[QuadList] Non-Contact Extraction of the Program from Quad Tape - Ampex non-moving head

[Tim Stoffel]

On Mon, 2009-02-16 at 16:15 -0800, C. Park Seward wrote:

> 
> The quad head pushes so hard into the tape that the documentation  
> talks about the "tent" shape that is caused by the penetration. The  
> heat generated is tremendous. So a stationary head would cause much  
> less damage to the tape.
> 

All rotary head VTRs exhibit some degree of head tip penetration. Sony
even included an 'impact compensator' circuit in Betacam machines to
lessen the timebase instabilities caused by tip penetration tape
stretch. It has been steadily getting less as head technology improves.

There has been some talk of using a hall-effect head, with (I imagine)
the preamp very close to the head itself to reduce noise. This head
design could play back, but not record. Still, I think a focused-gap
head design could minize tip penetration in quad at the expense of some
minor interchange issues. (Unlike helical scan, tip penetration in quad
has a lot to do with interchange. Ennes covers the head-tape
relationship in exhaustive detail in his books.)

My 'quad of the future, dubbed the AVR-5 is actually something I have
thought over from time to time. The machine has a form factor similar to
a later Ampex 1 inch machine, except the supply and takeup reels are
above each other. It will mount in a 19 inch rack. The tape is simply
wrapped around the outside of the machine, between the reels. The
compliance arms swing out into the tape from top and bottom of the
transport area. (Or, vacuum columns can also be used in this design.)
The audio heads have a cover that moves up after threading. The female
guide shoe works like an AVR-1's Mark 20 head.

And has been discussed here, the head tips are a special 'low contact'
design, which reduces tape wear and increases head life. Sensors check
the tape for foreign objects (like zebra tape) and stop tape movement
before the debris reach the video head. The video head may not have air
bearings, as we have made substantial improvements in bearings since the
early quad days.

The electronics are in a bay below the tape transport, just likke in 1
inch. A full-frame TBC does whole-field velocity compensation, as well
as providing a meaningful picture in shuttle. The servo system would be
a modern digital equivalent of the AVR-1 and offer near-instant lockup.
The machine would be easier to set and use than a 1 inch machine.

I believe a digital version of this machine could also exist, and have
excellent performance. HD is also a strong possibility.

Its fun to dream.....
Tim Stoffel