Need amp with 200 kOhm input impedance

hasselbaink · 22nd August 2011, 12:28 PM

Hi ,

Can any of you tell me if there is a solid state amp with more than 200 kOhm input imp. or if there is a design where this parameter can easily be changed?

Best
Kris

Samuel Jayaraj · 22nd August 2011, 01:28 PM

You can always put a JFET/FET buffer in front of the amp and tune it to whatever input impedance you want. The buffer can be discrete or opamp based.

ingenieus · 23rd August 2011, 08:16 PM

The easiest way to do this is to use a FET input op-amp in non-inverting mode. For a really high input resistance look at something like the ISL28110/ISL28210. The datasheet give it at about 550 giga-ohm! Slew rate is quite respectable at 23 V/us. You add an extra resistor in parallel with the input with the value you want it your input resistance to be.

22nd August 2011, 12:28 PM	#1
hasselbaink diyAudio Member Join Date: Aug 2006 Location: Copenhagen, Frederiksberg	Need amp with 200 kOhm input impedance Hi , Can any of you tell me if there is a solid state amp with more than 200 kOhm input imp. or if there is a design where this parameter can easily be changed? Best Kris

22nd August 2011, 01:28 PM	#2
Samuel Jayaraj diyAudio Member Join Date: May 2001 Location: Bangalore, India	You can always put a JFET/FET buffer in front of the amp and tune it to whatever input impedance you want. The buffer can be discrete or opamp based. __________________ Sam

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23rd August 2011, 08:16 PM	#3
ingenieus diyAudio Member Join Date: Apr 2011	The easiest way to do this is to use a FET input op-amp in non-inverting mode. For a really high input resistance look at something like the ISL28110/ISL28210. The datasheet give it at about 550 giga-ohm! Slew rate is quite respectable at 23 V/us. You add an extra resistor in parallel with the input with the value you want it your input resistance to be.