bassballs envelope modification

[yousufferbutwhy]

So I've parsed all of the previous threads and reviewed schematics, but it's all not quite coming together for me.

I'm modifying a Bassballs that was given to me with a bad switch. Since I'll mostly be using this in a studio/synth capacity with a Pedal Power supply, I'm replacing the stompswitch with a simple on/off and wet/dry pot. No trouble there in prototyping. I'm also pulling the filter trimmers to the panel with 10K pots. Simple stuff.

However, I would most of all like to add an input for envelope follower only.

I am completely indifferent about the fuzz and even the idea of "fixing" it with Mark Hammer's suggestions. In my semi-modular approach, it would suit me better to discard the fuzz section completely and use external distortion,  with the unaffected signal (or a completely different one) feeding the 1458 for the envelope only. With the fuzz disabled, the filters are processing the sound passing through only the first section of the 1458, am I right? So I would like to interrupt the circuit with a switching jack that feeds the "control" path only. But this is leading me to think I'd need another op amp buffer section. If it makes a difference, I'm mostly working with line level signals and usually attenuating the audio input. So, could a full line level signal drive the second half of the 1458 by itself?

Any suggestions or thoughts would be appreciated.

Thanks,
Ryan

[Mark Hammer]

Personally, I tend to use ONLY the "fuzz" section/signal of the BB these days, simply because all filters sound more robust with a harmonically rich input signal to filter, and having it built into the BB is more convenient for me than having to step on two separate pedals (filter and distortion).  Of course, you have to like the distortion that is possible from a BB and if you don't it's obviously no convenience at all, right?  If you have a distortion that you prefer more as a signal source to filter, then there is absolutely NOTHING wrong with skipping the normal/fuzz switch in the stock unit.

However, I would most of all like to add an input for envelope follower only.

Hard to find an easier mod than this.  Install a closed circuit jack that makes the connection between the 10uf output cap and the sensitivity pot when there is nothing inserted in the jack and breaks the connection when an outside signal is used as the envelope source.  The .047uf cap from the 10uf component can probably be omitted if the 10uf cap is going to remain hardwired to the inputs of the filter sections and the fuzz signal path left out.  On the other hand, the huge difference in value between the 10uf and .047uf caps may have something to do with maintaining one frequency response for the envelope follower and another for the filter, so let yor ears guide you.

If you feed the 10k sensitivity pot directly, any residual DC will be blocked by the .047uf cap on the input to the 2nd op-amp so yo don't really need to do anything to adapt the unit further to permit use of external signals.  If the signal source is high impedance out thenperhaps you might need a buffer of some kind between the jack and the sensitivity pot, but my guess is that you'll likely be feeding it with something that has already been converted from high to low impedance.  Naturally, if you're going to skip the fuzz part, you can omit the .047uf/100k/47k network between the 2nd op-amp and the Fuzz switch.

So, could a full line level signal drive the second half of the 1458 by itself?

Absolutely.

I can't emphasize enough the utility of adapting the 330k decay-setting resistor to a variable control.  Folks who followed up on my suggestion will likely chime in and echo that.  Replacement with a 47k fixed resistor in series with a 500k-1M pot is probably enough control and able to yield a wide range of different feels.

[yousufferbutwhy]

Thanks very much for the response, Mark.

Last night I got determined and fleshed out more than I thought I could in such a short time. Aside from being a novice, I've got a serious case of ADHD and uh "production deficiency."

- dry "clean boost" / global wet control pot -  I just replaced bottom half of the stomp switch with a 50k pot. Works well but I need to add the series resistor at least to the dry side. I don't really need true bypass at the moment and this helps with using it as a more general sound sculpting tool, for adding body & grit to all kinds of audio sources, especially digital ones.

- "clean" / fuzz wet/dry control pot - This replaced the fuzz switch. Might also benefit from series resistance, but working okay.

- auxiliary filter input - Instead of a switching jack, I used what used to be the fuzz switch to select the audio from the clean boost/fuzz path or a second plain 1/4" input jack. I put it in later in the circuit, actually, directly from the clean/fuzz pot. So it's the original audio input that feeds the envelope at all times, and my added jack just allows an external audio source. It seems more prudent for now to let me switch them without unplugging things. Variable control of some kind might be very interesting at another time (e.g. envelope signal pulls to internal path during attack, decay fades to external reverb signal    ) It could probably use a cap/resistor but sounds fine for the moment.

- filter trimmers -> front panel (same value, 10k). Duh. When I find the right (bigger) enclosure, I might add vactrols in parallel OR series for external CVs, but it's not crucial now.

- LED replacement Someone had "touched up" the original one with blue permanent marker for some reason. The ultrabright I used might be pulling too voltage much out, and is annoying to look at. So, I'll go digging around for a "special" but smaller one.

