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Old 15th May 2012, 12:10 AM   #5481
SY is offline SY  United States
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Vac, good point on source impedance.
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Old 15th May 2012, 01:02 AM   #5482
Pano is offline Pano  United States
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Good point, I'll measure the output current and voltage into 8 ohms. I don't think that's the problem, but it's certainly wise to check!
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Old 15th May 2012, 01:19 AM   #5483
SY is offline SY  United States
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And, sous entendu, vary the frequency!
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Old 15th May 2012, 01:27 AM   #5484
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Just thinking,

High output impedance would result in a higher than expected peak in the frequency response; a peaked Q at the resonance frequency.

Perhaps IM distortion?

DT
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Old 15th May 2012, 09:37 AM   #5485
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Re Turntables:

AR invented the subchassis design while Thorens invented direct drive in the '30s but never implemented it except very much later on on two or three models which were re-badged EMT tables.
Goldmund/Lenco invented belt drive but equally didn't implement it, sticking with idler wheels.
The Linn LP12 was a bolt-for-bolt copy of a Thorens deleted the year before Linn started selling theirs. Pretty much all Linn parts except the arm board were directly exchangeable with the deleted Thorens but unlike Linn they used better springs which allowed the use of the heavy Dynavector arm.
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Old 15th May 2012, 10:39 AM   #5486
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Lenco seems to have a bit of cult about it these days. The Lenco guys I know are adamant that tables like mine (VPI) or John's (Linn) are junk, incapable of properly reproducing music. Their setups do sound quite good, better than I would expect from a rim drive, but I haven't been able to do a side by side comparison, and I suspect that the objective flaws of a rim drive might become more evident in that kind of listening test. But who knows, maybe they're right and the rest of us are wrong.
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Old 15th May 2012, 11:16 AM   #5487
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Personally I never understood the obsession with idler wheels either.

If I could have any TT I'd go for a EMT 950 Widebody in BBC spec.
They are almost affordable now that they are 20-30 years old and they can be had for 2000+. When new they cost about as much as a comfortable London family home.
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Old 15th May 2012, 11:26 AM   #5488
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Default Perfect turntable

I was once asked to describe the perfect turntable concept . My answer was to buy a windmill or lighthouse as a starting point ( if only ..... ) . I calculated that a bobbin of fishing nylon wound around the typical 10 mm diameter centre bearing would need to be the height of a lighthouse as a gravity drive . It would have a quick rewind when changing LP sides . Even if impractical it is good to have a definitive answer to work from .

Apparently some 78 cutting lathes were done this way .


On a turntable I made I had to get a motor built . It was studded at Greenwich University and was recommended for patent ( it got they guy his degree ) . All I will say is it is an induction motor and has very low noise bearings and massive power compared with a Linn ( 28 times used at 7 times ) . It is run from a 150 watt power amplifier of 0.006% distrotion at 52 Hz ( only because that part was easy so why not do it well ) . The amplifier seldom using more that 50 W . I went on to use that amplifier for music so developed it to do both jobs .


Mostly all other aspects of turntable design have been perfected . Many versions exist of how to do it .

A Platine Verdier with lighthouse drive would be nearly perfect . A magnetic brake used to speed regulate and damp the system .

The Lenco's problem is the idler is almost under the stylus . On the rim is easier . Lenco's do sound good .

In amplifiers life is easy . Class A exists so no lighthouses required . Class B , C , D , G , H are other choices .

If asking my design was mechanical class B ( analogy ) .

Last edited by nigel pearson; 15th May 2012 at 11:34 AM.
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Old 15th May 2012, 11:49 AM   #5489
a.wayne is offline a.wayne  United States
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Quote:
Originally Posted by SY View Post
Lenco seems to have a bit of cult about it these days. The Lenco guys I know are adamant that tables like mine (VPI) or John's (Linn) are junk, incapable of properly reproducing music. Their setups do sound quite good, better than I would expect from a rim drive, but I haven't been able to do a side by side comparison, and I suspect that the objective flaws of a rim drive might become more evident in that kind of listening test. But who knows, maybe they're right and the rest of us are wrong.
My observation also .......
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Old 15th May 2012, 12:36 PM   #5490
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Default ARX . Good enough for any music lover .

One funny thing the designer of the AR turntables said is he wouldn't know how to get his turntable to image . He didn't have to because it did .

Simply put he is right about it isolating . A vertical bounce is important on an ARX . (We always call his turntable ARX , not sure if it is correct ) .

I think Ed Villchur underestimated the friction forces on the stylus . That's all

Frenchman Verdier hypothesized that if a bearing has drag and the force required to defeat drag is 10 times that of anything the stylus might cause , then the system should not have dynamic wow . Dynamic wow if it exists at all , that is ( like TID it is controversial ) . Perhaps ARX does have dynamic wow ? Linn and Thorens are clones as are practically all other turntables .

Forgive me Mr Verdier if I misquote you . That's what I understood all those years ago you said .

Verdier pointed out that drag and magnetic damping are not friction .

Garrard bearings have a big drag problem . It takes 15 minutes to come to speed . Maybe that's the secret ?

Technics has high frequency dynamic wow problems to my ears . Not enough pole pieces per revolution . It is not very good as a cutting lathe motor I would say if music has pace ( used as motor replacement by some ) . A Sculley cutting lathe makes an ideal turntable . I have to say it , the better turntables are built like cutting lathes . The Lenco is not bad if looked at from that point of view .

I only say about the Technics as some would say it to be perfect . It is in many ways . Denon direct drives are probably better as they run their stepper motors on AC and had the patent for that . Strange how paying royalties stops intelligent design . The Garrard 201 made before 1939 was virtually identical to a Technics SP 10 except having mechanical speed control . The 201 is fancied to be superior and was AC drive .
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