cleaning heads on a DAC / DCC

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Joined
Jun 5, 2004
Messages
6
Location
Hastings England
hi all, I've got one of those funny missing links machines - a DAC a.k.a DCC - i.e a digital cassette. You remeber the things - between a normal cassette machine and a DAT. records on digital cassettes and plays normal ones. Never caught on.
Here's the thing - I need to clean the heads cos it's very dull, but it says on it "do not use head demagnetiser" and as it loads the cassette VCR style it's very hard to get to the heads.
Any ideas?
 
[quote author="MelonMachine Giles"]I need to clean the heads cos it's very dull[/quote]
...You sure about that???

If you mean the sound of a digital recording is dull then I fail to see how head cleaning can have a difference. I know that the DCC marketing thing was that it could also play back analogue tapes, and those might conceivably lose HF response if they got clogged, but the digital playback alter...? in any way other than increased dropout/error correction...?

Nope.

Either it's your imagination, or some other thing.

Keith
 
Hi,

Some do indeed say 'clean head' in the display (at the most inconvenient times... :)

What model DCC-deck do you have ?

When using the DCC-cassettes (so the digital mode) with dirty heads I guess dropouts will develop (not getting all bits properly from tape and when the error correction can't any longer mask this, I expect the sound will go nuts.)


There were cleaning cassettes, like SBC3500 iiric. I'm afraid it's unlikely you will be able to still get these but then you know at least where to look for.
But - depending on the model; I don't know if you're able to reach the heads - it was OK to clean them 'analog cassette-style': cotton bud & alcohol (or special head cleaning fluid).


Never caught on.
That's right... they became interesting buys afterwards, low price and despite the datareduction defin. decent sound quality imho. You had to stock up on tapes though, or just use them for their converters. FWIW, the DCC-format 'did' even 18 bits in its latest incarnation. End of advertisement for past products...


Peter
 
"do not use head demagnetiser"

Forgot to add, yes, indeed don't use any demagnetizer. The DCC-heads work by another principle - called MR I thought, magnetoresistive. Demagnetizing such heads won't cure any hi-freq loss but means end of life.
 
Never used DCC, but thought I'd be a pain in the arse and make a small point anyway!

Just wanted to say that the DAT tapes that I recorded in college did have severe playback problems by the time I graduated (no, no gap years!) and surprisingly I did find some of them just sounded mainly dull. I don't remember what machine I was using when listening, but I think it had some form of error correction indicator, that seemed to be working very hard. And yes it did sound mostly dull. My theory on this is weak, and mostly based on a book on DAT error correction that I read a long time ago. But in a nutshell, if error correction is pushed to its limits, then you can reach a point where the error correction can only recover every other sample on average, and is forced to approximate the values inbetween. That is pretty much like having sampled the original recording at half the frequency, and hence having the HF response drop accordingly, since approximating doesn't actually 'add' any more information; it's more like a low-pass filter.

If anyone wants to explain this properly, that would be great, as I think my explanation is a bit shite (indeed, if I'm full of it, do let me know...). I do know about parity bits and interleaving and bla bla bla, but it's late and I'm drunk, so good nite!

Bjorn
 
Hey Bjorn,

DATs are PCM, I forget exactly which flavour of data reduction DCC used: The MiniDisc version was ATRAC if I remember... DCC has another acronym, which I used to remember even while I could never remember ATRAC... funny, now it's quite the reverse! -I remember that I always wanted to *never* see another DCC machine again though!!! :evil:

Ah yes... PASC. -Precision Adaptive Subband Coding. -Now it all starts to come flooding back!

Anyhow, the reconstruction system is a little involved, but there's still no real way to dull the signal... Errors will be spread randomly, but not entirely uniformly, such is the nature of these things... there are always clusters, and -as with DAT- there is a muting induction if things get hairy. The low speed and static head format of DCC -even with the data reduction- means you're close to the edge...

