Hi Gerald,
I see this thread has not been active for awhile. I have not been online fo=
r several months. I hope this is still helpful.
I was asking these questions a couple of years ago and got useful advice.
Raimund Specht pointed out to me that the lower the resistor values in the =
battery box, the lower the gain of the FET that is built into the EM172 cap=
sule, so you don't want to go too low. You can't eliminate the resistors co=
mpletely or you may burn out the capsules with too much current. You'll als=
o compromise the FET gain.
I am using the megalithia battery box with a 9v battery and 6800 ohm resist=
ors (as in the schematic), and that gives me 5.3 volts and 0.54 mA across s=
ingle capsules. Just right.
With two capsules in parallel, that drops to 3.8 volts and 0.4 mA across
each capsule, which is still within the specs of the EM172 (3 - 10 volts, 0=
.6 mA max) and seems to work fine.
You could try the resistor value specified by Primo, which is 3900 ohms.
That would give you about 5 volts and 0.5 mA across two capsules, which is =
just right, but if I understand Raimund, these resistors would also cut the=
FET gain about in half, which might not be ideal.
I tried it every which way: two capsules, one capsule, high resistor values=
, low resistor values. I listened to the s/n on all of these trials and cou=
ld not hear one whit of difference. So I ended up staying with the single c=
apsules for simplicity and getting a good balance of voltage, current and F=
ET gain. Your mileage may vary!
John Crockett
Westminster, VT
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