Re: Keeley Katana...is this right? And popping.

Posted by induction on Feb 26, 2014; 4:16pm
URL: http://guitar-fx-layouts.238.s1.nabble.com/Keeley-Katana-is-this-right-And-popping-tp8377p8383.html

That 15nF on the switch is only in the circuit with the boost mode on, so it shouldn't affect the sound with the boost off. If the non-boost mode sounds different when you swap caps, the switch is probably wired wrong. (It sounds like you have the cap in the circuit in non-boosted mode, and switch it out of the circuit for boosted mode. That would explain why it was so dark in non-boosted mode, and much brighter in boosted mode.) Of course, if you like it, that's all that matters.

Putting a resistor inline with the 10uF will affect the amount of boost. The gain of that jfet stage is dependent on the ratio: drain resistor/source resistor. The switch puts the 10uF in parallel with the source resistor, which reduces the effective value of source resistance, thus increasing gain. Putting a resistor in series with that cap increases the effective source resistance, so the gain will not increase as much with the resistor in there.  The larger the resistor, the lower the boost, which is why the pop gets quieter. No matter how large the resistor, the gain will never be less than in non-boosted mode, but above 100k the boost will be too small to notice. The resistor shouldn't affect the frequency content very much. It will add a bit more bass (technically, it will cut the bass less than the treble), but it's mostly below 100Hz, so it shouldn't be too noticeable.

I think the reason it pops is that the floating (positive) side of the 10uF will hover around ground, and the jfet source will be higher than ground, so there will be a dc shift when you flip the switch. You might be able to get rid of the pop by keeping the 10uF connected all the time, and put a 500k or so resistor in series for non-boosted mode. Then use the switch to jumper around the resistor. I'd breadboard it first, though. I haven't tried it, and it might pop anyway.

Edit: Of course, if your switch is wired wrong, fixing it may fix the pop (or make it worse, I guess). I'd figure out the correct switch wiring first, and work on the pop second.