I haven't said that for several weeks now,
I know! I was thinking it was about time. LOL.
We really could use that SPI controller.
Everyone is doing Smartphone interfaces.
I don't think I would want to place the trust of a live recording in my Smartphones's battery.
People want knobs.
OK, I calculated the Q of my alleged-to-be-misbehavin' circuit using Gary's formulas and my circuit values.
I did a differential to half-circuit transformation and used the following values from my original schematic posted at the beginning of this thread.
Ccoupling 47 uF
Rinject 100K (half circuit value)
Rbias 2K5 (half circuit value of Rterm including phantom resistors)
Gain 60 dB
Servo tc 0.235 (500K*0.47uF)
With the input capacitor in place fo is 4 Hz.
The Q calculates out to be 0.704.
At lower gains the Q lowers, and with lower Rinject, Q also lowers.
It's slightly underdamped at even the highest gain with
a coupling capacitor.
Not quite hitting the exact nail on the head for a Bessel response but pretty damn close for being determined empirically by a hick from Texas with only a high skool (sic)
With the real measured physical properties being subordinate to the theoretical I'm glad we determined that the AC characteristics of the servo meet the mathematical requirements for stability.
Man do I feel better now.
But we gotta divert to some other Red Herring 'cause this is the internet.
Are we going to now have to discuss the subject of clicking during gain switching again?
If so I'm just going to send links to the 5 or 6, maybe 10 other times its been discussed.
What I've learned in the last couple of days is that I need to build one of these that can travel.
Maybe after enough other people say "Hey, this thing really does work" we can move on from "it can't be done!"