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Author Topic: Swiss Army Knife R2R  (Read 5992 times)

Offline ironbut

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Swiss Army Knife R2R
« on: September 28, 2012, 09:26:24 PM »
Quite a while back, Larry Toy (astrotoy) was kind enough to give me his Ampex ATR700. I was curious to see just how good a machine it was and planned to go through it and get it up to snuff.
A couple of years passed and it sat on my bench gathering dust waiting for me to whittle down my backlog of projects.

A month or two ago, I was flipping through the pages of Ampex offerings on eBay (alway in search of that ATR102 that nobody wants) when I spied a full track mono headblock for an ATR700. It was cheap enough so I picked it up and quickly forgot about the '700 once again.
I should say that for whatever reason (can't rightly say!), I started collecting very old tapes in every format you could think of and some of them are full track and 1/2 track mono.
Once the headblock arrived and it looked to be in decent shape, I started to look for a full service manual. Luckily, I found one and started to think about what I wanted to do with the machine.
Seeing that I had the full track head and the stock 1/2 track could be used for 1/2 track mono, making this into a dedicated 'odd format' machine seemed like a natural.

Of course, all those old tapes are early acetate which can be very fragile. Keeping that in mind, once I did the usual cleaning/lube and voltage checks, I adjusted the machine to factory spec's. Once I was satisfied that all was working correctly I lowered the tension bit by bit until I started to lose signal level (home made multiband test tape) then I increased the tension a hair and put the machine through it's paces for a day or two and tested it again.
Then I did the same for the brakes making sure that they would stop the reels precisely with the least amount of tension for 7" reels only (not far off of the specs actually).

Then, it was time to actually play some of my weird format tapes. Using Y connectors, I listened to a number of my mono tapes and they sounded way better than I had hoped. Except for having to change the headblock, it was fantastic to finally hear the full track tapes as they were meant to be played (instead of using a 1/2 track head). They seem to sound fuller with the full track head.

But now came the real test.
The ATR700 is a 1/2 track record and playback machine. Some come with a 4th 1/4 track head like my Technics or some Otari's (this one didn't), but it's also one which the record head can be switched to sync for 2 track overdubbing. I'd heard that some machines with this feature have the correct distance from the gap of the record head to the gap of the playback head to listen to the old "staggered heads"  stereo tapes.
So, I put a staggered head tape (Atlantic AT 7-8 BN) on my Technics regular 1/2 track stereo machine and recorded it into some digital editing software. In that software I'm able to zoom onto a transient and line up the two channels visually as well as by ear.
Once I was satisfied that I'd lined the two channels as it was originally recorded, I put the same tape on the Ampex, put the left channel of the record head on sync (playback), and let 'er rip.
A/B comparisons revealed just a tiny bit of smearing and I adjusted the sync head by ear as well as adjusted the balance till it sounded about right.
I was more than pleased! Even though the sync channel doesn't have the same frequency extension or as nice a curve, the stereo image was killer!
I then recorded the playback from the Ampex into the editing software and took a look. It was pretty much spot on.

I've heard that one of the selling points of the staggered head stereo format was "no crosstalk". I haven't really sat down to see if that makes any real world difference and at this point I don't think my excitement would allow me to make any objective opinions on the sound.
All I know is that even with a less than optimum set up (sync rather than a second 1/2 track repro head) it sound like music to me and I'm really happy with the results.

Fun little project and I have to thank Larry and that eBay guy that sold me the mono headblock for helping me get a "swiss army knife" reel to reel up and running.

Now, about that home brewed electrostatic headphone amp,..

steve koto
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Offline Listens2tubes

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Re: Swiss Army Knife R2R
« Reply #1 on: September 29, 2012, 05:03:47 AM »
Hi Steve, I too have come across some mono two track and staggered head tapes. I was thnking of using a spare Otari headblock with a pair of 2 track heads for staggered head playback. Can you tell me the center to center distance between your play head and the sync head? Thanks for waking me upon this.
Neal - Ampex Fineline F-44, 3 - Otari MX5050BII-2, Revox A77 Mk II , Teac A 4010s, 4070, Sony TC102A, Magnecord 1020, Systemdek IIX/Dynavector Karat 17D2MKII, CEC CD3300 CDP, K Works NanoMax DAC, Van Alsine Transcendence Eight+ tube preamp, Dynaco MkIV amp pair, Paradigm Reference Studio 100 v1

Offline ironbut

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Re: Swiss Army Knife R2R
« Reply #2 on: September 29, 2012, 12:36:26 PM »
Hey Neal,

IIRC, the first time I heard of using a sync record head with the right channel of the playback head for staggered tape playback was with an Otari. Which model I don't recall but it's easy enough to give it a try.
That's what I did and lo and behold, it worked like a charm.
I don't think I'd get too crazy about getting the channel to channel alignment perfect since any variation during the production of the tape, subsequent tape stretch etc, will cause some variations anyway.

