effort! I probably spent more time writing down and editing this post than I spent on swapping the Lenco between plinths, recording samples and doing the measurements ...

    Next up some thoughts for a new plinth and things I'd like to experiment with.

  2. #2
    Join Date: Jan 2013

    Location: Birmingham

    Posts: 6,772
    I'm James.

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    Interesting Kai. So would you say just removing the rubber grommets you found an improvement or does it make the plinth more likely to pick up airborne vibration?
    Main system : VPI Scout 1.1 / JMW 9T / 2M Black / Croft 25R+ / Croft 7 / Heco Celan GT 702

    Second System : Goldring Lenco GL75 / AT95EX / Pioneer SX590 / Spendor SP2

  3. #3
    Join Date: Mar 2015

    Location: Finland

    Posts: 237
    I'm Kai.

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    Quote Originally Posted by Jimbo View Post
    Interesting Kai. So would you say just removing the rubber grommets you found an improvement or does it make the plinth more likely to pick up airborne vibration?
    I think airborne vibration would be a lesser problem than having the top plate resonate with whatever gets through from the motor and idler arm. Removing the grommets was an improvement for both subjective sound quality and measured rumble. Without the grommets the turntable become more prone to acoustic feedback, but this gets into tricky territory because each room is so different and there's so many factors at play from speakers, to placement of turntable, what it is resting on, what kind of flooring you have etc. In my case the TT sits on a (quite resonant) wall shelf because I have very springy wooden floors, and adding some different footers solved the problem. Actually I plan to try how the rubber grommets would work as feet for the plinth, I think they might be ok for that.

    I don't think the Lenco engineers were stupid, just that the way the Lenco is stock is a compromise to allow your average Joe to just place the turntable on whatever and get adequate sound without too much sensitivity to foot-falls, feedback etc. - it's same with all the other consumer oriented TTs of the era really, Duals have the top plate sitting on springs, but like the Lenco IMO they are far better off without the springs.

  4. #4
    Join Date: Nov 2008

    Location: North Down /Northern Ireland/ UK

    Posts: 19,484
    I'm Neil.

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    Reduced in value, not worthless, with no photos.
    Regards Neil

  5. #5
    Join Date: Nov 2010

    Location: Yorkshire

    Posts: 9,302
    I'm Andrew.

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    Excellent post, looking forward into incorperating some of your experiments, so its a from me!
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  6. #6
    Join Date: Mar 2015

    Location: Finland

    Posts: 237
    I'm Kai.

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    Hi Neil, yeah I know I'll try to take some when I have the deck in pieces the next time, which should be pretty soon. I should have plenty of time in the coming week or two to fettle with the Lencos - one thing I want to try is a skeletal "two-story" plinth. I was thinking upper bamboo board with cutout for the top plate, then 4 sand filled coke cans or similar between the upper and lower board. If I bolted the whole thing together from the top plate, the lower board could also support the bearing from the bottom. If all goes well, it should have enough mass to deal with vibration, yet provide good damping higher up the frequency range than a typical heavy mass affair. If I understand anything about how damping, vibrations and resonances in a TT plinth work - it's very much possible I don't, but I could always reuse the materials if it doesn't turn out well

    On the tonearm front, the Sumiko MMT the new Lenco came with was a pleasant surprise, I think it's a very good sounding arm. My only gripe with it is there seems to be some harshness or 'grain' in the upper frequencies and somehow it sounds more like "hifi" overall compared to the Fidelity Research FR-54 on the other Lenco. It might be actually doing some things better than the FR (which really was quite affordable arm in it's day), but there's just some natural and musical rightness to the way that FR-54 behaves that's hard to put into words.

  7. #7
    Join Date: Mar 2015

    Location: Finland

    Posts: 237
    I'm Kai.

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    Ok, here's a photo of the original plinth with the mods. The insides are not exactly pretty, but that's not the point The acrylic mass doesn't dry completely hard, it's retains a little bit of elasticity. I stuck some leftover pieces of rubber-cork in there as well. The very thin veneer of the plinth was in quite rough shape with many nicks, so I smoothed them out with some filler paste and painted the whole thing black.
    lenco-mods.jpg


    Here's a pic of quick test run resting the top plate on 3 cans of well-known soft drink. Two of the cans were filled with sand and one was unopened, to balance out the seismic micro-vibrations and retain good spatial relationship between the stylus / groovewall interface and 3-dimensional rotational forces. Seriously though, I just wanted to try what no plinth does to the sound. The amount of 50Hz rumble doesn't seem to change much with this deck no matter how it is mounted, while 100Hz is very sensitive and shows changes instantly. 100Hz rumble is also a lot more intrusive if there's any coming through. Resting on the coke cans the rumble @ 100Hz was up about 3dB compared to the modified plinth, but still -7dB compared to the same plinth with the rubber grommets in place. It sounded good overall and running the deck this way gives a little bit of a taste of what the deck is capable of, which the original plinth with springs & grommets and all really doesn't IMO (at least not the one I got).
    lenco-cola.jpg

  8. #8
    Join Date: Mar 2015

    Location: Finland

    Posts: 237
    I'm Kai.

