In article , UnsteadyKen
wrote:
Don Pearce said...
Hold an LP up balanced on two fingers at opposite edges - you will see
how much it sags quite easily. Obviously it doesn't sag as much as
that with six suspension points, but it sags much more than enough to
generate a huge signal.
The Hydraulic was designed for the thick'n sturdy pre 73 oil crisis
discs which are a totally different animal to the later floppies.
My unreliable recollection is that many 'pre 73' LPs were far from flat, or
even very thick.
I got a couple of lp's last week, a Decca ffrr from 1965 and a bog
standard EMI Columbia from 1966 and neither droops on your finger tip
test,
Weird. Most of the pre 73 LPs I have are ones I bought when they first came
on sale! :-)
However, a sensing system like a stylus might be able to detect variations
from flat thay you can't see using your mark 1 eyeballs. So your "neither
droops" may simply tell us something about your eyes, not the LP. :-)
You could check by holding a straight-edge just above the LP, touching at
the suspension points. Then see if daylight floods though the gap. That way
you may be able to see a droop which your eyes would otherwise not notice.
That said, since most LP sensors are essentially velocity sensitive that
might help here given the low frequency of 6-point support at 100/3 rpm. I
guess it then depends on the suspension of the cantilever and the response,
etc, of the preamp. And with luck the unwanted ripple will be below the
arm/cart resonance, not spot-on that value!
on the contrary significant pressure has to be applied to deform
them.
....to the extent you find visible.
I have a vague feeling this topic did feature in a magazine set of
measurements a few decades ago. If I can find that sometime I'll let people
know.
Slainte,
Jim
--
Please use the address on the audiomisc page if you wish to email me.
Electronics
http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio
http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc
http://www.audiomisc.co.uk/index.html