Grimm Audio MP1, Руководство пользователя

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2. Modifiying factory settings
Your MP1 is factory set to the supply voltages of the microphone specified in your
order. In case you need to adjust the MP1 to the supply voltages of a different
microphone, there are various internal settings to facilitate this. We have to warn
you however that selecting a wrong voltage will very probably lead to damage of
the (sometimes very expensive) tube. So unless you are an experienced engineer or
like living dangerously, we do not advise to change the factory voltage settings! In
any case Grimm Audio cannot accept liability for damage to microphones. For those
people that still want to change the internal settings, please read the following in-
structions carefully.
In appendix 1 a list can be found of known microphone types with their factory
adviced supply voltages. Should your microphone not be listed, please consult the
original manufacturer. Please also check this MP1 manual on Grimm Audio’s web-
site, it might have had an update of the microphone list. Three preset high volt-
age are available from the MP1: 120, 145 and 210 V. These are set internally using
jumpers and not by external controls, to avoid costly mistakes while a microphone
is connected. A trimpot allows some (+/-8%) adjustment of these voltages. The HT
supply is inherently short-circuit proof as it is a shunt supply. As an extra safety a
“crowbar circuit” will shut down the current source in case the output voltage ex-
ceeds the nominal value by more than 12% due to malfunctioning. However, Grimm
Audio cannot accept liability in case of damage to microphones should even the
protection circuit fail.
For the heater voltage two preset values are available: 6.0 and 3.9 V. These values
are chosen in conjunction to what is prescribed for most classical microphones.
They too are set by internal jumpers. A third jumper position enables a trimpot and
allows the heater voltage to be set at any desired value between 3.6 and 7.0 V. In
addition, the output polarity can be reversed as some mics require negative heater
voltage. Noise is very low: typ. < -120 dBV ( < 1 uV), an improvement of at least
30 dB over industry standard voltage regulators. The output is short-circuit proof,
the current limits at 0.5 A. As an extra safety a crowbar circuit has been added to
protect the mic against unforseen failures should the heater voltage exceed the
nominal value by 10% (in case of the variable heater voltage setting a second trim-
pot allows the user to set an appropriate threshold). However, Grimm Audio cannot
accept liability in case of damage to microphones should even the protection circuit
fail.
Check the voltages output of your MP1
How the MP1 is set, can easily be measured from the outside: a blue test socket
allows the measurement of the heater voltage, a red socket gives acces to the HT
divided bij 10 (for safety reasons); a black socket povides a ground reference. These