# Reel-to-reel - different speeds on each reel? **URL:** \ **Category:** Factual Questions\ **Created:** [August 29, 2012, 7:04am UTC](https://boards.straightdope.com/t/reel-to-reel-different-speeds-on-each-reel/633013 "2012-08-29T07:04:29Z")\ **Posts on this page:** 12\ **Page:** 2
**Author:** ![Chefguy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chefguy/32/138_2.png) [@Chefguy](https://boards.straightdope.com/u/Chefguy)\ **Post date:** [August 29, 2012, 8:17pm UTC](https://boards.straightdope.com/t/reel-to-reel-different-speeds-on-each-reel/633013/21 "2012-08-29T20:17:58Z")
> [@Senegoid](#): > > The machine I had in the 1960’s was a Sony reel-to-reel tape recorder. It did have a slipping clutch (I guess that’s what you’d call it). The take-up mechanism consisted of: > – The motor. > – Rubber belts from the motor pulley to the take-up reel pulley. > – Take-up spindle had an inner ring (driven by the motor, via belt and pulleys). > – Outer ring surrounding the inner ring. > – Layer of felt separating inner and outer rings. This constituted the slipping clutch. > – All of the above is hidden below the deck. > – Above the deck, spindle for take-up reel is attached to the outer ring. I had a Sony in the late 60s, too. It came with speakers that were hinged to the tape deck and could be removed. It also had a futuristic option, wherein if the machine sensed a section of tape with no signal that lasted for more than about five seconds, it would reverse automatically. Prior to that, one had to apply a piece of sensing tape to make that happen. The only problem with that feature is that you had to be careful not to allow too large a gap between songs when recording. Bloody thing was hella heavy. ---
**Author:** ![Hail\_Ants](https://avatars.discourse-cdn.com/v4/letter/h/dc4da7/32.png) [@Hail\_Ants](https://boards.straightdope.com/u/Hail_Ants)\ **Post date:** [August 30, 2012, 4:51am UTC](https://boards.straightdope.com/t/reel-to-reel-different-speeds-on-each-reel/633013/22 "2012-08-30T04:51:50Z")
> [@Musicat](#): > > Only partly. If there wasn’t any back tension, the spring-loaded arms wouldn’t have any effect at all, would they? (There’s negligible friction on these contraptions.) Oh yeah, that makes sense. I went to college for Communications in the early 90s and they still had reel to reels in the radio booths (along with the two manually cue-able turntables, cart machines etc.) The teacher acknowledged that their technology was disappearing but we still learned their basics. Even did some razor editing (which was surprisingly easier to do than it sounds!) I also started in IT 20+ years ago and we were still using reel to reel drives on the mainframes too. I guess because they were always digital and had to be very precise they used low pressure, vacuum chambers on either side of the heads to maintain slack. Again, being digital, the reels never just rotated smoothly but always moved in spurts. Surprisingly we only retired the last reel to reel mainframe drive less than 10 years ago. ---
**Author:** ![jovan](https://avatars.discourse-cdn.com/v4/letter/j/0ea827/32.png) [@jovan](https://boards.straightdope.com/u/jovan)\ **Post date:** [August 30, 2012, 7:53am UTC](https://boards.straightdope.com/t/reel-to-reel-different-speeds-on-each-reel/633013/23 "2012-08-30T07:53:26Z")
> [@Hail\_Ants](#): > > Even did some razor editing (which was surprisingly easier to do than it sounds!) On the other hand, if it doesn’t sound, razor-editing a tape is _hard_. ---
**Author:** ![rtrg](https://avatars.discourse-cdn.com/v4/letter/r/dfb087/32.png) [@rtrg](https://boards.straightdope.com/u/rtrg)\ **Post date:** [October 9, 2014, 1:35am UTC](https://boards.straightdope.com/t/reel-to-reel-different-speeds-on-each-reel/633013/24 "2014-10-09T01:35:01Z")
> [@Small\_Clanger](#): > > The tape speed is controlled by the capstan, not the reel motors. The tape is squeezed between the rotating capstan and the pinch roller, the pinch roller spins because it is in contact with the capstan and gives the friction to pull the tape along. > > As **Alpha Twit** says the reel motors are quite puny, you can easily stop them with a finger. The capstan motor is much beefier, try gripping the running capstan\* you won’t be able to stop it. > > - Take the tape off first. Since