StompFLO & OneShot in a box

[Matthew Sanford]

So I'm working on a StompFLO in its own box to send the LFO into other things, and it is going to work once I put a 470R to the LFO out! Well, I think. I tried taking the LFO coming from before the npn, and after the emitter, both turned off the LED (all colors to ground), so I figure lack of current due to resistance imbalance, throwing all the current to the LFO out...with it showing a top of 0.5v. So I'll get that done next (finally learning to test and math more sanely)

The quickly drawn to be done scheme - essentially abbr. & compiled version of the ways of the Druid with add ons (not shown are 10n hanging and 10k series off the CV pins, best practice thing right)



I want to keep the red on and the other two to get it between yellow and...oh shoot, it's green I want to ground so it's yellow and light blue. Anyway, I just want to make sure it looks workable? Full voltage to replace ground on the inverting LED (LFO instead of ground truly) to get the resistance change in opposite but equal proportion (ignore the "(or divider?)", silly me). For output I'd wired it to a TS jack, but realized building vactrol and other options on this side means just inserting a TRS NC jack between the pot and pcb on the pedal side (with appropriate taper resistors on each side), much easier. Wired T-> 2, R -> 3, S -> 1. I'm thinking 2 TS jacks for Rlfo and   -Rlfo ( iRlfo? , and a TRS to work both sides, but yes/no on doing LFO & iLFO, but pretty much everything works on resistance, say first 2N5088 in a bassballs...or maybe not.

Mostly a mission to be able to mess with all the things on any build, once this is made I'll put the One Shot together to make this one's LFO go really fast for a moment...or a Distortion + with sweeping distortion levels, bias levels, or whatever tone stack (I'll use TL072, so why not?), move on to pt2399 pitch and more. Should mod my boss pedals too, but will have make extenders for the bottoms to fit.

Things I'm still uncertain on:
1. Are there situations where voltage and ground would be preferable to vactrol control?
2. Should I maybe set up dedicated npn for each thing? Maybe not the ldr thing, LEDs don't need much, but if I choose an LFO out to make more current available?
3. Oh! Is it better to have a couple 10k out from the chip to separate the npn drivers? I mean one for led, on for vactrol?
4. Am I pulling the LFO voltage properly for the RGB LED? Maybe another vactrol or npn each to drive them from 5v?

The box as is:






Power on left, sync in under tap on top, LFO out right side of top, L-R pots (depth, waveform, frequency, offset)



Backside, TRS NC for each pot.

(Edit: thinking now better to tie the RGB LED to 5v and the LFOs on the other side...also question #4)

[ElectricDruid]

Looks good!

You're going to struggle a bit to do what you want with the RGB LED, I think. That's because it'll have a common cathode (or anode), so you don't get so much felxibility about how you wire it. Basically, you can't easily make some sections come on when others are going off. They'll operate together.

Oh, and 100n/1K for the filters. 10K series is probably workable, but it's a bit much. The CV inputs will start reading funny.

1. Are there situations where voltage and ground would be preferable to vactrol control?

Only for pedals that already have CV inputs. For hacking some modulation into a random circuit, vactrols are great. You can just tack them in across two legs of the pot and they'll make everything go wobbly! There will often be other side effects too, like control ranges changing, but that sort of stuff you have to deal with on a case-by-case basis.

2. Should I maybe set up dedicated npn for each thing? Maybe not the ldr thing, LEDs don't need much, but if I choose an LFO out to make more current available?

No need. One NPN can supply probably 100mA without too much trouble.

If you want a voltage-output LFO out, you'd need to add some filtering, at which point I'd say add an op-amp and build an active filter. That would provide a well smoothed LFO output and the op-amp will be able to drive whatever you plug it into.
The alternative would be a passive filter, but while that can work in certain situations, it's not a great idea here where you don't know exactly what you're going to be plugging into.

3. Oh! Is it better to have a couple 10k out from the chip to separate the npn drivers? I mean one for led, on for vactrol?

No, leave it with just one driver. If you had two drivers, then yes, I'd use two 10Ks too.

4. Am I pulling the LFO voltage properly for the RGB LED? Maybe another vactrol or npn each to drive them from 5v?

I mentioned this first. I think your diagram is about as good as you can get it.

[Matthew Sanford]

Thanks Tom!

I realize I do have 10n/1k for the filter, that was a mistype. I think I will take a 75k from pin 3 in parallel to the 10k to feed a sallen-key as on your data sheet.


