Discrete Vs Combi Cassette Deck Heads

[knobtwiddler]

>Again AFAIK they didnt transition away from discrete. They never adopted >discrete 3 head

I think my definition of 'discrete' head might be different from yours. I was thinking in terms of the Sony head (posted by John earlier in thread) as being 'discrete', whereas it would seem that you (and most likely the rest of the world ) think of it as a combi-head, but with individual adjustment.

If your definition of 'discrete' means that the heads have several mm of fresh air between them, then fair enough. Attached photo shows a Sony 3-head mechanism. Definitely discrete. But also mono! It's an interesting one, as the deck doesn't have any adjustments bar recording level, but it does have live monitoring...so I suppose the only benefit of the 3 heads is to check rec level...

Tandberg also used discrete heads, no? I get the impression that purists cite Nak and Tandberg as the only true discrete deck OEMs. Personally, I'd include Sony, if they have separate adjust screws - as per John photo.

[TIMTAPE]

Originally Posted by knobtwiddler

>Again AFAIK they didnt transition away from discrete. They never adopted >discrete 3 head

I think my definition of 'discrete' head might be different from yours. I was thinking in terms of the Sony head (posted by John earlier in thread) as being 'discrete', whereas it would seem that you (and most likely the rest of the world ) think of it as a combi-head, but with individual adjustment.

Of course they are discrete heads in one sense. At what point do they cease to merit the description discrete? When record and play heads are bonded together? When there is no separate adjustment for azimuth, or for tilt, height, penetration? I'm more interested in the innovations and applications themselves rather than which words we might choose to label things.


The Sony deck you picture with the play head in the right hand small window is interesting. I've not seen that before. Do you have a model number or any other information about the deck and its intended application?

[knobtwiddler]

Sony TC-142

If you go to a certain site and put it into the search you might even find the mechanism, inc. heads, for $23.60 USD.

Considering that combi heads are a lot (to put it mildly) easier to find than decent discrete heads, I was even wondering if you could hack a combi apart into discrete sections... But I suppose, even if you could do that without damaging them in the hacking process, you might have other issues as they're profiled / designed to be next to each other mechanically.

[knobtwiddler]

NB - one of two early Technics decks had fully discrete / 3 heads. The RS-9900US is one. I have read bad things about the 'HPF' head (hot pressed ferrite) in terms of noise and abrasion resistance. Am left wondering how accurate this is. One supposes that if HPF had been such a good compound, we'd have never had permalloy or amorphous heads...?

[Radio Wrangler]

Permalloy predates ferrite heads. Ferrite heads were reputed to be noisy, but I don't know of a mechanism for excess noise. I've used ferrite magnetics down to very low noise floors without measuring noise figures noticeably above what I'd expect from overall transformer losses at the ambient temperature. Maybe the head core ferrites are far different ones from the RF materials I'm used to?

David

[knobtwiddler]

Thanks!

My remarks about HPF heads were regarding 'hot pressed ferrite'. I read a posting at another group from someone who's tested hundreds of heads. My feeling is that he wasn't talking about self-noise, but noise in operation (could be wrong).

You can see the thread here (I hope I'm not breaking rules by posting a link...):

http://www.tapeheads.net/showthread.php?t=11301&page=2

As someone who was a compulsive cassette user, I can say that pretty much every deck I've owned developed grooves in the heads at some point - even ones bought in the 90s, with supposedly hard heads. People talk about lapping cassette heads, but my feeling is that they lend themselves to the process less well than the vastly larger R-R heads, which are routinely lapped.

[mitajohn]

Here is a pic I got for R/P head azimuth of B215 tape deck via a TDKSAX90 cassette after auto calibration, obviously less than 90 degrees at 10kHz/-10dB, but it is not stable and changes during recording in time and cassette side...but always less than 90 degrees.

[knobtwiddler]

Good work, John - thank you for sharing.

It would be interesting to repeat the test on various decks and see which ones are least / most afflicted. One imagines that Nak, with their famous azimuth system, will be on top in this regard. The hifi press must have done this in the 80s, right?

[Ted Kendall]

This thread reminds me of the late lamented John Longden's comment that applying Dolby and other refinements to cassettes was all very well but was essentially attempting to make something which is basically rather horrid work. Being EiC of Radio London and builder of the first BBC mobile stereo desks, he was, of course, prejudiced...

[TIMTAPE]

Originally Posted by knobtwiddler

Thanks!

My remarks about HPF heads were regarding 'hot pressed ferrite'. I read a posting at another group from someone who's tested hundreds of heads. My feeling is that he wasn't talking about self-noise, but noise in operation (could be wrong).

You can see the thread here (I hope I'm not breaking rules by posting a link...):

http://www.tapeheads.net/showthread.php?t=11301&page=2

As someone who was a compulsive cassette user, I can say that pretty much every deck I've owned developed grooves in the heads at some point - even ones bought in the 90s, with supposedly hard heads. People talk about lapping cassette heads, but my feeling is that they lend themselves to the process less well than the vastly larger R-R heads, which are routinely lapped.

Nak seems to have been the only OEM which attacked the cassette head wear problem at its source, by disabling the crude pressure pad. I suspect that Nak heads werent specially resistant to wear but without the pressure pad they now had an advantage in longevity. I've read comments that implied the Nak Crystalloy heads were the sole reason for the long life. But a valid comparison between head types would compare head wear under the same conditions.


