Question, what do these resistors do?

[vanessa]

I'm looking at the Ampeg Scrambler and I was wondering what the 47k resistors to ground do on either side of the 50k "blend" pot.

[varialbender]

My n00bish guess would be regular highpass filtering, but i'm getting just over 3Hz as the crossover frequency, which doesn't make much sense to me. Maybe someone can clear that up.

[Ardric]

They influence the impedence into each side of the pot.  When the pot is centered, each path to the wiper sees a 25k series resistance.  If those two sides are driven by largely different impedences, that 25k+25k won't be anywhere near a 50:50 mix.  These help set the end points of the sweep of the blend pot, and also the shape of the curve.

They also form high-pass filters with their respective coupling capacitors.  I suspect the caps are big enough that the corner frequency is very low, so it doesn't amount to much.

What's R18 for, the 4M7 across the output?  R6 and R16 already pull the output to gnd and swamp it's influence.  Wouldn't it be better to insert a buffer after the blend pot so that its sweep characteristics don't change with changing output loads, and the output can drive line inputs as well as instrument?

And give it an RC filter on the power input.  It'll like wallwarts a lot more then.

[toneman]

I only see one 47K resistor on the Blend pot.
It makes a constant load.
The 4M7, that's a 4point7 MegOhm resistor, is for de-poping, and changes the taper(i think)..
T

[rockgardenlove]

There are two, follow the trace that comes out the bottom of the pot.

[vanessa]

So those are also hi-pass filters? Would they have a big effect on a bass signal if used with bass guitar? Or are their value size acceptable?

[slacker]

If my maths is right the roll off frequency is 3Hz so they're not going to affect the sound at all.