D I O... P A P E R
this information may in part be aplicable to other tube amplifiers,
it is intended only to help people who own our Zen Triode amplifiers
diagnose and indentify the actual cause of hum problems in their
might find some irony in the fact that I would do a paper on
solving hum problems when our amplifiers are known to have one
of the quietest noise floors in the industy, but the assumption
that the amp is always the cause is generally incorrect.
is a 60 cycle (50 cycles in other countries) tone
that lives in the noise floor of all audio gear or when problematic,
becomes the noise floor. Hum can be measured at the output
of any amplifier with a decent AC volt/ohm meter. The
proceedure is simple; Just hook your speakers up to the amp,
remove the input cables from the amp, turn the gain knob (if
it has one) all the way down. With your meter connected
across one channels output jacks (with the speaker hooked up
at the same time) your meter should slowly drop to below 2 milivolts
AC. (All of our amplifiers fall below this value.)
value has been determined acceptable because to hear any hum
on a 90 dB speaker you have to put your ear on the dustcap.
On a 100 dB speaker you may hear it as far away as 2 feet
in a quiet room. The goal is simple, once you're in your
listening chair you should hear nothing.
are two types of hum problems. The first is a low level
background hum that you can notice when the music is not playing.
The second is an objectionable hum that makes trying to
listen to music basically not an option.
first type of hum problem is not considered a problem if the
amp sounds so good when music plays that you simply don't care.
Every manufacturer gets to guess where this threshold
is because it's subjective to every listener. High power
amplifiers coupled to power hungry speakers (the norm in todays
homes) make this threshold easy to beat but take a high efficiency
speaker and suddenly any hum or noise that was there is now
10 dB louder!
second type of hum problem is a mechanical failure of some componant
or wire to do it's job. This can be anywhere from the
source to the loudspeakers, although the problem typically stops
at the amplifier. The first objective is to find out if
the hum is being amplified by the amplifier, or if it is coming
from the amplifier itself. This is easy to do, just unhook
the single cables feeding the input of your amplifier. This
breaks the signal path at the point of the amplifier. If
the amplifier stops humming, you know the problem is before
that point. If the amplifier still hums, there is a problem
with the amplifier.
GUIDE FOR ZEN TRIODE/TORII AMPLIFIERS
1 - Remove the interconnects from your amplifier so that the
only thing hooked to it is your loudspeakers. Turn the
volume control (if it has one) all the way down. Turn
on the amp and let it warm up for a minute.
hear hum from both channels - If you hear hum from both
channels it could be caused from a bad input tube. Turn
the amp off and remove the input tube. On the SE84C, SE84CS
and SV83M this is a single tube located farthest towards the
front of the amplifier. On the SE34I and TORII this is
the small tube located farthest towards the rear. (Note: Only
the TORII-C has an input tube, the TORII-A and TORII-B do not).
Turn the amp on without the input tube. If the hum stops,
try a different input tube. If the hum continues with
different input tubes, and if your amplifier has a rectifier
tube, try replacing the rectifier tube. If the hum continues
there is a problem with the amplifier.
hear hum from only one channel - Hearing hum from only one channel
usually means that you have a bad tube. Try the same proceedure
above with input tubes. If that doesn't solve the problem,
try reversing the output tubes by swaping the left and right
tubes. If the hum is now on the other speaker, replace
that output tube.
is important to have clean tube pins. While this usually
won't cause an amp to hum, it can add to the noise. A
good tuner cleaner/lubricant works well for this if used sparingly.
Connectors are equally important. Use it on both the input and
output jacks also.
you have determined the hum is not coming from the amplifier,
the most likely causes are as follows:
interconnects that have a broken or cracked ground path.
input jacks on the amp, or on your source or preamp.
your source and or preamp in a different outlet than
two to three prong adapters to lift the ground.
interconnects parallel with power cords.
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2007 2008 by Steve Deckert