Mellotronists

kenmerb@... wrote:

>  In a message dated 10/14/2003 1:34:10 PM Eastern Daylight Time,
> charel196@... writes:
>
>> I was telling a buddy today about the inner workings of the MK2 and
>> he asked me a question I didn't know the answer to...since there
>> were
>> 2 speakers on each side of the tapes in close proximity to them what
>>
>> kept the magnets of the speakers from erasing the tapes?(even
>> gradually over time)
>
> ________________________Ken Merbler Added : ___________________
>
> This is a good question.  I think it's because the magnets are *at
> least* far enough away from the closest tapes so that they receive no
> damage.  I know that the magnets pose a significant risk to those
> close tapes when changing the tapes.  When I changed mine on MKII
> #247, I was warned about the tendency of loose tapes "diving" to the
> speaker magnet if given a chance, and this does erase them.  So, when
> I changed my tapes, I used a towel and a plastic bowl over the speaker
> magnet on each side, as shown on my web site.  But as far as tape
> erasure from normal use, I would say  that it's not a problem by
> design, although it looks like it would be. Ken M.

_______________________________________________________________

Greetings All,

The MK-I/II speaker magnets are low enough and  distant
enough not to cause any gradual degredation of tapes.
During normal operation ..... If a tape breaks,it will brush past
the magnet and partially erase the tape. LH Tapes 1-4 from
Gordon's ex-MK-I had noticeable drop-outs of audio.
Someone/something wasn't careful.....

The inverse squares law of physics applies to light , electricity,
and magnetism.   Ken M. was taking the proper precautions
during MK-II tape change.  I probably would have unbolted the
Wharfedales to make 100 % sure.

BTW, the JKMK6 has magnets even closer to the bottoms of
the M400 tape-frames within. No problems seen in two years +.
I installed mu-metal (mag. shield) adjacent to the spkrs.
to preclude a future disaster. My pro-active policy of safety.

That's why we 'Tron users cannot stress enough the need to
keep headblocks demagged,non-magnetized hand-tools,
electrical precautions when installing headblock cable,
yada,yada, yada.....

Cheers,  Jerry K.
(MK-I #124, 14,500 lines of flux within Spkr. RS/12/DD model. )

I was poking around on the web a couple weeks ago and ran across the claim
that the strength of a magnetic field drops off as the cube of the distance
rather than the square. I would have put big, big money on inverse-square.
Is this true? See http://www.dansdata.com/magnets.htm

So even smaller distances are involved. This pretty much kills my old "will
my String Ensemble mains transformer erase my M400 tapes?" question.

Best Regards,

- Gene

M400S #1023
M400S #1213
M400S #1289
(two of which are away from home at the moment, to be on somebody's upcoming
CD)

_______________________________________________________________ 
Greetings All, 
The MK-I/II speaker magnets are low enough and  distant 
enough not to cause any gradual degredation of tapes. 
During normal operation ..... If a tape breaks,it will brush past 
the magnet and partially erase the tape. LH Tapes 1-4 from 
Gordon's ex-MK-I had noticeable drop-outs of audio. 
Someone/something wasn't careful..... 
The inverse squares law of physics applies to light , electricity, 
and magnetism.   Ken M. was taking the proper precautions 
during MK-II tape change.  I probably would have unbolted the 
Wharfedales to make 100 % sure. 
BTW, the JKMK6 has magnets even closer to the bottoms of 
the M400 tape-frames within. No problems seen in two years +. 
I installed mu-metal (mag. shield) adjacent to the spkrs. 
to preclude a future disaster. My pro-active policy of safety. 
That's why we 'Tron users cannot stress enough the need to 
keep headblocks demagged,non-magnetized hand-tools, 
electrical precautions when installing headblock cable, 
yada,yada, yada..... 
Cheers,  Jerry K. 
(MK-I #124, 14,500 lines of flux within Spkr. RS/12/DD model. )

I have a Mackie mixer on top of my M400. Could there be any possible
magnetic damage?

-----Original Message-----
From: Jerry Korb [mailto:jkorb@...] 


Greetings All, 


The MK-I/II speaker magnets are low enough and  distant 
enough not to cause any gradual degredation of tapes. 
During normal operation ..... If a tape breaks,it will brush past 
the magnet and partially erase the tape. LH Tapes 1-4 from 
Gordon's ex-MK-I had noticeable drop-outs of audio. 
Someone/something wasn't careful..... 


The inverse squares law of physics applies to light , electricity, 
and magnetism.   Ken M. was taking the proper precautions 
during MK-II tape change.  I probably would have unbolted the 
Wharfedales to make 100 % sure. 


BTW, the JKMK6 has magnets even closer to the bottoms of 
the M400 tape-frames within. No problems seen in two years +. 
I installed mu-metal (mag. shield) adjacent to the spkrs. 
to preclude a future disaster. My pro-active policy of safety. 


That's why we 'Tron users cannot stress enough the need to 
keep headblocks demagged,non-magnetized hand-tools, 
electrical precautions when installing headblock cable, 
yada,yada, yada..... 


