Manley Langevin Dual Vocal Combo 1999 - 4/2001 LDVC000 - LDVC178 - Manual (Page 13)

TROUBLE-SHOOTING
There are a number of possible symptoms of something not quite right, some may be interfacing, others we will
touch on as well. The Dual Vocal Combo has a variety of balanced and unbalanced inputs and outputs optimised for typical
standards and most problems are due to the right cable in the wrong jack. However if you suspect a problem the following
paragraphs should help.
NO POWER, NO INDICATORS, NADA - Probably something to do with AC power. Is it plugged in? Check the fuse on
the back panel. A blown fuse often looks blackened inside or the little wire inside looks broken. A very blackened fuse is a
big hint that a short occured. Try replacing the fuse with a good one of the same value and size. If it blows too then prepare
to send the unit back to the dealer or factory for repair. The fuse is a protection device and it should blow if there is a prob-
lem. If the unit works with a new fuse, fine. Check the MAINS VOLTAGE SELECTOR if one is fitted. Some of our models
are able to have them and some don’t. It should be set correctly for your mains voltage.
LIGHTS BUT NO SOUND - First try plugging the in and out cables into some other piece of gear to verify that your
wires are OK. Assuming that it was OK into the other unit it probably is still a wiring thing. The AES standard calls PIN 2
HOT on XLRs but there is still lots of gear out there with PIN 3 HOT. When two units are connected and both are unbal-
anced but don’t seem to agree which pin is hot - the signal is shorted out. If it is not lost entirely, it will be almost gone and
extremely distorted. THE CURE - a phase reversing adapter that swaps pin 2 and pin 3 on one XLR - or get out a soldering
iron and swap wires yourself. All Manley gear after 1995 is pin 2 hot. Some Manley gear has balanced and floating outputs
and some has unbalanced transformerless outputs. This unit has two discrete line drivers - one driven from the other. If the
XLR pin 2 is shorted to ground or pin 3 there will be no signal from the XLR. If pin 3 is shorted to ground - a typical way
to drive unbalanced inputs - then the output on pin 2 will be 6 dB low. The best way to drive unbalanced inputs is with the
unbalanced outputs.
LEVELS SEEM TO BE WRONG, NO BOTTOM - Several possible scenarios.
The above paragraph describes the output line drivers. If you are using the balanced XLR outputs and feeding an unbal-
anced input (it happens) you will only be getting 1/2 the signal which means that you lost 6 dB. There is a “trick” if you just
want to use the XLRs but from time to time feed unbalanced inputs. Insert a 1/4” mono (tip - sleeve) plug (unwired) into
the unbalanced output. This makes the levels right. You could leave this plug in permanently but we don’t recommend it
because you can have 6 dB more headroom into balanced inputs if it is removed. More headroom is one of the biggest factors
of great sounding gear.
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 goofy and may tend to distort. Often
there are switches on the 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 happen-
ing. 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 Limiter exhibits this problem, it may be a problem in the Limiter.
See the next item.
If you have almost no signal and what you can hear is distorted then you probably have pin 2 shorted to ground or to pin 3.
This might happen if the cable is mis-wired and/or you are feeding an unbalanced input.
USING THE 1/4” JACKS BUT THE LEVEL IS LOW - The 1/4” output jacks on this unit are unbalanced and require a
mono plug (tip - sleeve plug) and not a stereo plug (tip - ring - sleeve plug. The Limiter uses the ring to set the output level
for this output. When the ring is shorted to the sleeve the output becomes 6 dB louder. This is needed because the XLR has
differential outputs which together give that extra 6 dB. Using the ring compensates for this difference and both outputs will
be the same level (+4 dBv). Other manufactures often use a common circuit that does this in a different automatic way. The
generic name is “transformer like” but unlike transformers, these outputs can be unstable (oscillates) into some cables and
often have low headroom into unbalanced inputs. Our method works better as long as one uses a mono phone plug.
We have included an appendix: WIRING YOUR OWN CABLES that may help.
For reference both the XLR and 1/4” back panel inputs are balanced electronically and not with a transformer. The inputs
will work fine and should reject hum from either balanced or unbalanced outputs. The 1/4” Direct input on the front is unbal-
anced and meant for guitars and basses. In many situations it can be used for low level sources but watch out for ground loop
related hum.
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