Today's $14 Question: How does one calculate a frequency limiter of inter-stage capacitors and resistors in parallel? I know the formula for calculating frequency knee/rolloff with a regular R/C filter where one goes to ground, like this low-pass filter: But I don't know one if they are in parallel. I.e., the front end of the Heavy Watter: There's the usual (a la Fender) .022uF capacitor that takes the signal off the plates and sends it on to the next stage. Here, they're followed by a 470K/3n3 and 470K/470p arrangement in the first and second stage, respectively. As I interpret that, the 470k resistor on the first one attenuates some signal coming from the coupling cap, and the 3n3 allows a set of higher frequencies to pass around it (mostly) unaffected. Same for the 470p on the next stage. The net effect is emphasis on higher frequencies, since a 'brighter' sound through a high-gain circuit (like this one) avoids farting later. That latter combination of 470k/470p is all over the triode coupling caps in the JCM800 preamp, an amplifier renowned in the Bad Ole Days for staying 'tight' when overdriven hard. Also to note, the cathode bypass cap on the first stage is smaller than typical. Again, my SWAG is that it's designed to emphasize upper frequencies. The following two gain stages have typical (read: Fender) values on all the caps thenceforth. I've been gargling the Googlemachine for some time now, but I'm striking out when it comes to a formula for calculating a frequency rolloff for resistor/cap in parallel. Also, I don't know if I would have to factor in the .022uF in series with the whole shebang either. Also suspect that the interstage calculation will probably be similar but different from the cathode bypass calculation. Is anyone willing to spin me round and point me in the right direction? THANK!