This question relates to overcoming the reluctance of the magnetic
domains in a high density 5.25 inch floppy disk. -Not a hard disk.

I am using an audio playback head, and its footprint is going to
be so wide that it ends up writing over adjacent tracks. If I
position the playback head further away from the medium, and use
a more sensitive preamplifier circuit, I can probably get away with
using a voltage that is in the 9 vdc range, instead of +5 vdc, which
I would otherwise expect.

What I have heard, is that there is the problem of supplying a read/write
head with too much voltage, in that the magnetic force is delivered far
too deep into the diskette, such that the natural graininess of the
ferric oxide embedded in the substrate constitutes a discontinuity
in the magnetic states.

That is, the overvoltage will result in the wrong magnetic state at
the surface of the disk, with the proper magnetic state realized
somewhat deeper down, inside the disk.

Is there any damage possible to a read/write head when you feed
too much voltage to it? And if I may digress, how about when writing
data onto a disk?

I can understand the problem with magnetic rebound, and perhaps the
over-writing of data on adjacent tracks, but is there any chance of
damaging the read/write head when too high a voltage is momentarily
applied to the read/write head? The read/write head that I am using
bears the following marks: AP 2112. I don't have any data sheets
for it, so I am wondering whether I can get away with using it.

I am not talking about reading data, for that you use a preamplifier
circuit, but what I am thinking about, is writing too strong of a
signal into the disk, possibly penetrating the medium and affecting
the other side of the diskette, which I don't mind, it's breaking
the read/write head, is what I am worried about.

Is there any damage possible to a read/write head when you feed
too much voltage to it?

Yes. Voltage beyond rating can open the coil inside the head. More current
flows, and either the power dissipation limit is exceeded, or it simply
opens like a fuse. In your case, with data pulses rather than a continuous
voltage, it might take longer, but I would still expect a premature failure
at some point.


Mark Z.

--
Please reply only to Group. I regret this is necessary. Viruses and spam
have rendered my regular e-mail address useless.

Mark D. Zacharias wrote:
|Is there any damage possible to a read/write head when you feed
|too much voltage to it?
|
|Yes. Voltage beyond rating can open the coil inside the head. More current
|flows, and either the power dissipation limit is exceeded, or it simply
|opens like a fuse. In your case, with data pulses rather than a continuous
|voltage, it might take longer, but I would still expect a premature failure
|at some point.

Is there any way to make an 'educated' guess on what the tolerances
might be for the typical run-of-the-mill audio read/write head? If I
may rely on the general consensus, what do you think the usual lifespan
of an audio read/write head might be, if I raise the input voltage as
high as +9 vdc before bringing it down to ground?

Matthew Montchalin wrote in message ...
This question relates to overcoming the reluctance of the magnetic
domains in a high density 5.25 inch floppy disk. -Not a hard disk.

I am using an audio playback head, and its footprint is going to
be so wide that it ends up writing over adjacent tracks. If I
position the playback head further away from the medium, and use
a more sensitive preamplifier circuit, I can probably get away with
using a voltage that is in the 9 vdc range, instead of +5 vdc, which
I would otherwise expect.

Are you trying to use old floppies to record analog audio? Trying
to use audio equipment to repair an old 5 1/4 drive?
Actually it isn't the footprint of the head that matters, it's the
gap, and I don't mean the gap between the head and the
recording/playback medium, because there isn't supposed to be any air
in between the two, unlike in a hard drive. I'm talking about the gap
between pole pieces. If you don't understand that I'm afraid you're
already in over your head no matter what you're trying to do.
Whatever you're doing I'm intrigued and look forward to your answer.

unitron wrote:
|Matthew Montchalin wrote in message
...
| This question relates to overcoming the reluctance of the magnetic
| domains in a high density 5.25 inch floppy disk. -Not a hard disk.
|
| I am using an audio playback head, and its footprint is going to
| be so wide that it ends up writing over adjacent tracks. If I
| position the playback head further away from the medium, and use
| a more sensitive preamplifier circuit, I can probably get away with
| using a voltage that is in the 9 vdc range, instead of +5 vdc, which
| I would otherwise expect.

I was hoping I could modify the read/write head by attaching two pieces
of metal (clipped from a paperclip, for instance) on either side of the
head, extending towards the medium. Both pieces of metal would be bent
so that they are closer together, but not touching (maybe keep them
separate with a piece of glass that is epoxied in between the two wires).

It was my understanding that the lines of force would extend from the
head and run down both pieces of metal, following their form, and
converging to a point that is maybe less than a millimeter in size. I
was going to be using a tool that measures spark plug gaps, to see
exactly how close I can get the paperclips before I finally epoxy them
into place. (That kind of thing *ought* to work, but how well? Have
you ever heard of anyone modifying a read/write head? I don't want
to use a head that writes two, three, or four tracks, just a head
that writes a single bit of data at a time.)

