The mechanical drain would operate by limiting the movement of the bearing cup, and by damping.
The energy that once allowed that cup to move would not be able to move the mass attached to the bolt as far, limiting it's movement. now, the vibrations would travel down and back through the rod/bolt.
The mass at the end of the bolt, being made of a damp material, would absorb and not reflect the vibrations back to the bearing.... the last thing you want to do is add something that resonates the bearing!
At least that is how I understand it -- the "never land" is the heavy damping device on the bottom. What I don't understand is why bother with it? Why not just screw the bolt directly through the plinth?
The energy that once allowed that cup to move would not be able to move the mass attached to the bolt as far, limiting it's movement. now, the vibrations would travel down and back through the rod/bolt.
The mass at the end of the bolt, being made of a damp material, would absorb and not reflect the vibrations back to the bearing.... the last thing you want to do is add something that resonates the bearing!
At least that is how I understand it -- the "never land" is the heavy damping device on the bottom. What I don't understand is why bother with it? Why not just screw the bolt directly through the plinth?
Given the many different HFN test LP recordings you have captured, assuming the same arm+cartridge set up, the only differences are the various bearing noise contributions. It should be possible to process the frequency plots to identify the noise components which are identical. This would include motor noise, recorded rumble, tonearm and cartridge vibrations. What remains is bearing induced noise.
I have never truly "grokked" the concept of a bearing drain. It seems to me that vibration generated as the bearing thrust surface can travel in many directions. Any making it to the platter surface or tonearm mount are bad. So the bearing drain is supposed to encourage vibration to head off in a preferred direction leading to a sink from which it never re-appears. For simplicity, suppose the thrust bearing noise is equally disposed to travel in the upward and downward direction. Why would the upward traveling noise know of or even care about the downward traveling sound? Damping the vibration at source seems the most logical approach.
I agree with Cats Squirrel that damping is paramount. In my experience utilising a well damped material in the construction produces superior results to pure mass and stiffness.
maybe a little 'thought diagram' may help. Vibrations (in objects we are talking about) are the same as those to be found in a simple panel of material, held at its edges, and bounced up and down. Primarily, the vibrations in a panel are up and down, but as frequency increases a side to side vibration is produced.
The vibrations associated with rumble are too low in frequency to be dealt with by mass or damping. What is needed here is stiffness, if the rumble frequencies are below the fundamental frequency of the construction. Connecting the bearing to a massive piece of rubber is not going to be effective.
Leading vibrations away to be dealt with somewhere else always reminds me of sheep being hearded into a sheep pen, ready for slaughter. The problem is two fold. First of all, for the vibrations to be led away, they must be allowed to exist in the structure, secondly, the path along which they are led is two way, not one way. Vibrations are not led away to be slaughtered, the whole structure vibrates, and mass and damping must be applied.
The vibrations associated with rumble are too low in frequency to be dealt with by mass or damping. What is needed here is stiffness, if the rumble frequencies are below the fundamental frequency of the construction. Connecting the bearing to a massive piece of rubber is not going to be effective.
Leading vibrations away to be dealt with somewhere else always reminds me of sheep being hearded into a sheep pen, ready for slaughter. The problem is two fold. First of all, for the vibrations to be led away, they must be allowed to exist in the structure, secondly, the path along which they are led is two way, not one way. Vibrations are not led away to be slaughtered, the whole structure vibrates, and mass and damping must be applied.
I believe this would depend partly on how resonant the noise signature is. Dampening, if it can be tuned to this resonance in some manner, may be preferable in that instance, especially if there are other factors that mitigate against adding or conducting to a mass. Otherwise, the mass loading may be preferred, as long as it does not provide a conduction path for other vibration.
maybe these would also be suitable, I'm using them on my Lenco's
http://i21.photobucket.com/albums/b253/waaza/tn_P1015523-1.jpg
http://i21.photobucket.com/albums/b253/waaza/tn_P1015523-1.jpg
I'd like to view those photos but photobucket is going to make me sign-up before they'll let me view them. And in the meantime my Firefox add-on "No-Script" is letting me know just how much add-ware will be attached to me when I do. At least 1/2 dozen cookies waiting to track my every move.
Plus, photobucket links are temporary. They go away soon, but this discussion may last years. any chance you can upload the photos into diyaudio?
-Steve
Thanks.
links back to photobucket.
The photo tells me you're using a wood bearing housing. And a heavy rod/rail clamp to: a) dampen the housing.... and/or b) to anchor it.
That's interesting. I couldn't find which wood is being used in the brg housing.
-Steve
no wood in the bearing housing, woodn't work, anyway, you need stiffness for such low frequencies, not damping. The bearing housing is brass, or at least a copper alloy!
yes, I'll post them here when I get time. I didn't want the pic posted as is, as the aspect ratio is incorrect on here! Please delete or re-size/shape. (It is copyrighted).
yes, I'll post them here when I get time. I didn't want the pic posted as is, as the aspect ratio is incorrect on here! Please delete or re-size/shape. (It is copyrighted).
