hotbox Q : cap in llel with resistor, what's it do??

[frankgb]

Hi,

Got a question about the Matchless Hotbox, the clean channel has a 220k resistor in parallel with a 560pF capacitor after the volume control.

I have used this same config in a Valve Junior, and it gives a really nice sorta 'edge' to the sound, so my question is, what is this snippet functioning as? A filter etc???

Also, what are the maths involved, if I wanted to add this to another amp, but with a different resistance value, how would I work out the 'correct' cap value?

many thanx

Frank

[Groovenut]

Hi,

Got a question about the Matchless Hotbox, the clean channel has a 220k resistor in parallel with a 560pF capacitor after the volume control.

I have used this same config in a Valve Junior, and it gives a really nice sorta 'edge' to the sound, so my question is, what is this snippet functioning as? A filter etc???

Also, what are the maths involved, if I wanted to add this to another amp, but with a different resistance value, how would I work out the 'correct' cap value?

many thanx

Frank

It's a high pass filter of sorts but the knee is dependent upon the resistor that is usually to ground after such a combo. The resistor cap combo tends to extend the knee a bit. If it is after the volume control prior to the tube with no resistor to ground following, it would the depend on the miller capacitance of the following stage.