The cassette was born in the mid 1960's, invented by
Phillips and mainly intended for use in dictation
machines - the format was inherently inferior to
full sized reel to reel and hence wasn't originally
intended to be used for reproduction of high quality
audio in Hi-Fi systems. The problems came from
actually fitting the tape inside a compact cassette
format case, only so much magnetic data could be
stored on the narrow tape and only so much tape
could be wound onto the spools inside the case; to
get a reasonable recording time the tape would need
to be run much slower than conventional full sized
reel format, under 2 inches per second.
Noise would prove a major problem for the cassette
format, it wasn't until the efforts of Dolby
laboratories that the cassette finally began to gain
acceptance into the realm of Hi-Fi.
Wow and flutter?
In audio cassette players this is a term given to
the fluctuation in frequency introduced into a sound
because of changes in speed of the tape passing over
the record/playback head. Record a steady tone onto
tape and then play that tone back and what you hear
will be a close resemblance of that tone but
distorted in frequency as the mechanical parts of
the deck vary speed slightly, altering the speed
which the tape passes over the playback head hence
the frequency of the tone.
It's impossible to remove this phenomenon
completely, some technology reduces it considerably
but on any analogue audio format (reel to reel,
vinyl, etc) it will always be there to an extent.
Flutter is most noticeable at mid/treble
frequencies, mostly on passages of music with solo
instruments in that pitch range. Play a piano solo
through digital format and then record the same
passage onto tape and play it back and you might
find it painfully noticeable.
Advantage of dual capstans
Most basic (lower end) cassette decks share the same
overall design, being 1 motor, 2 head machines. The
record and playback heads are combined with the
erase head being separate (the erase head is
basically an electromagnet which, when powered by AC
at high frequency, effectively demagnetizes a
portion of the tape which passes over it, erasing
any recorded media). The motor on a single motor
transport drives both the capstan and the tape
spools. We're talking the majority of low/mid range
Japanese decks here, auto reverse decks are usually
similar but use a different type of head and
mechanism.
An improvement on this basic design is to add a
second motor to drive only the capstans and/or add a
second capstan and pinch roller on the supply side
(left side) of the transport. The right hand roller
still has the most importance as it performs the
function of pulling the tape through at a constant
speed, the main reason for adding the second
capstan/pinch roller to the left side is to keep
constant tension on the tape so it stays flat
against the heads and runs smoothly, this design is
sometimes coined as 'Closed loop' or similar.
Pinch roller pressure is critical on these machines,
on the majority of designs the right hand roller has
around 300-500 grams of pressure, the left hand
roller usually a quarter or third of this.
A few points about restoration
Depending on the deck, it can take a lot of work to
restore to working order. In the case of the average
Pioneer, getting the actual transport working
involves disassembly to change all the belts and
tyres, then a case of cleaning and re-greasing the
mechanism, replacing a couple of microswitches which
invariably go faulty, cleaning and regreasing the
main play/record switches and starting the
reassembly. Motors are usually rebuilt.
 |
Rebuilding a
Technics RS-M03. This one is quite simple,
single capstan, two head |
Once everything is reassembled the deck is powered
up to check everything is working as expected and if
so, it's then on to setting everything up again
(tape speed, azimuth, playback levels, record bias
etc etc). The final thing I always do is a wow and
flutter test, even if the deck sounds like it's
running well. I'm not after a perfectly accurate
flutter test, I don't have access to the laboratory
conditions which the original manufacturer did -
just an indicator that everything's running
smoothly.
As with most vintage equipment there's always the
dilemma over ageing electrolytic capacitors
(elcaps), there's a section devoted to these in the
amplifier rebuild section. There is a case made for
replacing everything but this can get expensive
because of the sheer amount of time it can add to a
rebuild, as a cassette deck generally runs cool and
most of the elcaps are relatively safe in low
voltage circuits, there's not usually a board full
of dried elcaps causing noise or frequency problems.
Actually, most noise problems I encounter are down
to leaky transistors in the low level signal
circuits and nothing to do with elcaps whatsoever.
Most vintage equipment was assembled with tie wrap
pins where the single core wiring looms were
connected to the board via pins which the wire was
coiled around as the unit was assembled during
production, with age these oxidize in the space
between wire and pin and can cause noise problems
and odd faults, I prefer to leave the pins in place
where possible but to solder them.
