MONO diy cutter head

[Gridlock]

Don't wanna Ness up my k8 amp or the RCA head. 75+ years of age. Want to mount a diy MONO head on my k8. why do you all trying to do stereo cut heads? Isn't it just plate recordings of crappy punk rock then why stereo? Come On guys I need ideas since apparently nobody has ever tried to do this facepalm. I wI'll post pics and video my progreas

[markrob]

Hi,

I think that is a great idea. I'd go with a moving iron design. Much simpler to do and very rugged. With modern rare earth magnets, you should be able to get good performance in a small package. The coil winding is much easier since it doesn't have to move. You can use a lot of wire at larger gauges than you could get away with on a moving coil design. The head can be stiffer and allow for a higher system resonance (8-10Khz). No feedback needed to get decent results. Looking forward to seeing what you come up with.

Mark

[Gridlock]

Does anyone know a thing on a hardware store for to mount the needle? With a little screw setter to hold the needle And should that vibrate with the whole iron or just the tip? So tired of performing cpr on depression era coils. These old heads are tough as nails and should be on museums. I am doing something I can meds up and not feel bad about or sad I'm the wallet thanks for any advice.

[Fatrecco]

Some weeks ago I tried to built one of two speakers. Very stiff, with only 6Khz and not much amplitude. Magnets do influence each other

DSCI0140.jpg

DSCI0132.jpg

Next weeks I try to build another one, but not at the Desktop

[handcut]

You may find this useful:

http://downloads.bbc.co.uk/rd/pubs/reports/1943-32.pdf

[Fatrecco]

thanks !

[Fatrecco]

... two years later but not ready I read the Pdf's and looked many pictures and patents I found. My selfmade mono head is near made to the Presto heads. It was not a big thing. A little transformator, some st37 steel, some 08/15 aluminium and two neodym magnets. In year 2019 I will buy a diamond to test my heads. Until this moment I only emboss. ):
I have some things that I don't realy understand with theese moving iron cutterheads.

1. How is the coil mounted / fixed ? I think there exists a force at the coil wire. Like in a moving coil system. Not only at the armature. Glueing it at the laminated iron plates?

Edit: 1.1 The weight of the armature is about 2.8g I think this is too much. How much should it be?

2.The magnetic flux in the air gap is so high, that it is very difficult to set the armature in the middle without getting connect to one pole. I have to make the (omega) springs very stiff. It is hard to deflect the armature with the finger. Is it realy right that the springs are so brutal stiff? I know that it is important for the high resonance and for linear deflection when stylus comes in contact with the record. But how stiff it is in a original head? I never seen such thing in my real life ):

3. In the Pdf posted by handcut, I see two brass blocks at the side of the pole pieces. Have it the funcion of a shortening ring for the changing flux which goes inside the pole pieces. Or is it some kind of diamagnet to eliminate the flux outside the yoke`?

magnetsand.jpg

WithCoil.jpg

Here without magnets because it is stressful to work with strong magnets and metal tools (:

Many questions I know. But the fist one is important for me to go on with this project.


Fatrecco

[Fela Borbone]

Hello,
1- yes, the coils will buzz if not properly anchored by a "perfect fit" of the bobbin, or may be glue or alike. They also have tendence to shrink when energized. but this is not serious if they are tighly packed.

[Fela Borbone]

About the weigth, is not only how much, but also how far from the axis of rotation is the mass located.
In the Presto 1x armature block, the "huge"stylus screw and middle part, don't contribute that much as the far sides, even the stylus tip does. Thats why an aluminium shank is a must.
I can weigth a Presto armature for you and post it maybe tonigth, so you can compare....

[Fela Borbone]

2- The springs have to be very stiff, you can hardly deflect the armature with your fingers, Thats why the "magnetic" cutters are called "inneficient". It has to be so, as the resonance has to be high, around 8 khz in a Presto.
To easily check what the resonance is, you can connect the coils to the input of an osciloscope/smartphone app or even audacity through a pre anplifier. Pluck the armature (whith magnets an all elements in its place) and measure the main frequency of the wave. You can know more things with this test....

[Fela Borbone]

3- I think this blocks have no other pourpose than holding the parts together, but I may be wrong....
I've seen drawings of magnetic cutters with shortening rings to avoid alternating flux to run through the (Alnico?) magnets. Neos have not this problem.Neodymiun is like a "magnetic dictator" no other fields can figth it.
This is why bigger magnet not allways means high sensitivity...but thats along story. To make it short, try also shorter magnet, even with 0,5 mm or so air(or plastic) gaps separating them. The best combination is better found by experiment.

[Fela Borbone]

.

