Terminology question: does "tangency" just mean "wrap"?

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sweetbeats

sweetbeats

Reel deep thoughts...
Working on my 388. Look at this page from the service manual:

https://www.torridheatstudios.com/documents/Tascam/Tascam%20388%20Service%20Manual%20pg%201-8.pdf

Look at section 1-3-6...the record/repro head on the 388 is semi-fixed...I believe the zenith is fixed, and there is little room for azimuth adjustment, but I just want to be sure that when they say "tangency" they just mean "wrap". I'm assuming I just slightly loosen the head mounting screw closest to the face of the stack, loosen the "tangency adjust screw" (the one to the rear of the head), reproduce a standard tone off the test tape and monitor the output from track 2 or 7 or both (or any track for that matter), swing the rear of the head back and forth (pivoting on the front mounting screw) and set it where the output is the greatest right? That's basically what it says but I got just a bit confused and wanted to make sure...

Here's a real-life shot of the head block...the record/repro head screws are at the right side of the picture...

IMG_0960_15_1.JPG
 
Wouldn't wrap more so refer to the overall backward or forward positioning of the head in relation to the tape? Tangency seems to be accurately described in the service manual in that they don't want you to mess with the wrap and only the angle of attack...akin the the angle of a razor blade on your chin while your shaving.

I'm sure they partially did this to give themselves the opportunity to sell you a new head when the wrap became too loose from excessive head wear.

Cheers! :)
 
Ghost is right - tangency is the angle that the tape makes to the centerline of the head (think rotation and remember that heads have a mechanical centerline and an electrical centerline often very close to the same).

And wrap which is how much the tape wraps around the head. This would be the Z axis or how far the head projects into the tape path.



--Ethan
 
Wow...I was always under the impression that wrap had to do with the, uh, tangency. Okay. so these heads feature fixed wrap, zenith, height, and semi-fixed azimuth.

I'm...learning...heh
 
Azimuth is the alignment of the heads perpendicular to the direction of tape travel. If the azimuth is misadjusted, any program recorded on both tracks will be played back slightly out of phase.

Zenith is the alignment of the heads in the same plane as the tape. For example, the bottom of the head can be kicked out too far, which may cause the top tracks not to fully contact the head, and would cause the tape to ride up on the head, snapping back down occasionally. The zenith can also be misaligned so that the top of the head is shoved too far out. The head should be aligned so that the tape rides against it with smooth contact to the entire surface.

Wrap is the alignment of the head so that the tape contacts the head at the center, aligned with the head gaps. The wrap adjustment causes the head to swing in an arc centered on the middle of the head, and moves the center of the head from the left to the right of center, depending on which way you adjust the screw.

Head height is adjusted so that the tape rides perfectly centered from top to bottom on the head. You can tell this immediately just by looking at the tape as it rides across the heads.

Tape-to-head contact is just that - the head should be positioned far enough into the tape path to ensure good contact with the tape. If it were too far back, insufficient pressure would cause playback to be inconsistent.
Click to expand...

Source:

http://www.churchsoundcheck.com/tra.html

So this reference is incorrect then...

And check this out from the Tascam 58 manual page 7-18 where it talkes about setting the tape-to-head contact in section B...the procedure it describes involves setting the tangency to address tape-to-head-contact. Read section B:

https://www.torridheatstudios.com/documents/Tascam/Tascam%2058%20Operation-Maintenance%20Manual%207-18.pdf

Head wrap is set for gap centering on the scrub or wear pattern.
Click to expand...

http://www.jrfmagnetics.com/tapeheadintro.html

That sounds like tangency to me...:confused:
 
Wrap does have to do with tangency....


Tangency is adjusted by rotating the head (one side out and the other in). To adjust wrap both sides go out or in equal amounts. Once you are no longer tangent your head is not symmetrical in how it contacts the tape and thus the wrap(around) left of center is different from the wrap right of center and may increase or decrease the total wrap.

In reality we want symmetrical wear on the head (the head is tangent) and enough wrap so that we get good head to tape contact without starting fires due to excessive contact (not to speak of excessive head wear).

--Ethan
 
Yeah, if you push the head deep enough into the tape, (wrap), the tangency looks after itself unless the tangency is seriously off to begin with.

More then one way to skin a cat, I guess, is the moral of this story. :)

Cheers! :)
 
Ooh - out of sequence posts

I cannot comment on how various folks have called the adjustments on their tape machines.

The wrap angle is the number of degrees in which a tape in contact with a cylinder (well this is not actually true as the wrap angle and contact angle are different in a complex way based on the physical distortion of the tape in the contact area)

Heads are not typically cylinders and this complicated the matter but we can disregard that.

Push the cylinder further into the tape and the contact area goes up.

If we define a center-line to the cylinder then we can have that center-line bisect the wrap angle (i.e. the cylinder is tangent) or the center-line can be offset in the wrap angle (i.e. the cylinder is not tangent).

The terms come from the math and may be used (improperly) by various vendors.

Here is a photo I snagged from an ieee paper on wrap.

--Ethan
 

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Everything you are both saying makes perfect sense and I think the inconsistency in handling of the terminology is what seems to have been throwing me.

True wrap adjustment is something I have not really had to deal with since the Tascam 48 and 58 have semi-fixed heads (along with all of Tascam's 1/2" 8-track heads), IOW fixed head height, fixed zenith, fixed wrap, semi-fixed azimuth (only small adjustments can be made since only small adjustments are needed because of the mounting principle), and adjustable tangency (i.e. wrap-angle). My 1" 8-track Ampex decks are a different story there which is a bit scary for me yet, but that's another "Story".

So this has really helped me and I appreciate it.

So here's another thought: am I right to think then that in a tape path like my 388 where the guides are fixed and the wrap is fixed (not the tangency or wrap-angle mind you, but THE WRAP...the protrusion of the head into the tape path), it may not be a good idea to turn the guides if there is a wear pattern on them and the heads? I mean, if the guides and heads have been able to wear in concert and then I turn the guides then (since the wrap is fixed) I'm actually changing the wrap because the new guide surface is now pushing the tape further out which would be the same as retracting the head or reducing the wrap? I realize we are talking about small increments here, and there are surely times when there has been an unhealthy wear pattern on the guides and they need be turned, but I'm talking about clean normal wear patterns on heads and guides...it'd be best just to leave 'em be until the head is shot yes?

Sweetbeats is fascinated...
 
If the wear on the guide posts is smooth and even, I'd probably just leave well enough alone because turning them to a virgin spot will reduce the wrap, thus reducing the tape to head contact pressure...and on an 8 track, 1/4" format, I'd want all the pressure the transport could safely bear.

If you had a brand new head, that would be a different story. Then, of course you'd want fresh guide post surface to match.

Make sense?

Cheers! :)
 
OK I give up

oK I give up. I just looked at my MCI headstack and the Wrap rotates the head (which is tangency) ... Now to see that the Ampex does.

-Ethan
 
Perhaps there's a variance in the terminology because of the varying shapes of all the various head manufacturers?

Some heads are very broad with gentle arcs while others have a very pronounced contact zone which meets with the tape.

Add to all of that, that there isn't a universal standard for how heads are mounted or what adjustment parameters are offered in aligning them!

So what it all boils own to, as far as what makes sense to me, is to follow the guidelines of the service manuals and adhere to their nomenclature for each particular machine.

If the industry couldn't get their collective heads together, why should we be expected to?

Cheers! :)
 
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