Cheers,  Jerry K. 
(MK-I #124, 14,500 lines of flux within Spkr. RS/12/DD model. ) 


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--- In Mellotronists@yahoogroups.com, Jerry Korb <jkorb@i...> wrote:
> 
> 
> kenmerb@a... wrote:
> 
> >  In a message dated 10/14/2003 1:34:10 PM Eastern Daylight Time,
> > charel196@y... writes:
> >
> >> I was telling a buddy today about the inner workings of the MK2 
and
> >> he asked me a question I didn't know the answer to...since there
> >> were
> >> 2 speakers on each side of the tapes in close proximity to them 
what
> >>
> >> kept the magnets of the speakers from erasing the tapes?(even
> >> gradually over time)
> >
> > ________________________Ken Merbler Added : ___________________
> >
> > This is a good question.  I think it's because the magnets are *at
> > least* far enough away from the closest tapes so that they 
receive no
> > damage.  I know that the magnets pose a significant risk to those
> > close tapes when changing the tapes.  When I changed mine on MKII
> > #247, I was warned about the tendency of loose tapes "diving" to 
the
> > speaker magnet if given a chance, and this does erase them.  So, 
when
> > I changed my tapes, I used a towel and a plastic bowl over the 
speaker
> > magnet on each side, as shown on my web site.  But as far as tape
> > erasure from normal use, I would say  that it's not a problem by
> > design, although it looks like it would be. Ken M.

 Just how far does a magnetic field extend from the speaker magnets? 
Wouldn't it pass thru a platic bowl? Nowadays since there are 
magnetically shielded speaker setups available I would think that 
would be a significant upgrade...

In a message dated 10/14/2003 8:16:02 PM Eastern Daylight Time, 
charel196@... writes:

> Just how far does a magnetic field extend from the speaker magnets? 

Not sure, but we know the tapes can live pretty close to the speaker magnet 
without causing damage.  During the tape exchange, I was working under the 
assumption that the tapes wouldn't be damaged unless they actually landed on the 
magnet, that's why I used the precautions. 

> Wouldn't it pass thru a platic bowl? 

Yes, not the best choice, but it was what I had available at the time.  I 
used that in addition to a towel when I realized there was still a strong field 
going through the towel.  The shape of the bowl would keep the tape at a 
greater distance if one spilled out in that area, and it wouldn't be sucked onto the 
magnet.  Obviously, Jerry's suggestion to remove the speakers is the better 
solution, but I was willing to take the risk and be careful, using what I had, 
and it worked.

Nowadays since there are 
> 
> magnetically shielded speaker setups available I would think that 
> would be a significant upgrade...
> 

Probably, but the tapes are at risk mainly during tape change, which isn't an 
everyday event on a MKII.  I suppose you'd have a problem if a tape near the 
magnet broke while playing, but then that tape would be gone anyway (and I 
haven't lost one yet on my MKII).  I like the original Wharfedales, so I'm not 
really interested in replacing the speakers.  These issues just come with the 
territory.  Owning a MKII is a Religious experience.  Every time you turn it on 
you hold your breath and pray ;-).

Ken M.

well I think.... er.... what where we talking about? mind's gone blank.....

I was pretty sure it was a cube law too. the best way to find out how 
dangerous magnetism is (when it's going to be close to tape, anyway) is to experiment 
with something that doesn't matter. magnetism doesn't travel very well 
through air.
 
many tape-recorders from portable cassette machines to full-blown grown-up 
pro machines like nagras have speakers right under the tape-path, and quite a 
few of the cheaper cassette portables used permanent magnets as erase heads, 
moving them into position when required from as close as a few mm away. erasing 
tape is quite difficult, even with older formulations, while the new 'tron 
tapes are quite a bit hotter to start with.
I expect les must've tried it to be on the safe side, though.

as for perching other things on the 400's lid, you're more likely to 
encounter HF interference if anything; the pre-amp is pretty-well shielded against 
anything else. 1098 complained about a cheap midi controller once, but then who 
wouldn't?

duncan/1098, currently propping up a sick schaltwerk, and waiting for a 
second sh1000 to show up.

FYI on Chamberlins (a bit of de-lurking...) and magnetic fields: On the
M series, the cheap preamp transformer doo-hickie is provided as an
outboard appliance with a warning to keep it away from the machine -
perhaps Harry and Richard were concerned that the tight real estate
space in the 'tabletop' design could create a problem for the tapes...or
they were just paranoid. 
Either way, I used to plop my Crumar T1 organ on the top, which has a
sizable transformer in it...no problems. In my M2, I by-pass the old
pre-amp and take my headblocks direct to a Cerwin-Vega rack-style
pre-amp - just need to remember not to run the tapes while I'm turning
the pre-amp on in case of a 'pop' ending up feeding back onto a tape....

Vance

-----Original Message-----
From: ferrograph@... [mailto:ferrograph@...] 
Sent: Wednesday, October 15, 2003 5:24 PM
To: Mellotronists@yahoogroups.com
Subject: Re: RE: [Mellotronists] MK2 Spkr.Magnet Question

well I think.... er.... what where we talking about? mind's gone
blank.....

I was pretty sure it was a cube law too. the best way to find out how 
dangerous magnetism is (when it's going to be close to tape, anyway) is
to experiment 
with something that doesn't matter. magnetism doesn't travel very well 
through air.
 
many tape-recorders from portable cassette machines to full-blown
grown-up 
pro machines like nagras have speakers right under the tape-path, and
quite a 
few of the cheaper cassette portables used permanent magnets as erase
heads, 
moving them into position when required from as close as a few mm away.
erasing 
tape is quite difficult, even with older formulations, while the new
'tron 
tapes are quite a bit hotter to start with.
I expect les must've tried it to be on the safe side, though.

as for perching other things on the 400's lid, you're more likely to 
encounter HF interference if anything; the pre-amp is pretty-well
shielded against 
anything else. 1098 complained about a cheap midi controller once, but
then who 
wouldn't?

duncan/1098, currently propping up a sick schaltwerk, and waiting for a 
second sh1000 to show up.


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