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Hi Cats Squirrel. I don't understand the popular current interest in the Lenco L75 as a worthy restoration project unless it is just for the challenge and their ready availability. The design has a serious flaw. My interest in turntables goes back to the late '60's in the UK where the choices were, Garrard, Lenco or Thorens. (this was the era pre Ariston, Linn, Roksan etc). I chose Garrard 401 at the time mainly because I wanted to experiment with different tonearms. The Lenco alternative L99 has the same drive system as the L75. During a comparative test in Hi Fi Sound magazine, it was found that the Lenco drive system produced a large amount of vertical rumble. This was principally due to the horizontally mounted motor with vertical idler running on the underside of the platter. In conjunction with the tapered motor shaft, this was Lenco's way of allowing simple speed adjustment with the fixed speed induction motor used. As a result, motor vibration due to bearing shaft/sleeve tolerances, are directly coupled to the vertical motion of the platter. This construction was carried over from earlier Lenco turntables used during the pre-stereo era. Of course mono pickups only respond to horizontal groove modulation and completely ignore any vertical modulation. Vertical modulation is out of phase and out of phase noise has the potential to compromise the stereo image. It might be confused with an airy quality to images but it is an artefact.
brianco, just finished reading the whole epistle. Can't say that I found any objective evidence about why the Lenco is potentially superior to all others. However the writer admits he is not a DIY'er or knowledgeable in physics or engineering. What we have is a users testimonial.
I have described previously why the Lenco system has to address issues avoided by other idler drive systems. Since I don't know what the exact mods are, I can't comment on how, or if, they address my concerns. I suppose a perfectly balanced motor running in a sleeve bearing of zero play, together with a platter with a perfectly flat and true underside, mounted on a zero play main bearing, would not exhibit any vertical motion.
Anyway, I won't comment further so as to keep this thread on topic.
My apologies everyone, for the distraction.
not wanting to hijack this thread, but I thought Bon needed a reply.
There has been a lot of opinion expressed on the subject of the Lenco, and most of it must be just that, unfortunately. I speak with anywhere between five and eight Lenco's, from a low mass platter '69 to a top of the range G99, but mostly 75's and 78's, and designs for uberLenco's.
My interest in them goes back to the mid 60's, when the school I was attending had a G99, Leak amplification and tuner, and Ferrograph (Wearite) tape machine. As I studied music, I was very acquainted with this system. Although my first turntable was a Garrard, I soon 'progressed' to a Thorens/SME and that remained for some time, 'til after the kids grew up and flew. I still coveted the Lenco sound (or lack of it!) and eventually purchased a GL75, then another, then a G99, and so on.
I must add I am a musician as well as a scientist (now retired) but continue to do research for the 'perfect plinth' material.
Your points are well presented, and I don't have any problems with what you have penned. But from a user's point of view, although a stock Lenco can have a measured amount of motor noise, mostly at 23Hz, in practice, this can be ameliorated quite easily but ensuring the top plate, and specifically the pan where the main bearing sits, does not move (essentially up and down). I have done this by using brackets and M8 bolts, securing these to an immovable base. Then rumble is not a problem. Using a Lenco as a donor rather than a classic model to be restored, one has a turntable with good (if not superb) engineering, which has lasted for 50 odd years with just a 'plastic' idler tyre and v-block bearings in the stock arm the only bits which succumb to the vagaries of time. Replace these with better ones, and one can have the basis of a turntable for not much more than beer money.
Put on a half decent arm (I use Regas) and half decent cartridges (I use Denon and Dynavectors) and give them really decent plinth systems, and I can live the rest of my life not wanting anything different. And what I like is that the sound I get is the same sound I hear when playing music myself, and I have played in everything from a youth symphony orchestra to folk, rock and jazz over a 59 year playing period, which continues.
To conclude, I believe the secret to a decent Lenco is a really decent plinth, which ameliorates against the stock Lenco's failings, but once done, I wouldn't change it for any turntable within my price range, including Linns and DD, (OK, maybe an SP10 with decent plinth) he said, trying to get back OT.
There has been a lot of opinion expressed on the subject of the Lenco, and most of it must be just that, unfortunately. I speak with anywhere between five and eight Lenco's, from a low mass platter '69 to a top of the range G99, but mostly 75's and 78's, and designs for uberLenco's.
My interest in them goes back to the mid 60's, when the school I was attending had a G99, Leak amplification and tuner, and Ferrograph (Wearite) tape machine. As I studied music, I was very acquainted with this system. Although my first turntable was a Garrard, I soon 'progressed' to a Thorens/SME and that remained for some time, 'til after the kids grew up and flew. I still coveted the Lenco sound (or lack of it!) and eventually purchased a GL75, then another, then a G99, and so on.
I must add I am a musician as well as a scientist (now retired) but continue to do research for the 'perfect plinth' material.
Your points are well presented, and I don't have any problems with what you have penned. But from a user's point of view, although a stock Lenco can have a measured amount of motor noise, mostly at 23Hz, in practice, this can be ameliorated quite easily but ensuring the top plate, and specifically the pan where the main bearing sits, does not move (essentially up and down). I have done this by using brackets and M8 bolts, securing these to an immovable base. Then rumble is not a problem. Using a Lenco as a donor rather than a classic model to be restored, one has a turntable with good (if not superb) engineering, which has lasted for 50 odd years with just a 'plastic' idler tyre and v-block bearings in the stock arm the only bits which succumb to the vagaries of time. Replace these with better ones, and one can have the basis of a turntable for not much more than beer money.
Put on a half decent arm (I use Regas) and half decent cartridges (I use Denon and Dynavectors) and give them really decent plinth systems, and I can live the rest of my life not wanting anything different. And what I like is that the sound I get is the same sound I hear when playing music myself, and I have played in everything from a youth symphony orchestra to folk, rock and jazz over a 59 year playing period, which continues.
To conclude, I believe the secret to a decent Lenco is a really decent plinth, which ameliorates against the stock Lenco's failings, but once done, I wouldn't change it for any turntable within my price range, including Linns and DD, (OK, maybe an SP10 with decent plinth) he said, trying to get back OT.
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