SME 3009 11 mproved. Exploded drawings ?

[sparkymike]

Are there any exploded drawings of the SME 3009 11 improved?
Mike.

[sparkymike]

I found them on vinyl engine site. SME service manual and SME parts list.
All very useful.
Anyone know the size of the base grommets for the four plinth small wood screws for the same arm?
Mike.

[Craig Sawyers]

Knowing SME's philosophy of making absolutely everything in-house (other than the tapered arm tube, which comes from Chicago White Metal), those grommets are probably unique.

Craig

[stevehertz]

I'm not so sure Craig. I seem to recall that mine were just like the ones I used to get for free from my place of work. I couldn't categorically say that they weren't a unique size, but I doubt if using a grommet of 'a suitable size' would make a real difference. In other words, if it slots into the mounting foot's aperture and seems right, it's ok. The biggest mistake is over or under tightening.

[Craig Sawyers]

I have to say I'm not certain what the purpose of the grommets are. SME also supplied "hard washers" to replace the O rings. These were whatever size fits in the recess the grommet goes in and allows the arm to be tightened into solid contact with the arm board.

Later arms like the IV and V attached to the arm board without any resilient element.

Craig

Craig

[Ted Kendall]

I think the original intention was that a little vertical compliance at the arm pillar would effect some kind of rumble filtering, bearing in mind that idler drive was the norm when the SME was introduced. The idea was current at the time - Walton's Decca ARI arm used a similar system.

[Craig Sawyers]

If you do the sum, the resonance frequency of a compliant system only depends on the compression. That is true of any spring-mass system, where the resonance only depends on how much the spring stretches.

Since the compression is tiny, the resonance cut off is in the kHz range, and does nothing for rumble frequencies.

Craig

[Craig Sawyers]

OK - just had to remind me of this by working it out again. If you have a static stretch of a spring deltaL, omega is simply root (g/deltaL) So if the weight of the SME arm compresses the grommets by 0.1mm (a reasonable assumption), omega is root (9.81/10^-4) = 300 radians per second, or about 50Hz.

That is actually lower than I thought.

But the thing is that it is a low pass filter. So everything below 50Hz gets through and then it cuts at 12dB per octave as a second order filter. So rumble frequencies get through unattenuated. In fact the Q will be pretty low because of the damping of the grommet rubber.

I guess that is why SME abandoned the rubber grommets.

Craig

PS the effect of the equation is interesting - to get a resonance frequency of 1Hz means you have to have a static stretch when you attach the mass of 27cm.

[ajgriff]

Reckon Steve's right about simply using grommets that fit. I have a box of assorted grommets and the closest match in terms of size is indistinguishable from the original SME item.

The grommets were always a mystery to me as I thought that a rigid (ie, non-compliant) relationship between stylus and groove was important in terms of trying to replicate the action of the original cutter. In any event the SME grommet issue has been the subject of debate in audio circles for decades.

My advice to Mike would be to experiment. When I did this many moons ago I decided that grommetless was the way to go although admittedly it was a subjective judgement and my ears were a lot younger then. Of the two experimental decks one was idler driven and the other was belt drive. Both were mounted in substantial plinths and the cartridge was a Shure M55E if memory serves.

One thing to watch out for is that removing the grommets affects the vertical tracking angle (VTA) and this needs to be readjusted in order to make a valid comparison. As a slight aside, I found a simple thin card gasket beneficial in terms of bonding the baseplate to the motor board in grommetless mode.

Alan

[sparkymike]

Going off on a slight tangent, but still same arm, what is the purpose of the side adjustable weight.? Is this to do with weight/bias of the particular cartridge that is fitted to the arm. ?
Mike.

[Beobloke]

Originally Posted by sparkymike

Going off on a slight tangent, but still same arm, what is the purpose of the side adjustable weight.? Is this to do with weight/bias of the particular cartridge that is fitted to the arm. ?
Mike.

Moving it backwards and forwards along the rider weight rod sets the tracking downforce.

Moving the whole rider weight left to right laterally balances the arm depending on the weight of the cartridge fitted.

[sparkymike]

This must be to counterbalance the "S" offset curve of the arm I assume ?
Mike.

[ajgriff]

Yes and without the lateral balance adjustment the arm would tend to twist inwards thus lifting the outermost of the knife edge bearings from its groove.

Alan