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