Project "Groove Scribe"- A DYI stereo 45/45 head.

[juba bc]

hi Snug , I found this picture not remember where it was supposed to be the design of a diy cartridge for turntables ... disregard the measures ... I found interesting to make a cutting head system with fixed coils

[opcode66]

its is possible for a cutter head construction??

If you check my bladerunner thread, I've experimented with in inverted transducer. I had some results that were promising. However, there were a number of complications that I could discuss at length. Essentially, you have to get the weight of the magnet and size of the coil and coverage just right. There is a sweet spot. However, as a dynamic design, I had enormous issues with low end. High frequencies seemed to get washed out by the momentum of the magnet mass that is accentuated for low frequencies. I think with feedback this might be viable. But, as a dynamic head, you have a lot of moving mass. Even with powerful neodymium. Too small and you have to drive your coil to the point of melting in order to get significant excursion (disc level). Too big and you get fantastic disc level but no highs and blaring lows/mids. You can actually see a difference int he cut grooves in pictures on my thread here http://lathetrolls.com/viewtopic.php?f=15&t=5250&start=220#p37507

I tabled the R&D to finish the normal transducer version with feedback. I plan to circle back to the inverted transducer design. What is nice about my modular design is that I can easily change out transducer cards for experimentation. The same body and torque tube could be a feedback, dynamic, inverted transducer or regular transducer cutterhead.

Not trying to hijack this thread, Bryan. I just thought I might chime in here.

[Snug Music]

Got the new coils (by hand!) wounded..., afterwards i only saw wires ... lol ... after that I looked like!

Scotty

[juba bc]

opcode66, thank you for your explanations

[Bahndahn]

its is possible for a cutter head construction??

If you check my bladerunner thread, I've experimented with in inverted transducer. I had some results that were promising. However, there were a number of complications that I could discuss at length. Essentially, you have to get the weight of the magnet and size of the coil and coverage just right. There is a sweet spot. However, as a dynamic design, I had enormous issues with low end. High frequencies seemed to get washed out by the momentum of the magnet mass that is accentuated for low frequencies. I think with feedback this might be viable. But, as a dynamic head, you have a lot of moving mass. Even with powerful neodymium. Too small and you have to drive your coil to the point of melting in order to get significant excursion (disc level). Too big and you get fantastic disc level but no highs and blaring lows/mids. You can actually see a difference int he cut grooves in pictures on my thread here http://lathetrolls.com/viewtopic.php?f=15&t=5250&start=220#p37507

I tabled the R&D to finish the normal transducer version with feedback. I plan to circle back to the inverted transducer design. What is nice about my modular design is that I can easily change out transducer cards for experimentation. The same body and torque tube could be a feedback, dynamic, inverted transducer or regular transducer cutterhead.

Not trying to hijack this thread, Bryan. I just thought I might chime in here.

Certainly tangental to this thread, but this is in interesting idea.

juba bc: This is an interesting design you have presented, and there are interesting features here that Todd likely didn't work with. In his moving-magnet experimentation, he likely flipped the location of the magnet and the coil and kept the springs and such similar to his previous renditions. What you have here is quite different and should not be discouraged by someone who has worked with something only mildly similar.

Your design, juba bc, appears to be springless and that seems very new to what we all have been trying. The only 'spring' is at the coupling of the left and right units– some spring or 'return' force would also come from the south to south magnets. I am not an expert, only a beginner, but this design you have proposed– if engineered well, seems highly plausible and certainly deserves encouragement. I think its safe to say that many people reading these forums are into seeing something dirastically divergent from the normal design standards.

Keep it up! Good luck!

[opcode66]

The springs serve many purposes. Possibly you are ignoring those Bahndahn? Or, are not aware of them. Removing them would be problematic with respect to actually tracing proper grooves. I didn't say don't do it. I merely threw in my experiential data.

[juba bc]

Bahndahn,this project is not mine ... I found on the net, it is an interesting cartridge designed to read the disks with higher definition I guess ... but found it very interesting to become a cutter ... for what I did in design, the rods are loose and slide the red prism, movements therefore completely independent ... interesting also the use of magnets to serve as a spring, and allow an adjustment control that can be useful not ... Todd did not say that can not be done, he just said he tried something and it did not work very well ... thank you for your comment

[Snug Music]

Hey Juba,..
The design looks good, but I think (as opcode also said), the emergence of many problems the first (if any) would be eliminated. That will not be easy!

Greetings Scotty

[Bahndahn]

The springs serve many purposes. Possibly you are ignoring those Bahndahn? Or, are not aware of them. Removing them would be problematic with respect to actually tracing proper grooves. I didn't say don't do it. I merely threw in my experiential data.

