Successive coupling capacitors

Started by mark2, January 20, 2022, 01:32:46 PM

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mark2

Reading through the tube screamer analysis it mentions "The emitter follower output feeds the Clipping Amplifier Stage through a 1uF non-polarized electrolytic coupling cap C2, large enough value to not interfere with any guitar frequency."

This is after the input signal goes through a 20nF C1 cap, though. So why does it matter that C2 is larger?

Similarly this article (https://www.coda-effects.com/2016/02/dead-astronaut-fx-chasm-reverb.html) notes the buffer is "very transparent because of the high values of the coupling caps (C10 and C13, 10uF)" but the signal also passes through C11 which is only 1uF - so why not make C10 and C13 the same as  C11? (schematic here)

Any tips to better understand why the size of subsequent coupling caps matters when following smaller ones?

PRR

In both cases, "transparent" is not the word I would use, rather "full bass". There may be (is!) all kinds of other signal damage, but the intent is to pass all the bass.

It is not just the cap! All our bass-cuts are a combination of an R and a C. In the TS, C1 feeds a large 510k resistor, C2 feeds a 10k resistor. They each work out to -3dB @15.6Hz. Two in cascade will be roughly -2dB @31Hz, -1dB @62Hz. Straight guitar has nothing below 82Hz, so very-very little effect.
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mark2

Ahh yes, of course. I'm not sure why that didn't click for me.
Sorry for the dumb question and thank you for taking the time to spell it out! :)

PRR

Quote from: mark2 on January 20, 2022, 02:00:33 PM...taking the time to spell it out! :)

Most of the time I was looking at the output mixer on our DeadAstronaut's design and wondering WTF? It's a complicated situation of signals and DC voltages. The 10uFd into 1uFd into a virtual ground does raise "??" which I can not solve on cold fingers. But I don't see where it hurt any audio, or how a different approach would save cost/space.
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