Pro Audio Design Forum

One of the major considerations is servo pulling imbalanced phantom currents. A quick experiment shows that Olaf's servo used in the MC preamp will have enough range to correct mic imbalance. Yes, that servo can probably be made to have enough correction range... I'm just not sure whether the pream...

I like this circuit. Glad it works not just for me. In the thread about the MC preamp you mentioned the reduced power supply rejection caused by the fact that the two non-inverting inputs of the opamps are not connected together. This is basically something I was already mentioning as a drawback of...

"it can't be done!" Please re-read my initial posing. I did NOT say that it can not be done. I was asking whether you came across any such interaction between the servo and the caps inside a microphone. Again, I did not say that it will not work in general. Or missbehave in general. Olaf

Still not exactly what I'm talking about. Look at the AES paper "DC Servos and Digitally-Controlled Microphone Preamplifiers" by Gary Hebert and read "3.1. Frequency-Domain Effects". In that paper Gary discusses the effect of the servo (in combination with phantom blocking caps) ...

The mic output DC offset issue is dead. Yes I know. Sorry for having mentioned the TLM103... in the context of some other potential problem. I think I recall the TLM-103 output structure from olafmatt's previous post was op amp output > 47 uF > 47 Ohm per leg. The AC output impedance is also lowere...

When I get a chance I will check for this: The worst combination would be at high gain with input coupling caps. But I should have seen it by now. Thanks Wayne for considering my "worries". - Some years ago I also experimented with a input-cap-free preamp with a floating input stage. And ...

I hope I found the latest incarnation of this thread and I'm not posting in some super ancient place... Recently I dedicated some brain processing power to the topic of interaction between DC servos and caps. Usually these are the phantom blocking caps. I thought about switching them out of the way ...

Even worse if ground is accidentally bootlegged to line, the equipment chassis is energized. Oh yeah, I've seen that. It was actually an outlet a computer was plugged into. Every time the user started the dial-up modem connection (right, this was 15 years ago) the mains voltage got connected to the...

Cool! Indeed. It basically goes like this: http://www.analoglabor.de/DIY/instamp_new_servo.jpg Just insert your favourite differential servo (but keep in mind that it needs to remove the CM component). When not using T-bias one could use a non-differential servo, just monitoring the voltage differe...

Yes I did try (and it did work). That's how I realized that my lazy assumption that the "new" injection nodes see the same (overall) gain applied as the bases do is wrong. - At low gains I was getting way faster reaction of the servo than I thought I would.

Olaf