sbeach
Active member
Hi,
I'm new to posting here but I've been lurking for quite awhile. I have been designing & building mic preamps for a few years - starting with basic opamp gain blocks - but lately have been trying to learn about & incorporate more discrete component stages. Here's a mic input stage design I'm trying to get a better understanding of ...
http://groupdiy.twin-x.com/displayimage.php?pid=1523&fullsize=1
I lifted the JFET differential input from a discrete opamp input posted here. Is this a legitimate way to use this differential-to-single-ended stage in place of an input transformer? If so, is there a way to determine and/or adjust the gain for this stage? I would like to be able to choose between 5 to 25 db of gain here if possible. Would the gain be adjustable by increasing or decreasing the 1k resistor on the JFET drain? What would be the problems in using such an approach? Crappy inteference rejection? High noise? I imagine the actual JFETs used would greatly influence the gain available.
In a complete preamp design the following stages could add from 30 to 50 db of gain but for clarity & simplicity I have left that part out.
Any ideas, comments or helpful suggestions are very welcome. I really want to learn this stuff. Thanks,
Skip Beach
I'm new to posting here but I've been lurking for quite awhile. I have been designing & building mic preamps for a few years - starting with basic opamp gain blocks - but lately have been trying to learn about & incorporate more discrete component stages. Here's a mic input stage design I'm trying to get a better understanding of ...
http://groupdiy.twin-x.com/displayimage.php?pid=1523&fullsize=1
I lifted the JFET differential input from a discrete opamp input posted here. Is this a legitimate way to use this differential-to-single-ended stage in place of an input transformer? If so, is there a way to determine and/or adjust the gain for this stage? I would like to be able to choose between 5 to 25 db of gain here if possible. Would the gain be adjustable by increasing or decreasing the 1k resistor on the JFET drain? What would be the problems in using such an approach? Crappy inteference rejection? High noise? I imagine the actual JFETs used would greatly influence the gain available.
In a complete preamp design the following stages could add from 30 to 50 db of gain but for clarity & simplicity I have left that part out.
Any ideas, comments or helpful suggestions are very welcome. I really want to learn this stuff. Thanks,
Skip Beach