buffer

TUBESMAN · 22nd October 2008, 03:49 PM

I need to build an input attenuator for my Lynx 2 sound card. like a 10 meg switched input for a VTVM. Mostly to put the voltage I measure in the proper range and to protect it from excessive voltage surges from mistakes.
My idea so far is a string of 10, 1M resistors followed by a unity gain buffer and some 1N4148 diodes to clamp the voltage output to 2 diode drops P-P.
So my problem is this. I need a buffer with low distortion it also must be quiet and have the ability to drive the Lynx 2 single ended.
Also it must have a very high input impedance so it doesn't load the divider string.
BUF03 is obsolete so is BUF04 and a TL071 has issues with a 600 ohm load.
I really only need bandwidth to 100k. Any ideas?

jcx · 22nd October 2008, 04:58 PM

a couple of fundamental problems with MegaOhm series resistors

Thermal noise will be large

bandwidth will be restricted with even pF parasitic C

what is your signal range, worst case over voltage to protect against?

TUBESMAN · 22nd October 2008, 05:03 PM

I need to measure from about 1 or 2 volts up to about 35 v rms from 20Hz to more than 20kHZ with THD down to less than -75 to -80dB.

myhrrhleine · 22nd October 2008, 05:30 PM

I'd use something like an OPA827 for the buffer or OPA627
For a divider, check out divider arrays in a DIP. Higher precision.

TUBESMAN · 22nd October 2008, 05:32 PM

ok, its a start. I'll look into those chips

22nd October 2008, 03:49 PM	#1
TUBESMAN diyAudio Member Join Date: Apr 2004 Location: New York	buffer I need to build an input attenuator for my Lynx 2 sound card. like a 10 meg switched input for a VTVM. Mostly to put the voltage I measure in the proper range and to protect it from excessive voltage surges from mistakes. My idea so far is a string of 10, 1M resistors followed by a unity gain buffer and some 1N4148 diodes to clamp the voltage output to 2 diode drops P-P. So my problem is this. I need a buffer with low distortion it also must be quiet and have the ability to drive the Lynx 2 single ended. Also it must have a very high input impedance so it doesn't load the divider string. BUF03 is obsolete so is BUF04 and a TL071 has issues with a 600 ohm load. I really only need bandwidth to 100k. Any ideas?

22nd October 2008, 05:30 PM	#4
myhrrhleine diyAudio Member Join Date: Jan 2006 Location: Avalon Island	I'd use something like an OPA827 for the buffer or OPA627 For a divider, check out divider arrays in a DIP. Higher precision. __________________ Just because you can't hear it doesn't mean no one can.

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22nd October 2008, 04:58 PM	#2
jcx diyAudio Member Join Date: Feb 2003 Location: ..	a couple of fundamental problems with MegaOhm series resistors Thermal noise will be large bandwidth will be restricted with even pF parasitic C what is your signal range, worst case over voltage to protect against?

22nd October 2008, 05:03 PM	#3
TUBESMAN diyAudio Member Join Date: Apr 2004 Location: New York	I need to measure from about 1 or 2 volts up to about 35 v rms from 20Hz to more than 20kHZ with THD down to less than -75 to -80dB.

22nd October 2008, 05:32 PM	#5
TUBESMAN diyAudio Member Join Date: Apr 2004 Location: New York	ok, its a start. I'll look into those chips

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