What innovative, unconventional cartridge designs can you recommend?

@pindac 

So FSE is an acronym that means roughly the same as FOS?

I think @lewm and others here are entitled to ask what you mean by a TLA without having to look it up.  I did look up FSE and the best fit was Fetal Scalp Electrode.  Not sure if that is a misspelling! 

An alternative is Field Service Engineer but they normally visit customers.

So please do explain what you mean by FSE?

It is normal courtesy to spell a Three Letter Acronym (TLA) in full the first time it is used.

Meanwhile it seems you have found a UFO who has convinced you what everybody else here knew intuitively - that the stylus shape and cantilever material are important for optical cartridges.

Oops - I forgot.  UFO = Unidentified Friendly Objector.

Now we have to deal with your frankly ridiculous assertion that optical sensors are non-linear and highly variable, which would logically lead to poor channel balance.  Does 0.3dB sound like bad channel balance to you?

Every digital camera and digital movie camera relies on optical sensors.  So does every optical mouse. Most astronomical telescopes, including the Hubble and Webb orbiting ones, uses optical sensors.

The relevant physics operates at the quantum level, as described by quantum sceptic Albert Einstein. When a photon of the right energy is absorbed by a photodetector, it displaces exactly one electron.  Nothing non-linear there.  The process is stochastic, but billions of atoms will average out very well.

There also nothing non-linear about the amount of shade cover provided to a photodetector in a DS Audio optical cartridge.

Quite remarkably, Tetsuaki Aoyagi, who was awarded TAS' 2025 Inventor of the Year TAS-Fall-2025_Innovator-of-the-Year_Tetsuaki-Aoyagi.pdf, published the circuit design for Equalizers about 4 years ago to encourage other manufacturers to produce them in direct competition with his own.  He provides technical support and there is no charge for other manufacturers, nor is there a licence fee.

He believes, rightly in my opinion, that optical cartridges should become a mainstream choice like Moving Magnet and Moving Coil.

@audphile1 

Apparently, mine is winging its way from Japan, and will Likely Meet the Bulldozers destroying Mountains of Parcels at the POff, Next Week. 

If Customs does not get there first.  They'll be collecting just 10% Goods and Services Tax.

Looks as if I'll have to renounce my British Citizenship if I ever want to visit there again.  No big deal, when I took my kids on a visit, they sauntered straight through on Aussie passports while I got royally interrogated by a gentleman from the sub-continent because I used my British one. 

@pindac 

If you are worried about non-linearities and poor channel balance, have a look at the Decca moving iron cartridges others have mentioned here.

Originally designed for mono horizontal wiggles in the groove, the design was extended to cover vertical wiggles but the mechanicals are not symmetrical. leading to different compliances vertically and horizontally.  

Furthermore, the transducer design uses two coils in one direction, and one in the other.  Single-ended versus double-ended.  Lots of non-linearity there, not to mention extreme production variations.

No, give me transducers arranged symmetrically at 45-degrees left and right to fit to my rather symmetric tangential Holbo tonearm!

@lewm 

Optical attenuators are said to be unreliable or nonlinear such that channel to channel balance is tricky

Had me wondering what an optical attenuator is in this context, but I guess you mean the shading plates!  These are purely geometric, and in effect are squares mounted at right angles to the cantilever, but rotated at 45-degrees. When the cantilever moves sideways at 45-degrees, one of the plates exposes more of less of a square sensor which is also at 45-degrees.  There is one set for each channel - giving two-channel stereo and perfect symmetry.

There is an engineering challenge between making the shade plates strong for rigidity at the expense of the lightness required for tracking ability. DS Audio halved the mass of the shade plates by swapping beryllium for aluminium, and claim the effective tip mass is now about a tenth of a more conventional cartridge.

It seems that in series 3, the two shade plates have a combined outline cut from a single sheet. No doubt it is hard to position the combined shade plate accurately on the cantilever, but I believe the result can be viewed through a window in the cartridge.  Aligning the shade during manufacture should be much easier than mounting a stylus, I'd have thought!

@richardbrand The Post has stated " It is also stated, there is also a Nonlinear function to be found in the Electromagnetic Inductance Cartridge design, but this is relating to distortion being produced and the unpredictable relationship between the B field and the Flux. The Precision of a Cartridges Assembly can substantially impact on the distortion that can be detected/measured, as changes to the positioning of critical parts impacts on the B Field / Flux relationship."

No Stone Left Unturned as a layman description which was supplied for myself to have an ease with understanding it. 

I have mentioned before in other posts that Ortofon has substantially improved Coil Winding finishing over the past 20 years, to the point their Coils will be difficult to surpass for uniformity of the wind. This in conjunction with the precision placing of the FSE and Armature alignment, is strongly suggested to be their technology to have a much improved control on distortion, or address the Nonlinearity found at this interface. 

@audphile1 Thank You for producing a summary of the Post I produced, even though I disagree with the willy nilly use of the highly polluting method chosen to produce the reduced content. Are you not capable yourself to do such an exercise?

Do you use AI to alter your own produced post content in general, for whatever reason?

Does adding a 1100 Word Annexe, to the content of my Post actually improve the situation as both will be read. Anybody with an interest in a modern Optical Read Cartridge, as well as by those who place their trust in the well proven technology used for Electromagnetic Inductance Technology.   

As a wild stab, I would suggest a 100+ have already / will be the minimum to read the content. A proportion of this number using the content will at some point be  working out what this means to them for their future direction for a Phono Cartridge. 

I also am happy to read another user review of the DS Audio Cartridge, why wouldn't I. Models of a few years past are already sat in front of whilst demo'd to me, and I have read approx' 100 user reviews from forums and a little from the audio media sites. 

I am a individual with a wider view on this matter and have been toying with the Technologies for a long time. If the end result of that means that I am not equally aligned to others sharing an interest, resulting in views between parties not being reconcilable. Then that is fine for myself, I do not return to post to project ill feeling towards anybody.   

As for the FSE - Visiting a Certain Cartridge Companies Web Pages might just be enough to Find Some Evidence.