Is one of those resistors changeable to a pot to change the offset range? I had been using this <a href="https://www.ti.com/lit/an/sloa097/sloa097.pdf?ts=1688719436942&ref_url=https%253A%252F%252Fwww.google.com%252F"> TI SLAO97 doc </a> to try to figure inverting it but making it offset to still be 0-5v, but using a 0 for the m or b wasn't seeing to get it, plus got me confusing myself on if the op amp puts out negative voltage anyway when it's a +9v power supply so 0v is the negative most...still, I'll use a TL072, have a ton, can I set a separate inverter to match the filter?


If I can do that I may put a TRS for both out together too.

I'm going to riddle on the RGB (common anode) on a breadboard after I get the 470 to balance the out, right now it just does it all in white with all cathodes to ground, but we'll see.

Thanks again! Even when I go through it properly I feel like I'm missing something, but you make me realize I am getting there!

[ElectricDruid]

Changing values on that Sallen-Key filter likely *won't* do what you want, unfortunately. There's a lot of interactions between one part and another,  and I basically got lucky finding a set of values that did what I needed (kept the waveform in the centre, didn't change the gain, or the resonance). Tweaking one thing tends to f4ck up everything else, frankly!

That's not to say that it's impossible. If you use an op-amp that can push the output right down to ground, then you don't really have aproblem anyway, and you can go ahead. Or you can add a mixer stage ahead of the filter, which can add a (potentially variable) offset. That would then feed an inverting filter (so probably a MFB filter would be a good choice, if I'm remembering correctly that they're inverting and S-K filters aren't.)

Not surprised you're getting all in white, bright/not-bright. I'm not sure how to fix that, honestly. Or at least, not with a typical RGB LED. You could do something with a Red/Green LED if they were wired cathode to anode, perhaps.
Or if you provided a invertor stage for the PDM output, you could feed the separate LED cathodes and have the common anode as the common point. But it adds circuitry - that's probably inevitable.

You *are* getting there, and "going through it properly" is the only way to learn it. Half measures are never going to do it! Get stuck in, do the experiments.

[Matthew Sanford]

The RGB LED is all cathodes to ground currently, so white is expected. I'll do the experiments, hopefully some today but our AC decided to quit just as we started the bloody hot cycle here in SoCal.

I've got the filterfx, digi-delay, and flangelicious PCBs here waiting, so I'll abuse em a bit with these to see how it control them, stay tuned...well, may be a bit, free time is a fickle thing and responsibilities rule priorities.

[Matthew Sanford]

Hi All! This is a post for posterity, but I did work on the op amp buffering! Posting a scrappy looking but correct scheme (I'll get better, I downloaded LibrePCB, and it is nice but I gotta figure out the design a part and have it available thing). Quick review - set up the invert/non-invert buffers by basic ways, realized it was loading too much into the stomp so put the passive filter from datasheet which improved it greatly. I had read SBOA114 (and now SBOA231) on MFBs from TI, well, scanned and read. Added things like the 100pf feedback cap, bias voltage, really 1.5k going to each side was key, etc. All the parts shown, I had tried various values and tried to understand the changes, which did happen a bit here and there.

Now I read:
Voltage after Filter
    2v-3.7v
-Vout
    6.5v-1.36v
+Vout

I really want the outs to match (inverted from each other) and be 0v-5v or 5v-0v.
My thoughts:
Add feed back resistor to non-inverting to increase range and vbias to change where it lands.
Get a handle on the large resistors, maybe no resistor for vbias on inverting (TL072, sboa114 states no R on JFET/CMOS inputs), and adjust to get it in the range.
Work to lower the R value on those resistors! The 1 Megs.... just too much, I think...

I'm going to check the voltages on all nodes from pin 3 to the buffers (well, passive filter) as I believe it's 0-5v but getting shaved down and boosted up on it's way - it goes through the 2n3904 feeding the 5v to the LED and pulling through a 470R, figure that is kind of what is messing with it, so may just do another 10k off pin 3 to the buffers.

I did try out the RGB LED though! Did it from 9v, 820r (1% but measurements show over that) on B & G to the +Vout/-Vout signals and R to ground through 1.5K (Oh! 1k5). With the imbalance in signals it lit up green/yellowish-green before quickly becoming light blue then darkening almost imperceptibly before going again. Really I wanted Green to be on so it would do Yellow to light Blue, but will have to work the R difference based on led forward voltage for it and blue, etc., and fix LFO imbalance but... it works!

