Search found 44 matches

by olafmatt
Wed Jul 12, 2023 5:24 am
Forum: Pro Audio Design
Topic: New: A Direct-Coupled Input-Capacitorless Active Mic Preamp
Replies: 142
Views: 353265

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

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 reje...
by olafmatt
Mon Jul 10, 2023 12:51 pm
Forum: Pro Audio Design
Topic: New: A Direct-Coupled Input-Capacitorless Active Mic Preamp
Replies: 142
Views: 353265

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

The first page you can maybe read by just looking at an enlarged version of the image used on the audioXpress website: https://audioxpress.com/assets/upload/images/1/20220712163606_audioXpress-August202-MicPreamp-Web.jpg In the description for the photo it says that the author is using this with hom...
by olafmatt
Sun Jul 09, 2023 4:28 pm
Forum: Pro Audio Design
Topic: New: A Direct-Coupled Input-Capacitorless Active Mic Preamp
Replies: 142
Views: 353265

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

Had a look at the article. He is floating the frontend and then uses a 220n cap to avoid the level shifting. The floating frontend is a SSM2017 with a DC servo (470k/470n) sampling the output and then injecting correction ("balanced", by also inverting the servo output) into the input thro...
by olafmatt
Tue Jul 04, 2023 5:19 am
Forum: Document
Topic: Active Volume Control
Replies: 1
Views: 10559

Active Volume Control

Looking for alternatives to the well-known Baxandall volume control circuit (see here: https://sound-au.com/project01.htm ) I came across these ones: https://up.picr.de/45947024us.png Robert Sontheimer, "Audio-Schaltungstechnik", Elektor Verlag, 1994 https://up.picr.de/45947025vx.png JVC A...
by olafmatt
Thu Jun 22, 2023 12:20 pm
Forum: Pro Audio Design
Topic: ZTX851 and ZTX1053A Noise Measurements and Comparisons
Replies: 2
Views: 9281

Re: ZTX851 and ZTX1053A Noise Measurements and Comparisons

Any idea how to plot the output impedance over frequency for a dynamic mic? I'd guess that doing it the normal way (injecting test signal into the XLR through a voltage divider) will not give proper results because the mic would then be a "loudspeaker" (i.e. nothing that holds the membrane...
by olafmatt
Thu Jun 22, 2023 12:19 pm
Forum: Pro Audio Design
Topic: New: A Direct-Coupled Input-Capacitorless Active Mic Preamp
Replies: 142
Views: 353265

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

"Higher" noise floor with 22uF is because I forgot to set the full-scale level of the ADC. So the whole dBu scale should read 14 or 18dB less, as in "more negative" (it's been a while since I made these plots so can't remember which ADC I actually used).
by olafmatt
Thu Jun 22, 2023 11:30 am
Forum: Pro Audio Design
Topic: New: A Direct-Coupled Input-Capacitorless Active Mic Preamp
Replies: 142
Views: 353265

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

Sorry that I'm a little late to the party. - After having experimented with a input-cap-less micpre circuit for a while I went back to using caps to avoid a bunch of potential problems. Tried instead to minimize the impact that those phantom blocking caps have. Here is the noise floor of a micpre wi...
by olafmatt
Mon Oct 07, 2019 2:18 pm
Forum: Pro Audio Design
Topic: New: A Direct-Coupled Input-Capacitorless Active Mic Preamp
Replies: 142
Views: 353265

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

I look at it this way: From a DC perspective if the output of the mic is a few hundred millivolts out of balance and the servo forces the resistance bridge back into sub-millivolt balance how is that any worse than it being in perfect balance to begin with? It can even be a good thing! If you have ...
by olafmatt
Mon Oct 07, 2019 12:57 pm
Forum: Pro Audio Design
Topic: New: A Direct-Coupled Input-Capacitorless Active Mic Preamp
Replies: 142
Views: 353265

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

Olafmatt's servo that I used in the MC preamp works great at controlling the Vbe offset but I'm not sure it has enough range to also correct the larger offsets the mic presents. I would guess it would allow for large enough a correction, but it would need less attenuation at the output of the servo...
by olafmatt
Mon Oct 07, 2019 2:23 am
Forum: Pro Audio Design
Topic: New: A Direct-Coupled Input-Capacitorless Active Mic Preamp
Replies: 142
Views: 353265

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

I think I've seen XLR chassis sockets with a switch that gets engaged once an XLR plug gets plugged in. That way a PIC (or some other logic) could detect when a mic gets connected and then run a callibration for a while and then store that value until the mic gets diconnected... but that way you wou...