Adding expression pedal to BASS BALLS

[Austin73]

Hi everyone, anybody got any ideas on adding an expression pedal to the russian bass balls? I've got a spare EV5 lying around and thought could add a jack to the pot so I could insert the pedal to control the sensitivity.

I think the EV5 is 500k off hand , I realise I would have to add a resistor in parallel to give me 10k but not sure of the value as evrytime i try and work it out using the formulae 1/r=1/1/r etc i don't get a high enough value.

Bit tired as on nights as usual so if anybody can help would be eternally grateful

Aus

[Mark Hammer]

There are easier and more difficult forms of expression to implement in the BB.  Which one/s were you interested in?

[Austin73]

Hi Mark, to be honest not sure just fancied having a bit more fun with it as it always seems you could do so much more with adding a foot control, if that makes sense.

As always would welcome any input you could give me.

Cheers

Aus

[widdly]

The EV5 is a 10k pot  which is the same as the sensitivity pot on the bassballs schematic I've seen.  You could just wire up a dpdt to swap between them.

[Austin73]

Hi Widdly, cheers for the info, just checked and yes its a 10k with a 50k attached for added control, will stick a socket on it later possibly tomorrow and let everyone know, (if the are interested)

Cheers

Aus

[Mark Hammer]

An external foot-controlled 10k pot CAN be used to sweep one of the filter sections, however there is still the matter of the other filter section.  Without making it too complicated, you might want to install a toggle that lifts one of the filter sections from the passive mixing node (where the two 2k7 resistors meet near the output).  That would permit a relocated 10k pot to sweep the filter like a wah.

[Paul Perry (Frostwave)]

The EV5 is a 10k pot  which is the same as the sensitivity pot on the bassballs schematic I've seen.  You could just wire up a dpdt to swap between them.

Or (probably) you could have a switched jack (I have some stereo ones that I use in this kind of application) that switches out the pot and switches over to the foot controller when the EV5 is plugged in. Saves the dpdt (unless, you meant to do it this way!)

[Austin73]

Hi Paul thanks for the input, actually decided to go a bit OT with the Bass Balls the plan is to take out both preset pots (keeping the settings intact for stock sound) add a switched stereo socket now between which then feeds a 3pdt toggle switch which will switch between preset and panel mounted controls.

Bit mad and stupid but I'm just feeling a bit soldering iron happy lol

Aus

P.S Will post the results when the switches come in

Also does the distortion come from the diode clipping?

[Mark Hammer]

Also does the distortion come from the diode clipping?

In the stock Bassballs, the distortion comes from a 1458 op-amp pushed hard.  Some folks like it, some don't.  I am in the latter camp, and replaced the passive/resistive voltage divider with a Distortion+ type clipping circuit (10k resistor in series and diode pair to ground).

One of the side-effects (and design weaknesses IMHO) of the "distortion" path on the stock unit is that the level of the signal varies with the sensitivity control setting.  If you need to crank it up to get more sweep, you will have a louder output signal.  By using diodes to augment the clipping, they set an absolute (rather than relative) ceiling ont he signal.  So, instead of having the stock divider network reduce whatever you feed it by some percentage, the diodes set a maximum ceiling at whatever their forward voltage is.  Mind you, you can still end up with levels lower than that, but at least you won't end up with levels significantly higher than the clean setting as you do on the stock unit.  I have tried to pick my diodes to achieve a level-match between bypass/clean-filter/dirty-filter.  A combination of one GE and one (low forward voltage) Si seems to work about right.

The alternative is that you use whatever is already there to get the distortion tone (more like a froggy voice, actually) and install a 50k log  output level pot instead of the 50k terminating resistor so that youcan get the desired effect/bypass balance