Right, now that I re-read it I realize you didn't discourage it, looks like my halloween hangover was adding some bogus to my reading comprehension. Pardon me!

[opcode66]

I plan to circle back to inverted transducers again. After I finish the standard design. I say, this has potential. But, has to be setup just so to work.

[EpicenterBryan]

Like usual you guys have had great inputs the last few days. I didn't get as much stuff done as I wanted but have a few things to go over.

Bryan, no problem in simulate this, but it has some limits...

So Fela, is it possible to simulate more than one magnet at a time? I understand the program is not 3D so for something like a ring magnet can it simulate that directly, or would you simulate it as a cross section with two bar type magnets like would be seen if you slice the magnet length wise?

So let's look at this with an eye on how it can be simulated:

On the left is the stock driver many of us are messing with. It has it's own internal structure and I'll go into in the next diagram. To the right of that is a big steel disc being used as a magnetic shield, with an air gap in between (really there is a plastic spacer there for clearance of the moving parts). Then I have a ring magnet on the right of the disc. That has two purposes. One is to create the field through which the coil will move. The coil is attached to the push rod (not shown). Also notice the magnet is in opposition to the end magnet in the driver (south to south with metal disc in between), so my thought was that it could help create a magnetic bottleneck keeping fields that originate inside the driver with in the driver.

Mechanical for Fela.jpg

Now if we look at the dimensions and more detail about how this all plays:

To the left again is the internal structure of the stock driver. These dimensions are my best guess and may not be exact. There are very large fields in there and I am trying to measure them with a digital caliper which moves around because of the magnetic attraction... The outer left structure is one piece of machined steel. In the center is a neodymium disc magnet. Red is North. Then there is a steel disc with a hole in the center. The outer 1.5mm of this disc is a ring of another kind of metal press fit on the disc. That ring is also magnetic and is not shown in the diagram. I've read things that mentioned Faraday shorting rings, and if this ring is intended to serve that purpose I would have expected that to be non magnetic like Aluminum, copper or something but it is not. I'm confused why it is there. Do you (or anyone) have thoughts?

Dims for Fela long magnet.jpg

So after the steel washer with press fit ring, you will notice there is an outer neodymium disc magnet in opposition. So two N magnets face each other through this steel disc / ring.

Next up is an air gap (plastic spacer) and then my 4mm thick steel "washer" acting as a shield. Then my ring magnet on the right where my coil will move inside. The actual dimension diagram reflects a longer magnet I received today and how it would be positioned. The new magnet is longer so there is more length of non-disturbed polarity on either end, and also has a smaller inside diameter so ultimately the form for the coil doesn't have to be as large. The mechanical view has not been updated. Only so many hours in the day...

So what do you think? Can a more complex structure like shown be simulated (several magnets at a time), and do you have time to play with this and post results? If you can model this, then I think it would be easy for you to add things like a washer on the right side of the ring magnet too and we could see what that does. Right now, I'm mostly interested in seeing what happens inside the right most ring magnet where the coil will go but I am extremely interested is seeing the effect of adding the disc and reversed magnet did inside the driver. Can we all learn something from what they did there?

Bryan

[EpicenterBryan]

Next up is an air gap (plastic spacer) and then my 4mm thick steel "washer" acting as a shield.

Oh crap. Should we also model steel bolts going through the front shield disc and driver body? Or should we assume non-magnetic stainless bolts? I bet I have used both over the last few months?

AARRRGGGHHHH!

[EpicenterBryan]

Yes, I have wider magnets on order...

I misspoke here and want to clear this up. The magnets I had on order were longer, not wider.

I receive the first of them today and want to show you why I ordered them. They also have different inner and outer diameters but what I really want to show is what happens in these radial polarized magnets.

So here is the original 5mm long magnet. I cut a slim piece of the green Magna-view film and placed it on the side for demonstration purposes. On this side, since I rotated the film 90 degrees from the end view we have seen in the past, now where we see "white" it's bad - like black on the end view. My point here is this is a region where the fields are not going in the correct direction for our coil to produce electricity from the movement in the field. Although I can't get a good photo, the exact same thing happens at exactly the same position inside the ring magnet. There is a zone exactly where the poles reverse where no energy will be produced by our coil.

IMG_4100.JPG

And here is the 12.7mm long magnet:
Notice a similar pattern. The exact same pattern is inside the ring magnet, with a similar dead zone (and wider). It is smaller proportionally to the usable region with increased cylinder length.

IMG_4101.JPG

So after seeing magnetic simulations from Fella, revisiting comments by Todd about changing the magnet, crazy moving magnet gizmos posted by juba bc (which relates to Todd's moving magnet version of Blade runner)... Oh, by the way Todd - there was no hijack and I'm glad you posted about it here....

