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Scotch "Master" vs. "Classic"



 
 
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Old December 3rd 04, 07:58 PM
DeserTBoB
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Default Scotch "Master" vs. "Classic"

I got a case of Scotch "Master" cartridges for cheap not long ago,
along with some of the older Scotch "Classics," so, of course, I had
to test them to see what they'd do. "Classic" was marketed in the
same time period when 3M's Wollensak division started selling its
Japanese-made decks, including the top of the line 8075. The
packaging of "Classic" even refers to using the "special" switch on
the 8075, and the 8075 user's manual specifically states use of
"Classic" for improved performance on this deck, so there was a
deliberate marketing tie-in. "Master" came out a bit later, and
there's no such tie-in, as the Wollensak line of recorders was already
defunct by this time. The only other model to have this
"special/normal" switch was the non-Dolby 8056.

So what's the deal with this "special" switch, anyway? Not a lot, it
turns out, and it's more or less a "quick fix" for tapes that require
less bias than the Wollensak was able to provide in stock form. All
this switch does is remove a ground from the equalization network for
the record amp...that's it, nothing more. What the idea here is that,
rather than cut the bias current to get flatter response, "fudge" the
EQ curve to essentially do the same thing. What you wind up with is
essentially (not exactly) the CCIR (later IEC) 3180/120 µS
equalization that was adopted for ferric cassettes, which gives more
boost to the top end starting more than an octave lower in frequency.
This is interesting, as it shows that "Classic" doesn't need the same
amount of bias current as does the old standby, 175, or its later
replacement, "Dynarange," to get the same top end at the slow speed of
3¾ IPS. The oxide is definitely an improvement over both of these,
and seems to be similar to that RTR favorite for years, Scotch 250. I
remember when 250 came out, and I spent a lot of time rebiasing and
equalizing Ampex machines to accommodate its better top end.

I decided to set the bias on my modified 8075 to its stock current
value and just use the "special" switch and see what happened. What I
got was some great performance, markedly better than "Dynarange" or
Ampex 381 in all areas. Top end was an easy 15 KHz at -3 dB, whereas
"Dynarange" drops down around 12 KHz. "Classic" has a bit more
headroom as well, as well as a lower noise floor...in other words,
pretty much what I remember Scotch 250 gave on RTR machines. Thus,
I'd bet that this is just basically Soctch 250 with the graphite back
coating, much the same way that Ampex back coated its 406 and called
it "Grand Master", catalog number 389. The EQ switch is obviously a
good compromise; the fluxivity standard for 8 track is 185 nWb/m, so
these machines can't really take advantage of a lot more headroom
anyway, so rather than go through the exercise of rebiasing, simply
peak up the record EQ to make it flat on playback using the standard
3180/50 µS NAB curve...and it works! Not being satisfied with that,
of course, I had to twiddle with biasing using the stock record EQ to
see what'd happen.

As it turned out, rebiasing the deck didn't give me a lot, mainly
because this format just isn't capable of exploring improvements in
tape oxides made in the mid to late 1970s, that mainly being in the
area of saturability. As earlier stated, this 8075 can handle a +5 VU
before clipping its record stage, and when properly biased for flat
record response, you can't get enough "ooomph" from the record stage
to truly take advantage of the extra headroom afforded. So, you wind
up where I was with Ampex 389, and to a lesser extent, TDK SD...there
IS a limit to what 8 track recorders will hit the tape at, and any
more than that's really kind of a waste of time and effort. What
rebiasing for these tapes will give you, however, is ultra low third
harmonic distortion while still giving good top end. This translates
to a very high MOL, which to me is 2% THD operating level. All well
and good, except, again, 8 track just can't take full advantage of it,
and I'm sure 3M's engineers were fully aware of that when they
designed the 8056 and 8075. So, they opted to just "fudge" the EQ on
record, thus giving still-good distortion characteristics while giving
oodles of top end without saturation.

