what does the EH Bass Balls do!?!?!?!!?

[nero1985]

ok i know its an autowah type of thing but it has two filters, but my question is........  are they  sweeping in different directions? if they are going in the same direction what could i do to make them sweep agains each other?? thanks guys

[Mark Hammer]

The two filters sweep in the same direction at the same time, and if the trimpots are set in a certain way, by exactly the same amount.  There is nothing on the board or in the schematic which would allow for counter-sweeping, although.....

Probably the best example of how to set up something like this for countersweep is Tim Escobedo's "Gargler": http://www.geocities.com/tpe123/folkurban/fuzz/gargler.gif

This is an earlier, more complex, and automatic version of what he does with the Gargletron, a more recent footswept unit.  What is key here is that the two control elements used (2N3904, J176) have opposite reactions to the same envelope signal.  One becomes a smaller effective resistance to ground when the envelope signal is applied, and the other becomes a larger effective resistance.  The resistance to ground from the junction of the two same-value caps in each filter section is what tunes the filter.  "Re-tuning" it is what sweeping it is all about.

Tim's idea suggests that one might use the same board (whether a stock purchased unit or a DIY like the Topopiccione board) but different transistors for control elements and different trimpots to do what Tim did within the context of the Bass Balls circuit.

Separate outs for each filter section is a smart idea.  If you take the Otto Filter module from Line 6 and plug it into a stereo dock (the standard retail Otto Filter pedal comes in a mono dock/station), when the "talking filter" setting is selected, the two counter-swept filter outputs go to separate outputs.  Very cool effect.  Your attention tends to be drawn to the filter sweeping upward and to upper mids.  Because that filter starts out low, the stereo effect is that the filtering appears to move from one channel to the other.  Neat.

[nero1985]

thanks mark, you always have a cool answer!!!! im gonna try the gargler ASAP!

[H S]

The two filters are supposed to simulate human speech formants.  The latest Boss Auto-Wah has something similar;, I hear it also is only partly successful.

[Zero the hero]

Mark, I was thinking to a dull solution, as is using an op-amp whose transfer funcition is opposed to the envelope follower op-amp and driving each filter with one different op-amp.
Using a PNP instead of the NPN (changing supply for this transistor) could be a solution?

[Mark Hammer]

I *think* you mean that you would feed one NPN with the normal envelope output, and use an op-amp to invert that envelope to feed to a second NPN transistor, right?

That would be the "classic" way to do it.  Tim Escobedo's solution is much smarter.  Remember also that it is usually not enough just to invert the envelope.  The downward sweep does not start at the complete opposite end of the range.  It must be adjusted to start from its own appropriate place.  This is why I like the Gargler circuit.  You can adjust each trimpot to sound good.