New: A Direct-Coupled Input-Capacitorless Active Mic Preamp

[olafmatt]

In 2008 I made a version basically using a discrete Cohen-style implementation. It did work.

The important thing is to only fly the differential gain stage and keep the diff-amp at "hard-ground". That way the diff amp will see variations in your flying ground as common mode signal and reject them. The way its shown in the audioXpress article with differential to single-ended in the flying part would need an additional diff-amp that would re-reference the signal to hard-ground (i.e. feed it the output of the SSM2017 and the flying ground). If you have a diff-amp at hard-ground you don't need that third order filter for the flying ground (unless maybe for CM induced distortion reasons).

[ilya]

I've been wanting to use the ZTX851 or ZTX1053 in a mic preamp.
Both are exceptional.

Me too!
However, given current situation in our region, it's very difficult to get parts from the outside. And I do have a ton of 44xx that I can play with. I'll see, maybe I will provide additional footprint for ZTX parts - seems quite easy to do.

The important thing is to only fly the differential gain stage and keep the diff-amp at "hard-ground". That way the diff amp will see variations in your flying ground as common mode signal and reject them. The way its shown in the audioXpress article with differential to single-ended in the flying part would need an additional diff-amp that would re-reference the signal to hard-ground (i.e. feed it the output of the SSM2017 and the flying ground). If you have a diff-amp at hard-ground you don't need that third order filter for the flying ground (unless maybe for CM induced distortion reasons).

Olaf, thanks for you comments. Will definitely keep that in mind. I think I'll make another thread where I'll post design decisions and we can take the discussion there. Although if mods think that this thread is more appropriate, I'll keep posting here.

[mediatechnology]

The ZTX951 PNP is slightly quieter than the ZTX851 NPN.
Both are quieter than the 2SB737.

The ZTX e-Line transistors are CBE so they have the same footprint as a 2N440X.