IPT RigB 500, Cartridge Body Upgrade For VM500 / AT440 Et Al, Reviewed

A short while ago I reviewed the RigB (Rigid Body) for the AT91 cartridge. The brainchild of Gary and Simon of The Audio Files and Improved Performance Turntables (IPT), the RigB took the generator from Audio-Technica’s bottom of the range cartridge lineup, the AT91 (now discontinued) and housed it in a rigid aluminium body, exquisitely machined and finished to exacting tolerances. A concept pioneered by Linn in the 80s when they souped up AT cartridges for their K series lineup, the RigB brought significant sonic advantages to what is a surprisingly competent generator when you allow it the opportunity to perform at its best.

But technology doesn’t stand still, even where the big black discs of old are concerned. The AT91 is now a discontinued cartridge, though the generator is the same as the AT3600 which is still very much alive and well, hanging from the end of the tonearm of many a super OEM turntable at the cheaper end of the market.

As for the RigB, a newer version is bringing the advantages of the RigB body to better generators to create some magnificent cartridges. IPT sent over the new RigB 500 and a VM540ML for evaluation.

As its name suggests this is a cartridge perfectly suited for upgrading the new VM500 series cartridges. But it’s equally suited to older generators including the AT440, AT150 et al. These generators date back decades and with the current VM series styli being fully compatible, all can be upgraded and given a new lease on life.

At this point, you may be asking yourself, as I was, where there is need for the RigB 500 given that the current VM700 and the older 150 lines are all equipped with an aluminium body. Look closer at the RigB however and you’ll see that its design differs significantly from the AT body. The RigB is manufactured to far tighter tolerances, its design gripping the generator canister at the sides with more uniform and more complete contact between canister and body. The canister is still secured by a bonding agent and a small screw, but it is clear on fitting the canister that the body is made with a far greater degree of precision.

The plastic body of the VM540ML also supplied for this review and the RigB 500 simply don’t compare. The Audio-Technica body is a lightweight plastic (actually a polymer resin) with angular sides and the necessity to install the mounting nuts above. The RigB, on the contrary, is beautifully sculpted and black anodised, with tapped mounts and a simplified aesthetic design. The plastic body weighs 0.77 grams, while the RigB 500 weighs 1.88 grams.

The RigB is supplied with mounting screws and a small bottle of liquid bonding agent. You first remove the cartridge canister from the original Audio-Technica body. This requires the aluminium cover plate be removed from the top of the body to expose the single screw beneath. A thin blade can be used with care to achieve this.

Once the screw is removed the generator canister should come free from the body. My sample separated cleanly leaving no residue behind though you may see some residue from the thread lock used to secure the screw. This should be scraped away if so to leave a smooth surface.

The generator can then be fitted to the RigB. Bonding agent is applied, the canister aligned and the screw replaced. Care should be taken to avoid spilling bonding agent into the screw hole on the canister or onto the connecting pins. I applied the liquid across the top and to either side to ensure secure adhesion. Any overspill was cleaned up and the canister was clamped overnight.

The RigB500 was installed in an aftermarket headshell weighing approximately 9 grams and the headshell installed into the arm of the Technics SL-1200G. It transpired that the combination was too light to achieve the necessary two grams of vertical tracking force with an auxiliary weight installed, but too heavy to be balanced with the auxiliary counterweight removed. I added a three-gram headshell spacer which resolved the issue. This is likely to only affect arms such as the Technics which have a low mass arm and arguably a sub-optimal weight system, a slight bugbear for a reviewer at times.

The RigB was connected to my Musical Fidelity M6 Vinyl phono stage with a low capacitance cable. Total capacitance seen by the cartridge was around 150PF which is ideal for an AT generator. The rest of the system was our usual reference. I did take some time to audition the VM500 in its standard form to refresh my memory, though I previously extensively reviewed the entirety of the VM500 and VM700 lines. I also own a VM740Ml (purchased for a project that I have yet to finish) so was able to make direct comparisons between its metal body and the RigB, swapping the same stylus between the two for consistency.

I previously described the MicroLine-equipped VM540ML as having “an even-handed tonal character with excellent imaging and a wide sound stage, helped by it being one of the quietest profiles in terms of surface noise”. While those observations primarily concern the stylus profile, I expressed my surprise at how close the Vm500 was in performance to the cheaper VM95ML, despite the latter having the inferior generator. It can be said with some truth that the stylus is the most critical aspect of a cartridge’s performance, once a generator of at least reasonable competency is in play. But the gap between the VM540 and VM95ML was far narrower than I had predicted and I now realise why, in part at least.

Both the VM540ML and VM95ML have bodies made from a polymer resin. It feels a lot like plastic, but in theory has some anti-resonance properties beyond ‘poor man’s plastic’, the full extent of which I am yet to discover. Switching to the metal-bodied VM740ML with the same stylus was a revelation in that it showed how much of an improvement the better generator ‘could’ be, given a better platform on which to do its job.

That is; a less resonant enclosure of far tighter machining tolerances and thus more essential rigidity in the interface between cartridge and tonearm. Yet in my initial findings, though I preferred the VM700 body, I found only minor differences between them.

Not so with the RigB. Though it is machined aluminium, the stock body of the VM700 is very similar in design to the Vm500. The angular sides and screw mounts are essentially identical, and in my humble opinion sub-optimal as the interface between the screw head (for the screws must be installed up-side-down) and the cartridge body is not perfect and this the rigidity of the assembly relies on clamping force, rather than the perfect and precise mating of materials and fasteners.

The RigB 500, however, has tiny side mounts into which a screw is threaded, and a top surface machined to mate perfectly with the underside of a well-machined headshell. Though due to the slope at the front the contact area isn’t as maximised as it could be, this design gives a far better interface between the cartridge and arm. So too do the tighter tolerances in the fit of the canister to the body.

The results are immediately clear. Control or the timing of notes and the ability of the cartridge to recover from a particularly harsh transient are vastly improved. Notes start and stop with a precision that the VM740 doesn’t match, let alone the VM540. A decrease in unwanted resonance and the increase in control has a huge impact on detail too.

Top-end detail especially is overflowing but in an extremely pleasing manner. But what struck me most about the RigB-equipped 540ML is just how much fun it is. It has a boundless sense of rhythm that revels in a good bass line and sends it thundering forth from the speakers.

It’s almost digital-like in its presentation, though remains on the ‘right’ side of digital without ever becoming fatiguing or wearing thin. But the benefits of digital – minimal surface noise, no inner-groove distortion, no splashy sibilance and exceptional channel separation, stereo imaging and detail are all present.

I described the VM500 / VM700 as being “among the best moving magnet carts around”. I stand by that statement as they are exceptional cartridges by any standard, though I would still hesitate to give the VM540ML an unreserved recommendation given how close the VM95ML gets you for less money. The VM700 series, however, of which the VM740ML is the introductory model, does earn that recommendation and deservedly so. Until now I would have claimed it to be approaching the sweet spot in moving magnet cartridge hierarchy, with the Shibata upgrade giving you a change of character rather than an upgrade and the SLC taking you into moving coil territory.

But that was then, and now we have the RigB 500. The RigB 500 thrashes the VM500 in every possible way, and it bests the VM700 too with a better design and better manufacturing. The VM700 is still a competent cartridge, but the RigB 500 is the body that demonstrates what this generator is capable of. I have few words to summarise; other than to suggest you buy one and avail yourself of what is undoubtedly one of the best moving magnet cartridges around.