Phantom power blocker for synth outputs

[Newmarket]

In addition, for the sake of perfect sound, it is worth connecting a minimum 100 nF Mylar or polypropylene capacitor in parallel with the biolar electrolytic capacitors in order to eliminate the high-frequency phase shift. I recently repaired a friend's Quad 66 preamplifier, all coupling capacitors were 50uF / 25 V bipolar. I measured the phase shift at 20 kHz at 48 degrees. (With a Neutrik A2-D Audio Test & Service System instrument.) In addition, when testing with a square signal, I saw "endless ringing" on the oscilloscope, at the top of the signal. I installed 680 nF polypropylene capacitors everywhere and reduced it to 14 degrees. The ringing has stopped. Synthesizer sounds are full of harmonics, phase shifting can result in a bad sound.

If you like. Personally I'd probably just go with a higher value capacitor. Or add them in parallel

 

[Newmarket]

35 KV? You are brave! I worked in a plasma physics research laboratory with 10 KV capacitor banks, but I had to be so careful

Well in context I am in the "Low power" section so current capability is low. It will still hurt / stun you though. We actually go to 70k +. The "High Power" section has a lot more current on tap.

 

[Newmarket]

Cheap ceramic caps have a pretty severe

voltage coefficient,

Yes. This a known thing (ask me how I know 🙄)

and NPO caps have limited values, so if a coupling cap, better to use a film cap, or even electrolytic.

Yes

Most SMT resistors are thick film, metal film are many times more expensive and not very common.

Use "Thin Film" or MELF. Yes they cost more. Although I've put standard Thick Film into a product (sorry - some decades past now 😊) and no one complained - at Trade Shows. Nor did the test kit. Capacitors were a different matter though.
Big disadvantage with MELF is that they'll just roll away and drop onto the floor 🤣

Active devices, I don't think SMD suffers any disadvantage.

True. All else being equal you're simply minimising lead inductance.