you are apparently good at this, I will ask you for help. For open reel tape recorders IPS speed ranges from 1/78 through 30. For each of these speeds there is a corresponding capstan RPM. For 3.75 and 7.5 using a 6mm diameter capstan those RPM’s are 303.3 and 606.6. How is the best way to check that accurately? I tried a laser non contact tach that uses reflective tape but I get inconsistent readings. Of course I do not have the users guide so there is every chance I am not applying the tape correctly which barely sticks to the capstan. Is there a mechanical way? Contact tach? Strobe wheel with light? Can I buy a strobe wheel to attach to the shaft at the top? Neon light? Contact tachs are more$s than they are worth. Strbe types cannot be found. Any advice welcome. ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [October 9, 2014, 5:30am UTC](https://boards.straightdope.com/t/reel-to-reel-different-speeds-on-each-reel/633013/25 "2014-10-09T05:30:01Z")
Does the capstan have a flat top? If so, I’d stick a little disc of white bristol board with a pattern on it, and use a calibrated strobe. ---
**Author:** ![Musicat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/musicat/32/20189_2.png) [@Musicat](https://boards.straightdope.com/u/Musicat)\ **Post date:** [October 9, 2014, 12:04pm UTC](https://boards.straightdope.com/t/reel-to-reel-different-speeds-on-each-reel/633013/26 "2014-10-09T12:04:36Z")
> [@rtrg](#): > > Since you are apparently good at this, I will ask you for help. For open reel tape recorders IPS speed ranges from 1/78 through 30… Those numbers should be 1.875 (one and seven-eighths inches per second) through 30 ips. Standard speeds were derived by halving the faster speeds again and again. 60, 30, 15, 7.5, 3.75, 1.875, and even further. I don’t have a solution to your speed calibration problem, but I’m wondering what your end product is intended to be. Are you trying to measure the linear speed of the tape past the capstan or the rotation speed only? If the former, slippage might have to be taken into account. ---
**Author:** ![johnpost](https://avatars.discourse-cdn.com/v4/letter/j/f17d59/32.png) [@johnpost](https://boards.straightdope.com/u/johnpost)\ **Post date:** [October 9, 2014, 2:12pm UTC](https://boards.straightdope.com/t/reel-to-reel-different-speeds-on-each-reel/633013/27 "2014-10-09T14:12:04Z")
the condition of the pinch roller also has a lot to due with the speed control. the roller can be coated or glazed, also it might be aged and hard. either might cause speed problems. ---
**Author:** ![md2000](https://avatars.discourse-cdn.com/v4/letter/m/73ab20/32.png) [@md2000](https://boards.straightdope.com/u/md2000)\ **Post date:** [October 9, 2014, 2:31pm UTC](https://boards.straightdope.com/t/reel-to-reel-different-speeds-on-each-reel/633013/28 "2014-10-09T14:31:29Z")
Maybe a better check on inches/sec. would be to get a disposable reel of tape. Mark the beginning with a sharpie pen. Run the tape for a minute or two by stopwatch; the longer, the more accurate. Mark the end. measure between the marks. Just under 2 inches a second, 120 seconds would be just under 240 inches, accurately measurable with a good tape measure. The only question is - how good is your on-off timing skill? To avoid start-stop issues, maybe mark the tape while running, mark end while running… The issue with any capstan and take-up was the theory that (especially cassettes with fine tape) the take-up would actually collect the reel under tension. If left this way, the tape would stretch over time. The recommendation for audiophiles was to rewind (no tension, no capstan) after playing. ---
**Author:** ![casdave](https://avatars.discourse-cdn.com/v4/letter/c/c6cbf5/32.png) [@casdave](https://boards.straightdope.com/u/casdave)\ **Post date:** [October 9, 2014, 7:20pm UTC](https://boards.straightdope.com/t/reel-to-reel-different-speeds-on-each-reel/633013/29 "2014-10-09T19:20:23Z")
The way you check tape speed is to read the frequency output from a calibration tape. This has recordings made on it from an accurate machine at specified values, you can use a frequency counter for ease of use, far better than trying to calculate it from a scope trace. For a cheap and dirty way to do it, you can use a signal generator to produce a 1khz tone and record it on another machine that is known to be good, and then put it through your test machine and check for frequency. Calibration tapes are really the only real way for the vast majority of sound engineers to get the speed accurate, those tapes are also used to adjust head azimuth, and head alignment across tracks. You also use them to ensure that the head amps are all performing at the same levels. Once you know all your heads and head amps are correct, you then set up your record amps, and your vu meters, but first you get that speed right, head azimuth and replay amps. ---