Matt:

Ay, ay....Ay..... ay!!! now-den, Now-den!!! You staaartin? Eh? ... eh???

-I believe that I left the door open for the problem being related to analogue playback, didn' I?

:wink:

keef
 
-I remember that I always wanted to *never* see another DCC machine again though!!!

That sounds like some horrifying experiences with this format - please share, I'm still using this format for certain applications, and I'm definitely satisfied with it (for what it is - for todays standards there are defin. of course a few drawbacks). So I'm just curious,

Peter


PS/FWIW,

If I recall it correctly PASC used some 31 bands. Or it just didn't and used another principle. Ehh, well, what I do seem to remember a bit better is that the datareduction ratio is somewhere around 1:5 or 1:4, which was a bit less datreduction than what ATRAC used in those days.
 
Ah yes... PASC. -Precision Adaptive Subband Coding. -Now it all starts to come flooding back!

Anyhow, the reconstruction system is a little involved, but there's still no real way to dull the signal...

When I went past the 'clean head' warnings I thought I got silence and/or starnge noises.

But whatever happens, dulling or funny sounds, if the original poster wants to keep using his DCC-deck for digital rec/playback, there simply seems no other way than to clean that head.

Bye,

Peter
 
I should've said - it's fine o the digi cassette, but very dull on the analogue ones. Frustrating as I have a load of stuff on old cassette I wanted to transfer to CD. The sound is very dull - maybe I need to align the heads ather than just clean them. No idea how to do that either!

Can't remember the make now (unobservant or what?!) I'll have to check when I get home.

MM G
P.S Red stadium and no Sun. Right on!
 
mmm maybe you're right, I should get something else. I do have a good casette deck but it plays too fast (next topic...!)
it does overdrive nicely - I've got it linking my CD to my hard disk recorder and I tried pushing a mix I'd done to see what mastering coud do - sounded great.
 
Ah... Good. I'm not mad then! :wink:

I would actually recommend against using analogue cassettes in a DCC machine. The friction, wear and general clog-ability of various formulations of analogue cassette tape will wear down a machine that one day you won't be able to get the parts to fix... also, the playback was generally compromised in these things, just getting it to work at all was considered a feat of engineering at the time!

Clean them with chamois sticks lightly moistened (not soaked!!!) in high-purity alcohol. Then if possible, if you intend to use it for DCC, restrict it to DCC use only. Using analog tape in there will only hasten it's death, doing a job that can just as easily be done by a machine that you can replace if it dies... your DCC might not be so easy to find a replacement for, whereas decent cassette decks are all over the local want ads.

Demagnetise the heads, and help a tech go to Bermuda on vacation! :wink: (in other words, DON'T demag...)

With a dedicated analog playback machine, you can also tweak the azimuth as needed. Check it in mono and see if the top end gets worse. If it does, you need to tweak the azimuth. Another reason why using a DCC deck for analog playback might be a bad idea... you simply do not want to be flexing a screwdriver inside it every half-hour! Also, the lack of ability to demagnetise can actually make analog tapes more noisy, simply by playing them...

While it was a fine marketing angle, the playback of analog tape in the DCC is so riven with 'issues', it's much better avoided!

Keith
 
from Keith:
also, the playback was generally compromised in these things, just getting it to work at all was considered a feat of engineering at the time!

I'm not sure here. If it's about the sound, I've heard people owning analog Nakam.-decks saying they actually liked the playback of so called ACC's better (that was weird yes, when DCC emerged, the old old compact cassette suddenly turned out to be an ACC :)
But back to the sound, that's of course entirely subjectively. Maybe related to the absent head-bump EQ-thingy ?

Or if it was about reliability, well, it'll probably have been a compromiose in more than a few ways.
But in practice, I haven't heard about the ACC-functionality being problematic nor did I experience that myself (true for the home-decks, but the transport of my portable unit has stopped doing ACC though).
I do minimize ACC-use though, you have a good point there.

Bye,

Peter
 
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