A $300-$400 turntable tweak

I most frequently use a Marantz TT-1000 direct-drive turntable with a bonded-on graphite mat and a Graham Phantom II tonearm.

In the past I tried a variety of clamps of varying construction, material and weight on this turntable, and have found that heavier isn't always better. In fact, usually it wasn't.

Today I am using a clamp that has adjustable clamping force. The clamp itself is fairly light and simply drops onto the record label (like a gravity clamp). Internally, however, there is a neodymium magnet which is positioned above the turntable spindle (which is normally steel). The magnet is mounted on a fine-pitch screw mechanism which allows the distance between the magnet and the turntable spindle to be adjusted in very fine increments. If the distance between magnet and spindle increases, the clamping force decreases, and if the distance decreases, the clamping force increases.

Since the screw mechanism that adjusts the magnet has nothing that binds directly to the turntable spindle, the clamping force doesn't need to be reset every time the clamp is removed from the record (unlike a normal threaded clamp).

With this clamp I have been able to experiment with clamping force and sound quality. I find that I prefer the sound when the total clamping force isn't so high. I'd guess that the clamp weighs about 200~250 grams, and I usually have the magnet set so that it adds another 250 grams or so (estimated). The clamp can be set for much higher clamping force that what I typically have it at, but I find that the sound quality starts becoming compressed both in dynamics and timbre when the clamping force is too high. Maybe someone who can't stomach any trace of edginess at all in their sound would like this. Me, I find it the sound less emotionally involving, less intellectually interesting, and far too polite.

Sonically, the difference can be pretty big. Enough to make you come to different conclusions about the same piece of equipment (or LP pressing).

I also find that some LPs benefit from less clamping force than others - it seems to vary according to label and production era.

OTOH, I have not found that leaving the clamp off completely is better - a certain amount of clamping force, but in moderation, is what I find to work best (in my audio system).

If any of you have a clamp which allows fine adjustments to the clamping force, I encourage you to experiment and experience for yourself how the sound changes.

cheers, jonathan carr

Hi Henry:

Yes, I've tried various peripheral rim clamps and vacuum clamps (both add-ons and integral). In this case I found that I usually preferred the sound without peripheral or vacuum clamps. Even on my Micro-Seiki SZ-1S, which has a 28kg machined stainless-steel platter and integral vacuum clamp as well as air bearings for the platter and motor/flywheel, I ended up keeping the air bearings engaged and defeating the vacuum clamp (although I did prefer to insert a mat between LP and platter surface).

However, this is probably due to the fact that I own very few warped LPs. If I had more warped discs, I suspect that I would feel a greater fondness for peripheral or vacuum clamps.

In fairness, none of the peripheral or vacuum clamps that I have used offered such fine-grained control over the clamping force as my adjustable magnetic center clamp. I suppose that I could design such a peripheral clamp, but I have far too much on my design plate already!

cheers, jonathan

Raul:

I'm not sure that I completely understand you, but my observations suggest that peripheral, vacuum and center clamps can all be positive, as long as the clamping force that they impart can be adjusted to the needs of the individual situation. And in general my experience has been that too little is preferable to too much.

I will add that center clamps help to terminate the noise and vibration caused by the spindle bearing - these devices address more than just the LP.

Also, the material and construction of the clamp are definitely audible.

BTW, was this question a prelude to some Raul-designed clamps which will again show how the AHEE has led audiophiles astray? (^0^)

cheers, jonathan

Dover:

My TT-1000 by itself has a little less mass in the platter system than stock (I needed to shave down the top of the platter to get a flat surface for the graphite mat to bond onto). Add the center clamp, and the net weight ends up pretty close to stock - not enough to warrant readjusting the servo gain.

Still, your point is valid - the servo control of a DD is typically set up with a certain load range in mind, and if the user alters the load significantly from what the manufacturer originally intended, it is a very good idea to reassess the servo gain.

I will add that many DD turntables were designed with a specific lubricant in mind. Some turntables were even designed so that the spindle functions like a self-pressurizing, self-centering Archimedes pump (similar to many PC cooling fans today), and if you change the lube, you may adversely affect the self-centering action of the pump/spindle.

I know that various DD models by JVC, Yamaha and Kenwood fall into this category. I recommend reading http://37282.diarynote.jp/200708102338400000/ and http://37282.diarynote.jp/200708111505150000/ These pages are in Japanese, so you may need to send them through a translator.