So, here's a quote from Richard Hess during a discussion of the delays on staggered head stereo tapes;

".., 1.25 inches is the correct spacing for Magnecord.

However, I've had several two-track staggered head recordings which seemed to work better at 120 ms (on a 7.5 in/s tape) than the 167 ms delay that the 1.25 inch spacing would indicate. The math indicates that this was 0.9 inch spacing. BUT it was hard to tell on this tape as it was two halves of a choir in a synagogue and there was little common information between the two mics with a good arrival time pedigree.

Remember, that sound travels about 1.1 feet per millisecond so plus or minus 20 ms would be a mic spacing distance of +/- 22 feet which, in a large worship space recorded long ago by someone else is difficult to tell.

I did run sections at 100, 120, 133, and 167 ms delay and the 120 sounded the best. 100 ms would, of course be a spacing of 0.75 inches and 133 ms would be a spacing of one inch.

I once had my hands on an Ampex PR-10 with four channels of electronics, and staggered quarter track record and play heads. I think the stagger was under 1.25 inches. This was a home-brew cobble, but apparently worked when other 4-track recorders all required 1/2-inch tape.

Also note that instrumentation heads are typically spaced by 1.500 inches. You'll find this on the 7-track 1/2-inch IRIG tapes as well as the 14- and 28-track 1-inch IRIG tapes."

So, it would seem that 1.25" is the more common but as Richard found, this was not set in stone.

I wonder if this 1.25" was somewhat standard?
The Ampex 700 was designed by Ampex but was build by Teac using Teac parts for the most part. I do have several machines of various makes around here so maybe I'll do some rough measurements when I get time.
Maybe having a standard distance from record to repro gaps has something to do with tape echo?
Just a WAG.
« Last Edit: September 29, 2012, 12:52:04 PM by ironbut »
steve koto
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Offline astrotoy

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Re: Swiss Army Knife R2R
« Reply #3 on: September 29, 2012, 01:08:48 PM »
Hi Steve, glad you were able to use the Ampex. Thanks to mep who originally sold me the Ampex and introduced me to a machine that could play 15ips 2 tr CCIR.  Larry
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Offline steveidosound

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Re: Swiss Army Knife R2R
« Reply #4 on: October 01, 2012, 08:58:57 PM »
Very cool Steve.
Glad you got it working. Is it possible to find a spec used for both the Magnecord PT-6BN "binaurl"  and for the Voice of Music 701, which, as far as I know were the only two machines set up for staggered 2 track stereo.  The designation "for staggered heads" on the box you would think would be made for some standard spacing which would be common to both. But this was the early 50s, so perhaps not.
BTW, if you are looking for more material to listen to, I think I do have one pre-recorded tape in that format as well as a few half track mono ones.
Steve Williams

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Offline ironbut

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Re: Swiss Army Knife R2R
« Reply #5 on: December 20, 2012, 02:02:24 AM »
Hey Steve,

I've been putting together a little "history of early stereo/tape releases" post and during my research, I've found more info regarding machines meant for playing staggered 2 track tapes.
The February 9th 1958 edition of Billboard contains the first of their periodic "Focus on Tape" sections. In that issue they listed currently produced stereo tape machines and since both inline and staggered tapes were available at that time, on most of the brief descriptions, they stated which formats the machines were capable of playing.
Even though the Magnecord PT-6BN wasn't listed with the inline stereo capable Magnecords they did list, I found 18 different machines from 9 manufacturers which were listed as staggered capable.
I believe that many were more on the "cheap consumer" side of the equation, however it appears that Ferrograph built a machine called the F106C which might have been pretty nice.

Regarding early stereo tape releases, so far my research indicates that Livingston may have been the earliest producer of consumer prerecorded stereo tapes. They also obtained licenses to produce tapes of many other companies.
The same 1958 Billboard mentions that a new Livingston tape catalog was being released which included over 90 stereo titles along with over 150 mono tapes.

An interesting addition to my "early tape " collection is a Sonotape test tape for 2 track staggered!
steve koto
 Sony scd 777es(R. Kern mods)> Vpi Aires>Dynavector XX-2mkll>Bent mu>CAT ultimate>CJ premeir 140>Magnepan 1.6qr(Jensen xover)Headphone Eddie Current Zana Deux>AT ad2000,HD800 ,Metric Halo ULN-2 (battery powered),
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