Part One of this series, I made some assumptions: Machines are older while
users and technicians are newer, with less analog tape experience
than Mix readers probably had ten years ago (or more). Next month, in
Part Three, Ill examine recorder bias techniques and present more
information on narrow-format machines; but for now, lets focus on
alignment, troubleshooting and mechanical issues.
One key tool in optimizing tape recorder performance is a calibrated test
tape, such as those made by MRL (http://home.flash.net/~mrltapes)
or BASF/Emtec (www.emtec-magnetics.com).
Test tapes are expensive and should be treated with care, so dont
play chicken with an unknown machine. They are also recorded full-track
and will not reveal tape path anomalies such as up and down vertical movement.
Though it may seem redundant, I perform a record test and
adjust bias before a playback alignment to help weed out electronic and
mechanical problems. To isolate channel-specific problems, swap cards
with the machine off, but only after labeling them. Note that swapping
cards might temporarily resolve a problem, so return cards to their original
slot apres test to confirm.
A selected list of service resources, including a demagnetizer, was detailed
last month in Part One of this article. Test equipment options were provided
in the May issue in this column. You have an oscillator now, right? Route
a 1kHz sine wave from the mixer to all tracks with the machine set to
Input. If the mixer meters seem consistent, it sometimes helps to throw
the subgroup faders all the way up (if applicable) to minimize channel-to-channel
Meters are often less accurate than the buses they represent, so an AC
voltmeter such as the Fluke 8060A is helpful in confirming levels and
calibrating meters. You can also use a patch cord to route one bus to
each individual track, one at a time. Steady state (with tones), mixer
and tape meters should agree, although all bets are off with Program Material
when integrating bar graph with mechanical VU meters.
1. If you dont have an operator/service manual, get one fast! In
researching this article, I was continually impressed with the amount
of useful, available technical information, from circuit theory to machine-specific
procedures. (Some machines have very specific test tape recommendations.)
Service manuals of olde are a far cry from current practice.
2. Always check the heads for oxide buildup.
3. Before rolling tape, sweep the oscillator through the extremesfrom
20 to 20k Hzjust to rule out bad capacitors (in the mixer or tape
machine) that can cause premature bass roll-off.
4. Quite often, a misplaced tweaker will have accidentally adjusted the
wrong channel or a speed-specific parameter, making some channels look
quite odd. You may want to bring the stragglers closer to
the herd, but novices shouldnt do any major tweaks yet.
5. Input Level calibration is perhaps the most inconsistently implemented
adjustment throughout the magnetic ages. Please read the manual for the
6. When monitoring Input, Sync and/or Tape (repro), most narrow-format
machines have only two heads, so they are always in Sync mode (playing
from the same head used to record or automatically switching to Input
when in Record). For those machines, the translation is Playback
After Recording, not during (PAR for the purpose of this article).
7. If noise reduction is part of the signal chain, set it to Bypass.
8. Dont rule out the patchbay, cabling and especially aged connectors.
I once saw a machine whose male XLRs were so black with oxidation that
the connection behaved as a diode, turning AC into DC, a.k.a. rectification.
9. If you are going to tweak, have the right tool for the job.
10. When playing old tape stock, be aware that oxide can come unglued
from the plastic, making a perfectly good machine seem possessed. If this
has happened to you, stop! Look closely at the heads and guides with ample
light. If you see funk, you can visit my Web site, www.tangible-technology.com,
for more information on tape restoration.
to Page 2
Reprinted with permission from
Magazine, September, 2000
© 2000, Intertec Publishing, A Primedia Company All Rights Reserved