JLM mic pre

danielle · Jan 19, 2005

Hey Joe,
Do you have a shopfront in Brisvegas or a 07 **** **** number as I don't like transacting credit cards on the net?
If anyone thinks that this is an excuse for a "shameless bump" as stuff is sliding down the "pages of obscurity" faster than a cat on fire?
Well, you'd be dead right :wink:
Regards,
Danielle

tk@halmi · Jan 20, 2005

[quote author="PRR"]
As long as you have DC anyway, and need caps, have you ever pondered this differential amplifier?

[/quote]

Hmm... I have been pondering this for a while. Wouldn't U3 have to operate at less than unity gain?

tk@halmi · Jan 20, 2005

Also, instead of C18 being grounded, should it be at Vcc/2? Sorry for the confusion.

Tamas

JLM Audio · Jan 25, 2005

Technically if the power rails are all perfectly regulated you could connect C18 to 0v or +/- rails if you have the polarity of C18 right. Because the bias voltage would determine the output voltage not what C18 was connected to. But in reality usually 0v is the quietest reference point.

Joe

PRR · Jan 25, 2005

> Wouldn't U3 have to operate at less than unity gain?

That is one odd fact. The first amp runs at half the signal level (not necessarily half the gain) of the second stage. With real sloppy amps, this has some odd effects. The distortion spectrum with modest-gain "op amps" is neither odd nor even.

> instead of C18 being grounded, should it be at Vcc/2?

That end of the resistor chain should reference your output common.

In a +/- supply, it would go to ground, halfway between the rails.

This specific implementation is for a unipolar +48V supply. But using "op amps" with a big 0.6V offset, plus huge offset current. So the DC level at the left end of the resistor string is pretty unclear. However the AC output is referenced to ground, so the AC reference on the left end is ground.