Tôi hoàn toàn đồng ý với quan điểm của bác và đây ý kiến của 1 Guru về đầu tape deck AKAI steve lender(USA) về bản chất của đầu từ SONY FERRITE & FERITE cũng như AKAI GX để các bác tham khảo nhé: Comment #50 Subject: Reel to Reel Head Question Date: Wed, 21 Apr 2004 19:11:02 -0700 From: Jim Ellis Dear Steven: I recently read a post of yours on Dantiques.com regarding tape heads, and I was extremely impressed with your degree of knowledgability on the subject. Would it be fair for me to summarize your argument by saying simply that the GX heads are superb, and last forever, and that all others basically suck? I wanted to question your assertions that other Ferrite head designs are so vastly inferior to the GX heads. You said that the other designs head gaps would chip over time, and widen. Obviously, if you are correct about this, then this would be a very bad thing. However, I simply fail to understand why you think that if other Ferrite designs are subject to this problem, why Akai's are not. I fully realize that the Akai's are partially made of glass. From what I can tell, by looking at the heads of my GX 747, it seems as if glass is being used to sandwich the electromagnets for each channel inside the heads into position, rather than using a substance like plastic for this purpose. But, I fail to see why this construction would make the heads any more immune to the gap "chipping" effect on the ferrite portion that you wrote about, than are other very high quality ferrite heads, like the Sony F&F heads. One statement that you made that I noticed did not fit with my experience. You claimed that the High-End Sony's rejected the ferrite designs, and that only the lower-end, and older designs used the ferrite heads. I am familiar with the majority of the Sony R-R line, and the VERY best decks that Sony made (with only one exception, the 788-4) all had the F&F Heads. The 788-4 only lacked them because it was a 4 channel design, and Sony never made any 4 channel F&F heads. Of note, Sony's very best Decks the ever made: the 755, 756-2, 758, 765, 766-2, and the 880-2, all had the Ferrite and Ferrite Heads, as well as numerous other Sony Models. Your statement was correct about Teac, who did reject the Ferrite designs in the 80s, after using them for a while during the 70s. I had always thought that they rejected the ferrite designs to the higher permeability, and slight magnetic superiority of some other materials, not do to the chipping issue, but I could be wrong about this. Anyway, I sincerely hope that this email is not coming across as hostile: it is in no way intended to read that way. I actually have quite a bit of respect for you after reading your very knowledgeable posting. I simply want to understand your point of view better on this subject. Specifically, why do you believe that the glass inside the Akai heads would make them so immune to the gap chipping that other Ferrite designs are supposedly so subject to? And, do you really believe the Sony F&F heads are so much more fragile than the GX heads? I had always thought of these two heads designs as being about equally fantastic. Thanks for your help! Jim ********** And Bender Sez: ********** Hi Jim, I hope I'm up to the task of answering them... Yes, many high end Sony sets did used the F&F Heads, and it is truly difficult to know why any manufacturer did anything at all, some 20 or 30 years in the past, I'm guessing different design teams came up with differing sequences of mechanical, electrical, and conceptual designs, depending who was on a particular design team. And in some cases, there may have been a choice of "A" or "B" type heads, and someone just chose one. Next, the chipping effect on ferrite tape heads seems to be related to wear, with ferrite on the surface, the wear effect is minimal due to the hardness factor of said material. The problem of chunks of ferrite chipping off from the gap probably relates to bound oxide chunks, on a microscopic scale, hitting the gap edge a few billion times as the tape travels past. Over time, this failure mode was found to exist and so Ferrite heads don't quite last forever. I guess depending on the level of Calendering of the tape surface, this can influence the ferrite tape head's life. That also goes for the Akai GX heads, where the typical erase heads appear to be of a normal ferrite construction, and these do tend to show wear first. The top of the ferrite mirror-like surface turns a lighter shade of gray, and looks rough when wear is present. So even ferrite surfaces do wear away, eventually. The GX Record and Play types tend to show some central point of contact wear by some point. I've seen many and it is the construction of those which not only places the "pretty much" friction-free glass or crystal-ferrite inside the head, but also on the surface layered in front of the ferrite pole piece surfaces. If this patented glass covering layer wasn't present, then the ferrite poles would be exposed to the tape, and subject to wear and tear and edge-gap scatter or chipping just like the Sony F&F / Teac ferrite heads. I guess if they wanted to pay huge sums of money to Akai... Sony and Teac could have had this too. However, as much as the glass coverage prevents edge-gap scatter damage, it does appear to be a very thin layer of glass on the later GX heads. I've seen many instances where under magnification the glass clearly shows the pock marks of worn or chipped areas within the mirror-smooth glass surface. So it too can get worn away, in some respect, it begins to look like the surface of the moon, with craters and such. While this doesn't affect the physical parameters of the ferrite