Question RE preamp resistor/bypas cap values

[iknowjohnny]

Say you have a preamp similar to the typical marshall cascaded preamp. On V1a lets say you have 100k anode with a 1.5k/.68uf cathode. I don't understand much theory but thru experimentation i know that if i change the 1.5k to a 2.7k but leave the cap the same, i will get a bit less gain and the tone becomes thinner due to the cap passing a larger resistor. Whatever the theory behind it, to my ear it sounds that way and i see it as the same sort of thing as those R/C filters marshall uses between stages.....the larger the R the larger the portion of high end compared to the rest of the range. I know it's not exactly the same thing technically, but i mean in effect it sounds that way. The question is, if i were to increase it to 2.7k, can someone tell me whether changing the cap value can make it retain the same EQ curve or close as possible, and if so what value would do it? I assume it would require a larger value, but again I don't know the math or theory. Thanks.

[pdf64]

There's no need to do the math, see http://www.ampbooks.com/home/amplifier- ... capacitor/
Pete

[iknowjohnny]

Thanks. I see that the gain at 10k seems to stay the same but at 82hz it changes a lot. If i use a 1uf/2.7k it shows about the same as the .68uf/1.5k. So is this all you need to do, or is it possible that even with the 10k and 82k regions showing the same the curve in between might be a lot different?