sweetbeats
Reel deep thoughts...
These (i.e. the thread title) are the sorts of things I think about...another example: from the time I could drive and owned a car one of my favorite things to read was the factory service manual for any car I owned...read each one cover-to-cover several times and put it to use. And so I take a few moments to share some of these things I think about since I am now, as of the last few years, a renewed tape machine enthusiast. Enjoy, comment or ignore...or...whatever.
I remember wondering why, with its relatively recent manufacture, the Tascam BR-20 had a belt-drive capstan vs. direct-drive (i.e. the capstan motor drives a flywheel with an integral capstan shaft via a belt vs. the capstan shaft being an integral extension of the capstan motor shaft itself). I had asked the question in the past without any conclusive answer. I think I can answer my own question now...
I'd always associated "belt-drive" with being less professional or rugged. This happened because of my observations that many consumer decks would have one or two motors for all three basic transport functions (i.e. supply reel motor, takeup reel motor, and capstan shaft), and more "professional" decks had a separate motor for each...therefore "belt-drive" became, for me, a symbol of compromise.
There are so many things in play here that I've come to know that have helped me to shed my ignorance on this small topic...I remain very ignorant on a great many things.
DC servo capstan motors have an innate flutter component as a by-product of their drive mechanism when compared to AC hysteresis capstan motors. IOW a direct-drive DC servo capstan motor has a higher potential to induce flutter into the tape path depending on the motor design and notably the diameter of the capstan shaft (e.g. the smaller the capstan shaft diameter the higher the rotational speed for a given tape speed...the faster the capstan shaft spins the higher the frequency of the flutter component which typically makes the flutter more audible).
A rubber belt that decouples the capstan motor and the capstan shaft acts as a damper of this flutter component.
Mass is also a damper and that's where the capstan flywheel becomes important.
SO...
My point...
Nothing wrong with belt-drive, and in fact it is a great solution to damping the natural flutter component that is produced by the capstan motor. It is not necessarily a compromise.
On a side-note, this question of mine was further irritated some time ago prior to this conclusion when I brought my Ampex MM-1000 home and as I began to dissect the anatomy of this absurdly rugged, if not "crude" transport, I was shocked to find that the capstan shaft is...drum-roll (can you help me out, Otto)...belt drive! One obvious downside of a belt-drive component is that the belt can wear out, slip, break...so it is a maintenance issue albeit a minor one. Ampex addressed this by utilizing a composite mylar belt, not rubber. Supposedly never needs replacing. Also, the capstan shaft is *huge* on the MM-1000 (about 3/4" in diameter), and the flywheel is also huge...best of all worlds? Dunno...makes a racket, that's for sure.
Hope to learn more from anybody's responses to this including corrections to anything about which I'm in error.
I remember wondering why, with its relatively recent manufacture, the Tascam BR-20 had a belt-drive capstan vs. direct-drive (i.e. the capstan motor drives a flywheel with an integral capstan shaft via a belt vs. the capstan shaft being an integral extension of the capstan motor shaft itself). I had asked the question in the past without any conclusive answer. I think I can answer my own question now...
I'd always associated "belt-drive" with being less professional or rugged. This happened because of my observations that many consumer decks would have one or two motors for all three basic transport functions (i.e. supply reel motor, takeup reel motor, and capstan shaft), and more "professional" decks had a separate motor for each...therefore "belt-drive" became, for me, a symbol of compromise.
There are so many things in play here that I've come to know that have helped me to shed my ignorance on this small topic...I remain very ignorant on a great many things.
DC servo capstan motors have an innate flutter component as a by-product of their drive mechanism when compared to AC hysteresis capstan motors. IOW a direct-drive DC servo capstan motor has a higher potential to induce flutter into the tape path depending on the motor design and notably the diameter of the capstan shaft (e.g. the smaller the capstan shaft diameter the higher the rotational speed for a given tape speed...the faster the capstan shaft spins the higher the frequency of the flutter component which typically makes the flutter more audible).
A rubber belt that decouples the capstan motor and the capstan shaft acts as a damper of this flutter component.
Mass is also a damper and that's where the capstan flywheel becomes important.
SO...
My point...
Nothing wrong with belt-drive, and in fact it is a great solution to damping the natural flutter component that is produced by the capstan motor. It is not necessarily a compromise.
On a side-note, this question of mine was further irritated some time ago prior to this conclusion when I brought my Ampex MM-1000 home and as I began to dissect the anatomy of this absurdly rugged, if not "crude" transport, I was shocked to find that the capstan shaft is...drum-roll (can you help me out, Otto)...belt drive! One obvious downside of a belt-drive component is that the belt can wear out, slip, break...so it is a maintenance issue albeit a minor one. Ampex addressed this by utilizing a composite mylar belt, not rubber. Supposedly never needs replacing. Also, the capstan shaft is *huge* on the MM-1000 (about 3/4" in diameter), and the flywheel is also huge...best of all worlds? Dunno...makes a racket, that's for sure.
Hope to learn more from anybody's responses to this including corrections to anything about which I'm in error.