Layered plinth for SP-10

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jlsem

jlsem

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Joined 2003
Thanks! The salient feature of that plinth is the grey cast iron block which is coupled by a brass rod to the bottom bearing of the motor and acts as vibration sink. The result was an amazingly quiet turntable - actually more quiet and with blacker backgrounds than the Walker Proscineum. Not at all what we expected.

John
 
jlsem

jlsem

Member
Joined 2003
Any electric motor produces some noise, and a direct drive turntable motor is coupled directly to the platter and is not isolated from the rest of the 'table. The moving coil cartridges used have outputs on the order of 200-600 microvolts, so noise is obviously an issue. The grey cast iron block has a very high specific damping factor (highest among commonly available materials) and the brass rod makes a convenient transfer path for noise and vibration to the iron block, where they magically disappear. This base is admittingly a brute-force solution to the problem, but it worked very well.

John
 
Cobra2

Cobra2

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jlsem said:
Any electric motor produces some noise, and a direct drive turntable motor is coupled directly to the platter and is not isolated from the rest of the 'table. The moving coil cartridges used have outputs on the order of 200-600 microvolts, so noise is obviously an issue. The grey cast iron block has a very high specific damping factor (highest among commonly available materials) and the brass rod makes a convenient transfer path for noise and vibration to the iron block, where they magically disappear. This base is admittingly a brute-force solution to the problem, but it worked very well.

John
Click to expand...

What noise? What problem?
"What HiFi" + other reviewers did measurements of niose/rumble++, and found it better than most high-end belt-drives (of it's time)...

Arne K
 
W

woodturner-fran

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Joined 2006
Exactly how did you couple the brass rod to the motor/spindle?

I had an idea for something similar for a lenco. Fix a spring metal bracket to the motor and then hang a weight off that to one side - like a tunable vibration damper that you sometimes see on larger machines. It sets up a vibration thats exactly the opposite of whatever is feeding into it and hence cancelling it out. The energy is dissipated as kinetic.

Fran
 
EC8010

EC8010

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Joined 2003
I've done a similar trick on my Garrard 301. I clamp the bottom of the platter bearing firmly to the underside of the (solid) plinth. It made a big improvement to the tightness of the bass. When I saw that the SP10 had only a rubber cover to prevent a similar trick being applied to their bearing I immediately wondered if their designers weren't decades ahead of me.
 
jlsem

jlsem

Member
Joined 2003
Exactly how did you couple the brass rod to the motor/spindle?
Click to expand...

The rubber seal described by EC8010 was carefully cut away from the bottom bearing and the threaded brass rod seen in the pictures was run up through the iron block until it touched the bearing with firm pressure and then locked into place with an eccentric cam. The brass rod where it contacts the bearing is polished with a large radius.

What noise? What problem? "What HiFi"
Click to expand...

Unless "What HiFi" measured zero rumble and noise from the SP-10 I'm inclined to believe this plinth represents an improvement. Remember that we were comparing it very favorably to the Walker Proscineum which is a highly regarded TT at this time.

As a side note, installing this set-up on an isolation platform killed every gain made by the plinth alone.

John

P.S. There appears to be some skepticism among Norwegians.:)
 
jlsem

jlsem

Member
Joined 2003
I had an idea for something similar for a lenco. Fix a spring metal bracket to the motor and then hang a weight off that to one side - like a tunable vibration damper that you sometimes see on larger machines. It sets up a vibration thats exactly the opposite of whatever is feeding into it and hence cancelling it out. The energy is dissipated as kinetic.
Click to expand...

That method would of course be limited to a single vibrational frequency whereas the iron block used here takes advantage of the internal vibration damping property of cast iron, which is exceptional and covers a wide frequency spectrum. I don't have any calculated or experimental data to share since this was mostly a casual experiment using a brute force method. I am sure that such a system could be optimized.

John
 
Cobra2

Cobra2

Member
Joined 2002
Paid Member
jlsem said:

--
Unless "What HiFi" measured zero rumble and noise from the SP-10 I'm inclined to believe this plinth represents an improvement. Remember that we were comparing it very favorably to the Walker Proscineum which is a highly regarded TT at this time.

As a side note, installing this set-up on an isolation platform killed every gain made by the plinth alone.

John

P.S. There appears to be some skepticism among Norwegians.:)
Click to expand...

Not skeptic, the work looks beautiful! (maybe a little envious)
(Beeing a DD fanatic myself)

I remember a line from test; below measurable limits, test only showed surface noice from test-disc...

Arne K
 

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