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    A little trip to Ikea and came away with 2 Lämplig bamboo cutting boards. Wasn't really any cheaper than getting similar 18mm boards cut to size, but they were there ready waiting for me and couldn't resist the call of bamboo.

    This is one idea I'm gonna try out, thought the coke cans are a bit too tall to look pleasing aesthetically, but good enough for testing the concept and playing around.
    ikea1.jpg


    This would be another way, and that center cavity could be filled with all kinds of "stuff" like silicone putty, acrylic mass, peanuts, small rocks and pine cones or whatever, and I like the sleek look. Would have to cut material away from both boards though. Without any cutouts I think the two pieces weigh a little over 6kg total. But if wanting more mass, I could always do the filling thing or get two more of the boards and do a 2nd arrangement like that, either a double decker skeletal thing or just add them to the bottom of the existing plinth. Or add a bottom and top layer of some thin birch ply. Thin because I'd like to cut it so the top plate sits flush with the plinth.
    ikea2.jpg

    Let's see how this goes, might have something put together tomorrow if the weather permits.

  9. #9
    Join Date: Mar 2015

    Location: Finland

    Posts: 237
    I'm Kai.

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    I ditched the sand filled coke can idea for now, initial results were somewhat promising but it was too f' ugly. I opted for a good bit shorter nuts and bolts instead, it's still kinda ugly but this setup now is really tweakable for trying out different things.

    How it works the bottom board has nuts glued in the corners and 60mm M10 bolts screwed in, which support the upper board. If you look at the photo you can also see some bolts under the pan - these are not fastened anywhere, but simply have nuts extended so that they provide some upward pressure from the bottom board up to the pan. For now they have some rubber cushions at the top, whether that is a good or bad idea will be seen, but initially it seems better than without the cushions. I ran out of hours, so proper test will have to wait till tomorrow because I had only one long enough M4 threaded rod - the idea is the whole thing is kept together by 4 such rods, mounted into the threaded inserts in the top plate and running through both boards, but currently it's only one and the other 3 short ones just fasten the top plate to the upper board. I also added one wood screw through the hole which originally had the L75 arm rest. It might be even with all 4 threads going through both boards the structure might not be solid enough, but I'll find out tomorrow. I hope it's good enough to see if this kind of build is something I want to commit to, I could still easily revert to a more traditional plinth and I have a feeling a sleek plinth with the center cavity (see previous post pic #2 to see what I'm talking about) filled with some appropriate goo for damping might sound pretty nice.

    I did run some little tests with the setup as it is and it could hold promise, but will have to run it everything properly bolted together. Should be wiser tomorrow.

    boltlenco.jpg

  10. #10
    Join Date: Mar 2015

    Location: Finland

    Posts: 237
    I'm Kai.

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    Now the whole thing is stuck together with the 4 threaded rods, M4 rod is quite flexible so it's not a super rigid assembly, though adding tension upward tension from the large bolts helps with that.

    Doing some low volume listening and a couple measurements while at it, fiddling with the pan support bolts. There's a definite if somewhat subtle (at least at these volumes I'm currently using) change with / without the bolts. Not sure which I prefer, with added pan support the sound seems to tighten up somewhat, but I also sense there might be a certain harshness somewhere in the midrange perhaps - definitely need more listening. Without the pan supports the sound loosens up some, overall the sound is a bit more relaxed, but not in a bad or imprecise way - more like there's just a better natural and flowing quality to it. But for now I'd be inclined to say the pan supports add "fake precision" ie. colorations in the mid-range (and upper bass perhaps) which initially might make it sound more "tight" but doesn't hold water in longer listening. But that's my initial impression... I need more listening, but am also feeling impatient and might move forward before I get a chance to do that

    I tried the pan supports with and without rubber cushions between the bolt and top plate and there wasn't much difference to be honest. Measuring it seems without pan support is better (at least the way I'm doing it atm). This is interesting, because screwing / bolting down the pan seems to be the "standard" among tweakers, but so far my ears tell me to let the pan do it's thing without additional support. To be fair the way I'm doing it now is not exactly same as bolting it down. Though I recall talking in person to one Lenco enthusiast who has done many builds, and his opinion was supporting the pan kills the sound. We'll see.

    I'm inclined to probably ditch this skeletal thing altogether, glue the two boards together and fill the insides with something viscoelastic, leaning towards the acrylic mass I have used in many other TTs for damping because I'm familiar with it and it seems to do a pretty good job. Unless extended listening convinces me otherwise, but this far nothing suggest this arrangement is better than the plinth of my #1 Lenco which is my reference for now. That arrangement would still make it possible to experiment between bolting/screwing down the pan and not.

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