Recharge the magnet on a Presto 1D head,solve your problems.

[EpicenterBryan]

The Presto 1D head that came with a system I'm working on had very low output, a goofy response curve, some strange resonances, and some distortion I could not explain.

IMG_2880.JPG

It had been rebuilt by Bruce Leslie in 1993 (he has passed away). So I decided to open it up and investigate. The damping material was like new, there were a few screws loose on the round disc that makes a mechanical connection to the damping material which I tightened. Next, I inspected the gap for debris, found none and everything was well centered with feeler gauges. Next, I checked the horseshoe magnet to see if it could hold something like a screwdriver, and not only found it was weak, but one pole was especially weak compared to the other.

So next thing I did was use a compass to determine which pole was North and which was South and marked the head.

Comp 1.jpg

Then the first test - I used two small neodymium magnets, determined the N and S poles, and put one on each pole on the 1D horseshoe magnet (neodymium S to horseshoe N, and separate neodymium N to S horseshoe), and then placed a steel plate over the two neodymium magnets to complete the force lines. I left it there for a few minutes, removed it all and checked again with a screwdriver and the pull was much stronger and equal on both poles.

Comp2.jpg

I did a test cut with pink noise, and was shocked at the level increase and the change in the response curve. So I went a step further...This time I used a stack of 4 neodymium magnets salvaged from computer hard drives. The interesting thing about these is that they have both a N and an S on the same face so no iron keeper is needed to complete the magnetic circuit. Think of them like a flat horseshoe but super powerful.

So as you see, after being re-magnetized with these super magnets the head could hold up the weight of a screwdriver which I could not before all this. And the result? Insanely crazy output. Now I have to drop the drive down! And all the Goofy response and resonance issues are gone.

comp3.jpg

There are a few things to note. You could jump to the final step with many hard drive magnets. But they are so powerful, you need to make absolutely sure which pole on the horseshoes is which. A stack of any of these super magnets are so strong they will swamp out what you would normally feel as resistance if in the wrong direction, and you could potentially demagnetize the horseshoe without realizing it. Also, these are so strong, if you get your fingers in between these magnets as they attract you are sure to experience instant blood blisters and severe pain. Also, keep all magnetic tape and credit cards away from these magnets, and stay away from old school CRT's with these. You run the risk of magnetizing the front screen on a CRT (like I did this many years ago - The CRT was shot).

[Steve E.]

dang!!!! amazing! thank you!

[tragwag]

this is excellent for reference, thanks!

[aaron]

Is there any reason you couldn't just replace the horseshoe magnet with a couple of neodymium magnets..?

[opcode66]

Exactly what I was thinking

[Stevie342000]

My thinking would be originality and it was the easier option. However I had figured this was how you did it, as may some other members.

But there are lot of newbies here and those with limited knowledge, this method works for most of us and for them. We are not all inveterate fiddlers.

It is very useful as a resource and a point of reference.

[Fela Borbone]

This part is not neccesary to be built with laminated metal, as eddy currents only affect the parts with changing fields, solid metal will do the same work

Is easy to saturate the magnetic circuit this kind of magnets, but is not a problem, just a "waste"

[EpicenterBryan]

This part is not neccesary to be built with laminated metal, as eddy currents only affect the parts with changing fields, solid metal will do the same work

Wow! That is a fabulous job and great idea.

One thing I should note about what I did: I got the idea from a forum that discussed phono cartridges that had horse shoe magnets in them and lost charge. In the forum they said once the horse shoe was placed on a magnetic charger (and they discussed building an electromagnet) you were to shock the horse shoe by striking it at the bend with a brass hammer or using a spring loaded punch at the same point. They said that step was necessary for the magnet to hold the new charge. I was too chicken to do that since I didn’t want to risk breaking the horse shoe.

I think these neodymium magnets are so much stronger than the electromagnet they used that shocking the house shoe isn’t necessary but time will tell. Had I broken the magnet I’m not sure I would have come up with such an elegant solution as Fela Borbone did! Very cool, and from the outside it looks stock!

[Steve E.]

Fela Borbone, can you explain a little more what you did? I can't tell if I am looking at a before or after picture.

[Fela Borbone]

Fela Borbone, can you explain a little more what you did? I can't tell if I am looking at a before or after picture.

Hello, yes I will soon explain this and more in a separate thread, I think here is a bit out of topic, I just wanted to answer aaron, that what he says is possible.
Thanks, epicenter Bryan, for sharing.This thread will be a great help for other trolls.

[Fela Borbone]

...And striking one magnet against a weak one helps in the process of remagnetizing . In fact if a nail pointing the earth north pole is knock with a hammer, gets magnetized. Other method less agressive is rubbing one part against the other.

[aaron]

In your picture, where are the magnets? Are they on the top, and the sides are just pieces of steel or something stacked up?

[Fela Borbone]

In your picture, where are the magnets? Are they on the top, and the sides are just pieces of steel or something stacked up?

Hi, the magnets are this cheap 2mmx30mmx10mm neodymium

and there´s two parts like the one shown in the middle picture in my other post(front face is in the back in this pic), linking the head polepieces whith the magnets....and of course no glue is needed for the magnets!

[aaron]

Very cool, I think I'm going to do that.. Did you just use steel for the side pieces?

[Fela Borbone]

Very cool, I think I'm going to do that.. Did you just use steel for the side pieces?

Hi, side pieces are made out of tranformer metal sheets, 1 cm wide and 5 cm long are perfect, and the rug is meant to mimic the original alnico magnet shape.Care must be taken when drilling this sheets, I lost one nail of my finger doing this when I was a child.
A thread about this with more info coming soon when I find time...(not about my finger! )

[45rpmdude]

i certainly oculdn't think of anything that complexx.. i dont have any knowledg. so to speak.. i dont mean to to say this but i am dumb.. in a way cause im not good with this stuff at all.. basic shapes and simple round figures maybe,, but not this,, your post helps a lott.. thxxxx. sir.

[electronrancher]

Great idea that I plan to try soon! Bumping to get a link for later reference

[Presto Repairs]

I love the ingenuity, but for originality you cant beat a magnet charger...

They're pretty easy to build and can be built cheap...

Here's a you tube link of a home built one in action (Not mine)

https://youtu.be/NSEQs7XbWj8

Rubbing magnets or passing through fields is only a temporary solution...

[electronrancher]

Love the video, but I'm a little dubious about their tapping. I suppose that if the coil could barely make enough field, some physical whacking might help the domains flop over.. But I thought that all you needed was to expose the material to a field greater than it's saturation limit, and poof - it's magnetized. I believe when making Neodymium magnets, they are pulse magnetized by dumping a few kA into a coil for a few ms - it would melt the wires to try to set up a steady field of that strength!

I'm guessing that when recharging a presto the Nd's, with a field of about 1T, could remagnetize whatever's in a presto head pretty much instantaneously. But it's just my guess.. What is the magnet in a presto, anyone happen to know?

[opcode66]

Tapping with a brass hammer is and was a method employed to magnitize.