Grimm Audio MP1, Manual Manual

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In addition, J4 must be set to the upper position when 210 V HT is chosen. (Failure
to do so will still output 210 V but the shunt supply will not be able to function op-
timally, possibly degrading sound quality).
Choose the lower position for J4 if you want a wider range of 0-160 V available for
polar pattern control in the 120 V HT case. This will also work for the 145 V HT,
resulting in a 0-184 V variable voltage, although no microphone is known to us that
needs this setting.
The trimpot allows some adjustment of the HT output voltage. The crowbar protec-
tion thresholds remain fixed. Trimming the output voltage close to the treshold
values is not recommended as this increases the risk of ill-triggered shutdown.
To reset a crowbar action it suffices to switch of the MP1, wait a few seconds and
switch on again.
Heater Voltage Settings
The jumpers setting the heater voltage are located to the right in fig.1.
First take a look at the two jumpers J2 & J3 in the right-hand top corner. They set
the heater voltage’s output polarity: || is positive. Change their orientation by 90
degrees: == is negative. Check with the red (plus) probe of the multimeter inserted
into the blue test socket (no mic connected yet!).
Fig 1. Voltage adjustment jumpers inside the MP1.