Throbbing Balls - LFO modulated dual filter with video demo

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Nocentelli
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Post by Nocentelli »

Essentially a mash-up of the twin filters from the EHX Bassballs, modulated by the LFO from the Tremulus Lune and mixed with inverted dry signal to give a mix/effect depth control:



Video is long, as it goes through all the controls (L-R = Fast/slow switch + Spacing (both side-mounted), Shape, Rate, Ramp, Range, Depth, Filter Blend, Mix, Filter-shift switch (side mounted)). EHX SuperEgo synth engine is used for most of the video to provide a sustained pad sound to mess with, and I switched on a sub-octaver (Pearl OC-07) around 9m30 to provide some sub bass for the wubwubwub.
throbbing balls schematic_nocentelli.bmp
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modman wrote: Let's hope it's not a hit, because soldering up the same pedal everyday, is a sad life. It's that same ole devilish double bind again...

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lapsteelman
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Post by lapsteelman »

Looks like a cool circuit.. should there be a feedback resistor on IC2B?
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Post by moidphotos »

That sounds excellent Nocentelli, thanks for posting it! Do you mind me asking a (probably daft) question? Do the points marked va, vb and vc all connect to each other? To the power line marked va anyway, or do they connect elsewhere?

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Post by Nocentelli »

lapsteelman wrote:Looks like a cool circuit.. should there be a feedback resistor on IC2B?
Good spot! Yes, believe I have a 22k in there. I tried a 33k but I think it was a bit much. 25k or 50k trimmer might be a good idea.
moidphotos wrote:That sounds excellent Nocentelli, thanks for posting it! Do you mind me asking a (probably daft) question? Do the points marked va, vb and vc all connect to each other? To the power line marked va anyway, or do they connect elsewhere?
Thanks, I like it. The vref question is a good one... I drew the schem to represent exactly what I have on the breadboard right now, each 1/2 supply (a, b, c) is separate. I feel sure I could use fewer, or even one single vref (not LFO, though) and was planning to try either a rail splitter. regulator type thing or even a buffered vref - I'm not too keen on adding another opamp, though. If you're breadboarding it, maybe try it with just the 47k pair supplying input buffer, IC1+2.

I'm away for a few days, but I intend to keep tinkering with it
modman wrote: Let's hope it's not a hit, because soldering up the same pedal everyday, is a sad life. It's that same ole devilish double bind again...

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Post by moidphotos »

Thanks, so I'd need to make sure I have multiple versions of the power section of the circuit (top right in your schematic) to supply each of the va, vb and vc areas (3 for the vc's, 2 for the vb's, I can't see a connecting point for va now) - but I could tie the two 47 input buffers' CV points together to connect to their own power section. I won't be able to breadboard this for a while; mine is full of a traced circuit that is undergoing a lot of extra experimentation... but as soon as it is free I'll need to look at this; you've got some great sounds in that demo, especially around 4min56 onwards - how much of that part is a super ego? I have a super ego myself, and I could see myself enjoying putting it into this pedal.

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Post by Nocentelli »

moidphotos wrote:Thanks, so I'd need to make sure I have multiple versions of the power section of the circuit (top right in your schematic) to supply each of the va, vb and vc areas (3 for the vc's, 2 for the vb's, I can't see a connecting point for va now) - but I could tie the two 47 input buffers' CV points together to connect to their own power section.
No: Va is the filtered +9v supply that comes from the 100r/100u on the right: This same voltage point is connected to all points with the upwards arrow, including opamp pin 8s and the top of the three voltage dividers. There are only three physical voltage dividers (a pair of 33k, a pair of 47k and a pair of 1M resistors. I used Vb and Vc to denote points that shared the same Vref (IC1 uses he vref from the 47K||47k, whilst IC2 and the mix pot use the Vref from the 1M||M pair). I will try running ALL points of a single 47k pair and see how that works out, probably in the next few days.
moidphotos wrote:...you've got some great sounds in that demo, especially around 4min56 onwards - how much of that part is a super ego? I have a super ego myself, and I could see myself enjoying putting it into this pedal.
I have the superego on the auto setting with the speed almost maxed which increases the sustain of the note played to infinite. Without any other effects applied this setting appears to make the sustained note subtly change slowly over the duration of the note - I think it might just be getting slightly louder which interacts with the fairly crude but effective dual filter.
modman wrote: Let's hope it's not a hit, because soldering up the same pedal everyday, is a sad life. It's that same ole devilish double bind again...

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Post by Nocentelli »

I tried just using a single 47k||47k divider to supply all the vref points and it worked fine: I then stuck in a TLE2426 rail splitter i had kicking about (cool little transistor package regulator that kicks out a steady 4.5v from a 9v supply) and that also works fine, so that is probably what I will use in my build when I box it to save a bit of space on the board.

Whilst I was fiddling, I tried to improve the depth/range control I have over the CV and came up with the arrangement shown below on this updated version 1.1, with a series resistance control for the range alongside voltage divider depth pot - Works MUCH better, and allows a far greater range of CV pulse widths and depths to be dialled in.
throbbingballs2_nocentelli.bmp
modman wrote: Let's hope it's not a hit, because soldering up the same pedal everyday, is a sad life. It's that same ole devilish double bind again...

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Post by Nocentelli »

Here is the most recent iteration, with two LEDs: The small red is just for status and tempo display, the big yellow one tracks the depth as well (much more satisfying, but goes almost imperceptibly dim at very low depths, hence the red one for confirmation it is on).
throbbingballs3_nocentelli.bmp
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modman wrote: Let's hope it's not a hit, because soldering up the same pedal everyday, is a sad life. It's that same ole devilish double bind again...

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