Mellotronists

kinchmusic@... wrote:

>  Hi guys.I've been onto Martin, discussing whether I should replace
> the pinch rollers on my machine. They are original and most definitely
> showing signs of wear. He says he can regrind them angling the edges
> so making better tape contact. However, I have the feeling that as
> they have become worn, it has affected the tuning of one note with
> another. Surely if you have pinch rollers that are a slightly
> different diameter from each other, they will be out of tune with each
> other to an extent. So I'm inclined to go for a complete new
> set.Anyone else have any opinions on the science of all
> this?Cheers.    Andy K   ,    EMI m400 #E4/140S
>
> -----------------------------------------------------------------------
>
> Greetings All ,
> To-date, I have resurfaced,reconditioned and chamfered
> pinchrollers on 10 Trons .   No change in  note-to-note pitch
> should be expected whatsoever.
>
> Here's the theory  behind it.  The capstan diameter  and its
> rotational velocity is the sole determining factor for trans-keyboard
> stability of  pitch.
> The pinchrollers are simply "idlers", following the capstan's
> movement  to bring tapes into motion.
> In principle ,  if their diameters were smaller, each roller would
> turn more quickly relative to capstan dia. & speed. Reverse is true
> if the pinchroller were of larger diameter...it  would turn slower.
> But each tape regardless is moving at 7.5 IPS  .
>
> However, if the resurfaced roller has a flat spot, that would
> induce  pitch variations for that particular note. The dreaded
> "wobblies" is related to pinchroller rotation problems, but more
> associated with wear of the shaft and nylon bushing within.
> And of course, alignment squareness to overall tape path .
>
> For example, I cleaned/resurfaced all 70 pinchrollers in MK-I
> #124. Though 40 years old, None needed replacement.
> They had a "glazed" look to the rubber surface which
> straightaway was removed with abrasive pad and treated
> with reconditioning fluid.
>
> Feel free to respond with your ideas on this very good point
> of Andy's.   Have a wonderful weekend ....Cheers,  JK

What is the rotational velocity of an unladen pinch roller?

Kean or Streetly?

I don't know that!

aaaaarrrrrrrrggghhhhhh!!!!

So anyway, yeah, diameter won't matter.  My experience:

- Scruffy is better.  Sand 'em so they're not shiny.

- Get rid of the edges.  I just round off the edges a little so more 
central meat gets to the tape.  Martin makes them look like motorcycle 
tires (or tyres) that makes for narrower but stronger central contact.

- Clean.  Out on the 'net they discuss how to clean pinch rollers, and I've 
read it's best to use a water-based cleaner, like Formula 409 or Windex, 
not an alcohol.  Alcohol dries out the material.  Do a Google search for 
more info.

- However when the pinch roller doesn't turn all that well, try the 
"Merbler Flick" (see "Wobblies" on 
http://www.kleonard.com/gear/tronecdo.htm).  It actually works.  I don't 
know if you have to use alcohol---maybe one of the other cleaners will work?

- Make sure the pinch roller is exactly parallel to the tape path.  I use 
pipe pliers to twist the pinch roller holder a bit to make sure the pinch 
roller is dragging the tape through straight.  You may have this problem if 
you see chafing on the edges of your tape or a stripe along your tape.

- Always adjust the machine properly - 
http://www.kleonard.com/mellotron/mellotronia/techtalk.htm

I've seen machines where the pinch rollers are cranked 
down.  Wrong!  'trons don't have to play like lead or mush.


Replacement is needed when:

- The axle or nylon bearing is trashed.  Sometimes a drop of lubricant in 
there can help, but most lubricants will cause the bearing to completely 
die sooner--but at least you'll get a bit more time out of it.

- The pinch roller is cracked/cracking or too hard to compress a little.

- The pinch roller has a flat spot.

- When you can't get the damn note right, and you've tried everything else 
you can think of!  :-)

...kl...
M400 #805 - meaty, beaty, big, and wobbly
M400 #1037 - went for 2 replacements

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