Rolling or rotating lifters and arms?

[jviss]

(Second in a series of stupid newbie tape questions):

Why don't tape deck lifters and tension arms have rotating contact surfaces?

Is it because of potential flutter issues?

Is it because of magnetization issues?

I think rotating contact surfaces would last much, much longer, and would be inherently more easily renewable, albeit more expensive to make.

However, as a hobbyist, I can easily rationalize the time and trouble of fabricating something if its a big improvement.

Thanks,

jv

 

[jpmorris]

Cost, I expect. The high-end decks - i.e. studio ones - tend to have rotating guides, the cheaper ones don't.

 

[sweetbeats]

There are arguments both ways.

Tape gliding over a stationary surface produces scrape flutter, but tape gliding over a rolling surface with less than precision bearings can induce mechanical "noise" into the process too.

Also, I've read something about rolling surfaces being less effective as tape guiding instruments or potentially inducing more edge damage if the path isn't setup right because you have a sweeping surface as an edge guide rather than a stationary surface.

Also, depending on the transport, a stationary guide provides sme impedance which can be important.

So, yeah, it likely comes down to a cost issue, because it takes $$$ to do the rolling stuff right.

David Ollard (thinbrownline) may chime in. He is the only source of which I know who makes replacement/retrofit Ampex MM 2" rolling guides and he did it to serve a need and purpose. Shameless plug. They are very nice. Done beyond Ampex specifications. Nearly impossible to find otherwise. You'll pay for them too but they aren't cheap to make, not to that specification. Why go to such an nth degree? The tape paths are fixed on the MM transports, and with signficant lengths of unsupported tape precision is key and having rolling guides to minimize scrape flutter is key as well. Look at any of the 3M professional wide-track machines and compare to the Ampex MM machines and you'll see what I mean...tape goes everywhere on an MM (especially the MM-1000), but stays nice and compact on the 3M path. Ampex did go to great lengths to combat scrape flutter and according to an article I read held its own against the M-79, but there is a lot of componentry to do it. My MM-1000 in 1" trim has two precision jewel-bearing scrape flutter idlers on the headblock, and then there is a viscous-damped idler upstream of the headblock. Both of these components are pretty standard Ampex fare for the day. The tension arms are stationary but provide little tension so its not really critical, IMO. Everything else prior to the capstan (save for the heads of course) is rolling *except* for the guide right before the erase head. Gonna replace that with an offset rolling guide someday. But one of the Ampex machines cost bucoup bucks back in the day.