PreSonus Forums

Absent schematics, does anyone know what type of input topology is used in the Series III mic/line inputs? Is it a three-stage op-amp instrumentation input with output offset servo-control? Single-stage differential input op-amp?

The difference isn't trivial: 3-stage op-amp inputs (or high-quality transformer) offer best common-mode rejection ratio (CMRR). Cheaper product often use single-stage op-amps to achieve a differential input.

With a 3-stage input functioning as an instrumentation amp (not to be confused with an instrument input!) unbalanced sources can be connected directly to the balanced input without tying one side of circuit ground and otherwise affecting circuit CMRR.

Paul

These are Presonus’ renowned XMax preamps with some extras to allow electronic gain control (no servo’s). AFAIK XMax pre’s used a balanced first stage built from discrete components followed by a balanced opamp stage. Probably still the case or they wouldn’t be XMax preamps anymore, right?

If it is similar to the legacy models:

http://forumsarchive.presonus.com/posts ... 14017.page

roblof wroteIf it is similar to the legacy models:

http://forumsarchive.presonus.com/posts ... 14017.page

But with extra Cajun sauce for recallable settings.

Hehe, I see that you were in that old thread as well .

Damn, that hand drawn picture was pretty bad quality! I wonder what crappy phone camera I was using back then...?

Skip Jones wrote

roblof wroteIf it is similar to the legacy models:

http://forumsarchive.presonus.com/posts ... 14017.page

But with extra Cajun sauce for recallable settings.