[Fatrecco]

Thanks Fela. That are good to know. The Resonance is with about 3200Hz and to low. I know the physics about the moment of inertia. tonight I will calculate it. But I have concern about making the armature too thin, when removing material. And at the moment I haven't a lock screw. Try to find a M1.8 or make it by my self


First desktop tests with a plate touching the armature shows that I need much power out of the amp. But the sound is very OK it doesn't sound very hollow. At the moment I have no damping installed at these head. I will try a little bit silicone near the stylus hole.

ohnedeckel.jpg

Edit: I see the presto armature has the most of material near the axis where it rotates around. That helps me a lot. I have to minimize my armature like the presto ones.

Now I glued the coil to some polycarbonate from one of my hundreds of fail records. So I can disassemble it without removing glue.

Fatrecco

[Fatrecco]

My Armature is now 2,25g without stylus and set-screw. The resonance is 3200Hz. With a CAD program I calculated an moment of inertia of 0,041 kgmm². It's late in the night but I think this should be J = 0,000000041kgm².

1) f = sqareroot ( D / J )*1/(2pi)



2) f²*J*4*pi²=16.7Nm/rad
This should be the stiffness of the tordional movement.

With the first formula I calculate that the resonance frequency at 8kHz need an moment of inertia wich is around of 1/8 of my current armature. It's unimaginable to remove more material. When I let the armature as is and put the spring stiffnes higher to get a resonance freq about 8kHz. I need a value of 100Nm/rad. Thats are 6 times more than now. I think thats too much and I have to change my spring setup to a tordional spring like the pdf says it. mmmmh...

1.jpg

2.jpg

3.jpg

[jjwharris]

This is awesome!

I'd love to see more photos, did you use mostly off the shelf components?

What sort of frequency response are you getting with your embossing?

[Fatrecco]

The Frequency Response looks very poor:

respnse_emboss_notIRAA_but RIAA.jpg

I use components that I have and that I can get quickly. Don't have the patience to wait days and weeks for material In my little flat I only have a little turning lathe. Actually mounted in the kitchen

milliing2.jpg

milling aramture.jpg

A life without a turning lathe is senceless

I decided to make the a torsion spring. With my current armature I over 100Nm/rad for calculated 8kHz resonance. Too late I checked out Fela's threads.

[jjwharris]

You're probably doing alright...I wouldn't expect much over 8khz with a tunsten stylus, maybe 12khz with a sapphire.

Do the laminations stay in tact after being faced with the lathe?

This is very very cool, I'd be interested in purchasing something like this from you if you were every considering selling them.

[Fatrecco]

I have to say that this is something like a try or experiment. I live in europe and it seems that theese cutting heads a rare on ebay or elsewhere. So I can't buy. And you see here now a not good working emossing head.
I take only a ~0,1mm chip from the laminated iron. After that I grinded it with >12000u/min and as you wrote it, the iron delaminated it self and flyed around the room. So you see on the pictures that some iron plates a misplaced and locks not well turned and grinded. And one little plate is missing I used cyanacrylat glue, Epoxy whould be better. Before when I searched for something that I can use for this I choosed a transformator. The thickness of the rion plates are only for <400Hz. Eddy currents reduce efficiency in higher frequencys. The main flux in there should be the static from the magnets. But sometimes people use such trafo to match the impedance on old tube radios. So I think it shouldnÄt be the problem. Mayby the unbalanced airgap makes problems?!? I believe not.

wrong glue.jpg

Now I'm changing the armature to a torsional spring and wind a bigger coil.

[Fatrecco]

now I made the siffnes to circa 100Nm/rad with one torsional spring. And the calculated resonance frequency should be 7,8 Khz. In reality when I emboss/impress its a little bit under 7 kHz with set screw and mounted steel (1,2mm) stylus. Because the stylus "rings" I use a little bit cyanacrylat to glue it to the armature at the ending hole. The sound is quiet better than before. I wound two coils with 0,25mm Wire (~AWG30) with 3 Ohms together. I connect them serial. The springs at my old construction generates some auxillary resonances and "ringings". These problems are solved. Only the coil movement I have to get under control. But sounds not bad for my personaly emboss/impress records.


Here is a picture of a white noise record with low amplitude ); I used no EQ or Anti-RIAA for record. But the playback amp uses RIAA. The dark blue graph is the background noise. The radius of the groove is 70mm.

ananewmono.png

Much background noise: no heat lamp, no fluid and quick grinded stylus with under 90 degree. I recorded some songs and it sounds ok.

Next step is to wind better coils and to reduce some of mass of the armature.


Near the center hole.

newmonotorsion.jpg

[jjwharris]

You're convincing me I need to do something similar to build a 'proper' embossing head. That frequency response looks great.

What sort of stylus are you using? Peter King uses tungsten to a 90 degree point, anything sharper and you tend to get a bit more background noise. The polycarbonate blank will also have a residue from the adhesive that will need to be removed otherwise it will cause background noise, CRC or lighter fluid should remove it...