How does "Classic" sound? I like it better than TDK for magnetic
reasons, mainly because it can eat up anything you can throw at it,
incuding high level Dolby "B" encoding, with ease, probably moreso
than can TDK. Recordings make with Dolby in the circuit come out with
the same top end that goes in, for the most part, showing no hint of
top end compression. However, the advantage of TDK SD...those finely
designed and made cartridges...trumps Scotch yet again. Even after
"limbering up" a "Classic" cartridge with five passes through the
machine, I wasn't able to get anywhere down near what TDK could
produce for wow and flutter readings. For that matter, neither could
anyone else's cartridges. For serious music, TDK's still the best
choice, based on that parameter alone. "Classic" shows some readable
and listenable advantages when I hit the tape really hard, true,
making it probably a better candidate for the car than TDK, but for
home, I'd just about call it a wash. What's nice about TDK is that
you don't really have to resort to re-equalization, either. Not doing
this on "Classic" will yield and overly bright top end.

On to "Master," probably the "last word" in 3M cartridges. This stuff
came out later, and offers more of all that "Classic" offered...even
lower noise, possibly even more headroom, and even more top end...in
other words, more of everything that most 8 tracks can't really take
advantage of due to the limitations of the format. This tape behaves
and looks much like Scotch 306/307, a favored Scotch mastering and
production tape from the '70s. Like Ampex's competing "Grand Master"
389, it's just TOO good for 8 track, making it something that only the
recordist with epicurian tastes would lust after. I couldn't hit 2%
THD on "Master" before the record amps on the 8075 and 8056 started
clipping horridly, thus the tape has no limit on MOL; hit it as hard
as you can, and obviously your machine starts to get in the way long
before the tape does. Back off the bias, and distortion's STILL good,
and noise goes down even further, but then you get the old problem of
too much top end...LOTS of it. Even at 0 VU, I could get all the way
out to 17 KHz on the 8075 using "Master." I learned when playing with
the good Ampex tapes that I had to bypass the FM MPX pilot filter to
get all the top end I wsa trying to get, since that 19 KHz filter will
start to erode extreme top end when using good tape. Anyone with a
good tuner wouldn't need such a filter anyway in their recoders; only
cheapie tuner pass the 19 KHz through to its baseband output without
at least trying to filter out most of it.

So, "Classic" is good...really good...somewhat better than TDK is some
areas, not as good when it comes to speed...and "Master" is the equal
to Ampex's "Grand Master" when used on an 8 tracker. Only when you
get into serious RTR machines will the differences between these two
tapes become evident. To the 8 track recorder, both tapes make the
tape "disappear" as an impediment to good saturation performance, and
puts the onus directly on the machine's ability to exploit all that
headroom and top end. Worth the effort to get? Only if you have
really GOOD machines at home. For the car? If you're serious about
fidelity in the car, sure, but who is?

One thing about Scotch, a problem with ALL Scotch oxide binders from
that era: They do NOT like water or humidity. Any Scotch tape stored
in a humid or wet environment for any length of time will shed its
oxide on the first play, making a mess out of your contacts, head and
capstan in short order, and also destroying whatever's on the tape.
As a desert dweller, I have no problems with Scotch, but friends of
mine in LA who make their bread by digitizing old masters just about
choke every time they have to deal with transcribing and old Scotch
master tape. "Will it make it, or will it fall apart?", is the
question they ask as they spend hours "baking" these tape to try to
get them through an Ampex just ONE more time. Add the acetate backing
of a reel of ancient Scotch 111 from the '50s, and it's "recording
engineer CPR time." Ampex? NEVER a problem, even with the old Irish
products.

Next: Ampex's rare mid-line "20/20+" 388, and some "junk tapes,"
including the numbers on using old prerecorded carts as blanks.
This'll be awhile, I'm sure, since I'm in the middle of rebuilding a
very nice Ampex 440B-2 as my new 2 track machine for home. After
that, I'm going to install a Nortronics head in the 8075 and see what
happens with that. Happy tracking and watch out for flying
"spaceballs!"

dB
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