Vintage decks do have a problem with rubber
components including the pinch rollers hardening
with age, if your deck has bad wow and flutter then
new belts alone are unlikely to cure it. Yes, belts
can (and do) cause running problems but the common
advice around that wow and flutter is mostly caused
by loose belts is misleading. The tape is actually
pulled through the mechanism by the pinch roller(s),
the take-up spool merely turns in playback mode to
keep the slack taken up as the tape passes through
from the feed spool to the take-up, in the same way
that they are driven when rewinding but at higher
torque and speed.
When the pinch rollers harden they lose the ability
to grip the tape properly and pull it through the
capstan and past the heads, if it keeps losing grip
then the speed will vary and you will get the
dreaded wow and flutter or worse the tape will slide
off of the roller and get chewed (imagine trying to
drive a car and then steer and brake with old,
hardened tyres with worn treads). Many people don't
realize that it's the capstan and pinch roller part
of the mechanism which controls the tape speed.
Most transport faults will cause the machine to eat
tapes, occasionally at first but more often as the
part in question wears more. Most tape eating faults
are caused by the tape take up spool not keeping up
with the tape as it rolls through the pinch roller,
as the tape comes through it needs to be wound onto
the take up reel in the cassette and kept fairly
taught, otherwise it ends up wrapping around the
pinch roller and making a mess, probably ruining
that portion of the tape too.
Usually it's the rubber idler tyres which fail (or
harden to the point where they can no longer
transmit enough torque to the reels to drive them).
Usually the idler tyres are buried nice and deep
inside the transport and take a lot of disassembly
work to actually gain access to, CT-F Pioneers are
offenders here. The tape can also slip off of the
heads and/or the pinch rollers and become eaten,
this can be caused by worn pinch rollers but more
usually happens in dual capstan decks and is caused
by lack of friction on the tape feed spool or from
the heads being out of line with the pinch rollers
(usually the erase head is the culprit as the
playback head has a forked guide attached to prevent
this).
Getting everything apart, and back together again
afterwards
 |
Toshiba
PC-6030. Probably one of the more difficult
decks. Main power supply and control boards have
been removed, hence the loose connectors |
Sounds simple, until you pull the case and start
looking at all the wires, screws and start trying to
figure out how to remove the transport from the case
even if you ever manage to get it unbolted in the
first place. You're not alone, cassette decks are
complex, cramming all of that complexity into a
small sized case makes the whole situation worse.
With most decks there's little you can do with the
transport still in place, you can sometimes just
about change the main belt if you don't mind
scraping your knuckles; for anything more though,
the chances are that the whole transport will need
to be removed. Besides, the transport itself often
contains dozens of small springs, washers and clips,
you'll really need it on a clean, well lit surface
to make the job easier, and to find and tiny parts
that may inadvertently get dropped. If you are
determined to have a go yourself, good luck.
Pinch rollers
Just to be difficult, most manufacturers reserved
some really oddball components for their top end
machines, pinch rollers for high end cassette decks
are almost always difficult to find and sometimes
expensive - as a strange twist of fate, it's the
higher end decks where these usually cause problems
and need replacing.
The pinch rollers in one of my own Pioneer decks had
degraded badly. When I bought the deck about 5 years
ago not working I replaced everything else and
soaked the rollers in restorer for a few days to
soften them. For a while it was fine but they
gradually hardened up again. Most later high end
Pioneer (CT-F) decks use twin 9.5mm rollers, new
replacements are unavailable from Pioneer nowadays
but are still in the catalogue priced at a heart
stopping £35 each, all for a tiny lump of
brass/rubber. I did find some high quality
replacements for higher end vintage decks, have used
them several times on decks for customers but
quality costs and they are expensive.
I tried a pair of 'generic' 10mm rollers from the
US. These aren't expensive brass like the originals
(these are nylon) but are still good quality, I've
used these parts in other decks and they are still
perfect after a year of regular use. Problem is that
these are a size meant for modern dual cassette
decks, not only are they slightly narrower than the
originals, the bores aren't drilled large enough to
fit on the Pioneer axles either. I bored them out to
2mm on a lathe (without a lathe of some kind you'll
never get them bored straight and they will be
unusable), on initial fit they were surprisingly
near perfect. I stamped out some shims to pack them
out to the same width as the originals and the 0.5mm
difference in diameter wasn't noticeable at all,
once in the deck they worked perfectly.
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