Anyway, if that idea doesn't fly, I'll just go ahead and get a more
expensive head, something that is significantly smaller in size.

The read/write head gets suspended from a shuttle, and the magnetic
medium is underneath it, laid out flat. A stepper motor will cause
the shuttle to move horizontally 5 inches in 255 steps. Another motor
will cause the medium to spin at about 200 revolutions per second, maybe
faster, maybe slower, it all depends on what kind of success I am going
to end up having. Even if the medium is moving only 128 revolutions per
second, that will still make me happy.

| Are you trying to use old floppies to record analog audio? Trying
|to use audio equipment to repair an old 5 1/4 drive?

I am trying to design a brand new disk drive for my own purposes,
and I especially do *not* want it to be compatible with anything
else, hence the unusual read/write head. I want to have exclusive
control of the data that is written on the medium.

| Actually it isn't the footprint of the head that matters, it's the
|gap, and I don't mean the gap between the head and the recording/
|playback medium, because there isn't supposed to be any air in between
|the two, unlike in a hard drive.

okay

|I'm talking about the gap between pole pieces.

Yes.

|If you don't understand that I'm afraid you're already in over your head
|no matter what you're trying to do.

Yes, I do understand what pole to pole transitions are, and I was going
to ignore the actual north and south states, just count either one of
them as a flip-flop. I was thinking of using a Pic microcontroller
to regulate just when and for how long the 9 vdc gets supplied to the
read/write head. So, with all of that in mind, I was wondering what kind
of lifespan I am going to be looking at, like a mean-time-between-
replacements of the read/write head.

| Whatever you're doing I'm intrigued and look forward to your answer.

Say, do you know where I can get disks of unusual sizes and dimensions?

|unitron wrote:
|| Whatever you're doing I'm intrigued and look forward to your answer.
|
|Say, do you know where I can get disks of unusual sizes and dimensions?

How about 8 inch disks for the ancient 8 inch disk drives? Do people
just buy their own rolls of mylar impregnated with ferric oxide, and
then use scissors to cut their disks to fit?

Matthew Montchalin wrote in message ...
unitron wrote:
|Matthew Montchalin wrote in message
...
| This question relates to overcoming the reluctance of the magnetic
| domains in a high density 5.25 inch floppy disk. -Not a hard disk.
|
| I am using an audio playback head, and its footprint is going to
| be so wide that it ends up writing over adjacent tracks. If I
| position the playback head further away from the medium, and use
| a more sensitive preamplifier circuit, I can probably get away with
| using a voltage that is in the 9 vdc range, instead of +5 vdc, which
| I would otherwise expect.

I was hoping I could modify the read/write head by attaching two pieces
of metal (clipped from a paperclip, for instance) on either side of the
head, extending towards the medium. Both pieces of metal would be bent
so that they are closer together, but not touching (maybe keep them
separate with a piece of glass that is epoxied in between the two wires).

It was my understanding that the lines of force would extend from the
head and run down both pieces of metal, following their form, and
converging to a point that is maybe less than a millimeter in size. I
was going to be using a tool that measures spark plug gaps, to see
exactly how close I can get the paperclips before I finally epoxy them
into place. (That kind of thing *ought* to work, but how well? Have
you ever heard of anyone modifying a read/write head? I don't want
to use a head that writes two, three, or four tracks, just a head
that writes a single bit of data at a time.)

Anyway, if that idea doesn't fly, I'll just go ahead and get a more
expensive head, something that is significantly smaller in size.

The read/write head gets suspended from a shuttle, and the magnetic
medium is underneath it, laid out flat. A stepper motor will cause
the shuttle to move horizontally 5 inches in 255 steps. Another motor
will cause the medium to spin at about 200 revolutions per second, maybe
faster, maybe slower, it all depends on what kind of success I am going
to end up having. Even if the medium is moving only 128 revolutions per
second, that will still make me happy.

| Are you trying to use old floppies to record analog audio? Trying
|to use audio equipment to repair an old 5 1/4 drive?

I am trying to design a brand new disk drive for my own purposes,
and I especially do *not* want it to be compatible with anything
else, hence the unusual read/write head. I want to have exclusive
control of the data that is written on the medium.

| Actually it isn't the footprint of the head that matters, it's the
|gap, and I don't mean the gap between the head and the recording/
|playback medium, because there isn't supposed to be any air in between
|the two, unlike in a hard drive.

okay

|I'm talking about the gap between pole pieces.