Moving forward I'll fix the buffers, put them all on vero, fix the LED, then finally get to work on the effects!




(Edit: to note the JFET input thing)
(Edit2: also surprised the inverting went under 2v, data sheet states issue with negative rail is +2v over, or 4v on super version...)

[Mark Hammer]

One of the reasons why I pestered Tom?Druid to come up with the One-Shot in the first place was to use it in conjunction with the StompLFO or similar, the idea being that a single slow cycle (or more, if you want) of the One-Shot could be "assigned" to one of the control inputs on the StompLFO and produce a dynamic change in the slaved LFO.  So, for instance, a log-up or log-down output from the One-Shot could feed the Frequency control input of the StompLFO to produce a gradual increase or decrease in rate, or use repeats of the Sine or Inverse sine on the One-Shot to produce a cyclical change in a StompLFO parameter, like LFO depth.  And so on.  For that matter, I imagine with suitable buffering, the One-Shot output could be fed to MORE than one control input on the StompLFO.  So imagine a rising log wave from the One-Shot being fed to both the Frequency and Depth inputs on the StompLFO, but a little more on one than on the other, such that the final modulation increases a bit in frequency over time, and increases more in Depth over that same time frame.  Now THAT could make for a more natural-sounding vibrato.

Worth noting that which chip is used to influence which doesn't HAVE to be in any fixed order.  I started making a synth module using the two chips, but have to get back to it.  Too many projects.

[Matthew Sanford]

Too many projects.

A truth I believe we all share, since diving in I am distracted by so many shiny circuits!

I am so glad you pestered him for it, and my intentions are the same. I was working stomp and pt2399, getting almost bird chirp +2 octaves on random levels and thought on the one shot could do it on demand (or 9v through a momentary to vactrol...or FSR under a plate to push with your foot..)... then thought on a switch to swap with the extra doing something else, to all the other circuit's variables to drive, to sidechaining, staring at a desk overloaded with full breadboards. I made a Vero on a wood slide and a million sockets (and poor soldering skills), still not working but led me to this and more decent soldering! Plus, I love these little pot/TRS combo, but maybe they should have pin sockets on wires to the TRS for pot switchability?



I figure after I get two of these done, then another for envelope follower...maybe with offset and attenuvert stuff, I'll build all the pedals with a TRS for each thing, and later when I find go to things build that as a standalone. I've got a stray copy I'm working on setting the pickups in any serial/parallel order or phase with 3 dpdt and 4 dp3t. Signal might get too hot in serial though...

[Rob Strand]

Moving forward I'll fix the buffers, put them all on vero, fix the LED, then finally get to work on the effects!

Move your 1k5 connection from the filter output to the opamp buffer output.  As it is the 1k5 + 10k at the input of the inverting stage will affect the filter.  The cut-off will increase and there will be considerable low frequency attenuation:  in effect a divider of 10k+100k=110k feeding 1k5+10k=11.5k to ground.

[Matthew Sanford]

Thank you Rob, I've been thinking on that extra...but I need to work out the correct gain and offset. In that situation I would pull the other side's 1k5 from the filter side of the 10k?

I found the voltage after pin 3(StompLFO) is nearly the 0-5v after the 10k(instead of 2v-3.7v from npn) so I'll run another 10k (or change it to 75k like to the active out on data sheet). Once I do that all the values need rework.

Side note: led/ldr vactrol diy.
I made some the superglue and shrink wrap way - made some, but leaky, 6.7k - 40k, (1.5v-3.95v, 470R), thinking I need to buy a small tube of black silicon and fill the sides, is red shrink even light tight?, ... then found silicone tape for plumbing leaks, super stretch and melts to itself (per ad). Tried it, and same one gets 2.5k-220k (2v-3.75v, 510R), 20M+ @ 0v, 910R @ 9v.

[antonis]

FWIW, flat-head LEDs aren't "efficient" (compared to round ones) due to light internal reflection..

[Matthew Sanford]

Makes sense. Not sure how efficient my glue job was, but that silicone tape is, just kind of like stretch wrap.

[Rob Strand]

Thank you Rob, I've been thinking on that extra...but I need to work out the correct gain and offset. In that situation I would pull the other side's 1k5 from the filter side of the 10k?

Maybe better to sketch what you mean.

[Matthew Sanford]

Will do. Going in to work, so I'm going to doodle

[Matthew Sanford]

Thank you Rob, I've been thinking on that extra...but I need to work out the correct gain and offset. In that situation I would pull the other side's 1k5 from the filter side of the 10k?

