Pro Audio Design Forum

Doug - What John said. Old school electrolytic caps had the outer metal case connected to ground, new school caps not so much. You might still want to determine which terminal. + or -, is the outer wrap even though the can floats. (I think you'll find it to usually be the - terminal.) I found large ...

I had wondered about eliminating the coupling caps. I think "might" might have been the wiggle word. I suppose you could say that the virtual ground needs to be "virtual" at DC too.

If we remove the I-V stage after the VCA (5534); remove the summing resistors (15K); remove C1 & C2; and leave L1 in place (inductor/ferrite bead), we're essentially there in theory? Yes, I think so. You might could leave C1 and C2 if you wanted to. I was just thinking today that the SSL 82E26 ...

I have seen a single core variant for mic pre input filtering where the inductor presents a different impedance to CM signals than normal signals (actually a transformer of sorts IIRC). JR I think Benchmark used to sell one and used it in their preamps. haven't thought about a coil in emitter of mi...

These wind up in the emitters aka Rgain lines. http://www.ka-electronics.com/Images/jpg/1510_Servo_Schematic.jpg The thread is here: http://www.proaudiodesignforum.com/forum/php/viewtopic.php?f=6&t=256 I'm trying to remember in the 990: Do the two input transistor's emitter inductors share the s...

I was thinking that in the current summation approach a little bit of inductance locally right at the CFB amp's emitters could negate the VCA's 15 pF/channel output C. In a 16-channel that's 240pF or so of distributed C. The 1570 may not have the performance advantage though using "resistorless...

I am apprehensive about putting any capacitance on the emitters of CFB amps.. I have been thinking of a more conventional opamp for the current sum amp, since it is operating at much reduced noise gain, and must be unity gain stable to support the capacitive feedback to mitigate input capacitance, ...

Here's one version of the summing amp I did where the servo samples the emitters: https://www.ka-electronics.com/Images/jpg/1570_Balanced_Summing_Amp.JPG This one samples the output to pin it to DC baseline: https://www.ka-electronics.com/Images/jpg/1570_Balanced_Summing_Amp_Rev_A.JPG The bases, pin...

When attempting to get best s/n at high gain you want low total impedance in feedback network (Rf and Rg in parallel). The pot varying the leg to ground give you lowest impedance at highest gain. The above hits the nail on the head. Safari is cutting off the right side of the image here, but Firefo...

John - Thanks for posting this. To our readers: The summing bus discussion in John's article begins about here: http://www.circularscience.com/des_art.pdf#page=4 I did figure 13 with a 1570/1246 and it worked pretty good. I used a servo to bias up the bases to remove the -Vbe offset at the emitters ...