holbo MK 2 turntable

@dover 

If you adjust VTA on your Holbo whilst playing, the stylus position will move away from the tangent. This is basic geometry

I am with @hb22 on this one!  The Holbo VTA adjustment raises or lowers the arm vertically, and if it is done to compensate for different record thicknesses, the tangent geometry is completely unaffected.  If you check pictures of the Holbo you will see that the support rod the tonearm pivots around is pretty much in the plane of the record (cartridges do vary in height a bit).  My description of the tonearm as a T is oversimplified - it is more like a + where the | sits over the - .

Now, trying to compare Eminent Technology tonearms (model?) with Holbo is interesting.  If you sketched the architecture of each on a table napkin, you might think they were the same.  The way I see it, the excellent reviews of both tonearms validate the architecture of each and highlight how much better they can be than conventional pivoting tonearms.

Properly adjusted pivoting tonearms have Horizontal Tracking Angle errors rising to 2-degrees at two points during playback.  For stereo records, where each channel is cut at 45-degrees, HTA is just as important as VTA.  Many audiophiles obsess about VTA but conveniently forget about HTA.

Despite the architectural similarities, the design details vary considerably between ET and Holbo.  For example, the balance weight alone on an ET tonearm weighs about as much as the entire Holbo moving assembly.  Remember, the total sliding mass is what the stylus has to pull sideways!

When Colin Chapman wanted to improve the trackability of his Lotus sports cars, he famously "added lightness".  

The Holbo is fully integrated.  When you push the button to start the platter spinning, the air pump automatically switches on.  When you stop the platter, the air pump keeps going for a few minutes before automatically shutting down.

The tolerances on the Holbo air bearings are so tight, almost no air flow is needed.  The air pump is very quiet to the point where I cannot hear it at all unless I press its box into my skull bones.  Complaints in reviews of AT tonearms suggest its air pump is so noisy it needs to be in a separate cupboard, if not a separate room.

The Holbo does not have a detachable head shell so swapping cartridges will likely take 20 minutes or more.  But for the price of a system with an AT tonearm, you could buy two Holbos!

@lewm 

Just from your verbal description, the Soulution tonearm sounds very much like a modern version of the Rabco SL8E

I have no direct experience with Soulution and my description is my best guess at how it works, based on how similar machines do operate!

I am reminded of the codebreakers at Bletchley Park who in effect has to reverse engineer the settings of the Enigma machines every day.  They were helped because early Enigma machines could be bought commercially, and they captured enough rotors so they could work out how they were wired internally.

Then the Germans introduced plugboards, more rotors, and the navy went to four rotors rather than three.  Of course, the radio transmissions were in hand operated Morse code.

Completely separately, encrypted radio transmissions started in teleprinter mode.  Without ever seeing the encrypting machine, the British worked out that it must have 12 rotors, the architecture of the rotor advancing mechanism, and the repeat frequency of each rotor.  They then built the first digital computer to crack the daily settings.

I cannot claim my desk-top reverse engineering is anywhere near that league!

@dover 

Well think of king pins and preloading on a car, no preload and your steering wobbles its way along the road. By putting a very small load on the stylus ( using very small overhang ) you may stabilise the stylus in the groove.

Our last posts crossed in the mail, so to speak!

Surely, there's already a big load on the stylus from the friction / tracking force stopping it wobbling in the groove?

This force directly pulls the tonearm and, unlike my cars, there is virtually no play because the tolerances on the air bearing are around 10-microns over an interface about 60-mm wide.  The friction-free bearing and very light sliding mass means neither toe-in nor power steering is needed.

My trigonometry is rusty, but each 1-mm change in height will change the VTA by about 0.35-degrees on a Holbo. That will move the stylus closer by about 3 microns.  Far too small to worry about ...

@dover 

I've mulled over some of the differences between the Eminent Technology tone arms and the Holbo. 

It is almost as if the ETs are early proofs-of-concept, and the Holbo is the production-ready version.

The ETs have a fixed tube to which air is fed.  The tonearm assembly slides inside this tube, and is an L shape with the cartridge at the tip of the L.  At full extension the axle (the bottom of the L) extends out from the bearing tube by the full width of the playing surface - about 4" or 100-mm. The axle is the full length of the bearing tube plus 100-mm.  This all adds to the sliding mass the stylus has to move sideways.  The tracking force and stylus drag are cantilevered out from the bearing.

The Holbo radically changes the configuration of the bearing.  The short outer tube is part of the T configuration of the tonearm and carries the air supply via a tiny flexible hose. The long inner rod is fixed, and can be as heavy and rigid as the designer chooses.  The tracking force and stylus drag are centred symmetrically on the bearing surface - surely a better design. The sliding mass is much lower too.

On the question of whether VTA should be adjusted vertically or in an arc, I think this theoretically depends on the use case.  If you want to compensate for record thicknesses, vertical is correct.  If you want to compensate for the original cutter head not being vertical, the arc wins.  But how many records are cut with the cutter skewed?

A third use case would be compensating for manufacturing tolerances in stylus rake angle, which is also affected by tracking force; misalignment of the stylus faces in the cantilever. and / or a bent cantilever.  In this case, the VTA adjustment should be done as a fixed baseline.