Maybe better to sketch what you mean.

So my thoughts changed on it. I had meant branch the signal to the non-invert from the beginning node of invert op amp Rf. I know believe I need to branch off from the StompFLO pin3, 10k to npn->led, and 75k to active filter/buffer...and ditch the passive one. I think if it branches to each I'll work the invert into a proper mfb , but Mr. Stab got me thinking, so I'll try 3 ways to get the two signals.

The chicken scratch

[Rob Strand]

So my thoughts changed on it. I had meant branch the signal to the non-invert from the beginning node of invert op amp Rf. I know believe I need to branch off from the StompFLO pin3, 10k to npn->led, and 75k to active filter/buffer...and ditch the passive one. I think if it branches to each I'll work the invert into a proper mfb , but Mr. Stab got me thinking, so I'll try 3 ways to get the two signals.

The chicken scratch

Circuit 2 is the least problematic since it does not load the LFO output at all.    If the LFO output came straight off an opamp output then there's less difference between the options.

FWIW, you might want to look at the Boss Dimension C schematic.

[Matthew Sanford]

Circuit 2 is the least problematic since it does not load the LFO output at all.    If the LFO output came straight off an opamp output then there's less difference between the options.

FWIW, you might want to look at the Boss Dimension C schematic.

I will give #2 a go, but as the one Mr. Stab posted on a different thread, start with his values and work from there. I was almost to the point of doing a Sallen-Key for + and a properly set up MFB for negative, but less parts is alluring.

That Boss...is pretty complex to my eyes, at least on (edit: on aionfx, not SoundCloud). I am guessing the R&L outs are where I'm looking, and the emitter keeps it + to one with the source inverting the other side? I will try the simpler one (with proper components) to start, and load them in different ways to test stability, maybe work in other things. This has been a great task in learning the why, the ultimate quest in learning, and I'm grateful for the support. Grateful to do and fail and adjust! But yea, goal is still balanced LFOs in voltage range, so we will see.

Of note, I'm going to take the out off of the npn/led setup and instead tie it to pin 3 with a 10k-75k resistor and work from the more correct range...maybe I'll put a pin socket on the wire to figure that resistance first, still, it's my next step.

[Rob Strand]

I will give #2 a go, but as the one Mr. Stab posted on a different thread, start with his values and work from there. I was almost to the point of doing a Sallen-Key for + and a properly set up MFB for negative, but less parts is alluring.

That Boss...is pretty complex to my eyes, at least on SoundCloud. I am guessing the R&L outs are where I'm looking, and the emitter keeps it + to one with the source inverting the other side? I will try the simpler one (with proper components) to start, and load them in different ways to test stability, maybe work in other things. This has been a great task in learning the why, the ultimate quest in learning, and I'm grateful for the support. Grateful to do and fail and adjust! But yea, goal is still balanced LFOs in voltage range, so we will see.

Of note, I'm going to take the out off of the npn/led setup and instead tie it to pin 3 with a 10k-75k resistor and work from the more correct range...maybe I'll put a pin socket on the wire to figure that resistance first, still, it's my next step.

The whole process you are going through is the way you can learn a heap.  A big thumbs up.

[ElectricDruid]

Circuit 2 is the least problematic since it does not load the LFO output at all.    If the LFO output came straight off an opamp output then there's less difference between the options.

+1 agree. You really need *some* filtering in somewhere along the line too, so if the passive filter goes in before the first non-inv buffer, the buffer becomes even more essential.

The problem is the single supply. The StompLFO/Oneshot outputs go right down to ground, and most opamps run on 0-9V *don't*, so the bottom of the waveform will likely get clipped. The possible solutions to this are to find an op-amp that can cope, to add an offset, or to use bipolar power to give you enough space around 0V.

HTH

[Matthew Sanford]

Maybe do offset to bring it to 2-7v to keep the op amp happy then use a voltage divider to put 2 of it to ground? I was thinking on that, if I doubled it with gain to 0-10v then used resistors to cut it in half could I take 0-5v in two places? But I think those may have just been the crazy thoughts...

I'll be home tomorrow for the AC install, I plan to work on it then. I'll look at the other op amps I have, maybe lf44 or something...

Edit: or get it to a diode drop above 0-5 and put back to back diodes on the output to get it to 0-5v, gotta data sheet that idea for sanity