Yes.

|If you don't understand that I'm afraid you're already in over your head
|no matter what you're trying to do.

Yes, I do understand what pole to pole transitions are, and I was going
to ignore the actual north and south states, just count either one of
them as a flip-flop. I was thinking of using a Pic microcontroller
to regulate just when and for how long the 9 vdc gets supplied to the
read/write head. So, with all of that in mind, I was wondering what kind
of lifespan I am going to be looking at, like a mean-time-between-
replacements of the read/write head.

| Whatever you're doing I'm intrigued and look forward to your answer.

Say, do you know where I can get disks of unusual sizes and dimensions?


People using old 8" floppy drives probably use whatever old 8"
floppies they still have or search eBay for somebody selling them, but
we're talking about a very, very few people. There's not enough
demand for anybody to be making new ones and I wouldn't put much faith
in the operability of homemade ones.
If you want to build your own record head just wrap some magnet wire
around a straightened out paperclip and bend the ends around 'til they
almost touch, creating the gap. Feed your signal into the two ends of
the coil of magnet wire.
There's probably a commercially available audio or data head
somewhere that will be able to read any disks which you write with
your homemade head. If you want exclusive control of the data written
on the medium I suggest encryption. If big brother government wants
to read your data bad enough they'll build a machine to do so (or just
use the one you built, if they've gotten interested enough in you to
want to read your private disks they'll seize all of your equipment as
well).
Before you build your own head, however, you need to do a lot more
research into how commercially available heads are made and why
they're made that way. If you look at the head you're looking to
modify you'll see one (or more, depending on how many tracks the head
is designed for) little horizontal strips, i.e., their long dimension
is in the direction of tape travel. That strip is actually both pole
pieces, if you look closely enough, perhaps under well-lit
magnification, you'll see a very small gap in the center. It is only
at that gap that the lines of force escape, to any great degree, from
the electromagnet that any record or playback head is into the medium
itself. Trying to make an "extension" for it won't gain you anything
worth having.
Perhaps you could take a working 5 1/4 " floppy drive and install
heads from a 3 1/2 " drive and set them so that they will write and
read in the space in between the tracks a regular 5 1/4 " drive would
write and read.

On 31 Mar 2004, unitron wrote:
| There's probably a commercially available audio or data head
|somewhere that will be able to read any disks which you write with
|your homemade head. If you want exclusive control of the data written
|on the medium I suggest encryption. If big brother government wants
|to read your data bad enough they'll build a machine to do so (or just
|use the one you built,

Actually, I was hoping they could get suckered into paying a licensing
fee, before I pass the details off to some 3rd world country, where an
isolated (protected) software market could be developed and maintained.

|if they've gotten interested enough in you to want to read your private
|disks they'll seize all of your equipment as well).

hehe

| Before you build your own head, however, you need to do a lot more
|research into how commercially available heads are made and why
|they're made that way. If you look at the head you're looking to
|modify you'll see one (or more, depending on how many tracks the head
|is designed for) little horizontal strips, i.e., their long dimension
|is in the direction of tape travel.

Yes.

|That strip is actually both pole pieces, if you look closely enough,
|perhaps under well-lit magnification, you'll see a very small gap in
|the center.

Yes, I'm already aware of that.

|It is only at that gap that the lines of force escape, to any great
|degree,

Well, it is that "to any great degree" thing, is what I was wondering
about. I had assumed that the horizontal strip of copper (a non-magnetic
metal) mounted over the head (measuring 3 1/2 inches long, mounted in
such a way that its length is along the motion of the medium) was there
for damping those lines of force that chanced to extend out at 90 degree
angles. But the use of a non-magnetic metal is puzzling to me. Can
lines of force be channeled through non-magnetic metals?

|from the electromagnet that any record or playback head is into the
|medium itself. Trying to make an "extension" for it won't gain you
|anything worth having.

So I have noticed.

| Perhaps you could take a working 5 1/4 " floppy drive and install
|heads from a 3 1/2 " drive and set them so that they will write and
|read in the space in between the tracks a regular 5 1/4 " drive would
|write and read.

I was going to try a variety of heads from a lot of devices, some
floppies, some tape cassettes, some cardreaders, and see how they
all behave, all other things being otherwise the same.

|| Perhaps you could take a working 5 1/4 " floppy drive and install
||heads from a 3 1/2 " drive and set them so that they will write and
||read in the space in between the tracks a regular 5 1/4 " drive would
||write and read.
|
|I was going to try a variety of heads from a lot of devices, some
|floppies, some tape cassettes, some cardreaders, and see how they
|all behave, all other things being otherwise the same.

Then I would post the results of each head's performance, and choose
the one that worked the best.