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Author Topic: What speed is your deck ACTUALLY running at???  (Read 9366 times)

Offline stellavox

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What speed is your deck ACTUALLY running at???
« on: May 12, 2008, 06:18:40 PM »
Thought you?d thunk enough today? Well think again! Here?s a think piece for you.

How do you know if your recorder is running at the correct speed?  And who cares? Let?s leave the ?who cares? part for later.  OK, I cared - this afternoon when I was trying to finish up tweaking my ?new? ASC 6002 recorder.  Finished setting the tape tensions, then the instructions mentioned how to adjust the tape speed.  Simple I thought, just record a high frequency tone and measure its frequency coming off the tape.  But; wait a minute dummy ? the tone gets converted to a wavelength on the tape and as long as the tape is playing at the same velocity when I ?listen? to it, it will have to be the same frequency ? which is certainly the case if I listen off the third (playback) head.  Even if I had a two head machine, as long as its capstan motor keeps turning at a constant speed, when playing back I?ll still measure whatever frequency I record.

OK, how to get the recorded wavelength "right"?  Let?s see, I guess you need to get a tape with some "standard? frequency recorded on a deck that?s running EXACTLY at whatever speed you want to check your deck at, with low enough wow and flutter to be able to measure the frequency ?precisely?.  Running to my trusty MRL Calibration Tape catalog, I find that these tapes certainly exist and are part of their 3150hz flutter and speed test tapes, which of course I don?t have as this test is not part of my ?standard? tapes (with level, azimuth and frequency sweeps only).  The MRL flutter and speed tapes have specs better than +/- 0.1% which equates to +/- 3.15hz from a speed perspective.  Oh great - another $100+ tape.

Then I remembered that the idlers on both sides of the Stellavox headblock have concentric marks which when viewed under a neon light (switching on and off at 60hz) create a stroboscopic effect that results in a non-rotating ?circle? when the tape speed is exactly ?on?.  The circle starts rotating slowly clockwise if the speed is too slow and counter-clockwise if too fast (I might have gotten that backwards).  Had an extra idler in my parts bin and was able to ?jury rig? a temporary mount on the deck; which enabled me to determine that the speed was a little slow.  In the process I found that the pinch roller pressure also seemed low and that the tape was slipping due to a hardened roller. Oh well; Terry Witt gets another pinch roller to rebuild, and I?m dead in the water till after VSAC2008.  More time to pack! 

This also reminded me that back in the 60?s??!! these stroboscopic, speed measuring, wheel thingies were advertised in Allied and Lafayette catalogs.

Does correct speed matter?  You tell me.  Enough thinking; now where?s that aspirin bottle ? better yet, a cockatail.  O yeah, PLEASE feel free to correct any missed-conceptions or outcomes mentioned above.

Charles

Offline ironbut

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Re: What speed is your deck ACTUALLY running at???
« Reply #1 on: May 12, 2008, 07:00:54 PM »
Funny you should mention that. I'd noticed a very slight drift on the strobe (@15 ips) on my Technics the other day. Looked in the service manual and and found where the adjustment of that is. I have the Tape Project test tape and hooked my Fluke up to a spare male RCA connector and away I went. I measured the 1Khz at the beginning of the tape and got 998.3hz on my meter. I figured that that was close enough and zipped up the back and listened to a few tapes to see if I could detect anything by ear,.. I couldn't.
So here it is a couple of weeks latter and I just try not to look at that strobe. If I just glance at it, everything seems perfect. But if i stare at it long enough, the mark will drift out of sight eventually. I'm wondering now, after reading your post, if the strobe light on my machine might just as well be indicating an increase(?) in the 60hz AC as a change in my deck? I hadn't adjusted anything before I noticed the drift (noticed could be the operative word here though).
While I'm waiting for a response, I surf over to WebMD.com and look up "Strobe Induced Psychosis".
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Offline Studer Fool

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Re: What speed is your deck ACTUALLY running at???
« Reply #2 on: May 12, 2008, 07:10:26 PM »
Accurate exact speed reproduction seems to be a parameter whose importance is variable from individual to individual.  Seems that it's most important to those with perfect pitch or near perfect pitch.  Typically musicians.  For those like me it's not so big a deal.  But different people really do hear differently.  I NEVER noticed that Miles' "Kind of Blue" LP second side was at the wrong speed.  Most people didn't.  But I've read there were a few who caught it immediately.

Charles, have you tried just measuring the 1KHz test tone on any alignment tape (including the The Tape Project one) with a frequency meter?  Given what you have just found, it would be an interesting data point, for future reference if nothing else.  I'm not sure what your needs for precision are, but plus or minus a hertz or two from 1000Hz shouldn't be too big a deal.  At least for me.  It's wow, & particularly flutter that are the fidelity killers.  

cdw

P.S.  - By the way I covet a Stellavox TD9 studio machine.  But I can't find even a single price quote on the web.  Do you know a range?
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Offline stellavox

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Re: What speed is your deck ACTUALLY running at???
« Reply #3 on: May 13, 2008, 04:28:06 AM »
Chris,

Regarding the TD 9 (and its predecessor the TD 88).  First of all, the Stellavox book indicates that there were less than 200 made and of those maybe only a dozen ever reached the US.  As you may know, Levinson used it initially for the transport on the ML 5, and one importer I talked with said that the FBI used a few especially modified units to read the "black box" recorders installed on commercial airlines.  That said, the ones I've seen advertised for sale all seem to be set up for film purposes with the "wrong" (i.e. film) headblocks and tensiometers.  O yeah, there are two broken ones down in the Nashville area (TD 9's apparently had the ability to go up in smoke and a VERY reputable repair facility couldn't get them going).   I and many others have/are trying to ferret one out but don't ever expect to find one.  Expect to pay thousands.  I do have the manuals.

Charles 

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Re: What speed is your deck ACTUALLY running at???
« Reply #4 on: May 14, 2008, 01:53:03 AM »
Thanks Charles!
I figured thousands.
But there's a Stellavox book?  How do I get a copy?
Less than 200 TD 9s made is a surprise, I guess I'm protected from ever becoming a "Stellavox Fool" though I'd like to be, or perhaps more accurately at least from becoming a "TD 9 Fool".  I've always admired Stellavox as a pinnacle of the tape recorder arts.

cdw
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Offline stellavox

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Re: What speed is your deck ACTUALLY running at???
« Reply #5 on: May 14, 2008, 06:46:25 AM »
Chris,

A gentleman in Germany produced a beautiful limited edition book devoted to George Quellet and his Stellavox recorders.  I helped out by editing the English translations.  My copy is in a box headed out to VSAC2008 so I can't give you particulars on how to (try and) obtain a copy.  Email me "off line" at [email protected]

Charles