The very first Philips DACs in the earliest CD players ran at 4x sample rates. Overheating wasn't a problem.
Yes, but do you know of them over-heating?
Some such constructions (mounted upside down) have emerged in the "bad caps era", maybe they sought to protect the PCB in case a cap becomes "incontinent"? Anyway, hot chips (and generally parts) tend to live shorter than cool ones, so maybe it's really worth checking.
In the context of bias I don't believe this applies as, typically, very little residual of the actual bias signal remains on the tape. Although the HF bias leaves the wanted audio on the tape in a far more linear state than otherwise, as far as I remember (I haven't been near an analogue recorder for over 20 years) the actual bias frequency is well beyond the point on the tape at which the self-erasure effect becomes dominant and very little residual of the actual bias signal remains.
I will measure it anyway after warranty expiry, for my own curiosity, and I did not make any claim, I am only curious in the context of #153 if it might be... I hope being curious is kindly allowed. If everything always was as it should, many things (experimenting, prototyping) would be unecessary. Veryifying people's crazy ideas is the business of science, sometimes (not in this case because I can do it myself).
If a CD was mastered directly from a tape made with one of the ‘domestic’ style PCM converters (PCM-F1 etc.), it would likely have the pre-emphasis enabled because these units always recorded with pre-emphasis and there was no simple way of doing otherwise. On the professional units (PCM-1610+) pre-emphasis was a switchable option which was, in my experience, seldom (if ever) used.
No! Although the same oscillator drives both, the erase head typically has a far wider gap and is a brute force device with no purpose other than to get rid of every last residual of whatever was on the tape previously. The magic performed by bias is written by the record head.
And that, my friend, is the crux of the matter. In any event, most general purpose microphones have no significant useful output much above 25kHz and it's highly likely that even if you could hear in that region, you wouldn't really like what you heard. There is some argument in defence of the use of anti-aliasing filters at higher frequencies so as to cause less ‘damage’ within the audible range, but that's a moot point.
Another reason that 44.1kHz floated to the top was that it was a number that could be made to work in both PAL and NTSC domains.
I'm sorry, but this is a gross oversimplification. The only way I can explain how bias worked, in a few words, is this: magnetic recording is, inherently, highly non-linear. By using an AC bias signal (typically >8× the maximum audio frequency of interest) whose magnitude was significantly higher than the wanted audio, as the tape entered the magnetizing zone of the head it would be pulled and pushed through several non-linear cycles of the bias waveform which gradually reduced to zero plus the required audio as the tape left the vicinity of the head.
That was why Sel-Sync was developed on multitrack machines. (Selsync was the Ampex term for it, I think Studer made up their own) This used the record head for playback into the monitoring system, so, for example, a singer could add their contribution without the timing error between replay and record. The playback quality wasn't as good, given the much wider gap of the record head, but good enough to maintain sync.No! Although the same oscillator drives both, the erase head typically has a far wider gap and is a brute force device with no purpose other than to get rid of every last residual of whatever was on the tape previously. The magic performed by bias is written by the record head.
As an interesting aside, the physical interval between the erase head and record head was always an issue when it came to precise drop-ins and, trickier, drop-outs. Some of the last and best analogue recorders had quite sophisticated timing circuits in an attempt to square this particular circle. Think about the problem and you will realize that it's more or less unsolvable
And always has been, to my knowledge.
