(Why) are there no stereo magnetic cutterheads?

[renegadescrew]

Hello, I joined the forum years ago and asked a daft question and regularly have lurked around ever since. I have read many posts on DIY stereo cutterheads and have read lots of very interesting PDFs/etc posted by other members. And then wishing I could build stuff

My question is pretty simple and I suppose the answer will be more simple, but one of things I see often in DIY cutterhead threads is the mantra that moving mass should be kept to a minimum. And yet, every design I see is made with 2 angled speaker drivers moving a lot of parts. What is the reason why electromagnets are never used in order to reduce moving mass to virtually nothing?

I am imagining a similar design to the usual one but with tiny neodymium magnets being moved by electromagnets. Moving mass would be little more than the cutting stylus, at least tiny compared to moving speaker drivers, cones on top, and so on.

I was more intrigued after trying to find an answer here and learning that old mono cutterheads used to work with electromagnets (I think, as I am not exactly sure how they worked). I have spent a couple of days trying to avoid asking this question but I can't find figure it out.

So apologies, I suspect it's like asking why we don't use square wheels.

[markrob]

Hi,

All of the heads you see here are electromagnetic based. You are thinking of a moving magnet design vs a moving coil. Both are still electromagnetic. The places of the coil and magnet are reversed in the two designs. In the moving magnet style, you need a big enough magnet to be able to generate the forces required. This design is possible, but its not a slam dunk that this would be lower moving mass than a voice coil design. You would have to do the math to see. I think you see so many designs based on speakers here is because you can get them off the shelf. You would be on your own with a moving magnet design. There is a third type of design that is also electromagnetic. This would be a moving iron type such as is used on the Presto heads. Many of the parts you see on these designs are needed to constrain the movement of the stylus to the axis of each driver. If this is not done, you won't be able to properly control the stylus motion.

Hope that makes sense.

Mark

[renegadescrew]

Hi Mark,

Thanks for the quick response. I see the problem with my searching/terminology now and glad you could figure out what I meant. I am such a layman!

I indeed mean moving magnets, which seems obvious now (given both types of cartridges). I suppose I may be underappreciating how light some of these parts might be in the moving coil designs, 3d printed in stuff like carbonite. And how the whole design contributes to stiffness if that's not the wrong word.

I see now that it has actually been done by opcode66 who says it can work well with feedback. Now I have more reading to do.
https://www.lathetrolls.com/viewtopic.php?t=8123

Thanks again,
Alan