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Q: No Power, No Indicators ?
Ensure the IEC plug at the rear of the unit is inserted
all the way. Wait at least five minutes before trying
the power switch again. If the unit does not power up
then check the fuse on the PSU. (See Servicing,
Diagram 3)
Q: The Unit Is Switched On, No Sound ?
First try plugging the IN and OUT cables into some
other piece of gear to verify that your cables are OK.
Next check the front panel, try BYPASS. If you have
sound now it might be a good idea to turn up the
output levels to about 1 o’clock (rather than fully
counterclockwise which is “minus infinity”.
Q: Levels Seem To Be Wrong, No Bottom ?
Several possible scenarios. Manley uses the
professional standard of +4 dBm = Zero VU = 1.23
volts AC RMS. A lot of semi-pro gear uses the hi-fi
reference of -10 dBm = Zero VU. This is a 14 dB
difference that will certainly look odd and may tend
to distort. Often there are switches on semi-pro gear
to choose the pro reference level. We do not provide
that kind of switch because of inevitable
compromises in the signal path. If the loss looks close
to 6 dB and it sounds thin then one half of the signal
is lost. The cause is probably wiring again. One of the
two signal carrying wires (the third is ground / shield
on pin 1) is not happening. Check the cables carefully
because occasionally a cable gets modified to work
with a certain unit and it seems to work but its wrong
in other situations. If only one side of the Nu Mu
exhibits this problem, it may be a problem in the unit
itself.
Q: Only One Channel Is Functioning ?
This may be due to a faulty tube. Most Manley gear is
two channel, meaning you can swap tubes to
determine the faulty tube. Switch one pair at a time.
VT1 & VT2, VT3 & VT4 are matched pairs.Leave the
unit switched off for at least 15 minutes before
removing any covers. If upon examination you see a
white topped tube instead of a silver top this tube is
likely to have cracked its glass envelope, fracturing
the vacuum, this tube will need to be replaced.
Q: How Can I Cure Low Frequency Hum?
Method 1
- The most likely cause is a ground loop.
This can be cured by lifting the chassis to signal
ground lift jumpers which are located inside the unit.
Please refer to the Servicing Chapter, Diagram 3.
Method 2
- Cutting the shield on one side of the
cable (PIN 1). This is done by some studios at every
female XLR to “break” all loops. You may get a loop
simply from the rack. All the other gear in the rack is
“dumping” ground noise onto the rack rails. Try
removing the Nu Mu from the rack so that it is not
7. Questions & Troubleshooting
touching any metal. You may have cured a non-loop
hum. Some gear radiates a magnetic field and some
gear (especially if it has transformers) might receive
that hum.
Method 3
-Another method of reducing all sorts of
hum and noise is to use a 60-0-60 balanced AC power
transformer. Hum is more likely with the unbalanced
inputs and outputs because these signals are ground
referenced. A common situation is using the Nu Mu in
a way that significantly boosts the low level signals
and what may have started out as a little hum
becomes nasty. Check out the gear feeding the Nu Mu
or use less limiting and make-up gain.
Q: Why is my Nu Mu Not Completing its Power-Up
Cycle?
The Nu Mu utilizes a custom designed, sophisticated
high voltage switched-mode power supply. This power
supply features protection circuitry to stop any
damage being caused to itself. If at anytime the unit
will not power-up the protection circuitry may have
been triggered. It is in protection mode if after
switch-on the power LED blinks for a fraction of
second then after a pause it blinks again. The PSU is
now in protection mode as the supply is trying to
reset. This condition will occur if the unit suffers
excessive heat exposure or there is a damaged tube
or component. Allow the unit to cool and try
powering-up again. If the protection mode persists,
the unit will have to be returned for service.
Q: Nu Mu Makes Noises When The Front Panel Is
Tapped?
Some tubes become microphonic over time. That
means they start acting like a bad microphone.
Vibration and aging has caused the supports for the
small internal parts in the tube to loosen and now the
tube is sensitive to vibration. The only remedy is to
replace the tube.
Q: Nu Mu Sounds Distorted?
This might be a tube. Swapping is a good way to find
out. It may be a wiring issue or mismatch. Wiring
problems usually accompany the distortion with a
major loss of signal. Mismatches are a bit tougher.
The Nu Mu 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. Also check your
patch bay in case there is a problem there too.
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