So, even with the imperfections, this thing absolutely smokes now, especially with a drum machine as the primary audio/envelope source. The best I got last night was actually with two very different sounding drum machines playing in sync but with very different patterns & pattern lengths. Both wet/dry knobs came in handy as well as the filter controls for improvised electro weirdness (and sleep deprivation). Later today I might try it on various instruments with shortwave radio as the control source.

And so, here's what I have on the top of my list now (aside from what I've mentioned):

- Diode fuzz with warp control pot - usual place as you've covered previously, will experiment with both series & shunted diodes
- Attack and decay control
- Filter independent outputs - someone else has mentioned this for a sort of stereo effect. The plan is to lift the signal after one of the 2.7k resistors near the output, and wire it to a jack that switches closed when nothing is plugged in for "normal" operation, probably with another 1uF cap on the output.
- Master volume out - just replacing the 47k shunt with a 50k log pot as mentioned before.

I was still hung up about decay control, so thank you for sharing that. I must have missed your post on it previously. I'd thought someone said adjusting the 330k resistor for it might be problematic, and because your ultraballs clone uses a switch, I was eyeing the 4.7uF tantalum sitting next to it.

And speaking of caps - this thing sure has a lot of electrolytics (incl. tantalums) in the audio path. Would replacing these with non-polars be ok/possibly worthwhile?

One disappointment came from trying to make my own adapter cable for use with the Voodoo Labs Pedal Power. I soldered a barrel connector to one side of a 1/8" mono plug, pin-positive, and first plugged it into one of the Pedal Power's lag outputs, to gradually bring up the voltage. I got nothing out of it, and quickly gave up so as to not damage anything. I thought this would do the trick, but back to the battery & drawing board. I might just make a new barrel -> 9V battery connector for now.

I feel it's necessary to say that nearly everything technical in my post comes from Mark Hammer's previous postings, Topopiccione, the Fuzzy Balls project, and others on this forum. Only the bizzarro implementation ideas are my own. I'm just a little too deep in the project and scattered with my notes to be able to provide in-text citations right now. 

[Mark Hammer]

Although it is tempting, there is no need to go nuts with this one.  The objective is to get the most flexibility with the fewest controls/changes.  Here is my suggested list:

1) Dual filter-tuning pots is fine but really all you need is one to establish variable "stagger" between the filter sections.  Leave the board-mounted trimpot for the lower filter section, and chassis-mount a pot for tuning the upper one.

2) A dry/filter mix pot is a good idea.  So is a filter-mix pot that adjusts how much each filter section contributes to the final sound.  I suspect replacing the pair of 2k7 resistors on the filter-section outputs with a 1k5-2k2, and the resistors going to the two outside lugs of a 10k-25k linear pot, would provide a usable blend.  Varying proportions of filter 1 and 2, and dry would produce a vast spectrum of tonal qualities.

3) The attack control is nice, but it takes such a large increase in resistance to produce a noticeable slowing of attack time that one loses envelope drive in the process and has to adjust sensitivity everytime you adjust attack time.  I find that variable decay provides just as much variation in feel of sweep, but without the penalty you pay for variable attack time.  That doesn't necessarily stop me from having variable attack time on one of mine, but if push comes to shove the decay stays and the attack goes.  You will note that, because of its generally fast attack time, the BB *feels* like it only sweeps downward, rather than upward.  This is an epiphenomenon of the ratio of attack to decay time.  As the attack time is increased and decay time decreased, the upwards sweep starts to sound more apparent.  You could, in theory, use a single pot to control both attack and decay.  The pot wiper goes to the junction of the + side of the 4u7 cap and 100R resistor.  One leg of the pot then goes in parallel with the 100R resistor (which you can change to 220R), and the other leg goes in series with a fixed 47k resistor to ground.  Rotate in the one direction and the parallel resistance of that pot leg and the smalled fixed resistor will vary between zero ohms (whip-fast attack) and 220R (more obvious rise to the sweep), and the other leg varies the bleed-off resistance for the cap.  Attack gets faster as decay gets longer and vice versa.

4) Because the "fuzz" setting draws its signal fro another part o the circuit under different circumstances, the fuzz level varies with sensitivity setting, whereas the non-fuzz sound is a constant level regardless of sensitivity.  You will note the complete absence of a volume control on the thing.  So, notwithstanding my "convenience" reasons listed in the earlier post, if you have to make cuts, scrap the fuzz and use it as a filter only.

So what do we have at this point?  Sensitivity, sweep speed, filter stagger, dry/wet mix and filter-balance.  Five controls.  A lot of feel options and a lot of tonal variation.  You can scrap one of the blend controls and still have lots of variation available.