Thanks, Raimund.
My numbers are definitely a little suspect because I do not
understand how the DC and AC components of the circuit interact.
But don't you think that my battery box, using a 9v battery and 6.8
kohm resistors has an unnecessarily high output impedance? To be
safe, one could use Primo's circuit that uses 5v and a 3.9 kohm
resistor. But I think that 4.8v and 1.8 kohm resistors might supply
the voltage and current the capsule needs with a lower output
impedance, by a few dB, than what I am getting, which might be useful
for folks using recorders that are a little noisier than the LS-11.
I'm now thinking that resistors any lower than 1.8k with a 4.8v
supply might raise the current too high. It depends on how the
apparent resistance of the capsule changes with the voltage, which I
do not understand. All I can tell is that the apparent resistance
goes up as the voltage goes up.
That's about as far as my limited knowledge can take me. I'm going to
try 4.8v and 1.8 kohms and see what happens.
John
John Crockett
Westminster, Vermont
Let us live in harmony with Earth
And all creatures
That our lives may be a blessing
On Dec 31, 2012, at 6:19 AM, wrote:
>> I am thinking that 500-600 ohm resistors with a 4.8v battery pack
>> would supply the voltage and current the capsule needs, and only a
>> 1.8 dB drop in voltage when it meets the LS-11, compared to the 9 dB
>> drop it is probably getting now.
>
> Hi John,
>
> I agree that reducing the resistors to 500 ohm would indeed lower
> the output impedance of the circuit. But I'm afraid that the (AC)
> output signal voltage would then be reduced too, which would mean
> that the signal level at the preamp input of the recorder is
> finally not being improved...
>
>> The battery box as
>> currently configured is using a load resistor nearly equal to the
>> impedance of the capsule, thus dividing the battery voltage in half
>> and presenting about 4.5 volts to the capsules.
>
> Yes, this is obviously the configuration that provides the best
> possible performance because the output signal level reaches it's
> maximum under these conditions.
>
> Bye the way, there is another Yahoo group that is dedicated to
> building microphones (http://tech.dir.groups.yahoo.com/group/
> micbuilders). Those guys might be able to provide more detailed hints.
>
> Regards,
> Raimund
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