of the underlying gap, eventually with enough wear, I suppose it would. I don't know if the original GX warrantee of 150,000 hours was based on actual 3.75 / 7.5 ips tests, or from simulated tests running tape across the heads - at accelerated high speeds. Don't know if they are in general truly accurate. Seems to me... earlier GX heads had both a thicker and wider surface of the glass covering and tended to remain unworn longer, while the later GX Record heads seem to have like an extended forward "plate" of GX glass, while the Play heads which seem to be full surface covered in glass. I don't really know why the different construction, it might be a cost thing in terms of construction... for better, or worse... As for the higher permeability, and slight magnetic superiority of some other head pole making magnetic materials ( such as Permalloy ) well, that I suspect goes to trade-offs, and costs. And yes, I think that soft permalloy heads as are present on many decks do indeed simply have a better "sonic" than any form of Ferrite, which includes the Sony F&F and Akai GX heads. I can not explain it in any other terms, but playing a tape on any GX Akai, a GX-365D, GX-267D, GX-400D, GX-747, or even a PRO-1000 seems to be perfect, until you then quickly switch the tape onto something like a Sansui SD-7000, or a Pioneer RT-909 with permalloy heads. Now, suddenly the same tape appears to have more dynamic range, more musicality, gives a sonic one step closer to the original than on the ferrite based machines. I design power amplifiers, and I have my own designs units which I strongly believe are more sonically neutral and more transparent than anything else on the market, exccept for a few mega-mega-buck and exotic high-end tube amps. And just maybe it does take this "extra level" of "sonic transparency" within the audio chain to be readily able to then discern these differences between the ferrite type and the permalloy type tape heads. Certainly the SD-7000 doesn't have lower wow and flutter or better distortion than than a GX-400D, or PRO-1000. Maybe the RT-909 does, but then its loaded with plenty of late 1970's level IC's in the audio path, which can't possibly make it sound better... so its' gotta be the heads, right ? Of course, the transistors / IC's used, and the coupling caps used in the audio sections, as well as the decoupling between channels within the power supply, would all have an added effect here; along with the amount of available headroom present in the playback electronics. Also the topology and complexity of the electronics the signal is being passed through ( the level of complexity tends to be about the same in these types of consumer decks, but not always ). So in the end, it can be extremely difficult to isolate this effect and truly say that it is the heads alone which are causing this effect... but well, that's MY guess. I was going to one day mount a set of later Akai GX Heads into a Sansui SD-7000 with worn heads, and try and run a bunch of listening tests, as it would be a really great project... I just never had the months of time and inclination to do it. I hope that sufficiently answers the important points in your questions! Steven L. Bender, Designer of Vintage Audio Equipment "" "
Thay đầu từ thì không khó nhưng để cân chỉnh cho đúng vị trí để đạt được các thông số kỹ thuật thiết kế của nhà sản xuất (tape pad, azimuth, level etc.) mà không có máy đo, test tape, các bộ ghá/ke cơ khí hỗ trợ thì không nên làm vì thay chỉnh mò chỉ làm máy hỏng thêm. nếu thích chất âm khác với Akai thì bác nên bán quách nó đi mua cái của hãng khác cong gin chất bãi không dùng đầu từ GX còn tốt hơn nhiều.
Việc cho rằng thiếu treble trên các đầu AKAI tape deck/casette deck cần được cẩn trọng khi đánh giá vì đầu từ GX rất dễ bị nhiễm từ nên có điều kiện ta phải khử từ trước cũng như cân chỉnh lại tape path & azimuth rồi nghe- đánh giá mới chuẩn được. Còn tôi cho tiếng treble là không thiếu nhưng có thể hay hay không hay thôi - mà việc này là phụ thuộc vào người nghe cũng như quan điểm về chất âm của từng hãng
Tôi thấy có cái máy khử từ, nhưng cũng khó kiếm. Nếu không có máy này thì có cách nào khác để khử từ hoặc vệ sinh đầu từ không các bác ?
Máy khử từ thì không phải là quá khó kiếm vì ta có thể đặt mua qua internet được nếu cần , nhưng kiếm được loại tốt hoặc của các hãng sản xuất chính hiệu như AKAI, Teac thiết kế thì thực sự là khó thật. Tôi có nghe qua thương diệu D-mag của Đức rất tốt nhưng cũng chưa tin hay chưa biết ai đã dùng đánh giá chát lượng của nó nên không dám mua để sử dụng vì chăng may nó không tốt thì đầu máy của mình coi như bỏ đi. Còn khi không chưa có máy khử từ thì cũng chả còn cách nào khác ngoài việc lau sạch đầu từ, hướng băng, tape path thôi, khi nào có nhiều nhiễu, tạp âm do bị nhiễm từ mới tính tiếp cách sử lý vậy.
Tôi đòng tình với suy nghĩ của bác và muốn bổ sung thêm một phần rất quan trọng đó là tư liệu, các bác nghe nhạc gì, chất lượng thu thanh thế nào ? Tôi có anh bạn chỉ chơi đầu Teac, Sony, Pioneer...mặc dù rất thích Akai, nhưng suy nghĩ cũng giống như các bác là đầu từ thủy tinh thì tiếng bì và thiếu treble, tuy nhiên sau khi được nghe thử và rút kinh nghiệm từ việc chỉ nghe người khác nói và ko chịu kiểm chứng nên bây h anh bạn tôi đã có vài chiế Akai trong nhà rồi, treble ko thiếu, cũng ko thấy bì, nếu ta có tư liệu tốt thì phần còn lại là chất âm do đầu từ thủy tinh mang lại thôi, có điều kiện thì các bác nên có trong nhà cả Teac & Akai.
công nhận! Nhiều bác chỉ đánh giá theo cảm tính và dựa trên thiết bị các bác ấy có. Thiết bị kém do lỗi lại nghĩ là "AKAI nó vậy". Vậy thì, thay vì nghe = tai người khác thì hãy nghe = chính đôi tai của mình!
