Cathode capacitror / resistor frequency cutoff

[grandmasterflash213]

Im modding my valve junior, with the main aim of getting nice crunchy OD and not the farty buzzy crap that it sounds like in stock condition. I know that correctly matching bypass cap values to the cathode resistors gives a certain frequency cutoff point, which can be tailored to reduce the low end buzzyness. Ive got a 1K resistor on the first 12ax7 stage and a 620R on the 2nd, which has helped in adding more crunch already. Ive seen on marshall circuits the frequency cutoff is around 86 Hz. Is it wise to copy this frequency? (at the mo the setup is 1k/22 uF 620R/22uF ie. full range). Do i aim for the same frequency cutoff in both stages, or is it only necessary in the first stage if the 12ax7?

I was thinking of:
1st stage: 1K / 2.2 uF - 72 Hz cutoff
2nd stage 620R / 3.5 uF - 73 Hz
please excuse silly questions, first time doing this!

[Jag]

I don't think it would be necessary to drop the frequency response in stages following a stage that had already dropped those frequencies.

Try a .68uf bypass on the first stage and see if it does what you want.

[Bruce / Mission Amps]

It gives no frequency cut off.
Read up a little more about bypasing the AC around a cathode resistor for additional gain at some frequency and all above that.
You'll see that as far as thinking of it as a filter, the Q is so bad that it only makes a few dB difference on way or another... you'll hear it of course but there isn't any cutoff.

Then go here and look at the chart I made up:

http://www.aikenamps.com/RC-FHz.htm

[Matt T.]

Here is a discussion from kg's site on it.