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C2N Datasette - Bias oscillator?

magnetic saturation recording doesn't use a bias oscillator
even the cheap analog recorders, like portable cassettes, just used 'dc bias'

all they are trying to do in the commodore circuit is produce a flux transition
 
It's an all digital signal, so no bias needed. It's only looking at pulse widths.
Unlike other tape systems back in the day that used FSK, Commodore just wrote to tape the same way a floppy disk does.
 
If you want an analogy, the Commodore cassette system works by laying down a series of little bar magnets on the tape. Brute force, which is why it can be a problem to produce a Commodore compatible tape using an audio recorder.
 
Sure, I get it.
If you want an analogy, the Commodore cassette system works by laying down a series of little bar magnets on the tape. Brute force, which is why it can be a problem to produce a Commodore compatible tape using an audio recorder.
So back when, how did they produce commercial runs of software on cassette? Did they have bespoke duplication machines just for the Commodore tapes?
 
Sure, I get it.

So back when, how did they produce commercial runs of software on cassette? Did they have bespoke duplication machines just for the Commodore tapes?
That is a very good question.

I don't think a standard audio recorder could get near the record energy at the head as the Commodore system which basically creates magnetically saturated dipoles on the tape. This produces also a much higher playback level than a conventional recorder which tries to operate the tape's B-H profile in a linear zone below that record energy level (hence the bias). Maybe Commodore program tapes made or copied to a standard recorder could work at times, but probably not as reliable with more dropouts I would guess.

So I'm guessing here that all the Commodore software tapes must have been created on Commodore recorders. Maybe a little cleverer than it seems, because in effect they created a type of bulk anti-copy system at the same time which would have inhibited others mass producing reliable tapes. But this is just a guess.
 
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This is hardly scientific, but I've just been through transferring all the programs on my 40+ year old tapes to digital files (via a PET2SD) and the cassettes that caused me most problems were all commercially produced tapes.

Colin.
 
This is hardly scientific, but I've just been through transferring all the programs on my 40+ year old tapes to digital files (via a PET2SD) and the cassettes that caused me most problems were all commercially produced tapes.

Colin.
If magnetic tape can hold onto its dipoles for more than 30 years it is actually doing pretty well. Where the task is more demanding, say video tape, where you can see the dropouts visually, many VHS tapes barely made it past 15 to 20 years before the data faded away. But in some cases, depending on the quality of the media, data and images from tape over 40 years old has been recovered.

One interesting video was a lost David Bowie recording not seen since 1973, the BBC wiped the original tape, but luckily there was a copy. The video quality looks very good, though it was subject to some repairs and the original tape stock was probably very expensive & good, this was the story:

"After the broadcast the BBC repurposed the tape so the performance was presumed lost until 2011, when John Henshall, a cameraman on the show, revealed that he had 2-inch tape copy of broadcast quality".


Perhaps one possible explanation why the original commercial tapes gave you more problems, they may be physically older than copies of programs, made later, by the users with the PET & Datasettes, but it is hard to know for sure, or maybe the copies were made to better quality magnetic media that has lasted longer.
 
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So I'm guessing here that all the Commodore software tapes must have been created on Commodore recorders.
I have a device some where that was used to copy a cassette from one C= recorder to another one. The box had to edge connectors, one marked "In", the other"out" plus a cable with connector that had to be plugged in your C64/128, just for the power. Inside was, IIRC, one 7407 Open Collector buffer IC. The only thing you had to do was to press "Play" on the source recorder and to start the other to record the data. So I can imagine that something like that was done on a massive scale: a C64 or other device, external power supplies, some buffers/amplifiers and a lot of C2Ns

I myself never used this copier. In fact I hardly used the cassette recorder: days after I bought my "build-yourself" C64 (long story) I bought a 1541. Cannot even remember when I was given (certainly never bought one) a C2N.
 
In business, time is money. We used high-speed cassette tape duplicators (for audio work). I am sure there was the equivalent for data cassette duplicators.

Dave
 
In business, time is money. We used high-speed cassette tape duplicators (for audio work). I am sure there was the equivalent for data cassette duplicators.

Dave
Maybe so, seeing that most pro-level tape equipment tends to be componentized into seperate transports & electronics. So in this case, only the record electronics would need to be changed.

I also noticed that the erase head runs straight DC as well. If memory serves, erase normally uses an AC signal, but I could well be wrong.
 
Maybe so, seeing that most pro-level tape equipment tends to be componentized into seperate transports & electronics. So in this case, only the record electronics would need to be changed.

I also noticed that the erase head runs straight DC as well. If memory serves, erase normally uses an AC signal, but I could well be wrong.
An AC erase would produce alternating N-S-N-S fields. I believe they are all DC but it works because the tape is moving.

FWIW, I know back in the day you could duplicate a tape by dubbing with a dual cassette deck and it is possible, though not simple to produce a usable data tape from a WAV file.
The record level needs to be higher than you would use for audio and a mono record head helps. A stereo signal mixed to mono can have a subtle phase difference between the L and R channels.
Also the signal polarity is critical because if it's reversed the pulse widths become inverted and the data isn't valid.
 
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