NE570-based NR compander (P-522) by JR

[JR.]

Nah.. electrolytic capacitors don't do well at low impedances, and in that circuit node the cap is dealing with ohms or at best tens of ohms.. DC couple and HPF elsewhere...

Unfortunately you don't want to wrap anything like this variable HPF around a mic preamp due to input impedances...

JR

[mediatechnology]

That particular node (Rgain) is not the best place to do stuff in series or parallel. In the 1510 (and most CFB mic preamps of similar topology) even a small amount of stray capacitance to ground ~1-2 pF is going to create issues. In series, a few thousand uF are required to make changes.

I agree with John that tricks are best performed elsewhere.

[JR.]

Yup.. I once had to locate a mic trim pot about 18" away from a circuit in a console (back in the '70s) for ergonomic reasons. The C in the shielded cable was enough to destabilize the circuits. I ended up driving the shield of the cable with a CM output signal I derived to keep it happy.

JR.

[Crusty]

I agree with John that tricks are best performed elsewhere.

Alright then, I shall resist. LOL

John, I remember you mentioned that bootstrapping trick once, and I stored it away in my noggin for possible later use. I'm more of a cookbook guy than a textbook guy, but examples of stuff like that are hard to come by. Also, your trick with the alternate input on the state variable filter I had never seen before...

...and to tweeze Wayne and to go even further off topic - once I think you mentioned that at your old gig you entirely eliminated trim pots from new designs...???

[JR.]

I agree with John that tricks are best performed elsewhere.

Alright then, I shall resist. LOL

John, I remember you mentioned that bootstrapping trick once, and I stored it away in my noggin for possible later use. I'm more of a cookbook guy than a textbook guy, but examples of stuff like that are hard to come by.

I am not big on documenting my old scribbling... From memory, I developed the CM shield driving signal with a passive sum of the two first stage outputs. I don't recall if I buffered that. I suspect a modest impedance passive sum might be adequate to drive the shield.

Also, your trick with the alternate input on the state variable filter I had never seen before...

Not sure I recall which one you are talking about. I have made many SVF based designs. Too many to list right now.

...and to tweeze Wayne and to go even further off topic - once I think you mentioned that at your old gig you entirely eliminated trim pots from new designs...???

Yes, trimpots in a factory environment are costly from a labor perspective, and problematic for circuit performance. How can you ever know when talking to a customer that their unit is not misadjusted?

My worst product to support was a 4 track cassette deck that I inherited. This had trims for everything from mechanical stuff (head alignment), to electro mechanical, (bias filter traps), to simple electrical (Dolby level calibration). Because of the medium and nature of the technology I couldn't make them go away. I did redesign the unit and removed some $20 worth of internal PCB connectors and such.. That product was always a loser though with two full time techs in the factory just to crank out several a day.

JR