**Author:** ![wolfpup](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/wolfpup/32/10618_2.png) [@wolfpup](https://boards.straightdope.com/u/wolfpup)\ **Post date:** [October 10, 2014, 12:01am UTC](https://boards.straightdope.com/t/reel-to-reel-different-speeds-on-each-reel/633013/30 "2014-10-10T00:01:19Z")
> [@Alpha\_Twit](#): > > I doubt there’s any kind of clutch in the take up reel mechanism. There wasn’t one in any of the assorted mechanisms I’ve studied and repaired over the years. It’s just a not very powerful motor turning as fast as it can and limited by the foot per minute feed speed of the tape reader and capstan. Some may have been designed that way, but you would have needed one or more powerful motors driving the reels for the fast-forward and rewind functions. When the tape is fast-forwarded or rewound, some part of the pinch roller/capstan assembly is mechanically moved out of the way and the left or right reel is powered directly. Inexpensive home machines typically did this with mechanical controls and a single motor with belt drives, while higher-end and studio machines had multiple motors and electronic pushbutton controls. > [@Hail\_Ants](#): > > Of course, because reel to reels were never really a consumer product but meant for professional use, many of them could do the above in reverse. Reel-to-reel tape decks were **absolutely** a consumer product and no self-respecting sound system enthusiast would have been without one. They came in a wide variety of price ranges from a vast array of vendors – Sony, Pioneer, and Teac were among the most popular. In fact the very term “tape deck” implies a hi-fi system component, as it needed the rest of the system – the power amp and speakers – in order to operate. Many purists stuck with them long after cassette decks became popular because of the superior audio quality. I’m sure I still have an old Sony deck packed away somewhere. [This](http://p2.la-img.com/1347/36976/15518270_1_l.jpg) is a typical basic consumer-grade deck with mechanical controls; [this](http://img.canuckaudiomart.com/uploads/large/184412-sony_tc765_reel_to_reel_tape_deckmint_.jpg) is a better one with electronic controls, but nowhere near studio grade. ---
**Author:** ![casdave](https://avatars.discourse-cdn.com/v4/letter/c/c6cbf5/32.png) [@casdave](https://boards.straightdope.com/u/casdave)\ **Post date:** [October 11, 2014, 4:11pm UTC](https://boards.straightdope.com/t/reel-to-reel-different-speeds-on-each-reel/633013/31 "2014-10-11T16:11:35Z")
That second machine you linked **Wolfpup** is not that far off studio grade given that its a Sony TC765, it could certainly be described as semi-pro, its close cousin the TC 766 which looks almost identical and has most of the same electronics definitely strays into pro use, given that its a 38cm/s 2 track machine. ---
**Author:** ![rsa](https://avatars.discourse-cdn.com/v4/letter/r/839c29/32.png) [@rsa](https://boards.straightdope.com/u/rsa)\ **Post date:** [October 13, 2014, 5:58am UTC](https://boards.straightdope.com/t/reel-to-reel-different-speeds-on-each-reel/633013/32 "2014-10-13T05:58:11Z")
> [@Small\_Clanger](#): > > …the reel motors are quite puny, you can easily stop them with a finger. The capstan motor is much beefier, try gripping the running capstan\* you won’t be able to stop it. I had a Pioneer reel-to-reel and the reel motors were quite large. I used metal 10 1/2 inch reels with 3600 feet of tape. Those big reels were spinning so fast during fast forward or rewind that they’d make quite a little breeze. You definitely wouldn’t want to try stopping that with a finger! [Previous page](https://boards.straightdope.com/t/reel-to-reel-different-speeds-on-each-reel/633013.md?page=1)