It all got me thinking about a totally different path. A retro path. A forgotten path (perhaps for a reason). I'm not saying it's a good path. It's an interesting path - and a detour that may be so interesting it may be worthwhile just for journey sake.

Todd has experimented with a design for moving magnet feedback. Let me propose this new "super poor man" ultra retro feedback idea:

Glue an ultra small super magnet on the driver rod.

r0500.gif

Then, use an old school magnetic tape play back head to read the movements. It totally shocks me that you can still find NOS heads on E-bay. For the total experimenter, you could use a mono head from a garage sale cassette recorder.

But I'll share some results from a 1/4" stereo head I have on order for this purpose as soon as it arrives.

s-l1600.jpg

Until then - think about it. The extra cool thing about this idea is that the other unused channel could be connected as a humbucker to reduce inductive pickup.

How Fela Borbone inspired is this idea? Fela Borbone rocks!

And I should also post this crazy video just to inspire a few people to experiment:

Bryan

[EpicenterBryan]

Got the new coils (by hand!) wounded..., afterwards i only saw wires ... lol :

Great looking coils! Bad side effects with your eyeballs!

[Stevie342000]

Got the new coils (by hand!) wounded..., afterwards i only saw wires ... lol :

Great looking coils! Bad side effects with your eyeballs!

Just going to chip in here, there may be an issue with using a tape head that you have not taken into consideration for feedback. If you put a magnet near them you will magnetise the cores of the head, which in turn will affect frequency response. Hence why you had to demagnetise heads, if you are using this as a feedback system for your cutter head then I would look no further than winding your coil on a former and using the magnet to induce the feedback in the coil rather than using a tape head. Whether you mount the coil or the magnet on the shaft will depend on which has the lower mass or which every mounting offers you the best results.

Your idea might work but there will be problems with magnetisation of the head core, which will mess with your feedback especially at high frequencies exactly where you do not want it to be messed with. Unless you can determine what the head core magnetisation would be you over time you could compensate for it electrically in the feedback circuit. I think the tape head and any further compensation makes the issue more complicated.

In addition you want to keep the mass of your cutter head down as low as possible overall as well as the mass of the moving parts. I do not have to worry about the mass of the head on my Sugden lathe as the head is fixed rigidly to the fixing plate and thus to the carriage traverse rails and lead screw.

Going the route of the feedback magnet on the coil rod/former with the coil mounted the faceplate and then putting a shield over that may get you some way to what you are looking for to induce feedback into the cutter head system. At the same time you should close your magnetic loop and reduce the chance of leakage from the magnetic field.

Why not for example move the feedback further down the rod and then mount the springs after the feedback then close it off with the shielding, the coil I saying should be near where your rod joins your cone. Not trying to throw you off you track here just thinking out loud, I am not following why you are moving objects such as feedback down the rod (away from the cutter coils), why not compact it rather than make it extended. Just thoughts to ponder and me thinking out loud but you will have issues with a tape head, I am sure.

[Fela Borbone]

Hi.
I dont have internet at home and have problems uploading pics in public wifis with a half working phone...so Im sorry if im slow.
Simulating rings is easy, Ill give atry to the complete drive this week ,I hope...Did already some test with the ring for feedback but I guessed some of thedimensions.
But its usefull for analyse the system....
Here it goes....

[Fela Borbone]

The rectangle on the rigth is the magnet. Heres no coil,instead the red line will display results

[Fela Borbone]

The field will be usefull for signal generation when it goes across the line

[Fela Borbone]

Angle affects the "usefullness" , as its sine is multiplied to yield the zones of the analized line that will generate signal.
In this plot, the x means the length of the simulated line. The black lines marks were the edges of the ring magnet are.green shows all flux avalaible.red is the sine of the incidence angle( escaled to fit in the graphic) ...
and the black is what really matters, the length of this line where the coil will be producing signal.
Conclusion. the flux density is not impressive but not bad for a"bare magnet".the good news is that the magnetic "fringe" is narrow. So, in my opinion, the coil( or coils,if you use 2 opposite winded ,one on each peak) have to cover the peak plus the expected displacement at each side,to work at its best

[Bahndahn]

Total curve ball idea regarding the tape heads! Awesome!

I definitely want to try my hand at this, I have some tape heads laying around from experiments in analog music composition. Just need to order some of those tiny magnets!

Here is a stereo 1/4" [for bi-directional tape use, putting two channels over 1/8"] head hooked up to some cables that I used to hand-swipe over lengths of tape fixed to a piece of paper, a bit like some of John Cage's techniques.

photo (1).JPG