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FET substitute for in-microphone amp
FET substitute for in-microphone amp
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Old 7th January 2008, 03:52 PM   #1
Gorantzhe is offline Gorantzhe  Serbia
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Location: Belgrade, Serbia.
Default FET substitute for in-microphone amp

Hello everyone,
I'm making modification of my two microphones, Oktava MK012 and Oktava MK219 by Scott Dorsey's schematic published in magazine. Modified schematic uses Toshiba 2SK170BL JFET which is so hard to find. What FETs i can try to fit instead?

Below is specification of 2SK170BL, and it's mean nothing to me, because I can't understaint it. It would be also helpful if someone can tell me what features are most important and is it better to bi high value or low, so I can search for substitute by myself also.

Junction type
N Channel
VGDS: -40V
IG: 10mA
PD/PCH: 400mW
IGSS (max): -1nA
VGS: -30V
IDSS (min/max): 6mA/12mA
VDS: 10V
VGS off (min/max): -0.2V/-1.5V
VDS off: 10V
ID off: 0.1uA
gm (min/typ): ??/22mS
VDS gm: 10V

I took it from here:

And here is more info about 2SK170BL:

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Old 8th January 2008, 11:06 PM   #2
dimitri is offline dimitri  United States
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Old 13th January 2008, 04:12 AM   #3
BrianL is offline BrianL  United States
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Join Date: Mar 2002
Location: USA
FET substitute for in-microphone amp
The 2SK170 is not the best choice for a condenser mic. It has relatively high input capacitance which will act as an attenuator to the mic capsule. I suggest browsing Toshiba's (Japan) website for FETs with low noise and low input capacitance.
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