Volume Pot In Distortion Pedal Question

[Slade]

Hi,
I've noted that in some high gain distortions like Dr. Boogey the value of the volume pot has a notorious effect in the sound. The recommended value for this pot is 100kA, but I've tried putting a 250kA instead and the distortion gets more bass and "granulated", loosing much treble!.
What is the reason for this? I've been reading some here, but didn't find any like this.

Greetings.

[davidallancole]

The schematic I am looking at says 1M for the volume pot.  Which schematic are you looking at?

[Slade]

What?!
http://gaussmarkov.net/layouts/drboo/drboo-schem.png

[BAARON]

A 250k pot raises the output impedance, which means you'll lose more treble over long cable runs between the effect and your amp.  It also affects the bass response of the tonestack to a small degree, which is probably why you're getting more bass there.

[JKowalski]

The reason that you get such a different sound is because right before it there is a large passive tone control network. The frequency response of the tone control circuit shifts slightly when it sees a different output impedance.

EDIT: Ah, too late.  

[Slade]

Thanks for your answers.
I haven't used the tonestack of the schematic, only the gain stages.

[BAARON]

Still, you'll have an output cap followed by a volume pot... Look familiar?  It's a capacitor, then a resistor.  That's a high-pass filter, which means it limits bass frequencies while letting highs through.  Making either part bigger (cap or pot) will let more bass frequencies through.  However, making the pot bigger will also adversely affect the output impedance, so you'll lose high frequencies on the signal's journey between pedal and amp.

If you wanted more bass without losing highs like you do with the bigger volume pot, it would be better to increase the value of the cap (rather than the pot).  Larger caps = lower impedance, therefore less treble loss.

[Slade]

Thanks BAARON, really clear now

I just used this 250kA pot because I don't have 100kA right now, but I will buy some soon  .

Greetings,

Fernando.-