Until about 20 years ago I serviced various makes of high speed cassette duplicator, and high speed tape travel - plus the crude pressure pad - gave all tape heads a hard time. The best heads in terms of wear seemed generally the Ferrite types but not all Ferrite heads seemed equal in that respect. Some ferrites seemed to suffer "crystal pullout" more than others. My impression is that over the years manufacturers were able to make much improved Ferrite heads. A problem with Ferrite heads though is that they cant be relapped using standard techniques.

Ferrite was always the head material of choice with standard VHS/ Beta/ camcorder 8mm/DV/DAT etc rotating heads AFAIK, regardless of make or model. Heads needed to be low wearing as they had a punishing job. Without Ferrite rotating heads, camcorders and VCR's would have worked at first but required a lot more frequent head replacement. Thanks to Ferrite heads, camcorders and VCR's had useable head lifespans.

Standard cassette heads can be relapped. When a head guide is attached to the side of the head, it's more difficult work, and because of cassette heads' smaller physical size they're more fiddly to relap than larger types. But they're still just tape heads.

Audio/control heads in VHS/Beta recorders can also be relapped unless they're Ferrite.

Even magnetic heads in Super 8mm sound movie projectors can be relapped if there's enough metal "meat" left on them. These unusual heads can develop a very nasty concave wear pattern due to the brutal plastic finger forcing the stripe onto the head face.

Here's a pic of an 8mm movie film sound stripe head, which I modified to fit an also modified removeable headblock, to fit a modified Revox A700. The reason was to transfer our family's sound striped 8mm movie films at decent original sound quality. Even good sound projectors are an audio compromise, usually adding hum, hiss and wow, and after a while the stripe to head contact becomes unreliable. Even access to the tape path in a projector for cleaning can be difficult. Here everything is open and visible. Maintenance is a cinch.

This is (or was) a projector NOS combi head with two erase sections to the left of the record/play sections. The remains of one erase coil is visible in the top track. After removing the erase sections I had to recontour the record/play faces for the altered tape approach angle - tricky doing it by hand. Of course no felt pressure pad in sight, or plastic pressure finger so the head should wear well.

[knobtwiddler]

Thank you, Tim. Did Nak patent the pressure pad? I took a look at an Alpine deck and although the photo wasn't great, I wondered if they also had it.

Looking at comments about combi heads, I've gotten the impression that OEMs stressed that modern production techniques enabled them to get the Rec / PB heads perfectly aligned, so there was no need to mount them separately... Because of the narrow width and slow speed, would it even be possible to get the pair aligned using a tool / jig? I tend to think that azimuth is so finnicky on cassette that a fraction of a mm is all that's needed to skew it. So, even if the head makers had precision tooling for aligning them, wouldn't there always be a wide tolerance once mounted in a machine?

[Ted Kendall]

Just to reiterate, if you dispense with the pressure pad, you need something like a hyberbolic grind on the head face and guttering at either edge of the polepieces, otherwise tape-to-head contact is likely to be insufficient, particularly as the head wears.

[TIMTAPE]

Originally Posted by knobtwiddler

Thank you, Tim. Did Nak patent the pressure pad? I took a look at an Alpine deck and although the photo wasn't great, I wondered if they also had it.

I'd be interested to know if Nak patented it, and also to see the Alpine photo. The only cassette pressure pad lifters I've seen so far are the ones I made and fitted myself to a few dual capstan decks.

Originally Posted by knobtwiddler

Looking at comments about combi heads, I've gotten the impression that OEMs stressed that modern production techniques enabled them to get the Rec / PB heads perfectly aligned, so there was no need to mount them separately... Because of the narrow width and slow speed, would it even be possible to get the pair aligned using a tool / jig? I tend to think that azimuth is so finnicky on cassette that a fraction of a mm is all that's needed to skew it. So, even if the head makers had precision tooling for aligning them, wouldn't there always be a wide tolerance once mounted in a machine?

Again I dont know although I believe these days, audio heads can be custom aligned in blocks using some sort of laser tool. Of course rotating video heads are precision devices but are installed without any facility to adjust azimuth, I guess because the machining tolerance of the heads and drums became so precise.

[TIMTAPE]

Originally Posted by Ted Kendall

Just to reiterate, if you dispense with the pressure pad, you need something like a hyberbolic grind on the head face and guttering at either edge of the polepieces, otherwise tape-to-head contact is likely to be insufficient, particularly as the head wears.

Yes many cassette heads use a larger radius head face but without a pressure pad, back tension alone may not be enough to eliminate spacing loss.

Also combination record/play heads as on the Revox B215 and many other brands probably cant dispense with the pressure pad because back tension alone cant provide the necessary "wrap" around each individual gap.

I havent tried yet to mill gutters in tape heads due to lack of the machining gear to do so. I did once pay a good machinist mill them them into some 1/4" reel to reel heads.
I think some of the higher end Nakamichi cassette decks had gutters in their tape heads. I have the older mid priced models like the LX, 480 etc. They dont have the gutters, so for good performance I've just hand relapped the heads when a slight groove developed.

One of the most annoying head wear patterns I've seen with a head which used a pressure pad is a small but deep dimple worn in the head right over the head gap area, making good tape contact impossible, pressure pad or not. It seems it only takes a small piece of hard material caught in the felt pad to create a pressure point, and the oxide surface on the other side of the tape at that point does the rest of the destructive work on the head. It's worse of course if the same tape side is played repeatedly.