[[email protected]]

I have an old Aiwa ADF-990 which hasn't gotten used much in the past
decade or so, and the belts fell apart. I was able to find the part
numbers (81-507-216-01 and 81-507-225-01) but I found that they are no
longer made. I eventually found a recommendation for where to get
replacements, but with no mention of which were the correct equivalent
belts.

I finally found a site in England that listed the dimensions. The
belts are 201 and 226 mm in circumference, (64 and 72 mm diameter) and
are 4mm wide and .6mm thick. I figured that would make it easy since
I already had a link to a source, but when I converted to inches, I
found that the sizes available are not quite the same.

The question I have is how close is close enough? Belts are going to
stretch anyway, and if they stretch too much, they will cause
problems, but I can't find anything to give guidelines.

The belts I found are 9 inches and 8 inches, and the metric
measurements above convert to about 8.9 and 7.9 inches. That doesn't
seem like such a big deal, but then again, if the net effect is to
increase the diameter by more than half the thickness of the correct
belt, I figured I should at least ask.

There are a few sites that actually list belts for this player, as
well as the ADF-660 and ADF-770 which use the same belts, but I don't
want to pay $30 for a pair of belts that could cost roughly a dollar
each, especially if I have no assurance that the so called correct
ones are any closer to the OEM size than the ones I found.

Are all these numbers close enough that there's nothing to worry about?

[EADGBE]

I specialise in Nakamichi, but I have repaired many different brands
of cassette deck.

In my experience, the slightly bigger belts you found might cause
problems, and they might not. I'm sorry to sound so vague, but it
really depends upon the design of the particular machine.

If a belt simply goes around two pulleys and doesn't touch anything
else, then you can *generally* go with a belt that is just a bit
tighter (but not TOO tight!) and the machine should work OK. I am
talking here about relatively straightforward belt travel, i.e. an
arrangement where you just have the capstan motor and the capstan
flywheel, OR, in the case of a direct-drive, dual-capstan deck, an
arrangement where you have one capstan flywheel that is part of a
brushless direct-drive capstan motor, and the other capstan flywheel.
In other words, if there are just two "circles" for the belt to go
around, then precision belt size requirements *may* be flexible.
NOTE: You will probably have to adjust the speed of the capstan motor
(which adjusts the playback speed) to compensate for the different
belt tension. ANOTHER NOTE: Tighter belts often increase wow/flutter,
so watch for that.

However, if the deck has some unique arrangement, you may have to try
to find an exact belt match if you are trying to maintain original
performance specs. Many classic Nakamichi dual-capstan decks consists
of a capstan motor linked to two capstan flywheels via a PRECISELY
sized belt. These Nakamichi transports are notorious for being very
picky about the size of the replacement capstan belt. In many cases,
if the belt is too tight, the deck has noticeably increased wow/
flutter or may even start to have tape skew problems or tape eating/
jamming problems.

To make a long story short (I know--too late!), variations in belt
size can alter a deck's performance significantly OR it can alter it
within acceptable limits. It's up to you to decide what is
"acceptable" to you.

Good luck!

[[email protected]]

On Jun 1, 7:34 am, EADGBE wrote:
I specialise in Nakamichi, but I have repaired many different brands
of cassette deck.
[snip]

To make a long story short (I know--too late!), variations in belt
size can alter a deck's performance significantly OR it can alter it
within acceptable limits. It's up to you to decide what is
"acceptable" to you.


Thanks. I think you summed it up well. Back when I got the Aiwa, it
was almost a given that if you wanted an audiophile grade cassette
deck (for those willing to accept cassette decks in that realm) you
got a Nakamichi. So back then, it was a matter of figuring out
whether the differences in performance were acceptable if I got an
Aiwa. I remember when Stereophile reviewed my deck, which surprised
me since I didn't think they'd touch something made by a mainstream
consumer equipment manufacturer, and was even more surprised when they
didn't stick their noses up in the air, but concluded that it fared
quite well compared to whatever Nakamichi they were discussing. But I
think their bottom line was that the Nakamichi still had the edge and
they effectively said that it's up to me to decide what's acceptable
to me, albeit in different words.

I ended up ordering belts after your post since it was not much of a
risk. Studio Sound Electronics has them for $1.25 each, and since I'm
not finding the supposedly correct ones, I figured it's not much of a
gamble. I also put a note in the comments section of the order form
asking about the differences between the specs I had and the
measurements of his belts. I was pleasantly surprised to get an
answer the same day (Sunday) as well as a notice that day that it was
shipped. The only down side was that the total order was so cheap that
it would have had a small order fee. So I bought his little tool for
installing belts, since it came out to very little more.

Their response to my question was that the belts have an allowable
variance of ± 5% since they get stretched when installed, etc. and
that mine were off by only 1 to 1.25% so it should be no problem. I
don't know if the OEM belts had tighter tolerances, but it's a moot
point since they are not being produced. I have the original service
manual, and it didn't publish the specs, so I'm not sure if any of the
so called correct belts are any closer than the ones I ended up with.
If at some point, somebody kept track of which part numbers were
equivalent to others, then it's possible that some people truly know
what's equivalent. But if at some point, somebody picked something
that's "close enough" and listed it as the official replacement, then
all bets are off.

The people who are charging $30 for the supposedly correct belts might
have picked the same ones I ended up with for all I know. Conceivably,
somebody might have determined the "correct" size by measuring an old
belt. I suspect that if they advertised the size so that I could be
assured that the belts are somehow closer to spec, they might end
losing business since people would be able to find them elsewhere. But
in all fairness, they might indeed have belts that meet exacting
specifications.

The bottom line is that I put them in, and things seem to be working
fine. But it's not something I can be very objective about. When I
bought the deck, the question of the day was how close it came to LP
quality. Plus my hearing was better. Since it hadn't been working
for a while, anything approaching an a/b test is out of the question.
And in all likelihood, the amount of use that the deck will get will
be extremely slim, given today's media choices. So whether the
tolerance mentioned in the email was relevant or not, or more geared
to typical mass market guidelines, I have something that works. The
regrettable alternative would have been the recycling center.