> the t power microphone is the easiest to modify for unbalanced working. i=
t will work on a 9-volt battery and=C2=A0needs just one 220 ohm resistor an=
d 50 mfd capacitor. (I think I published the circuit here or=C2=A0on mic bu=
ilders many years ago).
Umashankar,
The BBC Film Unit made its own Sennheiser power units which were taken over=
by Canford Audio. These used two PP3 batteries with about a 1K series
resistor to lose 6 volts, but it is not critical and they ran OK as the
batteries went down.
Your circuit will work as a balanced feed if you isolate the power
components, but you need a screened box like an Eddystone diecast box for
shielding. If you are fussy, you can split the capacitors to make the
circuit fully balanced with one capacitor on each leg, but the resistor
across the output to bleed off the DC is not critical and 1000 ohms would
still do fine.
You don't even need a PCB as you can just use a solder tag strip. The plugs=
can be mounted on the box or on short leads. Needless to say the resistors=
and capacitors must be low noise/low leakage types. I file a groove under
the lid and fix the leads with heatshrink tubing. All for a few $ or =C2=A3=
.
The actual output impedance of the MKH series is just a few ohms, and the
input impedance of most preamp inputs is 1K or more, so there is a lot of
leeway in the circuit values.
For the record, the optimum noise-matching impedance is different from the=
actual ohmic impedance of a preamp. For instance an input which is
noise-optimised for 150/200 Ohm mics can be much higher.
Anyone handy with a soldering iron could make an MKH power unit.
David Brinicombe
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