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Vintage threads from the first ten years

High Impedance buffer

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2/11/2003 8:44 PM
BoB	High Impedance buffer Can anyone point me in the direction of a high impedance buffer, for use as the front end of a piezo pre-amp. I need around 10M. Any ideas? Also, how would i go about mixing three seperate signals together to a common output? Can i just connect the outputs's together using a buffer? Thanks, Rob

2/12/2003 4:31 AM
jon	Rob, I can give you some suggestions on how to accomplish this with tubes.... Jon

2/12/2003 3:56 PM
Mark	I'm interested in a Tube buffer as well. Could you post a link or explain here? Thanks, Mark

2/12/2003 7:05 AM
Tim Escobedo	http://www.muzique.com/lab/buffers.htm Some good ideas here. JFET/MOSFETs and FET input op amps are prime candidates. Bootstrapping might be a good idea, too.

2/13/2003 7:48 AM
nic	I have an old net schem someplace... Let me figure out where and if I can locate the source. It was a jfet/mosfet combination solution. It did the job but I never liked the way piezos sounded so I never took it far. nic

2/13/2003 3:08 PM

Guys,
If you can let me know the HTML stuff to link you with an image on a remote server by clicking "here",
I'll draw up a simple high impedance tube circuit for you. I've tried the 10meg grid to ground resistor with no success; what works for me using a 12AX7 is a bootstrap to the cathode.

O'Connor has this pretty well outlined in his books...I recall having to tweak values a bit though.

I've tried different approaches for the remainder of it; a Baxendall tone stack ala Ampeg Gemini 1 or Magnatone 260/280 works well in there. Certainly warmer than SS to my ear....I do like running this into a SS power amp(typically after a tube outboard reverb circuit) in certain applications, though.
HTH
Jon

2/14/2003 2:52 PM
BoB	Re: High Impedance TRANSFORMER Just a thought that occurred to me. Could an impedance matching transformer be used to provide a high input z/low z output. This would be better for plugging into a guitar amp (low input z). Also, no batteries! I don't really need any boost, the output is more than adequate. Thanks, Rob

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