Ross Phaser hitting it's limit?

[auden100]

Just built a Ross Phaser. Pretty much based on the tonepad layout.
http://tonepad.com/getFileInfo.asp?id=99

It seems to work well, and sounds nice, but one trait I'm not certain about is when the Regen is in its upper quarter turn, the sound starts to bubble. It's like a fat, wobbly, soft distortion. Only when I play at full volume, and only during the low end of the phase curve. I wasn't sure if this was an idiosyncrasy, or a product of my doing. Anyone who made one these have the same problem?

btw, I play a Hamer with humbuckers.

[Mark Hammer]

The regeneration/feedback signal has too much bandwidth; specifically too much bass.  Consider replacing one or more of the 1uf caps around the regen control with something smaller, like .1uf.

[auden100]

Yes. Thank you, Mark. I had to replace both of those caps, and there's still a slight fart-iness in the highest settings, but I can live with that. I also ended up increasing the feedback resistor on the last opamp from 15k to 22k, as it seemed a little bit quieter.

You're an asset to the community, sir. 

[Mark Hammer]

My pleasure.

I've made maybe a half dozen of these things in one form or another, and they've been hit or miss when it comes to the sweep.  An 8-stager I made has a certain kind of "bubbliness" to the sweep as well, sounding almost chorus-like in certain respects.  I suspect there is an asynchrony to the sweep in the two 4-stage sections.