Manual

IT MAKES NOISES WHEN THE FRONT PANEL IS TAPPED - An easy one. Some tubes become microphonic over
time. That means they start acting like a bad microphone. Vibration has caused the supports for the little parts in the tube to
loosen and now the tube is sensitive to vibration. Easy - Replace the tube. Which one? The one that makes the most noise
when you tap it. It will have to be on , connected and speakers up but not too loud for the sake of your speakers.
IT GOT HISSY - Also easy. This is again a common tube symptom. You could swap tubes to find the culprit but an educated
guess is OK too. Generally the first tube in the path is the one with the most gain and dealing with the softest signals. The
usual suspect is the tube that is usually located closest to the front panel volume pot or the 5814 (or 12AX7, 12AT7, 12AU7,
6072 on other models). You may find that you need to choose the quietest tube out of several of that type.
DISTORTION - This might be a tube. Swapping is a good way to find out. It may be a wiring thing or mismatch as well.
Wiring problems usually accompany the distortion with a major loss of signal. Mismatches are a bit tougher. The Electro-
Optical Limiter has a high input impedance (HI Z) but some of our gear has a reasonably low input impedance. Without even
explaining the term "impedance" it is enough to say that a lot of gear is simply not capable of driving pro levels and low
impedances. It will sound like lost headroom, early clipping, distortion on peaks. Often changing the order of processors will
do the trick. Another not so rare place to look is the patchbay, your settings, the meter levels - it happens.
DC OR SOMETHING AT THE OUTPUT THAT IS INAUDIBLE - This might happen and it might be accompanied with
a strange hum or little whistles as it warms up. It only seems to occur with long cables. It happens on an older unit but not
on the newer one. Years ago we found a problem with our line driver section when it fed very long or cheap wire. The output
would tend to oscillate in the inaudible ultrasonic frequencies ( 200 kHz to 500 kHz) into high capacitance like a long cable.
We cured it by adding a simple 47 ohm resistor at the XLR. Newer units should not have a problem but if you have an old
one, we can FAX you a 25¢ fix. Real DC at the output would be such a rare find that we would be pretty surprised. We use
a $30 output cap to block DC. Most manufactures use a 30¢ electrolytic cap but we don't like the sound or reliability of these.
We invest more in these two output caps than most limiters spend on the entire parts list. A little very low frequency noise
might be seen at the output if you use a scope. This is generally very low level and caused by AC power fluxuations.
THE METERS ARE OUT OF CALIBRATION - If the problem only seems to be when the unit is just turned on it's normal.
It should warm up. It might be a half dB out for 15 minutes - relax. If they drift a tenth of a dB over the course of a day it is
because of bad AC power fluxuations - chances are other gear is doing worse, you just haven't found out yet. Your unit will
have been factory calibrated and tested twice before you received it. Sometimes parts drift a bit in value over the years, or
you have repaced tubes and want the unit calibrated at the same time, or you just want it as perfect as it can be. These are good
reasons to turn the page and go through the calibration procedure or sent it to a technician or the factory for a tweak. If you
send the unit to a tech, you should include this manual because they will need it. If you do it yourself, you will need an
Oscillator and a few screwdrivers and it would be nice to have a VOM meter and Scope but not necessary.
Once in a while we get a call from a client with a "digital studio" with confusion about levels. They usually start out by using
the digital oscillator from their workstation and finding pegged VU meters the first place they look and they know it can't be
the workstation. Even a -6 level from their system pegs the meters. Some of you know already what 's going on. That -6 level
is referenced to "digital full scale" and the computer might have 18 or 18.5 or 20 dB of headroom built in. That -6 level on
the oscillator is actually a real world analog +12 or +14 and those VU meters don't really go much further than +3. There are
a few standards and plenty of exceptions. One standard is that pro music (non-broadcast) VU meters are calibrated for 0VU
= +4 dBm =1.228 volts into 600 ohms. Another standard is that CDs have a zero analog reference that is -14 dB from digital
full scale or maximum. This allows sufficient peak headroom for mixed material but would be a bad standard for individual
tracks because they would likely distort frequently. This is why digital workstations use higher references like 18 and 20 -
to allow for peaks on individual sounds. It may be too much in some cases and too little in others. Add two other sources of
confusion. Peak meters and VU meters will almost never agree - they are not supposed to. A peak meter is intended to show
the maximum level that can be recorded to a given medium. VU meters were designed to show how loud we will likely hear
a sound and help set record levels to analog tape. By help, I mean that they can be only used as a guide combined with
experience. They are kinda slow. Bright percussion may want to be recorded at - 10 on a VU for analog tape to be clean but
a digital recording using a good peak meter should make the meter read as high as possible without an "over". Here is the
second confusion: There aren't many good peak meters. Almost all DATs have poor peak meters that do not agree with each
other. One cannot trust them to truly indicate peaks or overs. Outboard digital peak meters (with switchable peak hold) that
indicate overs as 3 (or 4)consecutive samples at either Full Scale Digital (FSD) are the best. They won't agree with VU meters
or Average meters or BBC Peak meters either. Each is a different animal for different uses. The Limiter should help digital
and analog achieve consistent levels but use each meter for it's own strength. The Reduction mode is useful with everything.
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