Gearslutz.com - View Single Post - links to a couple of interesting mic pre schematics.

manning1 · 9th September 2004

re: SSR . tiny my mistake terribly sorry,
i wondered about that after leaving the forum.
re: thermal noise.
well. maybe its just me . a bit of history.
it seems to me the original 57 and its predecessors
were designed in an era when transormers were more widely used on mic pre inputs. i really dont know.
i can only go from my experience and listening and with friends that a 57 seems to LIKE a transformer front end instead of a transformerless front end. maybe i'm wrong.
but its certainly sensitive to loading and the circuit impedences it "looks into", you know the old "low into hi" imp thing.
or maybe i'm out to lunch and its the darn iron in the mic pre xformer that adds some mojo.
i'm always willing to learn if you have any more input on this.
in transformerless designs one thing i HAVE found is low current noise figures in the op amp seem to improve things.
some burr brown op amps have very very low current noise
figs if i remember. but the op37/varaieties does it for me.

9th September 2004	#16
manning1 Lives for gear Joined: May 2004 Location: canada Posts: 3,998 Thread Starter	re: SSR . tiny my mistake terribly sorry, i wondered about that after leaving the forum. re: thermal noise. well. maybe its just me . a bit of history. it seems to me the original 57 and its predecessors were designed in an era when transormers were more widely used on mic pre inputs. i really dont know. i can only go from my experience and listening and with friends that a 57 seems to LIKE a transformer front end instead of a transformerless front end. maybe i'm wrong. but its certainly sensitive to loading and the circuit impedences it "looks into", you know the old "low into hi" imp thing. or maybe i'm out to lunch and its the darn iron in the mic pre xformer that adds some mojo. i'm always willing to learn if you have any more input on this. in transformerless designs one thing i HAVE found is low current noise figures in the op amp seem to improve things. some burr brown op amps have very very low current noise figs if i remember. but the op37/varaieties does it for me.