Dolby C
synonymous with consumer tape decks and broadcast decks was the last
attempt to make tape more palatable and provide an illusion of
increased quality and dynamics. Dolby C type in effect made yet
more compatibility problems, with tracking and frequency response
issues that were all instilled even in the highest quality
components. It always seemed that when encoding Dolby C recording,
it could never ever be played correctly on another machine; probably
why no pre-recorded tapes ever bothered with this compression type.
Considering the random adoption of Dolby B and the general complaint
that it made everything sound dull, Dolby C would mean this would be
several times worse. Hence, manufacturers of pre-recorded medium
could see more returns than they would be happy with due to this
respect. As most of the readers of this would undoubtedly have
sampled the delights of compact cassettes, noise reduction in
conclusion does have its merits. The narrow tape of cassettes does
exhibit a very narrow band of high frequency noise that isn’t
overall pleasant to listen in quiet sections. It seems that Dolby C
was an attempt to create a new home recording market and inspire
greater sales of ever more expensive equipment advertising
confidence head playback and direct motor drive and the like, even
when the music industry was at its peak in stressing illegal home
taping. Therefore, Dolby C in home recording was flawed due to
the technical limitations of the home recording medium. The only
true success of C type was in the professional range where higher
linear tape speeds and better calibration meant that it could
succeed and impact least on the recorded material. Many professional
implementations of C were out-board types for increased flexibility
meaning the inclusion of Dolby tones and levels for better
compatibility. The non-inclusion of the Dolby level signal in home
recording equipment aided the compatibility problems. With the
steady improvement in tape technology, material could be recorded at
higher levels and tape that exhibited low self-noise. This in effect
negated the importance of Dolby C, and allowing the less invasive
Dolby B to be used in its place, particularly important for very low
tape speeds. So, when it comes to digitising Dolby encoded medium
of unknown origins, it may be beneficial to sample the non-decoded
tape and re-encode later so no actual information is lost.
Improvements in single-ended noise reduction can actually mean Dolby
decoding is unnecessary for some material if accuracy is not
paramount, and the end effect can be sometimes be better than the
original decoding.
12/11/2012
We acquired an old Sony SL-C7 betamax recorder for restoration purposes and
were keen to compare the results with our production Sanyo VTC-6500. The SL-C7
required a lot of work; all new belts, a proper clean up, a new pinch roller, a
new idler conversion kit (for proper spooling). Once the mechanics were done,
the picture was surprisingly good which certainly looked every bit as good as
the VTC-6500. However, when listening to the audio it was evident that there was
high wow and flutter. The usual culprit was the threading motor, also doubling
as the capstan motor (this sounds bad, but in fact doesn't seem to affect the
tracking stability). The motor was extremely stiff to turn and even though a
generous dose of alcohol freed it up, it still exhibited the same flutter
problem as probably the bearings were completely worn out. The only solution was
to put in a new replacement, and when this was done, the wow and flutter problem
went away, and also the slow threading was much improved. It's unfortunate that
this motor has to do threading as well, as this must reduce the overall life and
put extra strain on its bearings. There is some light flickering in the video
output, so some electronic diagnostics is required, probably the usual caps
and/or oscillator instabilities. Also, ALL the timer switches were stuck so with
what appears to be the last remaining stock, some of the major switches were
replaced; not as though this is required for video playback, it is still nice to
actually set the timer and clock! We have a new ACE and video head to fit at a
later date which should improve performance as the current video head looks as
though it has had a hard life!
29/07/2012
When acquiring our Sony decks BVU-950P and BVW-75P, they had bad capacitors
particularly in the audio section. The BVU-950P experienced low level buzzing in
playback, and the BVW-75P electro caps were visibly showing signs of rupturing.
Even considering the age of these decks, it must be due to the placement of the
boards as the audio board is placed at the back between the cooling fans
therefore does not receive the same ventilation as other boards. All caps were
replaced, and problem solved.
20/07/2012
The U-Matic BVU-800P is a high band player that is a work-in-progress. A grinding
noise was noticed when the drum was rotating, so a lower drum was duly found
and replaced. However it turns out that a wire was fouling the lower drum due to
a clip missing, and being pressed against the power supply. However, it turns
out the that the original bearings are slightly audible compared to the
replacement, so the original was probably past it's best anyway.
