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Your point about unplugged amps holds. I zapped myself with 60V from supply even though amp had been off for minutes

Really cool modification of the pot!

Aren't we all

So what I mean by uncontrolled voltage at input is that the negative side of C4 has a direct DC path to the input. If the device upstream of the input has any + DC (such as a failing short output cap), that will will exceed the ~1.5V reverse DC voltage on C4 which then breaks the cap. Its...

I was asking a similar question a couple weeks back regarding how far is far enough. The truth is there isn't a definitive answer. I can tell you for me I have seen problems on 2 circuits of mine where @ ~40-50db of gain, I got oscillation. My assumed offending traces were ~3mm apart. This...

I would consider a non polar cap for C4 since the DC at the input is uncontrolled. It's probably just a me thing but still, plenty of space and very little change if any to footprint. Rotating C1 + towards left allows for cleaner routing, mainly aesthetic End stop resistors in series with...

You have a lot of margin to widen your signal traces as well. It does not hurt to widen audio traces. I find .5mm to be unobtrusive but you could even go fatter in some spots

One hack I found a while back was to always short pins 2 and 3 of pots acting like variable resistors. That simplifies drop in replacements of different tapers should the initial taper not work. Another recent hack was to create a footprint for the internal and external enclosure dimensions...

Very cool circuit! I like the gain control.

We have Jfets at home...😶

I mean if the 2nd stage is free.... Another use I realized was IF there is no gain in the input buffer, you can parallel the opamps stages to lower noise at the input. You just have to add a very small series R (1 - 100r) passive summer called ballast resistors. You can see the difference of...

Was talking to a peer about this the other day. The buffer ofc reduces the output impedance of the midpoint much closer to 0, which trends towards an ideal voltage source. You have to be careful though bc the opamps contributes its own self- noise.

So LMK if I'm re-hashing here but the leakage is the failure of the diode to act as an open circuit when "off" ? AND The series resistance is the failure to act like a short when it is on? I would think Vf is easily worked around by scaling input amplitude into the diode circuit.

I found this paper the other day. Not a complete examination but still interesting https://www.circuitsjournal.com/article/109/7-1-4-460.pdf

Schottkys suffer from noise to my knowledge yes?

So the leakage of a germaniums suggests you can emulate a germanium by inserting a resistor parallel to the silicon diodes... ?

I didn't know about using 4 layer for HV. That's a cool trick!

I was gonna say just that about DC, I know there is concern about supply noise on DC traces however I'm fairly convinced in most circumstances that is well enough filtered to be a non issue. I'm sure in your world voltage clearance is the bigger concern.

I have been turning my attention in layout to fighting instability. I've read the bulk of routine talking points about tight NFB routing, impedance scaling, separating GND planes (divisive in modern day), star grounding etc etc. The question I have is have you found empirically a general rule...

Best bet is ota based most likely. You could compress slow attack on way in but that only cover crunch of transient.