Adding fuzz level control to bassballs

[shooter_mi]

I've searched and know this has come up in other threads, but I haven't found the level of detail I need. Can I replace the switch that toggles the distortion with a pot that adjusts the level of the fuzz signal in the circuit? If so, what value pot should be used? If not, how exactly do people add the level control for the distortion?

[Mark Hammer]

Do you mean the amount of fuzz effect, or the level of the signal when fuzz is used?  Two different types of solutions.

This is, in fact, one of the chief problems of the Bass Balls, and a perfect example of not being able to get something for absolutely nothing.  The "fuzz" signal is simply the output of the gain stage that feeds the rectifying diode.  For whatever reason, the amount of gain supplied by that op-amp produces a bizarre sort of clipping (some like, I'm not a big fan), and that is what gets used as the "fuzz" signal.  Normally, a resistive divider is used to reduce it to somewhere in the ballpark of the non-fuzz signal.  But the problem still remains that since it comes from the envelope follower section, when you increase the sensitivity of the pedal to create more sweep you also create a louder signal.

There are a couple of solutions to consider.  One that I use is to simply clamp the absolute level of the fuzz signal via diodes.  Instead of the passive resistive divider normally used (see R8/R9 here: http://topopiccione.atspace.com/pjimages/EHBassBalls.sch.gif ), I replace R8 with a 10k resistor, and R9 with a back to back pair of diodes, essentially turning the fuzz path into a Distortion+ type circuit.  Keep in mind the R9/R9 divider simply attenuates whatever it receives in a relative manner; i.e., output will always be 1/3 the level of input.  Use of the diodes means that level is assured in an absolute manner.  If the input signal does not exceed the forward voltage of the diode, it passes through as is.  If it exceeds the forward voltage of the diode, then that portion exceeding the forward voltage is clipped/clamped at that voltage, which also happens to produce more distortion than what the 1458 chip does alone.  The tricky part is selecting diodes so that the ceiling loudness is what you want for bypass/effect level balance.  A pair of Ge diodes might be best, although a single Ge and opposite-orientation single Si might make a decent combo and level.

What I've taken to doing lately (because Alex Petrini's lovely layouts have made it so easy, and as a result, so tempting to make more than one of these...thanks Alex  ), is to simply skip the clean path, and hardwire up the fuzz path, omitting the switch.  Now, I only have to worry myself about effect/bypass level-balance, instead of bypass/non-fuzz/fuzz level balance (which is the problem you are grappling with).

The other solution, which is, I guess, less invasive but perhaps more elegant, is to simply replace the 47k fixed resistor on the output with a 47k log pot, and use it as a master volume control.  Undoubtedly, you'd want it at full volume for the non-fuzz setting, but you'd be able to turn it down for fuzz setting where you wanted to crank the sensitivity.

It's funny, you know.  This is one of those tail-wagging-the-dog designs where so much was available from the basic design, but the insistence on remaining committed to a single-pot/single-slide-switch chassis obliged E-H to forfeit a control that would make it a MUCH more usable unit.  Ordinarily I think of E-H as a brilliant company, but this is another one of those cases where you just shake your head and mutter "What the hell were they thinking?".  It's worth noting that even though the Bass Balls has migrated to the new chassis, for "vintage-iosity maintenance" purposes, E-H still clings to the single-pot/single-switch format, even though they have the latitude to machine another hole to make an improved product. I don't know who is stupider in this scenario, the customer who thinks the product is somehow lesser and not the same as the original with more controls made available, or the company that feels they would lose market share or endure production costs that would not be offset by greater sales.

[shooter_mi]

Thanks Mark, you're right about there actually being two issues here, the fuzz effect AND overall level of the signal. Ideally, I'd like to make both adjustable via pots. This is, by the way, a mod rather than build project. I'm working with a latest generation Russian unit. Planning to put the trim pots on the panel, install a barrel dc socket, and address these other issues, if possible. The master volume idea is valuable, I'll make the 47k resistor switch because you describe it as "less elegant" and that's definitely where my skills are. But for controlling the fuzz effect, what kind of "less elegant" options do I have?

It is curious how EH has stuck to it's guns on this pedal design, despite users clamboring for relatively minor changes. Perhaps that's part of the allure of the product?