The A.R.T. graphite mat that I have bonded to the TT-1000 (using a permanently non-hardening adhesive, causing it to function like constrained-layer damping) has a recess for the LP label, and yes, I have done much experimentation with washers under the LP. Here again, I suggest using these in moderation - only as much as needed to bring the edges of a dished-up LP back in contact with the mat (or platter surface). My testing has suggested that imposing physical stress on an LP while playing it (which is what too-enthusiastic use of washers is wont to do) will adversely affect the sound.

Dover, you have a Final Audio? So do I (grin). My unit predates the Takai-era Parthenon, but is new enough to have the SPZ plinth rather than the original granite. It also has the bi-phase motor controller. FWIW, Kitamura's preferred material for mat and clamp was chrome copper rather than gun-metal. I haven't done A/B tests on chrome-copper vs. gunmetal, but based on A/B tests that I have done on gunmetal vs. other metals, my conclusion is that gunmetal isn't a material that I would care to use for sonic applications. I prefer the results with phosphor-bronze or beryllium-copper, and I imagine that chrome-copper would also work well.

cheers, jonathan carr

Manitunc, Rockitman, magnetic bearings are another thing that I've done experimentation on. In my experience, using the magnets to unload most of the platter weight from the bearing, but leaving some mechanical contact intact sounded the best (a kilo or less, probably even a half-kilo would suffice).

IME, the sonic benefits of keeping a mechanical path to drain away vibrations trump the lower noise levels of a floating bearing. OTOH, if the finish and lubrication of the bearing points is such that significant noise and vibration are generated as a result of the mechanical contact, you may arrive at different conclusions.

Some of the La Platine Verdier turntables allowed the user to adjust the amount of magnetic levitation, and use the configuration that sounded best to him.

cheers, jonathan

Hi Dover:

I agree that a not-so-clearly-defined contact between spindle and clamp (neither snug nor free) is not a good idea. One some turntables, you'd want physical contact between the clamp and spindle, as this is what would allow the clamp to terminate the noise and vibration of the platter bearing. Something like a collet-chuck mechanism should do the job well. However, the FAR's self-lubricating polymer thrust plate is pretty quiet as far as I recall, and shouldn't need special treatment.

A slight overbore of the clamp combined with a polymer sleeve should be good. But not with teflon. Teflon is soft and has low elasticity, and once it is deformed, it stays that way. If you apply pressure across a wide area of teflon it stands up pretty well, but concentrated pressure on a small area is another story. Delrin or some grades of modified noryl (PPO) should be better.

You may also try a tripod-contact between the bottom of the clamp and the LP surface. For whatever reason, I thought that this worked pretty well on the FAR.

Regarding your second question, with the s-l-o-w spin-up time and all, would you really want a peripheral clamp on your FAR? (grin) Sounds damn fine without one!

I haven't had a problems with graphite mats, by Audio Tekne, A.R.T. and Boston. However, I have fabricated some parts in graphite, and I know that there can be sizable differences in the materials sourced from different suppliers. Some lend themselves to machining, and others don't. Also, for best results, graphite machining should be done by a place that is familiar with the stuff, IME.

As an aside (Dover, you already know this), in Kitamura's original FAR design, the platter was aluminum, and it was topped with a mat of machined chrome-copper. Either piece would ring beautifully on its own (although you'd not see it in the measured frequency response from the cartridge), but place the mat on the platter, and pfft! No more ringing, and a quieter, more even-handed sound delivery with greater dynamic range (although you't still not see anything on the cartridge's measured frequency response). The Japanese phrase for this type of mechanism would translate to "phase-interference damping". No idea what you'd say in English.

FWIW, I'm using the same principle in some of my cartridge designs (pressure-fitting of dissimilar metals which are chosen to suppress each other's resonant tendancies).

cheers, jonathan carr

PS. On paper, at least, another approach would be to get a snug fit between the clamp and spindle, and put a stiff grease on the spindle. The grease would lock the clamp in place and quash any ringing. You'd have to remember to wipe the spindle clean each time before removing the LP, however!

Yet another approach that you can take with clamps is to use a container filled with small ball-bearings. Staggering the bearing sizes helps to expand the range of affected frequencies.