Mellotronists

From:  "J.K.Beresford" <j.k.beresford@s...> 
Date:  Fri Mar 21, 2003  4:12 am

Subject:  Re: [Mellotronists] MK II station changing
  I don't necessarily "want" this John(I don't even own a MKII).I 
have just heard some of the horror stories about tape foulups from 
the shuttle mechanism.Just was curious if anyone ever tried to 
improve on the technology yet.               Charles
 

 
 

Why do you want to do this? It works pretty well unless you have a 
weak pulse - in which case Martin can provide a stronger pulse 
tape - and if it misses going one way it usually gets it on the way 
back. I think whatever system you come up with it will involve tape 
moving past a head of some sort. Actually the optical tape-stop 
sensor on my Revox B77 does work annoying well - picking up 
every bad splice it sees! If you're looking for a new system - there 
you go!
John 
M300#005

>Why do you want to do this? It works pretty well unless you have a
>weak pulse - in which case Martin can provide a stronger pulse
>tape - and if it misses going one way it usually gets it on the way
>back.

It does work, but it's somewhat complex and relies on analog circuitry to 
do its dirty work and thinking.  Every time you hit a station button you 
hold your breath.  :-)

Ken M's Mark II cycling was knocked out of whack when he installed new 
tapes.  The tapes now stop well short of the pulse mark, so the inching 
part of the cycling takes a lot longer than it should.  Jerry's Mark I 
Julia cycles very quickly in comparison, as little as 3 seconds with an 
average of about 5-7 seconds, because it stops fairly close to the pulse 
and doesn't have so far to inch along.  Ken's Mark II is probably 15-30 
seconds or so.  I am sure Ken's Mark II can be adjusted to correct this.

Interesting:  I noticed that the higher the station number the more the 
inching, and that applied to Ken's Mark II and to Jerry's Mark I.  The 
motor seems to go into inching mode further away from the pulse the higher 
the station number.  So there's some kind of slop in there.  Fortunately 
for Jerry that extra inching is almost negligible.  Oh well, Ken.  :-)

Anyway...If a new mechanism were to be designed, it could still use the 
pulse tape, but I'm more than certain the station control would be done 
with a microprocessor and not use resistors in series, a draining capacitor 
(Jerry---I don't recall what kind of circuit you said that was), and 
machine hunt-and-peck.  :-)

I will have to say that it *is* clever.  Did you know that if you disable 
the pulse tape and it did go past where it thought it was to go it'd 
reverse and try to find its mark?  How it knows that I don't know---would 
love to see the schem & theory.

...kl...M400 #805 - one station, no waiting

* Ken Leonard - Web Table of Contents:  http://www.kleonard.com
* Get Outdoors New England:  http://www.GONewEngland.org

In a message dated 3/21/2003 3:02:59 PM Eastern Standard Time, 
ken@... writes:

> Ken M's Mark II cycling was knocked out of whack when he installed new 
> tapes.  The tapes now stop well short of the pulse mark, so the inching 
> part of the cycling takes a lot longer than it should.  Jerry's Mark I 
> Julia cycles very quickly in comparison, as little as 3 seconds with an 
> average of about 5-7 seconds, because it stops fairly close to the pulse 
> and doesn't have so far to inch along.  Ken's Mark II is probably 15-30 
> seconds or so.  I am sure Ken's Mark II can be adjusted to correct this.
> 

I would love to see this adjustment (if there is one) written up and posted 
on a web site somewhere.  I'll post it to my site if someone can explain the 
adjustment to me.  I know there's only a handful of people who would be 
helped by this, but it would be good information to have.

Actually, the cycling speed issue doesn't bother me much, since I don't 
switch stations mid-song, but I'd like to fix it just so I don't have to keep 
hearing about it ;-) (as I did at the recent MONEYPIT 2003 get together in 
Vermont last weekend).


Ken M.
MKII #247 (mine's longer - cycling time, that is.....)




Ken M.

charel196 wrote:

> From:  "J.K.Beresford" <j.k.beresford@s...>
> Date:  Fri Mar 21, 2003  4:12 am
> Subject:  Re: [Mellotronists] MK II station changing
>   I don't necessarily "want" this John(I don't even own a MKII).I
> have just heard some of the horror stories about tape foulups from
> the shuttle mechanism.Just was curious if anyone ever tried to
> improve on the technology yet.               Charles

_________________________________________________________

Greetings All,  Having just completed restoration work
on MK1/124, I can quickly "encapsulate" the cycling
system for you on MK1,MK2,SFX,and M300 models.

Pulse-tape is the means for stopping the motor during
"inching." A strong(saturated) signal of 1000 Hz
works in conjunction with the SSCU board.

Once the button is pressed on front-panel,a "ladder"
network determines whether to run forward or backward.
This is the time that tapes are zooming-along at 36 i.p.s.
The keylock is engaged,and indictator light extinguishes.

The circuit then "times-out" from flank-speed and then
starts to "inch". It's looking for the pulse-signal on the tape.
Inching can be adjusted for stepping width and frequency.

As mentioned above,the pulse tape stops the inching.
Keylock moves out of the way,and indicator light again
illuminates.

The rotary "sync" switch is vital as it is a  safeguard
to ripping tapes out of the machine. Eight little brass dots
(1-6, and fwd/back direction change) are contacted by a
"wiper" during movement. Driven by Reynolds or Meccano
chain. The switch must be kept clean,and all connections
to it. There are several BA9 fittings in this circuit,
2-3  each for respective keyboard. From age,wear,etc,
they can get loose and potential disaster can occur.

Other weird-science is cycling working great from one
direction,and like crap from the other. Remember , these
machines are approx.  35-40 years old. Leave nothing to
chance and check EVERY cable,connection,solder-joint,etc.

"The sum of all fears" in cycling is complete failure of
pulse detection and tapes do not reverse at extreme ends.
And the keylock not working,and someone presses a key.
.....CRUNCH!!.....RIP! go the tapes......

A "torture-test" was devised to prove reliability of SSCU's.
Pushing the Station-Select button and releasing the detent
will cause the motors to move at flank speed from 1 to 6,
reverse direction(hopefully) and back from 6 to 1. Indefinitely,
until a button is pressed-in again.  Do not attempt this with
your machine !   BTW, I've encountered all the scenarios
mentioned-above.  Now I know why my hair turned-grey,
then fell-out !

A modern approach to cycling is the use of encoding stepper
motors,and digital ckts. (simple adj. "one-shot.") And the
drivers to power the motor/solenoid. If a "cycling M400"
were to be constructed (& we've discussed this years ago),
I suspect upgraded bits would be in order.

Hope this tech-talk answers a few questions,folks.
It's not in full detail here. The unabridged versions can be
found in MKII/M300 manuals.   Cheers, Jerry the  K.