stereo di box -10dbv to +4dbu balanced

[quote author="PRR"]> Disagree. 5532 offset is low enough it "should" not be a problem. That input cap is for protection against leaky consumer outputs. They are now rare, and I agree it isn't usually necessary to DC-block the input. I just think it is good practice to defend against the unexpected. Sure, for quick/cheap work, leave out the cap and see if it is a problem. [/quote]

Good point, but it should probably be something like 1µF if the circuit is to be good down to 20Hz.

> Insert a 100 ohm resistor in series with the opamp output, before the feedback resistor takeoff point (more stability).

I don't understand. Resistance between opamp output and feedback takeoff usually degrades stability. If you mean to take the 10pFd cap from opamp pin, resistor feedback after the 100Ω, that's not clear. And using couple-hundred ohm output resistors, keeping all else (including good supply bypassing) tight to the opamp, is usually plenty stable.

Click to expand...

No, I meant 100 ohms from the output pin to the feedback takeoff point, then 47k || 10pF for the feedback network, and the resistors to the output coming from the same point (junction between 100 ohm resistor and feedback network). My experience has been that the 100 ohm resistor adds to stability, at least with 553x and OPAx604 chips. YMMV, obviously, but that's been the case for me.

Peace,
Paul

> it should probably be something like 1µF if the circuit is to be good down to 20Hz.

Maybe I'm befuddled. I wrote 500nFd. What I meant was 0.5 microFarads, but the young guys here have this new (to me) thing called a nano. Which goes between micro and micro-micro (which they call pico).

Isn't 500 nanoFarad about like 0.5 microFarad? Or have I run out of working fingers to count decimal places?

Anywho.... 0.5 microFarad seems to be -1dB at 13.3 CPS (whoops, 13.3Hz). Being fully pessimistic: 47K -10% resistor, 0.47uFd -20% cap, is down 1dB at 19.8Hz.

OK, one stage like this is a little droop, but a bunch of stages like this will slump-off your bass like a California hillside.

(If anybody really has bass to 20CPS. Many folk just talk about it, and then play >42Hz. I do have recordings with strong 32Hz, and I can't find speakers to rumble what I can see in the spectrum analyzer....)

Darn. I hate huge caps. 0.47uFd is about my limit. But sure, use 1uFd if you want.

I thought it was just those Europeans who liked to use nanofarads
I just jump right from micro to pico (I used to work with guys who said micro-micro, and called them condensers too).
I always overkill the coupling cap value meself; recapping the signal path of my old console so that every pole has a 1-second RC time constant (about 0.2Hz corner) made the bass come to life. This console uses input transformers that roll off at 10Hz, so you'd think it wouldn't make any difference, but the change is clearly audible.
Hence the 47uF bipolar coupling to a 24k input in my version. Probably too big - oh, well.
I still think I got the gain right.