Microdrive Unit Design

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tcat
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Re: Microdrive Unit Design

Postby tcat » Fri Nov 03, 2017 2:08 pm

Hi Martyn,

Thank you.
As I understand it, writing involves the ULA 'switching' its inputs to outputs and driving the same (stereo) pair of coils with the 50/100KHz signals.


Yes, I agree ZX8302 ULA does FM coding / decoding, while MD ULA does FM amplification and TTL hysteresis correction when reading, in my opinion. As I think ZX8302 needs TTL signal levels to safely trigger transition states, you describe during read, while signal transitions should not also be slower.

TTL-signal-levels.png
TTL signals

When looking at `waveforms' in SM, I can see 2V and 1V in samples, which exactly hits TTL forbidden zone. That possibly means I do not understand it.

Tomas


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Re: Microdrive Unit Design

Postby tcat » Tue Nov 07, 2017 11:53 am

Hi,

Just mounted the good R/W head to MD Iss#5 unit here. What you see in the picture are two MD units connected in a chain, MDV3_ is Iss#6, and MDV4_ is Iss#5.

mdv3-4-2.JPG
Two drives connected in a chain

Now their speed is indicated by a simple program.
Iss#5 has mandatory mod applied.

mdv3-4_speed.png
Speed for two drives
mdv3-4_speed.png (5.46 KiB) Viewed 353 times


EDIT, now I have just freshly formated a cart in Iss#5, and I am getting 7,25 secs. While other reference cartridge indicate 7secs. The accuracy of the tool is 0.25secs.

Tomas
Last edited by tcat on Tue Nov 07, 2017 1:06 pm, edited 2 times in total.


tcat
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Re: Microdrive Unit Design

Postby tcat » Tue Nov 07, 2017 1:02 pm

Hi,

The tape map in MDV4_ Iss#5 after format of a used cart looks like this.

mdv4-map.png
MDV4_ map after FORMAT
mdv4-map.png (11.54 KiB) Viewed 320 times

EDIT, formatting further gives 224/227 total, on overage Iss#5 seems a good performer, but not as star a performer as Cristian or Rich reports here.

Tomas


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Cristian
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Re: Microdrive Unit Design

Postby Cristian » Tue Nov 07, 2017 7:47 pm

Of course I did'n get the super performance with all my tapes. Probably I have some "lucky" cartridge.
Can you tell me please which software did you use for this test?

P.S.
I finally succeed in demagnetize my mdv heads, so I'll run your speed test soon


tcat
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Re: Microdrive Unit Design

Postby tcat » Tue Nov 07, 2017 9:20 pm

Hi,

I managed to draw a magnetics curve, after quite a few emails exchanged with Louise, he has patiently guided me through it.
It shows an old MD tape record erased by a direct current, and a new record made with direct current premagnetics, that is a transition from one magnetic state to another.

Each writing to MD tape, begins with erasing record in both tracks, and then a new record is made either with (+) or (-) intensity per track. That should very roughly correspond to earlier picture showing `erase / write polarity on tape'.

write-erase.png
erase / write MD tape magnetics with direct current

Tomas
Last edited by tcat on Wed Nov 08, 2017 7:48 am, edited 3 times in total.


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Re: Microdrive Unit Design

Postby tcat » Tue Nov 07, 2017 9:48 pm

Hi Cristian,

Can you tell me please which software did you use for this test?

`mDoubler', program I coded for Italian preservation project, Outsoft - program idea contributor / tester, defacto so far the only user / licensee. It is fair to say, it was helped and inspired by Martin's Head work. Program is still actively developed.

I finally succeed in demagnetize my mdv heads, so I'll run your speed test soon

Excellent, how did you manage to demagnetise, as that is something I have not tried yet?

I believe yours and RWAP's Iss#5 drives really perform outstandingly, I wish to find out why, so I will be glad for your speed tests. I run my tests only on used cartridges, simply I do not posses new old stock ones.

Tom


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Cristian
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Re: Microdrive Unit Design

Postby Cristian » Tue Nov 07, 2017 10:41 pm

tcat wrote:Excellent, how did you manage to demagnetise, as that is something I have not tried yet?

A friend of a friend of a friend of mine came with something similar to this:
https://www.3345rpm.gr/wp-content/uploads/2015/04/Tape-Head-Demagnetizer-3345rpm.gr_.jpg
Surely the heads were already partially magnetized because now I can format and read more cartridges


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Cristian
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Re: Microdrive Unit Design

Postby Cristian » Wed Nov 08, 2017 10:31 pm

Cristian wrote:I finally succeed in demagnetize my mdv heads, so I'll run your speed test soon

So here are the values for my staight-edged microdrive units (seconds/rpm).

Cartridge A, first run:
mdv1 -> 6.75/2396
mdv2 -> 7.5/2156
Cartridge A, second run:
mdv1 -> 6.75/2396
mdv2 -> 7.25/2230

Cartridge B, first run:
mdv1 -> 7/2310
mdv2 -> 9.25/1748
Cartridge B, second run:
mdv1 -> 7/2310
mdv2 -> 7.25/2230
Cartridge B, third run:
mdv1 -> 7/2310
mdv2 -> 7/2310

Cartridge C, first run:
mdv1 -> 7/2310
mdv2 -> 7/2310
Cartridge C, second run:
mdv1 -> 7/2310
mdv2 -> 7/2310

Cartridge D:
mdv1 -> 7/2310
mdv2 -> 7.25/2230


tcat
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Re: Microdrive Unit Design

Postby tcat » Thu Nov 09, 2017 8:13 am

Hi,

mdv2 -> 9.25/1748


This value is high, I suspect that just one sector gap was missed, so I would just exclude it from measurement.
(7 + 7 + 7 + 14 ) / 4 ~ 9secs.

Other values measured are in the spectrum of 7secs which is nominal, given 0.25 accuracy.
I believe the tape loop time should be set to 7 (minimum) - 7.25(ideal) - 7.5 secs (maximum).

The values you get are not only influenced by the actual motor speed, but also by real tape load, as the loop is on some passes slightly tightened and then eased again, making drive run slower, faster respectively. Also worn out or a dirty roller loosing its friction will play some role here. Weak clutching side spring, etc, etc.

Your MDV2_ seems on average a bit slower, is that your star performer? Usually it is the drive mounted as MDV1_ , as MDV2_ picks some noise in the QL case, the QL board is a subject to applying the documented mod for better drive performance.

Tomas
Last edited by tcat on Thu Nov 09, 2017 11:07 am, edited 1 time in total.


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vanpeebles
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Re: Microdrive Unit Design

Postby vanpeebles » Thu Nov 09, 2017 10:46 am

This has been a very enjoyable and interesting thread to read :)



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